Difference in short focal length big nose syndrome

[TimothyPeacock]

I've just been having a think and can't quite work it out in my head, so wanted to ask the clever people!

When shooting portraits at a short focal length we are all familiar with the distortion that takes place, but what is the difference in distortion between a crop and a full frame camera?

For example, I take a headshot with a 28mm lens on a 1.6x crop camera, and with the same lens on a full frame camera. Because it is the same lens the distortion must be the same; so is it less noticeable on the crop sensor as there is a smaller field of view, or on the full frame sensor as there is a larger field of view?

On the crop sensor the 28mm lens has a similar field of view to a 45, but the distortion can't be as if it were a 45mm lens, as it is still 28....

I feel like I'm talking round in circles, but I hope it makes some sense.

Looking forward to your responses to my tangled brain mess!

Cheers,

T

 

[480sparky]

If you stood at the same distance from the subject, a 28mm in a crop body will produce the exact same amount of 'big nose distortion' and a 28mm would on a full-frame body.

If you tried to frame the subject the same between the two bodies, then the full-frame would give you more 'bigger nose distortion' because you'd have to get closer to your subject to get the same framing you have in the crop sensor.

 

[Gavjenks]

It seems like you are specifically referring to perspective? Like when people's noses look bigger when you shoot them close up with a 12mm lens?

1) Perspective depends 100% on distance from the subject. Focal length has nothing to do with it other than indirectly insofar as it tends to be inconvenient to shoot things close to you with really long lenses (people aren't fond of ear portraits, etc.).

2) It's not a "distortion." It is the correct geometry of the world. I made a diagram for you:


It doesn't matter what focal length either of those lenses are (I didn't even include their fields of view on the diagram). If the hair and the nose of that subject are within view, the hair will take up a much narrower portion of the visual angle of the top (near) lens than the nose, whereas in the further lens, the ratio of hair and nose in portion of the image are closer to equal.

These are all straight lines converging at a point, no distortions.


The only reason it seems "distorted" is that you are accustomed to seeing people in your everyday life from a distance of about 15ish feet.

 

[Braineack]

Why do people go out of their ways to compare their lenses to what the picture might look like on a different camera that you'll never use/buy?

 

[Gavjenks]

Why do people go out of their ways to compare their lenses to what the picture might look like on a different camera that you'll never use/buy?

People never use or buy full frame cameras? That's weird. I wonder then what this camera-shaped thing in my hand is with the bigger looking sensor on the inside than this camera-shaped thing in my other hand? Maybe I just need my eyes checked.

 

[TimothyPeacock]

It seems like you are specifically referring to perspective? Like when people's noses look bigger when you shoot them close up with a 12mm lens?

1) Perspective depends 100% on distance from the subject. Focal length has nothing to do with it other than indirectly insofar as it tends to be inconvenient to shoot things close to you with really long lenses (people aren't fond of ear portraits, etc.).

2) It's not a "distortion." It is the correct geometry of the world. I made a diagram for you:
View attachment 55293

It doesn't matter what focal length either of those lenses are (I didn't even include their fields of view on the diagram). If the hair and the nose of that subject are within view, the hair will take up a much narrower portion of the visual angle of the top (near) lens than the nose, whereas in the further lens, the ratio of hair and nose in portion of the image are closer to equal.

These are all straight lines converging at a point, no distortions.


The only reason it seems "distorted" is that you are accustomed to seeing people in your everyday life from a distance of about 15ish feet.

That's great thank you, the diagrams make it all clear. Seems obvious with a little drawing!

Why do people go out of their ways to compare their lenses to what the picture might look like on a different camera that you'll never use/buy?

I was purely asking out of interest; not because I was comparing what could be if I had a bigger better camera. It was a technical(ish) question that I wasn't sure of the answer for, therefore I asked.


Many thanks for all your answers!

 

[Braineack]

Why do people go out of their ways to compare their lenses to what the picture might look like on a different camera that you'll never use/buy?

People never use or buy full frame cameras? That's weird. I wonder then what this camera-shaped thing in my hand is with the bigger looking sensor on the inside than this camera-shaped thing in my other hand? Maybe I just need my eyes checked.

That's not what I said. But keep trying.

