# Confused about crop sensor vs focal length



## Flare (Jan 4, 2013)

If you have a EF-S 17-55mm lens on a canon crop sensor does the 1.6 factor still apply?  Is it 17mm or 27mm?

Flare


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## Derrel (Jan 4, 2013)

The focal length of 17mm will ALWAYS be 17mm. Always. On crop-body, or FF body. Buuuut--the equivalent field of view of a 17mm lens setting will be, "Like 27mm is on full-frame".


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## 480sparky (Jan 4, 2013)

Regardless of the 'comparison', a 50mm lens is a 50mm lens, no matter which sensor you're using.  What changes is the _apparent field of view_  between the two.  So if you were to take a full-frame and a crop-sensor  camera, set them up side-by-side with, say, 50mm lenses on both, and  looked through the viewfinders of them, this is what you would see:







Neither camera-lens combination 'enlarges' or 'reduces' the apparent size of the subject.  The bridge and the flowers are _the exact same size_ in both VFs.  What is different is the _size of the focus screens_, which is in direct proportion to the _size of the respective sensors_.  This, in turn, changes the field of view (measured in degrees).


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## Flare (Jan 4, 2013)

Ok the focal length is the same but field of view is the difference. So if I shot a 15mm focal length on a crop sensor that would have an equivalent of a 27mm field of view on a full frame sensor. Did I say that right.


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## 480sparky (Jan 4, 2013)

Flare said:


> Ok the focal length is the same but field of view is the difference. So if I shot a 15mm focal length on a crop sensor that would have an equivalent of a 27mm field of view on a full frame sensor. Did I say that right.



Close... 15 x 1.5 = 22.5 (for Nikon).. 15 x 1.6 = 24 (for Canon).  But you got the idea.


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## Flare (Jan 4, 2013)

Sorry bad math but I got. Thank.you for clearing that up.


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## dbvirago (Jan 5, 2013)

480sparky said:


> Regardless of the 'comparison', a 50mm lens is a 50mm lens, no matter which sensor you're using.  What changes is the _apparent field of view_  between the two.  So if you were to take a full-frame and a crop-sensor  camera, set them up side-by-side with, say, 50mm lenses on both, and  looked through the viewfinders of them, this is what you would see:
> 
> 
> 
> ...



From someone who just got his first full frame camera yesterday, thanks for this. I've been reading the math for years, but this is the best representation of real life examples I have seen and shows me what I was going to spend part of today discovering. After reading for years about the better 'reach' of a crop sensor, this puts it all to rest.

Thanks


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## shefjr (Jan 5, 2013)

480sparky said:
			
		

> Regardless of the 'comparison', a 50mm lens is a 50mm lens, no matter which sensor you're using.  What changes is the apparent field of view  between the two.  So if you were to take a full-frame and a crop-sensor  camera, set them up side-by-side with, say, 50mm lenses on both, and  looked through the viewfinders of them, this is what you would see:
> 
> Neither camera-lens combination 'enlarges' or 'reduces' the apparent size of the subject.  The bridge and the flowers are the exact same size in both VFs.  What is different is the size of the focus screens, which is in direct proportion to the size of the respective sensors.  This, in turn, changes the field of view (measured in degrees).



This should be a sticky. It's clear concise and to the point.


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## ratssass (Jan 5, 2013)

I understand what you're saying about focal length/field of view,but............why is it when I open my EXIF it's clearly listed as focal length in both apc-s and 35mm equiv.?Semantics?

Focal Length = 24mm
Maker Note = 33202 Byte
User Comment =                                     
Subsec Time = 0.90"
Flashpix Version = Version 1.0
Color Space = sRGB
Exif Image Width = 2448
Exif Image Height = 3696
Sensing Method = One-chip color area sensor
File Source = DSC
Scene Type = A directly photographed image
Custom Rendered = Normal process
Exposure Mode = Manual exposure
White Balance = Auto white balance
Digital Zoom Ratio = 1x
Focal Length In 35mm Film = 36mm


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## o hey tyler (Jan 5, 2013)

ratssass said:
			
		

> I understand what you're saying about focal length/field of view,but............why is it when I open my EXIF it's clearly listed as focal length in both apc-s and 35mm equiv.?Semantics?
> 
> Focal Length = 24mm
> Maker Note = 33202 Byte
> ...



