Ultra Wide-Angle distortion\compression question

[Tofuball]

I'm trying to figure out focal length vs sensor size and I haven't been able to find a satisfactory answer to this question, so I made an account to ask here (sorry if this is the wrong place!):

If I have an APS-C lens set at 10mm and a full frame (35mm) set at the equivalent FF size, 16mm, assuming all other things are equal (framing, lens and sensor quality, exposure, etc), what changes?

Does the picture taken with the 16mm lens have less "wide angle" distortion, or does it end up being the same?

Put another way, if I had a magic 10-16mm zoom lens that was full frame and had no lens distortion, took a picture with the camera in crop mode and 10mm, then set it in FF mode and took a picture at 16mm, what would change (other than the megapixel count due to larger sensor)?

[Polar01]

Jason wide angle distortion is a fact of life with any lens that works usually under 24mm. As to your focal length vs sensor size, basically it does not excess hear me out.
If you take a APS-C sensor camera (Canon) and you put a 10-20mm DX (for crop sensor camera) and set it to 10mm you will get a Field of View as if you were using a Full Frame sensor camera and a FF lens set for 16mm.
Math stuff crop factor 1.6 x #mm (10)=16mm
FF factor 1 x #mm (16)=16mm
As both lens are now equal in the number of mm's both 16 the Field of View and the amount of distortion will be equal.
As for your magic 10-16mm Full Frame lens now set camera to crop mode, lens at 10mm field of view =16mm, now reset camera to FF mode adjust lens to 16mm field of view is 16mm.
Hope that is of some help.

Cheers: Allan

[xpatUSA]

Welcome, Jason.

You will not be short of responses to your question but, if understand correctly, distortion has to do with the shooter's distance from the subject, not the focal length of the lens.

That is to say, If you shot a building from one spot at 10mm and 16mm, only the framing would change, not the perspective.

If, however, you shot at 16mm and then walked closer to get the same framing at 10mm, the perspective would change.

[edit] Say that you change a lens of given true focal length between two cameras - one APS-C and one FF - if they are at the same distance from the subject, the perspective still does not change.

This being a well-known subject, I've probably misunderstood the question

[Manfred M]

Jason - the other impact you will get from going from the full-frame to crop frame in the example you and Allan are looking at is that the crop frame will gain you the equivalent of around 1 stop in depth of field (DoF). In other words, if you shot at the full frame lens at f/5.6, you would get the same depth of field by shooting the crop frame at f/4.

The DoF on an ultra-wide angle lens tends to be deep anyways, so it may not have all that much real life impact. However in situations where you a have an object in the foreground that you are trying to keep in focus, you may see some impact of the background being a bit softer when shooting FF.

[Tofuball]

Thanks for the replies!

It probably has been covered before and I was just not getting it; I'm trying to make sure I understand how much crop factor influences the actual distortion I've got.

If I'm reading this right, you guys are saying that given nothing else changing (the subject and background is still the same distance away) the image would be exactly the same between an APS-C@10mm and an FF@16mm except for DoF?

I thought the extra stop of DoF was from your change to subject distance, if the distance remains the same won't the DoF be the same?

[xpatUSA]

Thanks for the replies!

It probably has been covered before and I was just not getting it; I'm trying to make sure I understand how much crop factor influences the actual distortion I've got.

If I'm reading this right, you guys are saying that given nothing else changing (the subject and background is still the same distance away) the image would be exactly the same between an APS-C@10mm and an FF@16mm [ .. ]?

I said that the subject was at the same distance but I wasn't including the background, Jason. A silly example might be a train leaving a station where you are keeping a constant distance from the engine but the station perspective changes as it recedes from the camera, or vice-versa for that matter. And I was referring to the perspective of the image, not just "the image". Plus, "APS-C" covers quite a wide range sensor sizes, which means that images would not be "exactly the same", eh?

Pardon my pedantry ;-)

Manfred will likely respond to the DoF bit . . . .

[george013]

I'm trying to figure out focal length vs sensor size and I haven't been able to find a satisfactory answer to this question, so I made an account to ask here (sorry if this is the wrong place!):

If I have an APS-C lens set at 10mm and a full frame (35mm) set at the equivalent FF size, 16mm, assuming all other things are equal (framing, lens and sensor quality, exposure, etc), what changes?

