# 35mm Equivalent on Crop Sensor - DX vs FX Lenses



## AlexGavillan (Aug 2, 2018)

OK so, I think I know the answer to this question but I just need someone to clarify. When looking at lenses (Nikkor to be specific) I know that there are FX and DX lenses. The DX lenses will have the mm as to how it relates to 35mm film, got it! But here is where I get confused and what I think they (The manufacture means)

I have the 1.8 AF-S Nikkor 35mm DX lens. I know that this gives me about 50mm since I have the 1.5 crop factor BUT on the lens itself (this is the DX version) it states 35mm. Here is my guess and please excuse the non technical terms as I don't think i know them.

My guess is that since the sensor on a full frame camera is bigger the opening on the lens itself (the part that connects to the front of the camera) is larger to accommodate for the full frame sensor, but the DX one, since its a crop sensor has the opening that works best for a crop sensor camera. 

I guess I get confused because I would just assume that on a DX lens the manufacture would put "Oh you want a 50mm on your crop sensor well actually put 50mm on that type of lens VS just putting the 35mm equivalent." Example, if I want a 105mm lens that's DX there is still a 1.5 crop factor which really gives me the focal length of a 155mm.

I hope this makes sense and someone can just say, "Yup, that's what that means." haha

Thanks,

Alex


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## john.margetts (Aug 2, 2018)

Your lens is 35 mm on any camera it is attached to and even when it is not attached to anything. Putting the lens on a DX camera does not and cannot alter the focal length.

The opening is the aperture and is entirely separate from the focal length and also does not change depending on FX or DX.

Unless you have both an FX and a DX camera, you should ignore the crop factor and just learn how your particular lenses work on your particular camera body.

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## BrentC (Aug 2, 2018)

Focal length of a lens never changes no matter what sensor camera you have it on.  Your field of view changes depending on the sensor.   So when we say a 35mm lens is equivalent to 50mm  on a crop sensor what we are really saying is that the FoV of a 35mm lens on a crop sensor is equivalent to the FoV on a 50mm lens on FF.


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## AlexGavillan (Aug 2, 2018)

Thanks guys .I used the wrong term when I said focal length. I know that that doesn't change. But I don't think my question is being understood .

This one might be easier. Why is there a DX and FX lens types? It's not all the same in that regard, what's the technical difference (if any) realted to that.


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## ceemac (Aug 2, 2018)

A camera with a full frame sensor requires a wider (diameter) lens so that the entire sensor is covered by the light from that lens. A lens for a crop sensor camera won't let in enough light to use the entire sensor on a full frame camera. A full frame lens will work fine on a crop sensor camera. It's just bigger, heavier and more expensive.


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## AlexGavillan (Aug 2, 2018)

ceemac said:


> A camera with a full frame sensor requires a wider (diameter) lens so that the entire sensor is covered by the light from that lens. A lens for a crop sensor camera won't let in enough light to use the entire sensor on a full frame camera. A full frame lens will work fine on a crop sensor camera. It's just bigger, heavier and more expensive.



Perfect OK so that really helps. Then my next question (and this is probably just an industry standard thing) Since I am dealing with a Crop sensor DSLR, ANY lens I put on it I have to multiply the focal length times 1.5, even if its a DX specific lens. Would it not make sense that if a lens is DX format the manufacture puts the (cropped) focal length? I.E if its a 50mm DX put 50mm on the lens vs the 35mm equivalent..

So what I can conclude, which affirms my thoughts, DX lenses have a smaller diameter so that it properly covers the sensor of a crop sensor camera. I understand that an FX lens will work on a crop sensor body but not the other way around, or just not as well, probably vignetting on the corners or something like that, or nothing at all.


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## snowbear (Aug 2, 2018)

AlexGavillan said:


> So what I can conclude, which affirms my thoughts, DX lenses have a smaller diameter so that it properly covers the sensor of a crop sensor camera. I understand that an FX lens will work on a crop sensor body but not the other way around, or just not as well, probably vignetting on the corners or something like that, or nothing at all.



