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05-02-2012, 02:49 AM   #1
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Lens compression effects on APS-C and full frame

Hello all.

I was wondering if anyone could tell me if the compression effects of lenses are different on the two systems? Ie would you see the same amount of compression with a 50mm on digital as on film?

Thanks

05-02-2012, 03:07 AM   #2
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Yes, that's the point of people wanting FF sensors. On APS sensors you get all the characteristics of a wider lens with the FOV of a longer one. That's also why 28-35mm lenses are NOT normal on APS, since the whole thing with 50mm lenses is that they give subject redention the same way a human eye would. (Not the same FOV of course)
05-02-2012, 05:23 AM   #3
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The effect you are talking about is about perspective and not a lens thing really.

So if you use FF and 50mm and you stay in the same spot when using APS-C the flatting effect will be the same but you need to use 35mm to get the same framing
05-02-2012, 05:26 AM   #4
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QuoteOriginally posted by Giklab Quote
Yes, that's the point of people wanting FF sensors. On APS sensors you get all the characteristics of a wider lens with the FOV of a longer one. That's also why 28-35mm lenses are NOT normal on APS, since the whole thing with 50mm lenses is that they give subject redention the same way a human eye would. (Not the same FOV of course)
Wrong....
Normal means you get an angle of view of 53 diagonally, this gives you a normal perspective when a viewer views your photo at a normal viewing distance.
For FF this focal length is actually 43mm not 50mm!!!!
645 = 75mm
67 = 90mm
4x5 = 150mm
5x7 = 210mm
8x10 = 300mm
APS-C = 28~30mm

05-02-2012, 06:34 AM   #5
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"Normal" is supposed to give you the same relationship between near and far subjects as you see it. 50s were/are popular since they're darn cheap to make and that's why they are considered "normal". The 43mm is "normal" since that's the diagonal of full frame film. Just like 28mm is for APS-C. But since 28mm is a wide angle, you get wide angle distortions, like huge noses and tiny backgrounds.
Human eye - Wikipedia, the free encyclopedia
05-02-2012, 07:21 AM   #6
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Portrait perspective distortion ?
Here it is on M4/3 at 10 mm:
The DOF is not natural but I took a family portrait like this and it looks good.
https://www.box.com/s/e784b418037950336975

Here is the DOF of a proper lens, SMC Pentax -A 1: 1.4 50mm I just posted on the -A thread
https://www.box.com/s/5ed9aab75cd3c182ed38
05-02-2012, 09:05 AM   #7
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QuoteOriginally posted by Giklab Quote
But since 28mm is a wide angle, you get wide angle distortions, like huge noses and tiny backgrounds.
Getting huge noses and tiny backgrounds is a matter of perspective [i.e. where you are relative to the things you are photographing], and has nothing to do with the focal length of the lens.
05-02-2012, 09:13 AM   #8
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QuoteOriginally posted by Giklab Quote
"Normal" is supposed to give you the same relationship between near and far subjects as you see it. 50s were/are popular since they're darn cheap to make and that's why they are considered "normal". The 43mm is "normal" since that's the diagonal of full frame film. Just like 28mm is for APS-C.
Preciesly, but you said that 28-30mm are not normal on APS-C in your first comment.

QuoteOriginally posted by Giklab Quote
But since 28mm is a wide angle, you get wide angle distortions, like huge noses and tiny backgrounds.
That distortion is caused by the perspective not by the lens, to say it more clear:
You get those big noses because you stand closer to the subject because you're using a 28mm and want to fill the whole photo with his face.
If you decide to stay on the same spot while using for example 50mm and 28mm lens then the perspective will be the same, your subject won't fill the photo as much as with the 50mm but the face proportions will be the same between the both.

05-02-2012, 09:48 AM   #9
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QuoteQuote:
Getting huge noses and tiny backgrounds is a matter of perspective [i.e. where you are relative to the things you are photographing], and has nothing to do with the focal length of the lens.
QuoteQuote:
That distortion is caused by the perspective not by the lens, to say it more clear:
You get those big noses because you stand closer to the subject because you're using a 28mm and want to fill the whole photo with his face.
If you decide to stay on the same spot while using for example 50mm and 28mm lens then the perspective will be the same, your subject won't fill the photo as much as with the 50mm but the face proportions will be the same between the both.
Wider angle lenses have a more pronounced barrel distortion. Why would people shoot portraits with short teles if wide/normal lenses would suffice?! Why do some landscape photogs swear on telephotos? Cause they compress the scene and enlarge distant objects more than near ones creating a better picture than with a wide angle, where distant objects are not magnified as much.

