Lenses on Crop Sensor Cameras and Distortions

First of all, a big thanks to DPReview for helping newbies like me learn the basics of photography.

I need to take some close-up shots of villagers where I live, for a research on facial deformities and diets. I'd like to avoid distortion of any kind when taking these photos. Ideally the faces in these photos would look very much like how we see them in real life. I'm referring to both the widths of faces and facial features.

I understand that, on a FF camera, a 28mm lens will distort my subject a little (close-up shots), and a 135 mm lens will flatten my subject’s features. My question is: what determines this distorting or flattening effect? Is it angle of view or focal length?

In other words, if I use a crop sensor camera like Canon 70D, and a 28mm EF lens, will faces in close-up shots look slightly distorted, like what we expect a 28mm lens on a FF camera would do, or will the faces look quite normal, like the ones taken with a (hypothetical) 44.8mm EF lens on a FF camera? (I'm under the impression that 40mm-65mm lenses are considered normal lenses on a FF camera - not distorting subjects)

Please correct me if I've got any point wrong. Thank you!

hanhasgotqi wrote:

First of all, a big thanks to DPReview for helping newbies like me learn the basics of photography.

I need to take some close-up shots of villagers where I live, for a research on facial deformities and diets. I'd like to avoid distortion of any kind when taking these photos. Ideally the faces in these photos would look very much like how we see them in real life. I'm referring to both the widths of faces and facial features.

I understand that, on a FF camera, a 28mm lens will distort my subject a little (close-up shots), and a 135 mm lens will flatten my subject’s features. My question is: what determines this distorting or flattening effect? Is it angle of view or focal length?

It's perspective, the distance of the subject from the camera.

In other words, if I use a crop sensor camera like Canon 70D, and a 28mm EF lens, will faces in close-up shots look slightly distorted, like what we expect a 28mm lens on a FF camera would do, or will the faces look quite normal, like the ones taken with a (hypothetical) 44.8mm EF lens on a FF camera?

28mm on the 70D v. 45mm on full frame:   If the subject is the same distance from the camera, same composition/framing, then then the faces will look quite normal.  Just as shooting from the same distance with a 10mm lens on a compact digital, or 5mm lens on a phone will give normal looking faces.

Use the standard 18-55 zoom and shoot at 55mm, comes out at 88mm which is pretty much ideal.

I shoot my headshots at 100mm with lights on a full frame and they look pretty neutral. Here's a link. Corporate Headshots so you can see what 100mm looks like. I use an 85mm for natural light. so 55 on a crop will be spot on.
There will be a bit of lens distortion on a zoom, but not enough to worry about, lightroom will take care of it automatically if you're worried about it. It's more the focal length you need to get right.
Don't shoot shorter 55 on a crop, it'll make the noses appear bigger than they actually are due to perspective.

hanhasgotqi wrote:

First of all, a big thanks to DPReview for helping newbies like me learn the basics of photography.

I need to take some close-up shots of villagers where I live, for a research on facial deformities and diets. I'd like to avoid distortion of any kind when taking these photos. Ideally the faces in these photos would look very much like how we see them in real life. I'm referring to both the widths of faces and facial features.

I understand that, on a FF camera, a 28mm lens will distort my subject a little (close-up shots), and a 135 mm lens will flatten my subject’s features. My question is: what determines this distorting or flattening effect? Is it angle of view or focal length?

In other words, if I use a crop sensor camera like Canon 70D, and a 28mm EF lens, will faces in close-up shots look slightly distorted, like what we expect a 28mm lens on a FF camera would do, or will the faces look quite normal, like the ones taken with a (hypothetical) 44.8mm EF lens on a FF camera? (I'm under the impression that 40mm-65mm lenses are considered normal lenses on a FF camera - not distorting subjects)

Please correct me if I've got any point wrong. Thank you!