I regularly use my 18-200mm DX lens on the FX D750 body.  However, the camera will default to going into "crop mode" meaning only the part of the sensor matching DX will be used.  This can be changed so it doesn't automatically crop, which will give you the mentioned vignetting.  If I get a chance this weekend, I'll post some examples.


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## john.margetts (Aug 2, 2018)

AlexGavillan said:


> Perfect OK so that really helps. Then my next question (and this is probably just an industry standard thing) Since I am dealing with a Crop sensor DSLR, ANY lens I put on it I have to multiply the focal length times 1.5, even if its a DX specific lens.


No! No! No! You do not have to multiply the focal length and you should not. Use your 35 mm lens on your DX camera and know that it is 35 mm. Know how it behaves on your camera. You have no need to worry about how it behaves on a camera you do not have.



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## AlexGavillan (Aug 2, 2018)

Thanks John. But you do see what I'm saying right? I cant buy a 105mm lens and expect it to be 105mm on my D3400 right? There is a crop factor Maybe I'm not having that light bulb go off haha, need that ah ha moment...

This for example:
     The DX sensor makes possible the production of lighter, smaller cameras, but because it covers a smaller portion of the image projected by the lens, a 1.5x crop factor (so called because the smaller sensor crops the image compared to an image from a 35mm film frame) is introduced. This means, for example, a 24mm lens on a DX sensor camera will provide an approximate 36mm view.

Reference: FX & DX Format Lenses Explained | Learn About FX Lenses & DX Cameras from Nikon


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## snowbear (Aug 2, 2018)

AlexGavillan said:


> a 24mm lens on a DX sensor camera will provide an approximate 36mm view.


yes - the 1.5 is the equivalent view angle.  Unfortunately a lot of confusion has been created with the terminology used.


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## 480sparky (Aug 2, 2018)

And this is why I wish the 'crop factor conversion' idea would disappear from the face of the earth. Erase it. Delete it. Send it to the Trash Bin. Eradicate it. As if it never existed.

What I find amazing is back in my film days, there was no such thing as a 'conversion factor' to compare lenses between 135, 120 and 4x5 formats. I never heard of a number to multiply (or divide by) when changing from 35mm to 6x4.5 format, or to 6x7 format, or to 4x5 format. I never had to 'convert' the 80mm lens of my Mamiya 645 to 'the equivelant of __mm on my 35mm camera". Nor convert the 150mm on my 4x5 to 'the equivelant of __mm on my RB67 camera".

I understand why the manufacturers created the 'conversion' factor. It was a marketing tool to help sell fledgling digital SLRs to an uneducated populace. The populace that had grown up with one format: 35mm. Everyone and their uncle owned a 35mm film camera. Most carried a 50mm 'standard' lens. Many purchased 28mm wide-angles and 135mm telephotos. So that was 'the gold standard' back then.

Then along came digital. But the sensors were smaller than a 35mm frame. So the manufacturers needed an easy way for those transitioning to digital to 'relearn' how focal length related to FOV. "Conversion factor' seemed like the perfect choice. And it was. At least back then.

But today, we have an entire generation that has never even SEEN a 35mm film camera, let alone understand focal length, sensor/film plane size and how the two relate to FOV. So today, the 'conversion factor' has royally muddied the waters. Not to mention the internet, and it's ability to spread incorrect information that will be accepted as gospel.

And next, the assumption (and even firm belief with some) that the 'conversion factor' applies to other properties of the lens, such as aperture and minimum focus.

I say it's time to deposit 'the conversion factor' to the dustbin of history. Let it reside the Hall of Useless Technology, next to ice picks, buggy whips and 8-track tapes.


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## john.margetts (Aug 2, 2018)

AlexGavillan said:


> Thanks John. But you do see what I'm saying right? I cant buy a 105mm lens and expect it to be 105mm on my D3400 right? There is a crop factor Maybe I'm not having that light bulb go off haha, need that ah ha moment...
> ]


No, not right. It will still be a 105 mm lens. What you need to think is not what happens if you buy a 105 mm lens. What you need to think is "I want a lens to do so-and-so. Which lens will do that?". When you buy a new lens, buy one that produces the pictures you want without worrying about a FX camera you do not own.