I'll rephrase: Why do people with crop sensors consistently care so much about what the focal length, distortion, or what-have-you of their lenses on a larger sensor will be like?

 

[480sparky]

.........I'll rephrase: Why do people with crop sensors consistently care so much about what the focal length, distortion, or what-have-you of their lenses on a larger sensor will be like?

Perhaps it's because they don't understand the differences........ but are wanting to learn what they are so their next major gear purchase is a bit more educated.

 

[Gavjenks]

Why do people go out of their ways to compare their lenses to what the picture might look like on a different camera that you'll never use/buy?

People never use or buy full frame cameras? That's weird. I wonder then what this camera-shaped thing in my hand is with the bigger looking sensor on the inside than this camera-shaped thing in my other hand? Maybe I just need my eyes checked.

That's not what I said. But keep trying.

I'll rephrase: Why do people with crop sensors consistently care so much about what the focal length, distortion, or what-have-you of their lenses on a larger sensor will be like?

You said "that they'll never use/buy." That is the wrong part. People upgrade all the time and obviously it would be dumb to do so if you didn't understand any of the differences.

 

[astroNikon]

That's not what I said. But keep trying.

I'll rephrase: Why do people with crop sensors consistently care so much about what the focal length, distortion, or what-have-you of their lenses on a larger sensor will be like?

Because we are curious.
I had to borrow a D700 just to find out. Now I want a FF but have to save up the $$$ for it.
FF definitely helps out inside (churches, real estate type, etc) for low light.

And for newbies, when we buy a 24-50 it's odd when someone says "well it's actually a 36-75". So we really want to know what 24-50 really looks like.

If you have a FF then it's common sense, if you don't have a FF then it makes no sense.

 

[snowbear]

Why do people go out of their ways to compare their lenses to what the picture might look like on a different camera that you'll never use/buy?

I had a full frame camera long before I got a crop-sensor; it's called 35mm film, and I still use it.

 

[cynicaster]

I'll rephrase: Why do people with crop sensors consistently care so much about what the focal length, distortion, or what-have-you of their lenses on a larger sensor will be like?

So... you'd have it that for all of us lowly APS-C folks, the learning process on FF shall not begin until the $2500+ purchase is made, and not a moment sooner? Please tell me I'm misunderstanding your comment, because as it sounds, it's absurd.

 

[Kolia]

Why do people go out of their ways to compare their lenses to what the picture might look like on a different camera that you'll never use/buy?

Why do people who have no intention of contributing to a topic spend time posting in them nonetheless ?


Nice graph Gav. Well portrayed !

 

[Derrel]

Well-known fashion and beauty photographer Stephen Eastwood did a very good comparison of focal lengths a number of years back, but he now has a new web domain, and the prior "education-centric" web site he used to maintain has been allowed to lapse; however, lucky for us, the comparison series he shot is still available on many other web hosts. It runs from 19mm to 350mm and can be found easily by google searching the term Stephen Eastwood + focal length comparison.

Stephen Eastwood + focal length comparison - Google Search

Since the OP asked SPECIFICALLY about the "big nose" issue, this comparison is one of the absolute best and most-appropriate visual comparisons I've ever seen on the web. In addition to the "big nose" issue, also take a look at the woman's eyebrows and forehead. Oh-My-Gawd...in the 19mm and 24mm example photos, her forehead and eyebrows look like they belong on a Neanderthal woman! Just LOOK at the very visually apparent size distortion of the forehead and eyebrows in the 19mm,24mm, and even to an extent, in the 35mm lens captures! Whoa! VERY unappealing!

 

[Dao]

Perspective distortion (photography) - Wikipedia, the free encyclopedia

Quoted from Wiki

"Note that perspective distortion is caused by distance, not by the lens per se – two shots of the same scene from the same distance will exhibit identical perspective distortion, regardless of lens used. However, since wide-angle lenses have a wider field of view, they are generally used from closer, while telephoto lenses have a narrower field of view and are generally used from farther away."



On top of that, a wide angle lens do have some level of barrel distortion and that is the characteristic of the lens. So if you take a photo of a brick wall, you will see lines from the wall are distorted. If the barrel distortion is a lot heavier at the edge of the frame, cropped frame vs full frame may shows some difference in that case.