As others pointed out, around 50mm on FF (crop: 50/1.6) gives about the look the human eye is used to in terms of angle of view. However, portraits are usually taken with slight tele, i.e. 85, 100, or 135 (FF). As pointed out, they key to perspective is distance. A person imaged with a wide-angle lens at 10meter distance in the center of the frame will have a perfectly fine portrait, but you might be left with a 100x100pixel crop (or whatever) for the portrait.

the key about perspective: closer objects are larger than further distant objects. (i.e. the big nose with wide angle portraits). If the person is very far, the distance to the nose, and to the ears will be virtually the same in relation to the total distance. For scientific purposes, it's better to have little perspective distortion, because that means, you can take a ruler on the image, measure features of the face, and they will be to scale.

Thus, I would recommend to go as long as you can (space, good illumination) to get relatively "flat" images. 100mm, 200mm whatever is feasible. Try to use always the same distance (like mug shots), even with a ruler in the background, then you can compare different shots. Of course, you may then take specific close-ups of particular features in addition.

Here is a simplified answer: Use what ever lens you want, but make sure you stand back at about 10'.

The kind of distortion you are talking about is caused by being too close to the subject.

The focal length or sensor size does not matter. You need to stand farther back to eliminate perspective distortion with any lens or camera. 10' is about the minimum distance you should be.

hanhasgotqi wrote:

First of all, a big thanks to DPReview for helping newbies like me learn the basics of photography.

I need to take some close-up shots of villagers where I live, for a research on facial deformities and diets. I'd like to avoid distortion of any kind when taking these photos. Ideally the faces in these photos would look very much like how we see them in real life. I'm referring to both the widths of faces and facial features.

I understand that, on a FF camera, a 28mm lens will distort my subject a little (close-up shots), and a 135 mm lens will flatten my subject’s features. My question is: what determines this distorting or flattening effect? Is it angle of view or focal length?

The perspective, which is associated with the angle of view.

In other words, if I use a crop sensor camera like Canon 70D, and a 28mm EF lens, will faces in close-up shots look slightly distorted, like what we expect a 28mm lens on a FF camera would do, or will the faces look quite normal, like the ones taken with a (hypothetical) 44.8mm EF lens on a FF camera? (I'm under the impression that 40mm-65mm lenses are considered normal lenses on a FF camera - not distorting subjects)

Please correct me if I've got any point wrong. Thank you!

Perspective doesn't change with the crop factor, so a 50mm lens still looks like a 50mm lens, it's just that you get a crop of that. So I would choose the best focal length that works for your project, in this case probably an 85mm, just take into account its minimum focusing distance which is about a meter if I recall correctly. A prime would have the advantage that you wouldn't run the risk of taking different subjects at different focal lengths like with a zoom, and be less cumbersome.

msowsun wrote:

Here is a simplified answer: Use what ever lens you want, but make sure you stand back at about 10'.

The kind of distortion you are talking about is caused by being too close to the subject.

yup

The focal length or sensor size does not matter. You need to stand farther back to eliminate perspective distortion with any lens or camera. 10' is about the minimum distance you should be.

well, focal length does matter, there is no point using an ultrawide at 10' distance if the facial features that are to be recorded become to small on the sensor.

I would actually recommend an even longer distance if space allows.

hanhasgotqi wrote:

J A C S wrote:

If you want to minimize those distortions, choose longer FL's or do not allow people near the borders. Another option is to use software correcting "volume anamorphic distortions" like DXO's ViewPoint. See this, for example. I use it often and the effect is very nice.

You guys are the best! Thank you for taking the time to answer my questions.

I searched and read a little more on barrel/pincushion distortions and perspective. As msowsun and BAK pointed out, I’ll back away at least 10’ to make sure perspective distortions are at a minimum. I can always crop down to a headshot for my purpose; the headshots don’t have to be pretty, as long as they show how the faces look.

To JACS, I am guessing the example you linked to is a kind of barrel distortion? Am I right in saying it is inherent in most wide angle lenses?

no, not necessarily. primes tend to be better than zooms, and in zooms it's mostly only the wide-angle end which has barrel distortion, but as you zoom in, it disappears, so you have to look at which focal length you use the lens.

best is to look on web sites (photozone.de,  the digital picture) and others, to see what distortion you get.

I’m considering Canon’s EF 35mm f/2 IS USM because I may shoot videos hand-held, and I’d like to have the IS. (I'll be using a crop sensor camera - 70D) But mostly I’d be taking stills.