That 105 mm lens will not behave the same on your camera as it will on an FX camera but that does not matter as you do not have a FX camera. It will behave the way that a 105 mm lens will behave on your camera. Comparing it to a camera you do not have does not help you - you might as well compare it to how it would behave on my medium format Bronica where it would be hellishly wide angle with a crop factor giving it a 'focal length' of 50 mm.


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## Designer (Aug 2, 2018)

AlexGavillan said:


> Why is there a DX and FX lens types? It's not all the same in that regard, what's the technical difference (if any) realted to that.


The simplest explanation is that lens manufacturers can make "DX" lenses cheaper than "FX" lenses.  

By now, you have the concept of the image projection circle which, in a DX lens is smaller in diameter than that of an FX lens.  

The lens mounting flange in Nikon cameras will accept either "DX" or "FX" lenses.  BTW: if a lens doesn't say DX, then you may assume it is an FX lens.  

Do a search of the forums on here and you will find some very good explanations offered, and some with outstanding graphical representation of the differences.

Meanwhile, try to ignore the folks on the internet who are obsessing over that "crop factor" term and are telling newbs that "a 35mm lens is really a 50mm lens", and other misleading BS.


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## ceemac (Aug 2, 2018)

Designer said:


> Meanwhile, try to ignore the folks on the internet who are obsessing over that "crop factor" term and are telling newbs that "a 35mm lens is really a 50mm lens", and other misleading BS.


What designer says.
Look at any photo and pretend it's a full frame camera with a 50mm lens. Now crop that photo by 30% or so. That's what a crop sensor camera sees with a 50mm lens. Absolutely no change in zoom. It doesn't matter whether it's FX orDX lens, 50mm will always be 50mm.


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## ceemac (Aug 2, 2018)

AlexGavillan said:


> So what I can conclude, which affirms my thoughts, DX lenses have a smaller diameter so that it properly covers the sensor of a crop sensor camera. I understand that an FX lens will work on a crop sensor body but not the other way around, or just not as well, probably vignetting on the corners or something like that, or nothing at all.



Sounds about right. With my Canon I'm unable to put an EFS (crop lens) on a full frame camera as there's no point.


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## Derrel (Aug 2, 2018)

If you want the "_classic Nikkor lens medium telephoto look_", the one made famous by the Nikkor 105mm f/2.5 lens models, and that focal length's angle of view on film-era Nikon cameras, then on a DX-sensor digital SLR, you want roughly a 68mm lens. The conversion factor is roughly 1.53 for Nikon d-slrs of the modern era. The short end of a 70-200 AF lens, or the short end of a 70-210mm manual focus lens, or the long end of a 28-70mm or 24-70mm zoom lens, will give a pretty close angle of view match to the classic 105mm lens that was so,so popular in the film era.

Now, if you happen to have a 105mm Nikkor lens, and use it on your *DX-senso*r model Nikon d-slr, multiply the actual focal length of 105mm by 1.53, and you come up with just a tad bit over 160mm...in other words, a pretty good, narrow-angle telephoto lens length, similar to the 150mm or 180mm lengths that we had in the 1980's on the 70-150mm zooms, or the 180mm prime lens models.


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## ac12 (Aug 2, 2018)

My approach is as mentioned, forget the crop ratio business and think based on your format.
As was mentioned, when I shoot 35mm film and 6x6 film, I don't think crop ratio.  I simply think in terms of the lens for that format, based on the normal lens for that format.
Normal lenses for the various formats are:

35mm film = 50mm 

6x6 = 80mm
4x5 sheet film = 150mm
If I want a tele on my 6x6, I go up based on the 80mm normal.
A 2x tele = 80mm x 2 = 160mm, then round to the nearest lens = 150mm.
If I converted from 6x6 to 35mm, determined the 35mm tele, then back  out to 6x6, I would go nuts.

IMHO, going through the crop ratio conversion just muddies the water.
Today when I shoot

micro 4/3 = 25mm normal lens
DX = 35mm normal lens
IOW, just reset your brain for the format that you are shooting in, and ignore the crop ratio nonsense.

