# DX vs FX focal lengths?



## darkblue-x (Oct 23, 2017)

I dont get it.
I have a DX lens for instance that is Nikkor 16-85mm and they say that the 16mm end is a 24mm equivalent on FX, I believe.
Which brings me to my question, an FX lens, the 24-120mm...what length would that be exactly in DX terms. How do you calculate these?


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## JonA_CT (Oct 23, 2017)

For a Nikon camera, multiply the focal length by 1.5 to get the equivalent field-of-view.


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## darkblue-x (Oct 23, 2017)

JonA_CT said:


> For a Nikon camera, multiply the focal length by 1.5 to get the equivalent field-of-view.


To see if I understand...So then an FX focal length of 24-70mm would look like 16-46 on a DX?


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## 480sparky (Oct 23, 2017)

darkblue-x said:


> JonA_CT said:
> 
> 
> > For a Nikon camera, multiply the focal length by 1.5 to get the equivalent field-of-view.
> ...



No. A 24-70 would be the equivelant to 36 (24x1.5) - 105 (70x1.5).


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## benhasajeep (Oct 23, 2017)

darkblue-x said:


> JonA_CT said:
> 
> 
> > For a Nikon camera, multiply the focal length by 1.5 to get the equivalent field-of-view.
> ...


Nope other way

24-70 on a DX camera would act like a 36-105mm lens on full frame camera (field of view FOV).
A 200mm lens on your camera would have the same scene in your viewfinder as a 300mm would on a full frame.


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## darkblue-x (Oct 23, 2017)

Okay what about a prime lens then?
I have a Nikon 35mm Dx f/1.8..
Would an Fx 35mm prime be the same or are they the same whether on dx or fx


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## 480sparky (Oct 23, 2017)

Focal length is focal length is focal length.  That NEVER changes.

What changes is the _field of view_.  A 35mm prime will provide the same FOV as a 16-85 zoom set to 35mm.


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## benhasajeep (Oct 23, 2017)

darkblue-x said:


> Okay what about a prime lens then?
> I have a Nikon 35mm Dx f/1.8..
> Would an Fx 35mm prime be the same or are they the same whether on dx or fx


Focal length on the lenses are the same.  What DX and FX designate is the size of the image circle they produce.  Since crop sensor cameras have smaller sensors the image circle does not need to be as large.  So the DX lens is designed for that smaller image circle.  But the lens focal length stays the same.

For example I can put a DX 18-55 lens on a full frame D800.  It will be a 18mm to 55mm zoom on that camera.  But it will not cover the entire sensor.  So, any lens you have on your camera you multiply by 1.5 to get the equavilant view on a full frame camera.


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## Braineack (Oct 24, 2017)

darkblue-x said:


> Would an Fx 35mm prime be the same or are they the same whether on dx or fx



Are you ever going to use an FX body?


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## Designer (Oct 24, 2017)

darkblue-x said:


> I dont get it.
> I have a DX lens for instance that is Nikkor 16-85mm and they say that the 16mm end is a 24mm equivalent on FX, I believe.
> Which brings me to my question, an FX lens, the 24-120mm...what length would that be exactly in DX terms. How do you calculate these?


Never mind all that because it hardly matters one whit in the real world. 

You see; there are just way too many people out on the internet who worry about such things and make statements and videos to try to confuse the newbies. 

The reality is that; if your lens fits your camera, you can use it.  Unless you already have some visual reference of  how a given lens will give you what field of view, there is no practical reason to be concerned about the mathematical relationship of a larger sensor vs. a smaller sensor.  The field of view is what it is, nothing more complicated than that. 

I'm going to make a brash assumption that you really don't already have a pre-conceived visual reference of what a certain field of view should look like, so my advice is to simply ignore all that ratio stuff, and don't let the internet take you for a ride.  Just enjoy whichever lenses you have or wish to purchase. 

Field of view: It is what it is.


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## Braineack (Oct 24, 2017)

exactly, how your lens looks/performs on someone else's camera has no bearing whatsoever on you.  so don't worry about it.


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## Tomasko (Oct 24, 2017)

Sure, but it's an important concept to understand if you're trying to learn photography more deeply than just point&shoot.


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## jaomul (Oct 24, 2017)

Tomasko said:


> Sure, but it's an important concept to understand if you're trying to learn photography more deeply than just point&shoot.


Not necessarily. I'll be prepared to bet there are working pros now who use m43 cameras that have never picked up a fullframe camera. 45mm is a nice portait lens, they don't know or care how it relates to ff


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## Tomasko (Oct 24, 2017)

You don't need to use other formats, but you should know the differences and pick the tool appropriately.


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## Braineack (Oct 24, 2017)

Tomasko said:


> Sure, but it's an important concept to understand if you're trying to learn photography more deeply than just point&shoot.


is it?


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## Tomasko (Oct 24, 2017)

Yes, it is. Anyone who calls himself/herself a professional (or even a more serious enthusiast) should know at least the basics.


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## Designer (Oct 24, 2017)

Tomasko said:


> Sure, but it's an important concept to understand if you're trying to learn photography more deeply than just point&shoot.


In what regard is it "important"?


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## Tomasko (Oct 24, 2017)

For example to know which camera format would be most suitable for your specific needs. Or when you're searching for a lens and you see people talking, so you don't have to ask questions like "oh, but I have a m4/3 and I see you have fullframe, why my fov is drastically different??". Or when you're switching to a different format so you know what to expect from your gear.

I'm not saying you should know some complicated equations or something, but I suppose every person on the planet should know basic multiplication. This is not a hard stuff by any stretch of imagination. If you're serious about photography, there are certain things you should read about and this is one of them. To at least have a faintest idea what's going on with your gear and how to use it to its fullest.