They put it in there for a 35mm full frame FoV I reckon. I wouldn't say it clearly lists it, as the focal length is up top and the FoV equivalent is way down the list.


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## ratssass (Jan 5, 2013)

my point only being they are both listed as "focal length".Possibly other Exif readers state it differently??


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## o hey tyler (Jan 5, 2013)

ratssass said:
			
		

> my point only being they are both listed as "focal length".Possibly other Exif readers state it differently??



It says focal length, but it's FoV. My exif reader just says "35mm equiv:" 

The top one is your focal length. The 35mm equivalent is of no concern to you when viewing exif.


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## ratssass (Jan 5, 2013)

[/QUOTE]

It says focal length, but it's FoV. .[/QUOTE]

...that's the only point i'm trying to make.When a person is learning,something as simple as this  lead me to state that I had the focal length of 18-300 covered via 18-105mm (dx),24-70(fx),70-200(fx),when in reality it was FoV.


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## 480sparky (Jan 5, 2013)

Here's a real-life side-by-side comparison:

I threw some of my stuff on a table, set my D600 up on a tripod, and mounted two lenses on it:  My kit 18-105 DX lens set to 50mm, and my kit 24-85 FX lens set to 50mm.  I also set the camera to FX mode so it would record the entire sensor when I use the DX lens.  These are SOOC images.  The only editing done is to resize them for posting here.  The EXIF data will be intact so you can check it yourself.

Results:



What the FX camera saw with the FX lens:






What the FX camera saw with the DX lens:







Notice the items are the _exact same size_.  The only difference is, the DX lens is not designed to cover a full-frame sensor, so it will have the black areas around the edges & corners.  The reason for this is a _crop sensor is physically smaller_ (in this case, 24mmx35.9mm for the full-frame sensor, 23.6mm x 15.6mm for the crop).  So a DX-format lens projects subjects onto the sensor the same as it's FX-format focal length big brother..... it just can't cover the entire FX sensor.  Had I switched the camera to DX mode for the second shot, it would record exactly the same image as what is shown in the second half of this demonstration:


I repeated the experiment swapping my D600 with my D7000, using the same two lenses.  This time, the subjects will 'appear' closer because of the crop sensors' narrower FOV.  Both images taken with the same two kit lenses, set at 50mm

What the DX camera saw with the DX lens:






What the DX camera saw with the FX lens:






Granted.... there's a _minor_ difference in the FOV in all these, but that's simply due to the margin of error.  I have no way of knowing _exactly_ what the focal length of the zoom lens is when I set it.  Even though it's _set_ at 50mm, it may be 48.7mm, or 49.2mm, or 51.6mm.......

The reason the DX images appears to be 'closer' or 'larger' is due to the FOV caused by the smaller sensor.  The images are all the same pixel size (800x530), so the DX format appears to make a 50mm into a 75mm.  But both 50mm lenses project the subjects onto the sensors at the same size.... the crop sensor is just smaller.


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## dbvirago (Jan 5, 2013)

Got my 5D MKIII yesterday and tried some real world examples of my own. Shot a house across the street at 50mm with it and the 40D. At first, when I opened them up in LR, I was astonished at the difference, thinking that the crop did indeed 'zoom' in tighter. Then, with both images side by side, I zoomed in to 100% on a detail. Identical size.


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## ratssass (Jan 5, 2013)

Focal Length = 24mm
Maker Note = 33202 Byte
User Comment =                                     
Subsec Time = 0.90"
Flashpix Version = Version 1.0
Color Space = sRGB
Exif Image Width = 2448
Exif Image Height = 3696
Sensing Method = One-chip color area sensor
File Source = DSC
Scene Type = A directly photographed image
Custom Rendered = Normal process
Exposure Mode = Manual exposure
White Balance = Auto white balance
Digital Zoom Ratio = 1x


> Focal Length In 35mm Film = 36mm



....ooooooooooooook,so we've learned that my fx lens on a dx bodyshooting at 24mm does not equate to 36mm.Nor is my FoV changed.Can someone,please,just tell me what exactly is meant by the last line??