An easier method is to think in terms of magnification, and ignore the crop ratio.
If you get a 105mm lens and put it on a DX camera you have a 3x magnification lens.  105 / 35 = 3
A 24mm lens on your DX camera has a 0.7x magnification.  24/35 = 0.7

_*The only time I get into crop ratios is when I am changing systems and want a lens with a similar field of view.*_
So if I have a 24mm lens on my 35mm film/FX camera, and want a lens for my DX camera, with a similar field of view (FoV).
A 24mm lens on a 35mm film/FX camera has an 84 degree diagonal FoV.​With a 1.5x DX crop.  24/1.5 = 16.  
I need a 16mm lens on my DX camera to give me the same FoV as my 24mm lens on the 35mm film/FX camera.
A 16mm lens on a DX camera has an 83 degree diagonal FoV.​So to *maintain the same 84 degree FoV* of my 24mm lens on a FX camera, I have to use a 16mm lens on my DX camera.


But if I put that 24mm lens on my DX camera, the 84 degree FoV of the 24mm lens on a FX camera, gets reduced by the 1.5x crop to 61 degrees on a DX camera.
*The focal length of the lens has not and will not change, it is still 24mm.*
The _FoV_ had been reduced _because of the smaller sensor size_.​
Going backwards_ gets into that "equivalent FF focal length" stuff.
That reduced 61 degree field of view of the 24mm lens on a DX camera, will *look like *a 36mm lens on a FX camera. (24 x 1.5 = 36), of 62 degrees._
Here we *maintain the FoV at 61 degrees*, and changed the focal length to a lens with a 61 degree FoV on a FX camera.
So to get the same 61 degree FoV, 

on a DX camera you use a 24mm lens, 

on a FX camera you use a 36mm lens._  This is the FF equivalent number._
If you want to play with this more, here is a site that lets you input the 2 variables (sensor size and lens focal length) to determine diagonal FoV.
Depth of Field (DoF), Angle of View, and Equivalent Lens Calculator | Points in Focus Photography{%22c%22:[{%22f%22:13,%22av%22:%228%22,%22fl%22:36,%22d%22:3048,%22cm%22:%220%22}],%22m%22:0}


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## AlexGavillan (Aug 2, 2018)

Thank you to everyone who chimed in and offered such detailed information, I really appreciate it. Ok so...I think I got it and FoV is what I needed to hear/understand and what was confusing me.

Ok so here goes 

A 35mm is a 35mm all day long, don't worry about the crop factor period. Got it. What I was trying to make sense of was the FX to DX, and like many of you said don't worry about that. I had that Ah Ha as I was sitting in traffic. I was trying to do an equation (that I didn't need to) to get what I thought was the focal length of an FX lens to be the same as a DX lens. But really what I was doing and didn't know it was a FoV conversion instead. 

Example, when looking for a 105mm lens I was really looking for like an 80mm or something around there thinking "that gets me to 105 on my crop sensor, which is the FOCAL LENGTH I want" WRONG!!! I was doing a damn FoV conversion which isn't really relevant. 

So is that to say (please don't slap me) if I bought a 105mm the focal length is the same, FX and DX but the FoV is what's multiplied by 1.5? So in reality, if it's the same exact lens on an FX camera and aaDX camera, I could achieve the same FoV if I backed up so to speak? I know there is probably more to it since the FX camera has a larger sensor and there are other factors to consider... But am I close to getting it?


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## 480sparky (Aug 2, 2018)

By jove, I think you've got it.

Another way to think of it is to take a photo with, say, a 50mm lens.  Print the photo without cropping it. 

Now, take a pair of scissors and trim off the outer 25% of the image, cutting equally on all four sides.  The image was still taken with a 50mm lens.

But the visual FoV makes it _appear_ it was taken with a longer focal length.


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## Designer (Aug 2, 2018)

AlexGavillan said:


> But am I close to getting it?


Yes. 

Now I'm curious as to why all that is a concern of yours.  I shall "project" into your situation, and try to imagine what is going through you mind.  

Say your have a limited space in a studio where you can't expand the space, and you still want to minimize distortion, so you would like to calculate what focal length of lens to use in order to produce optimum results.

You wish to make portraits with an apparent focal length of around 150mm, so you purchase a lens with a focal length of 100mm to get that look.  

This line of thinking will probably give you the results you want, or close to it.