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## KmH (Oct 24, 2017)

While focal length is focal length Nikon FX lenses tend to be better than Nikon DX lenses.
In large part because the 2x larger FX image sensor delivers better resolution, for an equal number of pixels because the FX pixels are larger than APS-C pixels.

It's also worth being aware that whether a lens is a DX or FX lens the lens rendering properties remain the same regardless the image sensor size in the camera.

As an example, a 35 mm prime lens tends to distort a person's facial features in a head shot making noses appear larger than they are and ears smaller than they are regardless the image sensor size in the camera.

I agree that any photographer that strives to consistently make quality images is well served by having a good understanding of the technical aspects of doing photography, like understanding how the camera works. Of course that same photographer also needs a good understanding of the artistic aspects of doing photography.


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## Ysarex (Oct 24, 2017)

KmH said:


> It's also worth being aware that whether a lens is a DX or FX lens the lens rendering properties remain the same regardless the image sensor size in the camera.
> 
> As an example, a 35 mm prime lens tends to distort a person's facial features in a head shot making noses appear larger than they are and ears smaller than they are regardless the image sensor size in the camera.



No. distortion of a person's facial features as you describe is a function of perspective and not the rendering properties of the lens. A 35mm prime lens may be inappropriately short to do a head shot on an FX camera but not so on a m4/3 camera.

Joe


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## Designer (Oct 24, 2017)

Getting back to the OP's question: 





darkblue-x said:


> Which brings me to my question, an FX lens, the 24-120mm...what length would that be exactly in DX terms. How do you calculate these?


As has already been explained, the actual focal length of any lens does not change by mounting it on a different body.  Call it the equivalent field of view, and you'll have a better grasp of the concept.

In Nikon, the ratio of sensor sizes is 1:1.5, so you simply multiply the actual focal length of your FX lens by 1.5 and you get the equivalent of that lens when mounting it on a DX camera.  

Therefore; the 24-120mm FX lens would appear to be a 36-180mm when mounted on a DX camera.


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## jaomul (Oct 24, 2017)

Tomasko said:


> For example to know which camera format would be most suitable for your specific needs. Or when you're searching for a lens and you see people talking, so you don't have to ask questions like "oh, but I have a m4/3 and I see you have fullframe, why my fov is drastically different??". Or when you're switching to a different format so you know what to expect from your gear.
> 
> I'm not saying you should know some complicated equations or something, but I suppose every person on the planet should know basic multiplication. This is not a hard stuff by any stretch of imagination. If you're serious about photography, there are certain things you should read about and this is one of them. To at least have a faintest idea what's going on with your gear and how to use it to its fullest.



I respectfully disagree here, and not to cause an argument. Someone, sometime decided to make 35mm film the standard by which everything is measured. Most of us enthusiast photographers know roughly what crop factors each setup has in relation.

But if I start with a micro four thirds today, learn everything about it, realize the basics of photography and in a few years turn pro churning out great images due my eye and creativity, then it is irrelevant what another format is in relation.

I will add that I know a woman who has very high standing with our national photography federation. She had achieved their highest accolades with her photos. She uses a 40d. One time I asked her about using fullframe, she said she was happy with her lenses and knew they would not be the same on fullframe but was not sure in what way they would be different, so wasn't changing


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## coastalconn (Oct 24, 2017)

Tomasko said:


> Yes, it is. Anyone who calls himself/herself a professional (or even a more serious enthusiast) should know at least the basics.


Being a chef, I meet many professional wedding photographers that are very talented and make good money at what they do... Guess what?  Almost everyone I have talked to knows very little about gear in general.. They tend to use older cameras and do not visit forums. They put there camera in P mode, and know how to use light to get their shots...


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## Tomasko (Oct 24, 2017)

I know many people don't know the basics, but I'm not sure I'd use that as an argument why to ignore certain knowledge.
Of course, you can take great pictures just by using auto/program/whatever modes and never learning more. You can also compose great music without ever learning how to sing or about great composers of the past, but...

I don't know. I think we all became lazy enough already. We don't need to take it a step further  This really isn't something you'd have to go through university to understand.


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## 480sparky (Oct 24, 2017)

jaomul said:


> .....Somone sometime decided to make 35mm film the standard by which everything is measured. ....



And that someone would  be the major manufacturers of DLSRs. Given they all started with crop sensors due to the expense of 24x36mm sensors of the day, they invented 'crop factor' and it's attendant multiplier to market the fledgling digital camera to the great masses who grew up using 35mm. 

While reasonable at the time, today we have an entire generation who have never _seen_ a real 35mm film camera let alone used one. Yet the industry still touts this easily-remembered formula much to the confusion of the younger market. 

Personally, I wish the entire crop factor and it's current multiplier fiasco disappear from the face of the earth..... as well as all written references to it. Wipe the slate clean. A total restart. Cntl + Alt + Del and start over without it. Let not anyone recall or reference it.

I used many a film camera back in the day. Can't say I recall most of the focal lengths of the lenses I used. I do recall the FLs of the 35mm film gear I had, as well as lenses for 6x45 and 6x7 formats.

But even shooting pro, NOT ONCE did I ever need to convert the FL of one format to another. I cared not that the 80mm for my 6x45 was close to what a 50mm on my 35mm SLR would capture. Nor did I convert my 6x7s 250mm to "the equivalent of" either the 6x45 or 35mm.

I knew that given the format I'm shooting, if I wanted "this much" of the scene in the viewfinder,  I would select a certain lens . When using a 50mm on my 6x7, it was not necessary to think in terms of "this is like shooting with a 24mm on my SLR. "

Crop factor and the crop multiplier was merely a gimmick invented on Madison Avenue to peddle new-fangled DSLRs to the mass consumer market that they felt needed to be weaned from 35mm film.