Remember: 40-60mm lenses are normal because they are. No barrel. No pincushion. The same magnification at all distances.

PS You wouldn't need to get in somebody's face as much with a 50 than you'd need to with a 28 because you want to make the face the same size on both pics. Therefore you stand back with the 50.
05-02-2012, 10:47 AM   #10
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QuoteOriginally posted by Giklab Quote
Wider angle lenses have a more pronounced barrel distortion. Why would people shoot portraits with short teles if wide/normal lenses would suffice?! Why do some landscape photogs swear on telephotos? Cause they compress the scene and enlarge distant objects more than near ones creating a better picture than with a wide angle, where distant objects are not magnified as much.

Remember: 40-60mm lenses are normal because they are. No barrel. No pincushion. The same magnification at all distances.

PS You wouldn't need to get in somebody's face as much with a 50 than you'd need to with a 28 because you want to make the face the same size on both pics. Therefore you stand back with the 50.
This is already a false statement.
Don't mislead others even more.
05-02-2012, 11:05 AM   #11
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OK, I won't post about the subject anymore. I'll do more research and see if I'm right or wrong.
05-02-2012, 11:22 AM   #12
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QuoteOriginally posted by Giklab Quote
Wider angle lenses have a more pronounced barrel distortion.
Barrel distortion has nothing to do with the perspective issues you described earlier. While it is more common on wider lenses, it's a property of the lens, not the focal length.

QuoteQuote:
PS You wouldn't need to get in somebody's face as much with a 50 than you'd need to with a 28 because you want to make the face the same size on both pics. Therefore you stand back with the 50.
You're talking about perspective again. You can get the same image with a 28 that you can with a 50 if you stand in the same place, and crop after the fact.
05-02-2012, 11:27 AM   #13
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QuoteOriginally posted by Giklab Quote
Wider angle lenses have a more pronounced barrel distortion.
while this is generally true, wider lenses may have more barrel distortion you would likely not notice this in a portrait.
QuoteQuote:
Why would people shoot portraits with short teles if wide/normal lenses would suffice?
because the perspective of wider lenses tends to do several things that are very unflattering, specifically if subjects are at the edge of the frame, or if the subject has a varying distance to the camera, it is not distortion as such, but often referred to as distortion even though it is just the impact of perspective, and the difference in magnification of the lens as a function of distance to subject. It can make people look very fat, or exaggerate any feature that is closer to the lens, like noses, hands and feet, making them look unnaturally long or big. A tele photo lens, on the other hand tends to flatten images making them look more pleasing
QuoteQuote:
! Why do some landscape photogs swear on telephotos? Cause they compress the scene and enlarge distant objects more than near ones creating a better picture than with a wide angle, where distant objects are not magnified as much.
true, unless you want to have foreground and background to emphasize distance Remember there is no rule just techniques
QuoteQuote:

Remember: 40-60mm lenses are normal because they are. No barrel. No pincushion. The same magnification at all distances.
no because they have the same relitive perspective rendering as what we see. not because of distortion like barrel or pincushion
QuoteQuote:

PS You wouldn't need to get in somebody's face as much with a 50 than you'd need to with a 28 because you want to make the face the same size on both pics. Therefore you stand back with the 50.
true, in simple terms

image size = subject size x focal length / distance
05-02-2012, 11:36 AM - 1 Like   #14
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Ahh, now I get what you all have been trying to tell me! Yes, I've mixed up some things /blush/.
05-02-2012, 12:17 PM   #15
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QuoteOriginally posted by tyronfall Quote
I was wondering if anyone could tell me if the compression effects of lenses are different on the two systems? Ie would you see the same amount of compression with a 50mm on digital as on film?
Here's how I would put it:

Lenses don't have compression effects. What we perceive as a compression effect is not an inherent property of the lens itself, but rather, of the *field of view it gives on a particular sensor size*. A 28mm lens produce a wide angle field of view on FF/film, and therefore produces the characteristic wide angle distortions (objects in a print looking smaller and/or further apart than they really are, etc) *when used on FF/film*. That same lens is normal on APS-C, and hence produces the same lack of persepctive distortion (objects looking to be the same size and same distance apart in a print as in real life) *when used on APS-C*. That same lens is a telephoto on, say, the Q, and hence produces the same characteristic telephoto compression effects (onjects appear larger / closer together than expected) *when used on a Q*.

This is because the so-called compressin effects are not inherent to the lens or even to the recorded image, but are simply optical illusions caused if you take an image taken with a given angle of view and then print it and view it from a distance that yields a different angle of view.
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