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## AlexGavillan (Aug 3, 2018)

Success haha!! Well I thought


Designer said:


> AlexGavillan said:
> 
> 
> > But am I close to getting it?
> ...



Well now there is no concern haha. I was just trying to wrap my head around all the DX, equivalent, etc stuff. Once for education and 2 so I can be informed when I go to purchase my next lens. This all cropped up because I was looking at picking up a wide angle lens to shoot some interior scenes for a family members rental property. I had been reading about ideal focal lengths, and once again thought, "I need X so that its X on my camera." but now that doesn't matter (as much) I should say.


BOOM:


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## ac12 (Aug 3, 2018)

re: the video
Today, focal length is not physical, but usually optical. 

Optics are used to shorten a long focal length lens.  This makes the lens easier to handle, than the old "stove pipes" of yesteryear.

Optics is used so that a SHORT focal length lens can be used on your DSLR camera.  If it were physical, the mirror would have to be locked UP, because the lens would be sticking so far into the camera that it would break the mirror.
I agree with one of his comments.  Many of the new generation of photographers were brought up on DX/crop cameras and have no idea what a FF/FX image looks like.  So to say "105mm FF equivalent" means nothing, because they don't have that FF reference point.  Going in reverse, a DX/APS-C equivalent would make more sense for them.

Personally I feel it less confusing to convert to magnification. 
Like degrees of angle in a "Field of View," magnification is a number that is independent of film/sensor size.  But unlike having to look up the FoV for a particular lens on a particular film/sensor size, magnification is easy to determine.
_Lens focal length / normal lens focal length = magnification_
A 24mm lens on a FF camera has 0.48x magnification (24 / 50 = 0.48). 
So you would need a 0.48x magnification lens to get the picture.​Once you have the magnification, all you need to know is the normal lens of the target format(s).
_Normal lens x magnification = desired focal length_
On a DX camera, you need a 17mm lens(35 x 0.48 = 16.7)
On a m4/3 camera, you need a 12mm lens (25 x 0.48 = 12)
On a 6x6 camera, you need a 39mm lens (80 x 0.48 = 38.4)
On a 4x5 camera, you need a 72mm lens (150 x 0.48 = 72)​Note that the magnification method is "good enough" for most uses but not exact.  This is because the "normal lens" is based on the generally used normal lens for that format, not the computed normal lens based on the diagonal measure of the film image or active area of the image sensor.
Example.  The computed normal lens for 35mm film/FF sensor of 24 x 36mm is 43mm, not the generally used 50mm.
For the curious, the equation for the film diagonal (normal lens) is from high school geometry for a right triangle  
A^2 + B^2 = C^2   =>   24^2 + 36^2 = C^2  where C=43​
There is also some minor adjustments that have to be made because of the different formats are different, and have different horizontal and vertical ratios.


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## Ysarex (Aug 3, 2018)

480sparky said:


> And this is why I wish the 'crop factor conversion' idea would disappear from the face of the earth. Erase it. Delete it. Send it to the Trash Bin. Eradicate it. As if it never existed.
> 
> What I find amazing is back in my film days, there was no such thing as a 'conversion factor' to compare lenses between 135, 120 and 4x5 formats. I never heard of a number to multiply (or divide by) when changing from 35mm to 6x4.5 format, or to 6x7 format, or to 4x5 format. I never had to 'convert' the 80mm lens of my Mamiya 645 to 'the equivelant of __mm on my 35mm camera". Nor convert the 150mm on my 4x5 to 'the equivelant of __mm on my RB67 camera".



So Sparky back in the day I used to shoot a modular Arca system that took interchangeable backs. I could leave the lens on the front standard and just swap out backs. One of my favorite lenses from back then was a 90mm Fujinon SW. So if I put the 90mm on the camera and started out with the 4x5 back the 90mm would have a crop factor of 1? And then when I swapped the 4x5 back for the 6x9 back without changing the lens that same lens would get a new crop factor which would change it's focal length from 90mm to 162mm?  And then when I swapped out the 6x9 back for the Nikon adapter the lens would get another new crop factor and change focal length again? Oh I'm so confused now and I didn't even know I was confused then!! 

