Stupid question about perspective and coverage

[conradyiu]

Dear all pros,
Sorry that I always post stupid question like this:

A. With same perspective, apsc sensor camera is with longer focal length than FF sensor camera, right?

B. With same image coverage, apsc sensor camera is with wider perspective than FF sensor camera, right?

C. With the use of old 35mm film lens on apsc sensor camera, there is image cropped as the lens is designed for 35mm film?

D. With the use of apsc sensor designed lens on apsc sensor camera like fuji x series, basically no image is cropped or it is just like using old 35mm film lens on 35 mm film camera?

 

[edge100]

Perspective (the relationship between near and far objects) has nothing to do with focal length; only with camera-to-subject distance.

A 50mm lens (for example) is ALWAYS a 50mm lens, no matter what system you use it on; the difference is that on an APS-C camera, you crop away 1.5x of the image, thereby producing the same angle of view as a 75mm lens on a FF camera. That makes a 50mm lens - a normal lens on FF - a short tele on APS-C (and a wide angle on 6x7).

So when Fuji writes "35mm f/1.4", they mean "35mm" and nothing else. The fact is that on APS-C, 35mm is a normal lens, rather than a mildly wide angle, as on FF.

If you want the same the perspective on FF and APS-C, you need to be standing the same distance from your subject. If you ALSO want the same angle of view, you need a shorter focal length lens on APS-C.

 

[Scrambler]

Dear all pros,
Sorry that I always post stupid question like this:

A. With same perspective, apsc sensor camera is with longer focal length than FF sensor camera, right?

B. With same image coverage, apsc sensor camera is with wider perspective than FF sensor camera, right?

C. With the use of old 35mm film lens on apsc sensor camera, there is image cropped as the lens is designed for 35mm film?

D. With the use of apsc sensor designed lens on apsc sensor camera like fuji x series, basically no image is cropped or it is just like using old 35mm film lens on 35 mm film camera?

I think you ate struggling with what perspective and image coverage mean.

The simple approach is that the images will be most similar when the lens focal length is in proportion to the sensor size.

For example, a 35mm film camera has a 24 x 36mm sensor. It is 43mm diagonally.

An aps-c sensor is something like 16 x 24mm with 28mm diagonally.

So proportionally a 16mm lens on an aps-c camera well be most like a 24mm lens on a 35mm camera.

If you take a 24mm lens off a 35mm camera and put it on adv aps-c camera it will behave like any other 24mm lens does. But this will be different to how the images looked with the same lens on 35mm.

Cropping refers to the fact that you could get the same effect by cutting of the edges of your 35mm picture.

Really all lenses could make slightly larger pictures of you could fit them on a larger format camera. Some aps-c lenses will work on 35mm. For this reason I don't find the idea of crop very useful. Nor do I worry to much about what larger image the lens could make.

If you are familiar with one system and will be bringing lenses in to that system, then the numbers of the adapted lenses mean the same as your original lenses.

Of you have lenses and are moving them between different formats, the proportion between the lens optical length and the format dimensions will change and so the angle covered will also change.

 

[willie_901]

I suggest an approach where perspective remains constant (a fixed camera to subject distance) think things through using angle-of-view as the variable.

 

[edge100]

I suggest an approach where perspective remains constant (a fixed camera to subject distance) think things through using angle-of-view as the variable.

Precisely.

Was this an issue back when APS-C digital (or APS film) didn't exist? Were people *this* confused about the difference between, say, a 100mm lens on 35mm, MF, and LF?

Put your camera where it needs to be to get the desired perspective, and then select the lens that gives you the desired angle of view. This is entirely format-independent.

 

[daveleo]

I suggest an approach where perspective remains constant (a fixed camera to subject distance) think things through using angle-of-view as the variable.

This is what we should have been doing as soon as sensors departed from the 35mm format into a wide variety of sizes. (Engineers would call this "non-dimensionalizing" the discussion.)

 

[Scrambler]

This is what we should have been doing as soon as sensors departed from the 35mm format into a wide variety of sizes.

My mind is boggling at this. If by "sensor" you include all image capture technology, then sensors have never been only 35mm format. There were plates, 1/2 plates, 1/4 plates, 120 roll film (in 6x9, 6x6 and 6x4.5cm), 4x5 cut film. In fact you can still get or use any of these. Not to mention all the variety of formats that came after 35mm. Or came before it but are now harder to get. Or the varieties of 35mm (32 or 34mm on the long side?)

People just didn't fret about it. Pretty much all cameras used "normal" lenses and the angular coverage was about the same. Interchangable formats were designed for their respective cameras, so if you had a Hasselblad you learned its lenses, etc.

It was the introduction of digital SLRs with the same mount but smaller sensor that created confusion. Suddenly your new camera did different things with your existing lenses.

I like the "equivalence" concept myself. Helps explain why you need particularly fast lenses on smaller formats. But use what works for you: crop factor, angular coverage, equivalence...