Does the picture taken with the 16mm lens have less "wide angle" distortion, or does it end up being the same?

Put another way, if I had a magic 10-16mm zoom lens that was full frame and had no lens distortion, took a picture with the camera in crop mode and 10mm, then set it in FF mode and took a picture at 16mm, what would change (other than the megapixel count due to larger sensor)?

May I ask what kind of distortion you mean? You might think what a strange question, but it isn't.

George

[Tofuball]

Sure! I don't know what the term is exactly (probably why I've had so much trouble articulating this) but when you take a picture with a telephoto lens the background looks closer to the subject than if you take the same picture with a wide angle lens. I think it's called compression. I'm wondering if that changes between Crop\10mm and FF\16mm.

It's not the fault of the lens design, but of the Field of View.

[xpatUSA]

I think it's called compression.

Also "foreshorting", perhaps.

https://en.wikipedia.org/wiki/Perspe...Foreshortening
.

[Dave Humphries]

Hi Jason,

I thought the extra stop of DoF was from your change to subject distance, if the distance remains the same won't the DoF be the same?

No, it is due to the smaller sensor patch and extra magnification that brings.

Basically; the same 'crop factor' figure (e.g. 1.6 in this case) that is used to 'do the sums' for equivalent angle of view for focal length also applies to aperture when it comes to determining the Depth of Field.

[george013]

Sure! I don't know what the term is exactly (probably why I've had so much trouble articulating this) but when you take a picture with a telephoto lens the background looks closer to the subject than if you take the same picture with a wide angle lens. I think it's called compression. I'm wondering if that changes between Crop\10mm and FF\16mm.

It's not the fault of the lens design, but of the Field of View.

That distortion is distance related. Put 2 people of the same length behind each other with a distance of let's say 5m. Now, if you take a picture at a distance of 15m from the first one, than the ratio between the distances to the camera of the 1st and 2nd one is 15:20.
Now if you take a picture at 1 m distance, then the ratio will be 1:6. The bigger the difference is, the bigger the "distortion". The focal length is only used to gain an angel of view to fill the sensor equally with the same image.
This means that comparing a crop and a FF sensor with the same frame, that the crop will have less distortion, just because the distance to the subject is bigger to get that same frame.

There is also a lens distortion, more obvious with wide angel. If that distortion is changeing lineair from the middle of the imagecircle to the borders, than a crop sensor will have less distortion.

I hope I didn't make a mistake.

George

[Manfred M]

The distortion you are concerned about has nothing to do with the lens focal length, but is associated with the camera to subject distance.

If you take a picture of a subject (let's assume it is a person's face) with a medium length telephoto lens, the subject will have a fairly flat and pleasing appearance. Now take an ultra-wide angle lens and repeat the shot with the subject at the same distance from the camera as the first shot.

Now take that second wide angle shot and enlarge it so that the face is the same size as the telephoto lens. If the camera has a high enough pixel density and resolution, you will see that two faces have the same amount of distortion. We tend to shoot wide angle lenses much closer to our subjects and this is the primary cause of the distortion you are trying to understand.

[george013]

Related to your distortion/compression question is the question of perspective. Perspective is the suggestion of a third dimension in a 2 dimensional plane. A photo is by definition 2 dimensional. The suggestion of that third dimension is bigger when your subject, or something else, is nearby. When everything is further away you'll get your compression. The feeling of that third dimension is less. Another word for compression is flattening, 2 dimensional.
If you want, I can show you some examples.

George

[IzzieK]

if you want, i can show you some examples.

George

p l e a s e ....???

[george013]

The distortion you are concerned about has nothing to do with the lens focal length, but is associated with the camera to subject distance.

If you take a picture of a subject (let's assume it is a person's face) with a medium length telephoto lens, the subject will have a fairly flat and pleasing appearance. Now take an ultra-wide angle lens and repeat the shot with the subject at the same distance from the camera as the first shot.