Joe


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## ceemac (Aug 3, 2018)

Aw you guys, just when Alex was starting to figure this out... I'm sure it can be explained by simple calculus or something.


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## ac12 (Aug 3, 2018)

ceemac said:


> Aw you guys, just when Alex was starting to figure this out... I'm sure it can be explained by simple calculus or something.



Boo hiss
I hated and still hate high math.


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## ceemac (Aug 3, 2018)

ac12 said:


> Boo hiss
> I hated and still hate high math.


C'mon admit it you feel the need to finally use calculus for something. That's up there with fitting Frederick the Great of Prussia into a conversation.


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## AlexGavillan (Aug 5, 2018)

Hahaha. 

See the below is why I've been so confused. Reading articles like the one sited, take a look at what they are saying. 

Link: Buying Your First Prime Lens - 35mm or 50mm?

"Another thing to consider when choosing between the 35mm and 50mm focal lengths is crop factor. When I bought my first prime lens, I was shooting with a Canon 7D as my primary body. I was actually deciding between a Canon 24mm f/1.4L and a 35mm f/1.4L. With my 1.6 crop sensor body, I wanted to achieve a 35mm look so I opted for the 24mm f/1.4L.  With the crop factor, that gave me about a 38mm lens."


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## Derrel (Aug 5, 2018)

AlexGavillan said:


> Hahaha.
> 
> See the below is why I've been so confused. Reading articles like the one sited, take a look at what they are saying.
> 
> ...



The above makes total sense. It's good information.


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## AlexGavillan (Aug 6, 2018)

Derrel said:


> AlexGavillan said:
> 
> 
> > Hahaha.
> ...



I think I get what he's saying, now but when reading that I guess the writer is assuming the reader knows a thing or two about photography. 

So when he says "35mm look" what's he reffering to, what he sees on the viewfinder or picture itself?


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## ac12 (Aug 6, 2018)

IMHO it is the wider FoV.  If your back is up against the wall with a 50mm lens, you cannot backup any more to get a wider FoV.  Hence the 35.
This is why when I shot 35mm film, I used a 24mm lens.  I did not always need that wide a coverage, but when I did, I did.  And the wider the better.  But because the 24 is so wide, I did not use it as my only lens.  I always used it in conjunction with another narrower lens.  Whereas a 35 could be used as the only lens.

He is also considering how the background and out of focus blur looks.


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## Designer (Aug 6, 2018)

AlexGavillan said:


> So when he says "35mm look" what's he referring to, what he sees on the viewfinder or picture itself?


Both, actually.  They should be nearly the same image.

As for me, I would recommend some other prime lens rather than either the 35mm or 50mm.  Something longer would be my first choice.  So many nice lenses available, that it is hard to pick just one.  

What kind of photography do you like to do?  The 35 might be nice for an all-purpose carry-around lens.  For portraiture, you should use something longer, with a good minimum focal length being 85mm, and going up from there, such as; 105, 135, 180, etc.


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## greybeard (Aug 6, 2018)

It is easy to get confused with this.   The 1.5 crop factor means that a 100mm FF lens on crop frame will have the same Field of View as a 150mm lens on a full frame camera.  The focal length doesn't change it is the size of the sensor that captures the image that makes this all happen.  Because the crop frame sensor is about 1/2 the size of a Full frame sensor  it only captures the image coming from the center part of the lens whereas the FF sensor is big enough to capture the entire image.  There are, of course, lenses made specifically for crop frame cameras.  Nikon specifies these as DX as opposed to FX for full frame.  Crop frame lenses mounted on a FF camera will NOT  produce an image that will cover the entire sensor.


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## AlexGavillan (Aug 6, 2018)

ac12 said:


> IMHO it is the wider FoV.  If your back is up against the wall with a 50mm lens, you cannot backup any more to get a wider FoV.  Hence the 35.
> This is why when I shot 35mm film, I used a 24mm lens.  I did not always need that wide a coverage, but when I did, I did.  And the wider the better.  But because the 24 is so wide, I did not use it as my only lens.  I always used it in conjunction with another narrower lens.  Whereas a 35 could be used as the only lens.
> 
> He is also considering how the background and out of focus blur looks.