Do cell phone shooters know what focal length thier phones have? Do they even _care_? Do they feel the need to convert this number to a 35mm equivalent? 

It has served it's purpose now, and that market no longer exists. Time to turn off the respirator, roll up the cord and shut off the lights on the way out. Get a shovel and bury it along with buggy whips, ice picks, 8-track tapes and pay phone booths.


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## Frank F. (Oct 24, 2017)

darkblue-x said:


> I dont get it.
> I have a DX lens for instance that is Nikkor 16-85mm and they say that the 16mm end is a 24mm equivalent on FX, I believe.
> Which brings me to my question, an FX lens, the 24-120mm...what length would that be exactly in DX terms. How do you calculate these?




DX crops the middle part of 15*23 sqmm from an FX frame of 24*36 sqmm.

That way the field of view gets smaller on DX like it would get if you would attach a lens with a longer focal length on FX.

You can mount an FX lens on both DX and FX cameras and work with it cropped and uncropped.

But you cannot mount a DX lens on a FX body and expect it to work normally. Most of the time the image circle of the lens is too small to project a picture on the FX chip. I will look like a circle of light with a round black frame on the left and right, cut on top and bottom.

Therefore I did not buy DX lenses but FX lenses only. They did work on my DX bodies and as soon as the D3 appeared I could use them uncropped too.


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## Designer (Oct 24, 2017)

As if we needed more fodder for this discussion; I wish to remind everyone that the common 35mm film cameras were originally called "miniature".  Meaning; they were a lot smaller that the more usual 4x5, 6x9, 8x10 (and larger) of the early days of photography.  

So now we call the 35mm size "full size", when it was the "small" size of camera sizes.

Kinda funny, huh?

And again; nobody worried about the "crop factor".


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## Braineack (Oct 24, 2017)

this thread:


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## darkblue-x (Oct 27, 2017)

Braineack said:


> darkblue-x said:
> 
> 
> > Would an Fx 35mm prime be the same or are they the same whether on dx or fx
> ...


I plan to upgrade to perhaps a D750, but that wont be for at least a year or two.


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## Braineack (Oct 27, 2017)

darkblue-x said:


> Braineack said:
> 
> 
> > darkblue-x said:
> ...



so I'd suggest to stop buying DX only lenses now.  If you want 50mm on you current body, just know that it will seem a lot shorter when you bolt it on your D750.  But you want to try to have an arsenal of lenses that are compatible.


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## darkblue-x (Oct 27, 2017)

Designer said:


> Getting back to the OP's question:
> 
> 
> 
> ...





Braineack said:


> darkblue-x said:
> 
> 
> > Braineack said:
> ...


I'm thinking of buying a Tamron 35mm F/1.8 VC as a portrait/creatives lens (this over the sigma art bc of the weight and size difference, VC, weather proofing and light macro ability.
Would this be the same focal length as my current Nikon DX 35mm f/1.8g looks through my D7100? Tbh I still don't get it.

As far as walkaround lens I have found my Nikon DX 16-85mm f/3.5-5.6g VC lens to be a great focal length range...a lot of the FX lenses seem to start at 24mm...kind of a bummer.


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## Designer (Oct 27, 2017)

darkblue-x said:


> I'm thinking of buying a Tamron 35mm F/1.8 VC as a portrait/creatives lens (this over the sigma art bc of the weight and size difference, VC, weather proofing and light macro ability.
> Would this be the same focal length as my current Nikon DX 35mm f/1.8g looks through my D7100? Tbh I still don't get it.
> 
> As far as walkaround lens I have found my Nikon DX 16-85mm f/3.5-5.6g VC lens to be a great focal length range...a lot of the FX lenses seem to start at 24mm...kind of a bummer.


Yes, the respective fields of view from those two 35mm lenses (of different makes even) will look very much alike.

Why are you disconcerted about the FX lenses starting around 24mm?  Is there something else that you're going for?


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## Ysarex (Oct 27, 2017)

darkblue-x said:


> Would this be the same focal length as my current Nikon DX 35mm f/1.8g looks through my D7100? Tbh I still don't get it.



A 35mm is a 35mm is a 35mm -- all 35mm lenses are 35mm lenses. Moving the lens between cameras doesn't change the lens. Here's what happens:




 

The whole image above is a 35mm lens on a FX camera. Don't move at all. Use the same lens but switch camera bodies to a DX camera and you'll get the photo inside the red lines. That's because by using the DX body you switched to a smaller sensor and so you're now recording less. Perspective is the same because you didn't move. The smaller sensor is cropping what you can record relative to the larger sensor. The lens is still a 35mm lens.



darkblue-x said:


> As far as walkaround lens I have found my Nikon DX 16-85mm f/3.5-5.6g VC lens to be a great focal length range...a lot of the FX lenses seem to start at 24mm...kind of a bummer.



A 24mm lens on an FX camera has the same field of view as a 16mm lens on a DX camera. That means if you take a photo with a 24mm lens on an FX camera and then don't move -- just pick up a DX camera with a 16mm lens and take the photo again you'll get the same content/framing in both photos -- basically taking the same photo but with a slight difference in DOF.

Joe


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## Frank F. (Oct 29, 2017)

Field
Of
View

is important. My 1.4/58G is a decent portrait lens on my D500.

For the same effect I take my D850 with a 1.8/85G attached.

That is the real world apart from theoretical rants.


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## WayneF (Nov 7, 2017)

darkblue-x said:


> I dont get it.
> I have a DX lens for instance that is Nikkor 16-85mm and they say that the 16mm end is a 24mm equivalent on FX, I believe.
> Which brings me to my question, an FX lens, the 24-120mm...what length would that be exactly in DX terms. How do you calculate these?