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## o hey tyler (Jan 5, 2013)

ratssass said:


> Focal Length = 24mm
> Maker Note = 33202 Byte
> User Comment =
> Subsec Time = 0.90"
> ...



It means that to equate to the same field of view on a full frame camera, that you'd need to be at a 36mm focal length.


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## ratssass (Jan 5, 2013)

whew........thank you so much,Tyler............that 1 question has really been bugging me.


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## o hey tyler (Jan 5, 2013)

ratssass said:


> whew........thank you so much,Tyler............that 1 question has really been bugging me.



Glad you got it sorted.


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## bratkinson (Jan 6, 2013)

In my opinion, all the 'negativity' towards crop sensor cameras leads anyone that owns one to believe their camera is somehow 'handicapped', or that they won't EVER take good pictures with that camera. Throw in all the numerical calculations with 1.5 or 1.6 affecting the 'focal length' of the lens mounted to it and they can quickly become paranoid about their capabilities as well as their camera.

Perhaps it's better that the term 'crop/cropped sensor' were eliminated from our vocabulary. It really serves little purpose other than to 'sell' someone on a more expensive camera.

Consider the film days of the '50s, '60s and '70s. People had cameras that used many different film sizes. Whether it was size 120, 135, 616, 620, 626, or whatever, the cameras used still faithfully recorded what their lenses 'saw'. Even the Kodak Brownie and Instamatic cameras with their tiny film sizes took pictures acceptable to most of their target markets.

So why the digital 'fixation' on the 35mm film size? Probably more to ease the minds of the photographers during the digital revolution years ('85-'99, roughly) to provide means to focal length conversion. But for anyone new to DSLR photography these days, is there really a need to know (initially) that 'this focal length is good for these types of photos, that focal length is good for those types of photos', and by the way, divide/multiply/add/subract/square root/to the power of everything I just told you by 1.6 because you have a crop body Canon!  It's simply zoom in/out until you see what you like in the viewfinder, and take the picture!  Who needs all the mental gymnastics!

I'll be completely honest...even though I spent roughly 15 years non-35mm and 20 years in 35mm photography before putting the cameras and gear away for about 12 years, after wearing out Canon G-3 and G-5 Point and Shoots, when I moved up to a used 30D and EF-S 18-135 lens, I had never, EVER, heard the phrase 'crop body'. 8 months and perhaps 5-6,000 shots with the 30D later, even after moving to a new 60D, I -STILL- never heard/thought about/considered that I was shooting with a 'handicapped' crop body! I was very happy with the pictures I was taking and the results were very noticably better than what I had been getting with the Point & Shoots.

Call it my lack of doing 'due diligence' on the web and finding websites like this one that explain the differences in field of view (not focal length!) of cameras with a crop body compared to what I had with 35mm film. But did I care? No. Did the lack of such knowledge cause me to make the 'wrong' purchases? Not in my book. Back in the '50s, my parents cars were either Fords or Chevys. Did I have any clue what the ride in a Cadillac was like? or a Rolls Royce? Of course not. The Fords and Chevys got us from here to there without any difficulty, and provided sufficient comfort to make everyone in the family happy. No different than a crop-body camera taking pictures the same way the 'expensive, luxury' cameras take pictures. One pixel at a time.


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## spd (Jan 6, 2013)

I don't know why we can't just say that on a camera with a crop-sensor (canon 7D for instance), a 17-40mm lens effectively becomes as a 27.2-64mm lens...

Just like my 100-400 'effectively becomes' 160-640 on my 7D, and 320-1280 when i put my 2x converter on...


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## greybeard (Jan 6, 2013)

I think a lot of the confusion has to do with trying to understand 2 formats at the same time.  If you shoot crop sensor, know that a lens that will give you a "NORMAL" perspective is around 35mm.  A good wide angle perspective can be had around 16-18, extreme around 10-12.  On the tele end, 50-55 is a nice short tele great for portraits and 200-300 good for sports-nature.  So when selecting a zoom, pick one that encompasses a range that you need.