Totally, and now I understand that haha. I'm a fairly quick learner, but there are some things where im like huh...1 more time haha .



Designer said:


> AlexGavillan said:
> 
> 
> > So when he says "35mm look" what's he referring to, what he sees on the viewfinder or picture itself?
> ...



I picked up the NIKKOR 35mm 1.8G DX and it works great for what I'm doing. Walk abouts and just random pictures here and there. Street photography and "things" if you will really draw my interest.  I'm a hobbiest, but I alos like to learn, so just buying a DSLR, kit lens and shooting in auto didn't cut it for me. I wanted to learn about exposure, different metering modes, etc. Im an enfiengi by trade, so I can't help it haha.



greybeard said:


> It is easy to get confused with this.   The 1.5 crop factor means that a 100mm FF lens on crop frame will have the same Field of View as a 150mm lens on a full frame camera.  The focal length doesn't change it is the size of the sensor that captures the image that makes this all happen.  Because the crop frame sensor is about 1/2 the size of a Full frame sensor  it only captures the image coming from the center part of the lens whereas the FF sensor is big enough to capture the entire image.  There are, of course, lenses made specifically for crop frame cameras.  Nikon specifies these as DX as opposed to FX for full frame.  Crop frame lenses mounted on a FF camera will produce an image that will cover the entire sensor.



Thanks. Ya I looked that up a ehioe back DX vs FF or just not notaded as DX. I would like a lenses with more reach, like an 85mm for portraits and what not right now just have a faster lens than tye kit lens has been an awesome treat. Now I'm looking into not shooting everything wide open, finding the sweet spot for this lense. So far I love everything I'm learning.


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## ac12 (Aug 7, 2018)

quote
I picked up the NIKKOR 35mm 1.8G DX​end quote

Just realize that a 35mm is a "normal" lens on your DX camera, not a wide.
A "normal" lens is just fine.  On my 35mm film camera, I used a 50mm normal for several years before switching to a 43-86 short zoom.

Nikon unfortunately does not make a 24mm DX wide lens.  You have to buy the more expensive FX 24mm lens.  Then you have to be careful which one you get, based on which camera you have.  Your D3400 cannot autofocus an AF or AF-D lens, because it does not have an AF motor in the body.


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## KB2 (Aug 7, 2018)

AlexGavillan said:


> Example, if I want a 105mm lens that's DX there is still a 1.5 crop factor which really gives me the focal length of a 155mm.



This is incorrect. With a DX camera and a DX lens, there is no crop factor. A 105mm DX lens will act as a 105mm lens on your DX camera. If you end up buying a full frame camera later, that lens will give you a bad vignette that needs to be cropped, and that can be done automatically by your camera. When I "upgraded" to a FX camera, I got rid of my DX lenses. That being said, if you buy FX lenses now for your DX camera you will want to take the crop factor into account.  For example, I've always had a 50mm FX lens, and on my DX camera I never felt like I could back up far enough in my house to take pictures of my kids, but now that it's on a FX camera I don't have that problem.


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## BrentC (Aug 7, 2018)

KB2 said:


> AlexGavillan said:
> 
> 
> > Example, if I want a 105mm lens that's DX there is still a 1.5 crop factor which really gives me the focal length of a 155mm.
> ...




No this is incorrect.  Once again Focal length is focal length is focal length.   What is stated on the lens is the focal length of the lens which is a physical measurement.   105mm DX lens is the exact same focal length as a 105mm FX lens.   And yes a 105mm DX lens will have the same FoV as a 155mm lens on a DX camera.


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## KB2 (Aug 7, 2018)

BrentC said:


> KB2 said:
> 
> 
> > AlexGavillan said:
> ...


Very sorry, I'm fairly new at this too, and what I said has been my understanding for a long time. Should have kept my mouth shut. Maybe my description of using both types of lenses on both types of camera bodies will be of some use...


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## 480sparky (Aug 7, 2018)

Let's put this to rest.