 

[daveleo]

Of course, I was limiting my remark to what the OP limited it to - common 35mm film format ("FF") versus digital sensor formats. I expected that was obvious.

 

[edge100]

I like the "equivalence" concept myself. Helps explain why you need particularly fast lenses on smaller formats. But use what works for you: crop factor, angular coverage, equivalence...

I've found that this concept of equivalence - making the exact same photograph with the exact same angle AND depth of field on different systems - confuses people even more than the "crop factor" nonsense.

 

[zuiko85]

For those of us who, in the 60's and 70's used both half frame and full frame 35mm cameras this whole angle of view, perspective, field size, etc, just came naturally. I still use both my OM and Pen F systems and conversion has become automatic.

I think if people worked with FF and APS and 4:3 sensors at the same time the confusion would resolve itself through actual experience. However when just starting out or only working with one size sensor, well this makes it hard to compare.

 

[kennylovrin]

This thread is quite clear in showing perspective changes: http://photography-on-the.net/forum/showthread.php?t=672913

 

[Scrambler]

I've found that this concept of equivalence - making the exact same photograph with the exact same angle AND depth of field on different systems - confuses people even more than the "crop factor" nonsense.

I agree on that - but it makes sense to me 🙂

Of course, I was limiting my remark to what the OP limited it to - common 35mm film format ("FF") versus digital sensor formats. I expected that was obvious.

Apologies daveleo. :angel:

I have excessive sensitivity to people speaking as if "full frame" 35mm is a large size, rather than a "miniature" format.

 

[Rob-F]

Dear all pros,
Sorry that I always post stupid question like this:

A. With same perspective, apsc sensor camera is with longer focal length than FF sensor camera, right?

B. With same image coverage, apsc sensor camera is with wider perspective than FF sensor camera, right?

C. With the use of old 35mm film lens on apsc sensor camera, there is image cropped as the lens is designed for 35mm film?

D. With the use of apsc sensor designed lens on apsc sensor camera like fuji x series, basically no image is cropped or it is just like using old 35mm film lens on 35 mm film camera?

A. You have it just backwards. To get the same perspective (same camera-to-subject distance), a shorter focal length must be used with the smaller sensor.

B. No. All cameras having the same angle of view, and used at the same camera to subject distance, will get the same picture. And they will have the same angle of view when the focal length of each one is "equivalent" to the others. They are equivalent when each camera has a lens of a focal length that is in the same proportion to its sensor as the others.

C. Yes.

D. Right. See (B).

 

[daveleo]

@ Scrambler ... I had too much caffeine this morning - makes me too edgy 🙂

 

[Godfrey]

Dear all pros,
Sorry that I always post stupid question like this:

A. With same perspective, apsc sensor camera is with longer focal length than FF sensor camera, right?

B. With same image coverage, apsc sensor camera is with wider perspective than FF sensor camera, right?

C. With the use of old 35mm film lens on apsc sensor camera, there is image cropped as the lens is designed for 35mm film?

D. With the use of apsc sensor designed lens on apsc sensor camera like fuji x series, basically no image is cropped or it is just like using old 35mm film lens on 35 mm film camera?

No question asked with integrity is stupid. Unfortunately your statements, A-D, are not correct. They demonstrate you do not understand what perspective is, are using the term 'coverage' incorrectly, and are confused about the relationship between field of view, format, and focal length. Here's an explanation of these notions.

A- Perspective is the relationship between the sizes of objects in a view. It is a function of where the camera is relative to the subject. An APS-C camera and a FF camera return exactly the same perspective when placed in the same position relative to the subject, regardless of focal length or field of view.

B- Field of view (FoV) is the combination of vertical and horizontal angle of views. Field of view determines how much of the subject a camera sees from a given position.

B1- Focal length is a property of a lens: It is the distance from the lens' primary nodal point to the imaging plane with the focus distance set to infinity.

B2- Format is a property of the recording medium: It is the physical size of the recording medium, for example, APS-C is nominally 16mm x 24mm, FF is nominally 24mm x 36mm.

B3- Coverage is a property of a lens. It is also known as the image circle: Coverage is the size of the image formed by a lens at the imaging plane. Coverage determines how large a format a lens can be used with.
​

FoV is a function of focal length and format. So, presuming that a lens has sufficient coverage (a large enough image circle) to be used with both APS-C and FF formats, the same focal length uses on APS-C will image a larger (wider) FoV on FF.

C- When using a lens designed for 35mm film camera on an APS-C camera, all the rules above (A + B) apply: the perspective from a given position will be the same, and the FoV will be reduced in the APS-C camera due to the smaller format.

D- The difference between a lens designed for an APS-C camera and a lens designed for a FF camera is that the coverage of the APS-C design might not be sufficient to be used on an FF camera. All other rules (A + B above) apply.

Hopefully, I've clarified this subject for you.

G