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## 480sparky (Jan 6, 2013)

spd said:


> I don't know why we can't just say that on a camera with a crop-sensor (canon 7D for instance), a 17-40mm lens effectively becomes as a 27.2-64mm lens...
> 
> Just like my 100-400 'effectively becomes' 160-640 on my 7D, and 320-1280 when i put my 2x converter on...



That's exactly what we all do..... and that's exactly what causes the confusion.


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## Robin_Usagani (Jan 6, 2013)

Sparky did a good job explaining.  This is a simple topic but it is so hard to explain.  It is also a very popular topic.  I think sparky should rewrite a thread with those images and stick the thread on top.


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## 480sparky (Jan 6, 2013)

Another way to look at it:

You're in a darkroom ( you know... the old-fashioned kind with a dim red lamp, stinky chemicals.....), and you put a negative into the enlarger.  Run the enlarger up so you can make an 8x10 from the negative.  Now, _without doing anything to the enlarger_, remove the 8x10 paper and put a sheet that's 5x7 in it's place.

Compare the 8x10 with the 5x7 after you're developed the prints.  The subjects will be _exactly the same size_.  The 8x10 print represents what a full-frame sensor records, and the 5x7 print represents what the crop sensor records.


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## Robin_Usagani (Jan 6, 2013)

Good explaination but most people who ask this question never seen or operate an enlarger. 



480sparky said:


> Another way to look at it:
> 
> You're in a darkroom ( you know... the old-fashioned kind with a dim red lamp, stinky chemicals.....), and you put a negative into the enlarger.  Run the enlarger up so you can make an 8x10 from the negative.  Now, _without doing anything to the enlarger_, remove the 8x10 paper and put a sheet that's 5x7 in it's place.
> 
> Compare the 8x10 with the 5x7 after you're developed the prints.  The subjects will be _exactly the same size_.  The 8x10 print represents what a full-frame sensor records, and the 5x7 print represents what the crop sensor records.


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## 480sparky (Jan 6, 2013)

Robin_Usagani said:


> Good explaination but most people who ask this question never seen or operate an enlarger.
> 
> 
> 
> ...




OK, slide projectors and screens.


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## ratssass (Jan 6, 2013)

I know I finally got it through my thick skull,but what was really making it hard to understand (for me) was that 1 line in the EXIF.Just couldn't get my mind wrapped around the explanation until Tyler answered that 1 question for me.


> You're in a darkroom ( you know... the old-fashioned kind with a dim red lamp, stinky chemicals.....), and you put a negative into the enlarger.  Run the enlarger up so you can make an 8x10 from the negative.  Now, _without doing anything to the enlarger_, remove the 8x10 paper and put a sheet that's 5x7 in it's place.
> 
> Compare the 8x10 with the 5x7 after you're developed the prints.  The subjects will be _exactly the same size_.  The 8x10 print represents what a full-frame sensor records, and the 5x7 print represents what the crop sensor records


^^^^This analogy works well for my simple mind.Thank you,all!


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## 480sparky (Jan 6, 2013)

Now, to explain WHY there's a difference:

Simply put, it's _because the sensors are different sizes_.  I put my D600 (FX/Full Frame) body next to my D7000 (DX/Crop Sensor) on a table.  I set both of them to_ Mirror Up For Cleaning_, and took this shot.







As you can see, the D7000 on the right has a _physically smaller_ sensor than the D600 on the left.


A lens has no way of knowing what body (full frame or crop) is behind it.  It wouldn't care, either.  It will still project the subject(s) the same whether there's a FF or crop sensor (or FF in crop mode) in the camera.









So while a FF body will record this:







A DX body will record this:








Note the difference in the size of the two examples.  The FF image is larger because the _sensor itself_ is larger.  Also note, the size of the subjects are identical.  This is because the lens' focal length didn't change.  It projects the subjects the _exact same size _onto both sensors.

  However, we, as humans, tend to think of images as generally the same size.  We know how big an 8x10 or 4x5 is, and we make our images fit those dimensions.

So we enlarge the crop sensor image so it matches the dimensions of a FF image.  And we end up with a comparison like this:

Full frame:






Crop:


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## o hey tyler (Jan 6, 2013)

spd said:
			
		

> I don't know why we can't just say that on a camera with a crop-sensor (canon 7D for instance), a 17-40mm lens effectively becomes as a 27.2-64mm lens...
> 
> Just like my 100-400 'effectively becomes' 160-640 on my 7D, and 320-1280 when i put my 2x converter on...