STM lenses would be even better if you want to use the automatic focus.

35mm qualifies as a wide angle lens on a FF; on a crop sensor camera, however, am I mistaken in thinking that, because the crop sensor is essentially recording what’s in the middle of the lens, any obvious barrel distortion at the peripheral wouldn’t register on the crop sensor? (I’m referring to stills)

it depends on the nature of the distortion, if it is complex, such as a moustache distortion (e.g. Samyang 14mm), cropping will remove some of the worst effects.

However, if the barrel distortion is a very regular curve, then cropping will only remove it partially.

Anyhow, I like the idea of backing away a distance and taking crops in post. For gathering information that is. Any suggestions will be much appreciated! Thanks!

just check how much resolution you need in the end.

hanhasgotqi wrote:

J A C S wrote:

If you want to minimize those distortions, choose longer FL's or do not allow people near the borders. Another option is to use software correcting "volume anamorphic distortions" like DXO's ViewPoint. See this, for example. I use it often and the effect is very nice.

You guys are the best! Thank you for taking the time to answer my questions.

I searched and read a little more on barrel/pincushion distortions and perspective. As msowsun and BAK pointed out, I’ll back away at least 10’ to make sure perspective distortions are at a minimum. I can always crop down to a headshot for my purpose; the headshots don’t have to be pretty, as long as they show how the faces look.

To JACS, I am guessing the example you linked to is a kind of barrel distortion? Am I right in saying it is inherent in most wide angle lenses?

I’m considering Canon’s EF 35mm f/2 IS USM because I may shoot videos hand-held, and I’d like to have the IS. (I'll be using a crop sensor camera - 70D) But mostly I’d be taking stills. 35mm qualifies as a wide angle lens on a FF; on a crop sensor camera, however, am I mistaken in thinking that, because the crop sensor is essentially recording what’s in the middle of the lens, any obvious barrel distortion at the peripheral wouldn’t register on the crop sensor? (I’m referring to stills)

Anyhow, I like the idea of backing away a distance and taking crops in post. For gathering information that is. Any suggestions will be much appreciated! Thanks!

I think from a technical standpoint the 60mm f2.8 macro would be best here. As a macro prime it has negligible barrel or pincushion distortion, and is a focal length that would get a lot of pixels on the face at 10'. It is also very high resolution so you will have lots of detail to work with.

Ember42 wrote:

hanhasgotqi wrote:

J A C S wrote:

If you want to minimize those distortions, choose longer FL's or do not allow people near the borders. Another option is to use software correcting "volume anamorphic distortions" like DXO's ViewPoint. See this, for example. I use it often and the effect is very nice.

You guys are the best! Thank you for taking the time to answer my questions.

I searched and read a little more on barrel/pincushion distortions and perspective. As msowsun and BAK pointed out, I’ll back away at least 10’ to make sure perspective distortions are at a minimum. I can always crop down to a headshot for my purpose; the headshots don’t have to be pretty, as long as they show how the faces look.

To JACS, I am guessing the example you linked to is a kind of barrel distortion? Am I right in saying it is inherent in most wide angle lenses?

I’m considering Canon’s EF 35mm f/2 IS USM because I may shoot videos hand-held, and I’d like to have the IS. (I'll be using a crop sensor camera - 70D) But mostly I’d be taking stills. 35mm qualifies as a wide angle lens on a FF; on a crop sensor camera, however, am I mistaken in thinking that, because the crop sensor is essentially recording what’s in the middle of the lens, any obvious barrel distortion at the peripheral wouldn’t register on the crop sensor? (I’m referring to stills)

Anyhow, I like the idea of backing away a distance and taking crops in post. For gathering information that is. Any suggestions will be much appreciated! Thanks!

I think from a technical standpoint the 60mm f2.8 macro would be best here. As a macro prime it has negligible barrel or pincushion distortion, and is a focal length that would get a lot of pixels on the face at 10'. It is also very high resolution so you will have lots of detail to work with.

sounds like a good suggestion.  And one doesn't need large aperture lenses for this, since you want to stop down for the purpose anyway.