A lens does not change focal length by putting a different size sensor on it. If it is 24-120mm, it is always 24-120mm, on any body.  All that changes is a smaller sensor "crops" the larger full size image that a larger sensor would see. With the same lens, smaller sensors see a  smaller field of view.  What we compare is the focal length of* a different lens on a different sensor* (specifically on a 35 mm film camera as the standard) that would give the same smaller field of view on that other camera.

The significance is that if we know what field of view that the "equivalent" 24 mm lens does on 35 mm film (and many people do have years of experience on 35 mm, even if some others have never seen a 35 mm camera), then we know what the 16 mm does on DX, which might be new to them.

That does NOT affect what the lens does on your camera with a smaller sensor. The 24-120 mm FX lens on your DX body will simply be a bit longer than the 16-85mm lens on same body, exactly as the numbers would make you expect. But due to the smaller DX field of view, the 24 mm will not offer very much wide angle on a cropped DX sensor.

It is a little tricky. 16 mm on DX has the FX Equivalent 24 mm.  However, when that same 24mm is on DX, its field of view on DX now has an FX Equivalent field of view of 36mm. The lens is still the same, but we are comparing field of view of the sensor size.

See Camera Sensor Crop Factor and Equivalent Lens Focal Length. Calculate Crop Factor for more, including the calculator you might seek.




480sparky said:


> But even shooting pro, NOT ONCE did I ever need to convert the FL of one format to another. I cared not that the 80mm for my 6x45 was close to what a 50mm on my 35mm SLR would capture. Nor did I convert my 6x7s 250mm to "the equivalent of" either the 6x45 or 35mm.



But you did know to buy the different focal length lens, right?  That certainly was the FL conversion for film format. Photographers (that ever used a different camera type) always knew that different size film cameras required different focal lengths to get the same expected field of view.  The only difference today is that our DSLR cameras might mount and use the exact SAME physical lens, and the sensor sizes make a different field of view possible with the same lens. That adds confusion that makes it a subject of discussion.

There was a time when cameras had no electronics and no automation. This required that we learned a few basics. Or at least the film box had a Sunny 16 data sheet in it that mostly worked if outdoors in sunlight.  I miss that time when most everybody knew at least a little about using the camera. However, the pictures are a lot better today, digital has made it tremendously easier.


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## darkblue-x (Nov 8, 2017)

Yep. Still dont get it.
Disregarding what the sensor covers completely...I'm only talking about what I see in the viewfinder the whole fkn rectangle ,while disregarding any sensor crop lines or what have you.
 At 16mm on my DX im able to go right beside something and have the viewfinder cover the whole thing for instance.
FX doesnt make lenses like that 16-85. Does the 24mm fx looks like it would for my dx in the viewfinder at that same focal length? Will the angle be as wide as that that i see on my Dx setup


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## Overread (Nov 9, 2017)

The angle of view (what you see through the viewfinder and get on the sensor) of DX at 16 is equivalent to FX at 24mm.

To convert the angle of view of a DX to FX you multiply the DX focal length by 1.5
To convert the angle of view of a FX to DX you divide the FX focal length by 1.5


NOTE focal length is always the same, a DX 16mm lens and an FX 16mm lens on a DX camera body will give you exactly the same angle of view. With Nikon many of their FX camera bodies can let you use a DX lens on it by activating only a portion of the central area of the sensor, as a result you'd get the DX lens performing as if it were on a DX camera body

FX = fullframe or 35mm
DX = crop sensor (cropped in terms of comparing it to 35mm)


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## Designer (Nov 9, 2017)

darkblue-x said:


> FX doesnt make lenses like that 16-85. Does the 24mm fx looks like it would for my dx in the viewfinder at that same focal length? Will the angle be as wide as that that i see on my Dx setup


You can get fairly close with the 24-70.

No.

Wider.


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## astroNikon (Nov 9, 2017)

darkblue-x said:


> Yep. Still dont get it.
> Disregarding what the sensor covers completely...I'm only talking about what I see in the viewfinder the whole fkn rectangle ,while disregarding any sensor crop lines or what have you.
> At 16mm on my DX im able to go right beside something and have the viewfinder cover the whole thing for instance.
> FX doesnt make lenses like that 16-85. Does the 24mm fx looks like it would for my dx in the viewfinder at that same focal length? Will the angle be as wide as that that i see on my Dx setup



Your viewfinder may not show 100% of what your sensor sees. It may only show 95%.  So composition of a subject has to take that into consideration if no post processing. 

The MIRROR's size is based on the sensor size.  Thus the VIEWFINDER will only show you what the Mirror reflects.  Technically you could have a mirror 3x the size of the sensor and the viewfinder would show you a gigantic area of which most won't be captured.

Generally, The lower end camera the darker and less of the actual subject size is shown - it's not by much but it's still there.
viewfinder info ==> APS-C field of view

But that mirror size, based on the Sensor size - the sensor defines the FOV which may change what a lens "sees".

If you have a lens that is a 24-70 that lens is designed as a 24mm-70mm.
On a Full Frame Camera which is considered 1x (as it's the base) makes that lens FOV as a 24-70.
On an APS-C camera which is considered 1.5x makes that lens FOV as a 36-105.

To compensate on a APS-C camera you need a 16mm lens to get the (16x1.5) FF 24mm equivalent on a FF sensor.
==> DX Lens Focal Lengths


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## darkblue-x (Nov 9, 2017)

astroNikon said:


> darkblue-x said:
> 
> 
> > Yep. Still dont get it.
> ...


So then 24mm FX is the same FOV as 16mm on DX?


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## Tomasko (Nov 9, 2017)

Yes. It's really just the most basic multiplication/division...


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## darkblue-x (Nov 9, 2017)

Tomasko said:


> Yes. It's really just the most basic multiplication/division...


soooooo then the FOV that an FX lens 24-70 gives off is similar to a standard zoom FOV on a DX of 16-45 or 50?