Now take that second wide angle shot and enlarge it so that the face is the same size as the telephoto lens. If the camera has a high enough pixel density and resolution, you will see that two faces have the same amount of distortion. We tend to shoot wide angle lenses much closer to our subjects and this is the primary cause of the distortion you are trying to understand.

We both state that the subject distance is an important variable for the distortion. I must correct myself, the angel of view is also important.
First we must distinguish between same distance and same frame.
Cropping the same frame out off a wide angle picture is narrowing the angle of view. The 2 pictures will be identical.
But when using the same frame the subject distance must be shorter with a wide angle lens. What happens is that the magnification difference of the subject is bigger compared to a different subject further away.. With a tele lens that difference will be less.
It's hard to get that feeling in words.

First 2 with a D80, DX-camera.
First picture 18mm


second picture 170mm . Distance from me to the Grolsch sign is 110m, to the building at the end 450m, Google maps.. There are 3 more canals between.

Somebody in Holland showed me and that's also you say, you can crop the 18mm picture out off the 170mm picture.

Now an example with a single photo.
70mm FF, D700. The canal is visible and you have a feeling of the size.


Now a crop out of that image. It's getting harder to guess the distance to the other side of the canal.


I don't know why the perspective is changing. Just because there is less information on the picture?


George

PS. That gnome on the right is not tortured, the rope is just hanging behind him.

[IzzieK]

OK I got it now...I had a chance to use my new wide angle yesterdee arvo (on a different but dry land scenario) and I sort of imitate your #1 and #3 shot. Or let us say, my version of your #3 shot was sort of always included the back of my car. I think I understand what you mean now...thanks for indulging me with your photo examples..

[george013]

OK I got it now...I had a chance to use my new wide angle yesterdee arvo (on a different but dry land scenario) and I sort of imitate your #1 and #3 shot. Or let us say, my version of your #3 shot was sort of always included the back of my car. I think I understand what you mean now...thanks for indulging me with your photo examples..

The photo's are more tele related. On my search for a good picture/drawing for the short site I came to this site https://www.cambridgeincolour.com/tu...gle-lenses.htm.
Capture "Wide Angel Perspective". It shows exactly what I was meaning.
The difference in magnification of 2 subjects in different distances is getting bigger as the focal length is getting smaller. Based on the same frame of the main subject.
Over and out.
George

[Timar]

There is really no better way to show the difference between subject magnification and angle of view than the Vertigo Effect:



The Vertigo Effect is achieved by zooming in or out on a subject (increasing or decreasing focal length) and at the same time steadily moving the camera back or forth (e.g. using a crane or dolly) to keep the subject magnification constant, thus compressing the background, or vice versa. Most often, as in the scene from the movie Apollo, the effect is used with an increase in focal length, in order to dramatically focus attention on the subject. Interestingly, in Hitchcock's eponymous film it is employed the other way around and quite ingeniously ideed - because there actually is no central subject the eye could rest on, the spectator gets lost in the dizzying effect of the perspective extension.

[IzzieK]

I understand, Bruce...I was using my 11-24mm Sigma lens and on that very same day before we left, I found out that I can remove the top part of my lens hood because there are two of them one on top of the other so I brought that one with me to test shoot while we were out to mail something for my DIL-to-be at FedEx...I stayed in the car while hubby does his duty and shoot as many examples to bring home to analyze...

Thank you for the explanation and the added info...

The photo's are more tele related. On my search for a good picture/drawing for the short site I came to this site https://www.cambridgeincolour.com/tu...gle-lenses.htm.
Capture "Wide Angel Perspective". It shows exactly what I was meaning.
The difference in magnification of 2 subjects in different distances is getting bigger as the focal length is getting smaller. Based on the same frame of the main subject.
Over and out.
George

[MartinJ]

The bottom line, as my first boss told me way back in 1967 (I was then a very junior medical photographer) is that perspective is entirely and only determined by viewpoint.

The fact that zoomed in images look more compressed is caused by the fact that you have effectively cropped out the parts of the image that are nearer you and so lost the parts that are much nearer to you. You can enlarge a wide angle / short lens image to the same scale as a telephoto / long lens image and the images will be identical assuming the camera hasn't moved between the exposures. Sensor size is equally irrelevant. Viewpoint is all!

Martin