A 50mm lens is............. _fifty millimeters_.   The glass inside a lens does not 'know' what format camera is behind it.  A 50mm full-frame lens doesn't go, "Oh, there's a crop sensor back there.  I'd better magically transform into a 75mm!"  Because one of two things would have to happen if it did.  One, it would have become longer.  It would have to physically move away from the camera an additional 25mm.  This means your 50mm lens would become about an inch longer.  If it didn't the second option would occur.... you'd never be able to focus the lens.


It doesn't matter if it's a µ4/3, crop sensor, full frame sensor, 6x4.5, 6x6, 6x7 or even 4x5.  It can be an obsolete 110-, 122- or 126-based film camera. 


Think of it this way:  You take a photo with a 50mm lens and have an 8x10 print made.  You now take a pair of scissors and cut out the center of the 8x10, and end up with a 6x7 photo.  Did that change anything about the lens you used?  No.  It was still taken with a 50mm.  Just because you lopped off the outer parts of the image didn't change that one bit.

Same principle for crop v full-frame sensors.  Crop sensors do the same thing to the projected image in a camera as your pair of scissors did to the print.... it just recorded a smaller area.


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## AlexGavillan (Aug 7, 2018)

KB2 said:


> AlexGavillan said:
> 
> 
> > Example, if I want a 105mm lens that's DX there is still a 1.5 crop factor which really gives me the focal length of a 155mm.
> ...



I was getting focal length and field of view confused. I know that the focal length doesn't change, that is something physical, I guess where I was confused was in the "35mm equivalent" they are reffering to the FoV? I swear I will get this  So the 50MM on your DX was giving you the FoV of a 75mm lens, really hope I got that right  



BrentC said:


> KB2 said:
> 
> 
> > AlexGavillan said:
> ...



GOT IT!!! HAHA Focal length and Field of View, thats what was getting me. 



480sparky said:


> Let's put this to rest.
> 
> A 50mm lens is............. _fifty millimeters_.   The glass inside a lens does not 'know' what format camera is behind it.  A 50mm full-frame lens doesn't go, "Oh, there's a crop sensor back there.  I'd better magically transform into a 75mm!"  Because one of two things would have to happen if it did.  One, it would have become longer.  It would have to physically move away from the camera an additional 25mm.  This means your 50mm lens would become about an inch longer.  If it didn't the second option would occur.... you'd never be able to focus the lens.
> 
> ...



Ya, now knowing about FoV all of this makes sense. Hopefully what I wrote above makes sense and I am getting this ingrained in my brain!


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## ac12 (Aug 7, 2018)

Quote
So the 50MM on your DX was giving you the FoV of a 75mm lens ...​
correction
The 50mm lens on a DX camera gives you a similar FoV to a 75mm lens _on a FX camera_.
Or more clearly:
The FoV of a  50mm lens on a DX camera is similar to the FoV of a 75mm lens on a FX camera.​You MUST state what platform the lens is on, or it makes no sense.  
This is because FoV is dependent on both focal length and sensor size.


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## AlexGavillan (Aug 7, 2018)

ac12 said:


> Quote
> So the 50MM on your DX was giving you the FoV of a 75mm lens ...​
> correction
> The 50mm lens on a DX camera gives you a similar FoV to a 75mm lens _on a FX camera_.
> ...


 
Got it!


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## ac12 (Aug 7, 2018)

I still prefer magnification, as it gets away from all this confusing "equivalent focal length" stuff.
And that is how I work.

m4/3:  25mm normal lens (1x), 2x = 50mm, 0.5x = 12mm
DX:  35mm normal lens, 2x = 70mm, 0.5x = 17mm
35mm/FF/FX:  50mm normal lens, 2x = 100mm, 0.5x = 25mm
6x6:  80mm normal lens, 2x = 160mm, 0.5x = 40mm
4x5:  150mm normal lens, 2x = 300mm, 0.5x = 75mm

When I got my tele for the 6x6, I did not do an equivalent focal length.  I did a 2x on my 80mm normal lens to get to 160, then selected the closest lens to 160, which was 150mm.

You NEED to think in the format that you are shooting, or this lens math will drive you nuts.


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## AlexGavillan (Aug 8, 2018)

LOL looks like this has been a discussion for a long time.

What does "..equivalent to 52.5mm in 35mm format" mean? - PentaxForums.com

Back from 2012


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