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## Tomasko (Nov 9, 2017)

70 / 1.5 = roughly 46,67


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## Ysarex (Nov 9, 2017)

darkblue-x said:


> Tomasko said:
> 
> 
> > Yes. It's really just the most basic multiplication/division...
> ...



Yes.


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## darkblue-x (Nov 9, 2017)

Tomasko said:


> 70 / 1.5 = roughly 46,67


Okay finally. I made that calculation weeks ago, everything else ITT served to confuse me further.

that's an okay focal length on the lower end, lacking a bit on the longer end though...
I saw that nikon makes a 24-120 lens though.. should I move on to FX maybe I should get that.
third party lenses are the same thing arent they?
and what if its a PRIME FX lens like 35mm? are they the same between DX and FX? Id imagine they make the DX lenses to make the FX equivalent in DX format and same with FX.
I may just be best going to the Camera store, I am a visual learner it may be easier having someone show me with the cameras and lenses physically for it to fully compute.


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## Tomasko (Nov 9, 2017)

Focal lengths are (to my knowledge)  always written in respect to 35mm / fullframe. It doesn't matter if it's Nikon/Canon/Sony/whatever brand, it's still the same thing. It also doesn't matter if it's a zoom lens, macro lens, telephoto, prime.. If the lens says for instance "24mm", you know they mean it gives you 24mm FOV on a fullframe camera and different FOVs on different sized sensors based on the crop factor.


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## darkblue-x (Nov 9, 2017)

Tomasko said:


> Focal lengths are (to my knowledge)  always written in respect to 35mm / fullframe. It doesn't matter if it's Nikon/Canon/Sony/whatever brand, it's still the same thing. It also doesn't matter if it's a zoom lens, macro lens, telephoto, prime.. If the lens says for instance "24mm", you know they mean it gives you 24mm FOV on a fullframe camera and different FOVs on different sized sensors based on the crop factor.


I'm confused again because the FOV of 16mm DX on FX is 24mm.
So then 35mm DX on FX is???? 50mm FX? To get a prime with same FOV as my 35mm DX do I have to buy a 50mm on FX?


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## Ysarex (Nov 9, 2017)

Tomasko said:


> Focal lengths are (to my knowledge)  always written in respect to 35mm / fullframe. It doesn't matter if it's Nikon/Canon/Sony/whatever brand, it's still the same thing. It also doesn't matter if it's a zoom lens, macro lens, telephoto, prime.. If the lens says for instance "24mm", you know they mean it gives you 24mm FOV on a fullframe camera and different FOVs on different sized sensors based on the crop factor.



No. My compact is here on my desk. The zoom lens is inscribed 5.2mm - 17.2mm, f/1.4 - 2.7. It has an equivalent FOV on the wide end that's the same as a 24mm on a FX camera or a 16mm on a DX camera.

There have been camera manufactures that inscribed lenses with FF equivalent focal length values --a horribly bad idea -- but typically they note that when they do it.

Joe


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## Ysarex (Nov 9, 2017)

darkblue-x said:


> Tomasko said:
> 
> 
> > Focal lengths are (to my knowledge)  always written in respect to 35mm / fullframe. It doesn't matter if it's Nikon/Canon/Sony/whatever brand, it's still the same thing. It also doesn't matter if it's a zoom lens, macro lens, telephoto, prime.. If the lens says for instance "24mm", you know they mean it gives you 24mm FOV on a fullframe camera and different FOVs on different sized sensors based on the crop factor.
> ...



Yes.

Put a 35mm on your DX and a 50mm on your FX and stand in the same place with both and see the same image through both.

Joe


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## Overread (Nov 9, 2017)

Tomasko said:


> Focal lengths are (to my knowledge)  always written in respect to 35mm / fullframe. It doesn't matter if it's Nikon/Canon/Sony/whatever brand, it's still the same thing. It also doesn't matter if it's a zoom lens, macro lens, telephoto, prime.. If the lens says for instance "24mm", you know they mean it gives you 24mm FOV on a fullframe camera and different FOVs on different sized sensors based on the crop factor.



Think of it like this; focal length is an optical property of the lens alone
Sensor/film size is a property of the camera alone.

It's only when you combine the two that you get the angle of view.

Most photographers speak in 35mm sensor equivalents for angle of view because it is the most widespread and popular of all the film sizes. So most people know what the angle of view looks like so it acts as a common ground. That said companies generally only mark lenses in actual focal length; where its equivalent they state it (equivalents tend to be more stated on compact cameras because it sounds more impressive and is easier to relate to than their actual focal lengths.


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## astroNikon (Nov 9, 2017)

darkblue-x said:


> Tomasko said:
> 
> 
> > Focal lengths are (to my knowledge)  always written in respect to 35mm / fullframe. It doesn't matter if it's Nikon/Canon/Sony/whatever brand, it's still the same thing. It also doesn't matter if it's a zoom lens, macro lens, telephoto, prime.. If the lens says for instance "24mm", you know they mean it gives you 24mm FOV on a fullframe camera and different FOVs on different sized sensors based on the crop factor.
> ...


IGNORE the FX / DX thing in regards to the lens.

the FX / DX thing has to do with the SIZE of the image being projected on the sensor.  Not with any distinction of the lens.
A 50mm lens is a 50mm lens whether it is for a DX or a FX sensor.

The distinction is the SIZE of the sensor.
If you are using a 50mm lens a FX sensor will capture a large sized image (which is considered 1x) of that image circle from the lens.   A DX will capture a smaller portion of that image, about 1.5x smaller.

because of that, when you compare the two image at the SAME SIZE Visually, the DX one is about 1.5x cropped or larger than it's respective size on a FX image.   The DX will have a smaller portion of the FX image.

does that make any sense.