No, your 100-400 is a 100-400, and your 17-40 is a 17-40. It doesn't "effectively" become a different lens. Your field of view is just narrower.


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## mchap7777 (Feb 23, 2014)

480sparky...(or anyone who knows what they are talking about) maybe you can help me with this also. I "get" the above...but I'm still stuck on this issue - that goes a bit deeper. [Sorry - I'm dense and maybe think too much]. My question centers on whether there is a difference between a DX lens and an FX lens (does the DX lens compensate?). I say this because I have several Nikon lenses with "DX" on them. If I put a "DX" lens (I have a Nikon crop frame camera) on my DX camera - let's say a 50mm lens, then I am seeing ("angle of view" - or "field of view") the same as a 50mm full frame lens on a full frame camera? I say this because all the things I'm reading seems to say if I put the exact same lens on the two different camera bodies - then there is the crop difference - I understand this. But I guess I wondering if the "DX" lens made for a DX camera somehow equalizes the field or angle of view - and the "problems" come in when you mismatch? This presents several scenarios in my mind - running between DX and FX lenses AND DX and FX camera bodies (sensor sizes):
DX Cam with DX lens
FX Cam with FX lens
DX Cam with FX lens
FX Cam with DX lens

Please run through these four possibilities for me, and clear up my confusion. (Maybe I'm assuming possibilities that are not even real).

Main question though is: Is 50mm DX lens on DX camera a true 50mm field of view? (Compared to 50mm Full frame lens on FX camera)?

Thanks in advance.


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## 480sparky (Feb 23, 2014)

mchap7777 said:


> 480sparky...(or anyone who knows what they are talking about) maybe you can help me with this also. I "get" the above...but I'm still stuck on this issue - that goes a bit deeper. [Sorry - I'm dense and maybe think too much]. My question centers on whether there is a difference between a DX lens and an FX lens (does the DX lens compensate?). I say this because I have several Nikon lenses with "DX" on them. If I put a "DX" lens (I have a Nikon crop frame camera) on my DX camera - let's say a 50mm lens, then I am seeing ("angle of view" - or "field of view") the same as a 50mm full frame lens on a full frame camera? I say this because all the things I'm reading seems to say if I put the exact same lens on the two different camera bodies - then there is the crop difference - I understand this. But I guess I wondering if the "DX" lens made for a DX camera somehow equalizes the field or angle of view - and the "problems" come in when you mismatch? This presents several scenarios in my mind - running between DX and FX lenses AND DX and FX camera bodies (sensor sizes):
> DX Cam with DX lens
> FX Cam with FX lens
> DX Cam with FX lens
> ...



The biggest difference between a DX and an FX lens of the same focal length is the diameter of the image projected.  DX lenses only need to make a circle big enough to cover the smaller DX sensor.  FX lenses need to make a bigger circle to cover the larger sensor.

A DX lens and an FX lens will be the same on a DX body.  A 35mm DX lens will look the same as a 35mm FX lens through a DX viewfinder.

On an FX body, you will have three choices..... let the camera automatically detect a DX-format lens and record just the DX-format image, or shoot in either DX or FX mode regardless of what lens is attached.


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## mchap7777 (Feb 23, 2014)

Thanks!


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## glun (Mar 30, 2014)

Flare said:


> If you have a EF-S 17-55mm lens on a canon crop sensor does the 1.6 factor still apply?  Is it 17mm or 27mm?
> 
> Flare



Yes the 1.6 factor still apply. The focal length of your lens is still 17mm but because of the crop senor of your camera it becomes 27mm.


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## table1349 (Mar 30, 2014)

glun said:


> Flare said:
> 
> 
> > If you have a EF-S 17-55mm lens on a canon crop sensor does the 1.6 factor still apply?  Is it 17mm or 27mm?
> ...



NO it does not become 27mm.  Focal length is focal length.  It is a property of physics.  Your 17mm focal length gives you the area of view of a 27mm lens.


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