formats, focal length and perspective

[iconoclastica]

Am I right to think, that from a print with suitable perspective lines I can estimate the angle of view and, given the negative format, the lens focal length. But there's no way to determine the original negative format, not even if there is an object with a reference size somewhere in the print. Therefore, a lens with focal length f yields the same perspective on a negative of size s as a lens of 2f would do on negatives sized 2s?

[Jim Jones]

You are right. Camera to subject distance determines apparent perspective on print.

[ic-racer]

Difficult but not impossible to get an idea of film format. As magnification increases, Dof decreases. Very shallow Dof of large objects cannot be achieved with small film formats.
For example projecting a large building on Minox format requires such a small magnification that Dof would appear nearly infinite.

Likewise a portrait headshot on 20x24 format has a magnification greater than 1.0 and resulting shallow Dof. Studio strobes are only so bright and 20x24 film only so fast that stopping down to f512 is not practical, etc.

[iconoclastica]

Difficult but not impossible to get an idea of film format. As magnification increases, Dof decreases.

True, but in the case at hand all I have got is perspective, since it is a painting based on a photo

Thanks, it 's good to have a confirmation on this subject!

[Doremus Scudder]

You are right. Camera to subject distance determines apparent perspective on print.

... and lens focal length (relative to format) determines field of view.

So, even if you don't know what the film format originally was, you can roughly assess whether the image was made with a long, medium, or short focal length lens.

Let's say I have an image I want to duplicate, kind of like yours. I would go to the location, find the spot where the spatial relationships between near and far objects matched and then choose a lens focal length to get all the image I want on the film.

So, if I were using 4x5 film and needed a "normal" view, I'd choose a lens like 150mm. If using 6x6, an 80mm, if using 35mm, then 50mm.

All approximate, of course.

Hope that helps,

Doremus

[MAubrey]

At a given subject size, there will still be differences. If you want a head/shoulders portrait to fill the frame, the amount of bellows draw you use relative to the format will have an effect on perspective, since keeping subject size in the frame constant requires to change other factors. A 35mm image doesn't change AoV much when focusing close, but a 8x10 image with the same framing might require 100mm extra bellows extension, narrowing the AoV of the image.

https://twitter.com/michaelgaubrey/s...96293320183808

[iconoclastica]

... the amount of bellows draw you use relative to the format will have an effect on perspective ...

Excellent point, Michael, I completely overlooked that. However, I wonder whether it is true. Of course, with greater extension the effective (used part of) the angle of view will decrease. But does that have an effect on the perspective? I suppose that effect will be the same as when cropping the resulting image, viz. none. For when extending the bellows, the image circle increases in diameter. The image circle does not "know" about the film format, so it must base its perspective on what it does see, what is the focal length. If not, refocusing would inevitably have a zoom-effect - something which is not unheard of, nor is it common or desirable.

Perhaps someone could supply the math to this...

[Bernice Loui]

Previously discussed..
Go to Post# 18

https://www.largeformatphotography.i...f-lenses/page2


Bernice