Thus, as I had posted if you look at the chart on this post ==> DX Lens Focal Lengths

Now, a lens designated DX will, in order to save money, make the glass elements smaller because the sensor is smaller.  Since the sensor is smaller it only needs a smaller image circle.  Thus the lens can be smaller with all else being equal.

That's why really small sensors can have really small lenses.


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## Tomasko (Nov 9, 2017)

darkblue-x said:


> Tomasko said:
> 
> 
> > Focal lengths are (to my knowledge)  always written in respect to 35mm / fullframe. It doesn't matter if it's Nikon/Canon/Sony/whatever brand, it's still the same thing. It also doesn't matter if it's a zoom lens, macro lens, telephoto, prime.. If the lens says for instance "24mm", you know they mean it gives you 24mm FOV on a fullframe camera and different FOVs on different sized sensors based on the crop factor.
> ...


What are you confused about? Once again, it's just a simple multiplication and division.

FOV of a 16mm lens on a DX body = FOV of a 24mm mounted on a FX body

Crop factor of a DX camera is 1.5, so if you have a lens with a certain focal length and you have a DX body, just multiply the values to know what FOV would it correspond to on a FX body. 

Seriously, this is primary school Math...


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## darkblue-x (Nov 9, 2017)

Tomasko said:


> darkblue-x said:
> 
> 
> > Tomasko said:
> ...


16mm dedicated dx = 24mm fx. conversely 24mm fx brought back to dx cam is 36mm. thats what confused me.


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## Braineack (Nov 9, 2017)

darkblue-x said:


> To get a prime with same FOV as my 35mm DX do I have to buy a 50mm on FX?



yes.

since 35mm focal length x 1.5 crop factor = 52.5mm FX equivalent









> 16mm dedicated dx = 24mm fx. conversely 24mm fx brought back to dx cam is 36mm. thats what confused me.




NO! come one.  this is basic math.   do they not teach math in school anymore?

if: 16 * 1.5 = 24   how can 16 * 1.5 also = 36

this is like 3rd grade math:

if: X * 1.5 = Y

and Y = 36, solve for X.

X * 1.5 = 36

X / 1.5 = 36 / 1.5

X = 24


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## Designer (Nov 9, 2017)

I guess we'll keep trying until you say "stop, I completely understand now. Don't keep trying to explain any further!"


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## darkblue-x (Nov 9, 2017)

Braineack said:


> darkblue-x said:
> 
> 
> > To get a prime with same FOV as my 35mm DX do I have to buy a 50mm on FX?
> ...


*Tokina 11-20mm f/2.8-22 Wide-Angle-Zoom Fixed Zoom Digital SLR Camera Lens, Black (ATXAF120DXN)*

by Tokina


1 customer review



Price: CDN$ 780.03 FREE SHIPPING.


Only 1 left in stock.



Ships from and sold by MIAMI TRADING.
15 new from CDN$ 727.61 2 used from CDN$ 815.98




F-Mount Lens/*DX Format. 16.5-30mm (35mm Equivalent)*
Aperture Range: f/2.8 to f/22. P-MO & Glass-Molded Aspherical Elements
Three SD Ultra-Low Dispersion Elements. Multi-Layer Lens Coatings
--------------------------------------------------------------------

F MOUNT ON A DX CAMERA SIR.

16MM DX dedicated is 24mm on FX dedicated.

16mm dx=24mm fx

to reverse FX dedicated 24mm put on DX is 36mm.

k? at this point youre misunderstanding me. im talking about the different mounts at the same time.


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## Tomasko (Nov 9, 2017)

Mount doesn't matter at all. *AT ALL*.

The text you posted even tells you what does it translate to when converted to the 35mm format (*16.5-30mm (35mm Equivalent)*)

And one last time:

If you convert one format to another, you use multiplication (DX -> FX). If you want to convert back, you need to use the OPPOSITE operation = DIVISION.

At this point I believe you're just having tremendous fun. Seriously, primary school Math.


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## darkblue-x (Nov 9, 2017)

Tomasko said:


> Mount doesn't matter at all. *AT ALL*.
> 
> The text you posted even tells you what does it translate to when converted to the 35mm format (*16.5-30mm (35mm Equivalent)*)
> 
> ...


why its bolded and underlined clearly.
16mm dx dedicated is 24mm fx
24mm fx to 35mm format (dx) is 36.
youre confused clearly or just dont like my method of explaining it


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## Alan92RTTT (Nov 9, 2017)

darkblue-x, Unless i have missed something you have one body, a D7100. If that is correct, there are a lot of details in this thread that do not matter to you. 

DX vs FX is irrelevant to you as far as what you will see when you use the lens. The FOV conversions and all the other math do not matter.  FX and DX lenses will provide the exact same image on your D7100.  If you want to take wider angle images get a lens with a smaller mm that what you have. If you want to zoom more get a larger mm lens. 

IF and ONLY IF you think you will get a FX body at some point in the future buy FX lenses as they will work on the FX camera. 

Ignore the DX/FX just get the size lens you want.


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## john.margetts (Nov 9, 2017)

Tomasko said:


> Focal lengths are (to my knowledge)  always written in respect to 35mm / fullframe. It doesn't matter if it's Nikon/Canon/Sony/whatever brand, it's still the same thing. It also doesn't matter if it's a zoom lens, macro lens, telephoto, prime.. If the lens says for instance "24mm", you know they mean it gives you 24mm FOV on a fullframe camera and different FOVs on different sized sensors based on the crop factor.



Good Lord! Completely wrong.

Focal lengths are written in respect of the focal length. If you buy a 80 mm Hasselblad lens it will be 80 mm focal length and Hasselblad do not care at all about "full frame" as their sensors are much bigger.


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## john.margetts (Nov 9, 2017)

darkblue-x said:


> I'm confused again because the FOV of 16mm DX on FX is 24mm.
> So then 35mm DX on FX is???? 50mm FX? To get a prime with same FOV as my 35mm DX do I have to buy a 50mm on FX?


I'm not surprised you get confused - most of the explanations are awful. Even where they are right they are very badly expressed.


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## john.margetts (Nov 9, 2017)

Alan92RTTT said:


> darkblue-x, Unless i have missed something you have one body, a D7100. If that is correct, there are a lot of details in this thread that do not matter to you.
> 
> DX vs FX is irrelevant to you as far as what you will see when you use the lens. The FOV conversions and all the other math do not matter.  FX and DX lenses will provide the exact same image on your D7100.  If you want to take wider angle images get a lens with a smaller mm that what you have. If you want to zoom more get a larger mm lens.
> 
> ...


Accurate and well expressed.


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## Tomasko (Nov 9, 2017)

john.margetts said:


> Tomasko said:
> 
> 
> > Focal lengths are (to my knowledge)  always written in respect to 35mm / fullframe. It doesn't matter if it's Nikon/Canon/Sony/whatever brand, it's still the same thing. It also doesn't matter if it's a zoom lens, macro lens, telephoto, prime.. If the lens says for instance "24mm", you know they mean it gives you 24mm FOV on a fullframe camera and different FOVs on different sized sensors based on the crop factor.
> ...


GOOD LORD!

Do you seriously think he needs to know about medium or large formats? He obviously has problems with the most basic Math. I'm talking about the most common commercially available gear that would be relevant for his needs using a crop/ff DSLR.


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## Tomasko (Nov 9, 2017)

darkblue-x said:


> Tomasko said:
> 
> 
> > Mount doesn't matter at all. *AT ALL*.
> ...


What are you talking about? 35mm isn't DX, it's FX.
I don't know what you mean by "dedicated dx". Focal length is focal length, doesn't matter what mount you put it on. If you're converting from DX (CROP) to a FX (FULLFRAME), you're multiplying. If you're converting back, from FX (FULLFRAME) to DX (CROP), you divide. Both operations involve whatever focal length you're interested in AND the crop factor you're converting to/from. Focal length after both operations stays the same, only FOV changes.


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## john.margetts (Nov 9, 2017)

Tomasko said:


> john.margetts said:
> 
> 
> > Tomasko said:
> ...



Any photographer only needs to know about the formats he actually uses. What you wrote about focal lengths being written in respect to 35 mm/fullframe was complete rubbish. The Op is confused, not because of his poor maths skills, but because of the poor explaining skills of a majority of posters in this thread.


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## WayneF (Nov 9, 2017)

Tomasko said:


> Focal lengths are (to my knowledge)  always written in respect to 35mm / fullframe. It doesn't matter if it's Nikon/Canon/Sony/whatever brand, it's still the same thing. It also doesn't matter if it's a zoom lens, macro lens, telephoto, prime.. If the lens says for instance "24mm", you know they mean it gives you 24mm FOV on a fullframe camera and different FOVs on different sized sensors based on the crop factor.



No. Maybe you just meant the Equivalent focal length is always with respect to full frame, but the marked focal length of the lens is Not about full frame sensors.  Not about any sensor. The lens is always marked to show what the lens actually does, how it actually focuses.  If any 24 mm FL lens is focused at infinity, the focused point is 24 mm behind the node in the lens, which is where any sensor has to be.  Sensor size does Not affect focal length.  Focal length is "distance to sensor", but the marked Focal Length is this focused point at infinity (focus at infinity is what is marked).   DX and FX can use the same lens only because the Nikon F mount is the same distance from sensor for every lens, in every case. The sensor size just frames that image, crops it so to speak, crops size which is also Field of View,  so that the Field of View seen by the sensor varies with sensor size. But the focal length is always as marked. Lens FL does Not change by merely attaching a different sensor.

A smaller sensor (perhaps like in a little compact camera) will use a much shorter lens (maybe 5 mm FL for a much wider view on this tiny cropped area), so that its small sensor will still show a normal field of view. Because we expect normal view photographs from it.  So its lens spec may say like 5 mm.  It probably also says "35 mm film Equivalent" is maybe 24 mm.  That's a very convenient comparison if you have 35 mm film experience (popular since about 1930). It simply means a 24 mm lens on a 35 mm film camera would see the same Field of View, but it does not change this lens which is still 5 mm FL.  This sensor size is further represented by saying the sensor  Crop Factor is 24/5 = 4.8x Crop factor (in this hypothetical 5mm / 24 mm case).


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## astroNikon (Nov 9, 2017)

FYI .. trying to make it easy to understand the basic concept ....

FX EQUALS 35mm.  Both are 1.0x for calculation for what you see on the lens.

with the lens IGNORE all indicators of DX or FX

The Field of View (which is NOT the lens) is totally based on SENSOR SIZE assuming all lens/camera are the same.

So a 50mm lens .. not matter what .. is a 50mm FOV on a FX/35mm film camera
on a APS-C Nikon (yes, Canon is slightly different and different size sensors are even more different) it's like a 75mm FOV lens.

For a 50mm lens ...
on DX is 50 x 1.5 = 75 FOV to get back to FX .. which is 75 x (1/1.5) = 50 for FX FOV


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## petrochemist (Nov 9, 2017)

There are a some fixed lens cameras that refer to their lenses using 35mm equivalent focal lengths. Apart from that the only place I've seen equivalent focal lengths used for describing lenses is in e-bay listings where someone is trying to gild a pile of s***e.

If you only use one format equivalence is pretty pointless - only being relevant for using old guidelines on shutter speeds (for things like hand-holding, star trails etc.). 
When I used my 120mm medium format lens on my crop DSLR it gave the same view/DOF/shutter speed as a native 120mm lens would on that camera at the same aperture. The total distance (lens surface to sensor) needed to focus the image was also the same as it would have been on the medium format camera at the same object distance...


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## Braineack (Nov 9, 2017)

darkblue-x said:


> F-Mount Lens/*DX Format. 16.5-30mm (35mm Equivalent)*
> 
> k? at this point youre misunderstanding me. im talking about the different mounts at the same time.



punctuation matters.   There's a period.  That means end of sentence.

it reads: This lens is a F-Mount Lens/*DX Format.  PERIOD, STOP.  This lens would be like a 16.5-30mm on an FX.*

All Nikon DSLR lenses are F-mount.  This is a 11-20mm DX lens.  It would perform like a 16.5-30mm on an FX.


again:

11 * 1.5 = *16.5mm*
20 * 1.5 = *30mm

*

this is why I said stop worrying about it.  it's causing confusing you don't need to worry about.   Don't buy DX only format lenses if you plan on ever going FX.


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## darkblue-x (Nov 9, 2017)

Tomasko said:


> john.margetts said:
> 
> 
> > Tomasko said:
> ...


See the biggest problem I have here is the fact that you insist on underhandedly calling me a dumbass. The belittlement isn't appropriate as much as you find this maelstrom frustrating.
The fact that you don't seem to understand what it is that I am asking may pose the problem. You cant expect a layman seeking education to magically give you a camera-club jargon definition of what they are wondering.

I want to window shop for when I buy FX. may be this Black Friday coming or more likely next year.

SO...when I jam a my 16-85mm DX nikkor at the 16mm focal length, I see a certain angle of view in the viewfinder.
What I understand and that I am being told is that in order to see the same angle of view on a FX camera with an FX lens, that that focal length would be 24mm.
Now is this correct or are we still going back to square one?

Refer to the following information:
Crop Sensor (APS-C) Cameras and Lens Confusion

Under the:
*Wideangle Lenses*

Section they advise what the focal length equivalents are between the two types, first the FX and then the APS-C.

Ysarex understood what I was saying and kept it simple.
31.3mm crop yields the same angle of view as 50mm fx lens on fx.

where I use 35mm prime on dx for portraits, I would be mistaken buying a 35mm fx lens for fx, it wont be the same angle of view. I would need to buy a 50mm lens to get the closest equivalent, or even better tamron makes a 45mm fx lens that seems to mimic eye view.


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## Alan92RTTT (Nov 9, 2017)

darkblue-x said:


> I want to window shop for when I buy FX. may be this Black Friday coming or more likely next year.
> 
> SO...when I jam a my 16-85mm DX nikkor at the 16mm focal length, I see a certain angle of view in the viewfinder.
> What I understand and that I am being told is that in order to see the same angle of view on a FX camera with an FX lens, that that focal length would be 24mm.
> Now is this correct or are we still going back to square one?



You should have put that in your initial post  

Knowing this, 1.5 is the magic number.

If you have a lens you like on your D7100 take its MM and multiply it by 1.5.  A lens with that result on a FX camera will result in the same field of view.  Its really that simple.


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## darkblue-x (Nov 9, 2017)

Alan92RTTT said:


> darkblue-x said:
> 
> 
> > I want to window shop for when I buy FX. may be this Black Friday coming or more likely next year.
> ...


Yeah definitely no problem there.
Some have told me to start investing in FX lenses now if I know I will make the switch. That's where it gets tricky...if I want a angle of view on FF camera of 39 degrees I need to buy a 50mm FX lens. but then that wouldnt give me the same angle of view should I jam it on my APS-C in the interim.
That's the trickiest part.
Being said. F all that noise. I'll chill for now and in the future ill know to buy the 50mm fx lens on FF to get the same angle of view as I do with dx lens 35mm on APS-C camera.


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## birdbonkers84 (Nov 9, 2017)

I have the D7100 and current use a 18-55 lens on it for landscapes (27-82.5). I'm actually looking at buying the Tokina 11-20 cos it will give me the equivalent of 16.5-30 on my camera which is far wider than I have at the moment. 


Sent from my iPhone using ThePhotoForum.com mobile app


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## WayneF (Nov 9, 2017)

Designer said:


> In what regard is it "important"?



Crop Factor is not likely important to a newbie, or to those that will never understand anything technical (as evidenced here recently). Sometimes technical experience is limited to how to turn it on.

When using their camera, the Field of View is what they see that it is. They don't need to know anything else about it, and many don't know, and don't care. But there are facts that are simply good to know.

In the early days of digital, and even still today, there are many users with years or decades of 35 mm experience.  They just simply already know exactly what field of view to expect from 24 mm or 200 mm, second nature to their experience.  But they have (or had) no experience with a new crop 1.5 or crop 2 or crop 5.5 digital camera. The Equivalent 35 mm focal length guides them about what lenses to buy for that new experience.  Or  what the body choice with fixed lens will do, in terms they  can relate to.  I would call that Extremely Important and Useful.

We might argue that that need is becoming dated today as more of us gain experience, except that all the confusion in places like this thread that proves otherwise.

This was true in film days too, large and medium and 35 mm formats with interchangeable lenses needed to know which lenses to buy for that choice.  Darkroom enlargers needed different lenses for the  different formats too.  But today, the FX and DX DSLRs mount the same lenses, so the situation is much more in our face.

But if they never have any intention of being interested in full frame, then Equivalent Focal Length is not important (to them), and is only a confusion (for some of them).  The term is not fully self-explanatory, needing a bit more reading, which some will never consider doing.


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## davidharmier60 (Nov 9, 2017)

Meanwhile I completely understand. And really want a Canon 20, 30 or 40D (ideally gifted but MUST be cheap) to use with Sigma 19-35 and 28-105.

Sent from my SAMSUNG-SM-G890A using Tapatalk


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