8x10 Bellows Extension and Angle of View

[Sheldon N]

So I've just started shooting 8x10 and am discovering that portraits are now more like macro work with the amount of bellows extension involved!

One thing I've noticed is that my lens seems to "feel" a bit longer in focal length than I would have expected. I set up a shot a couple days ago and focused and the resulting field of view was narrower than I'd anticipated based on my experience with 35mm lenses. I'm shooting with a 12" (305mm) lens, which the field of view calculators say should be roughly like a 35mm lens on 35mm film (with the edges cropped off the 35mm frame to match aspect ratios). But when I set up the 8x10 shot, it felt more like I was shooting with a 50-60mm lens equivalent.

Does significantly extending the bellows into a macro territory alter the effective field of view of the lens? Or is this all in my head?

[Bob Salomon]

A 305mm on 810 is the same as a 45mm on 35mm. 45mm is a true normal on 35mm. A 360mm is equal to a 53mm on 35mm. If you are doing tight portraits with a 305 or 360 on 810 then that is really too short a lens. To get away from the foreshortening from a normal lens on 810 you would need a 500mm or so. That would have the look of an 88mm lens on 35mm.

But you also have the film's proportion involved here. 810 is a short squat format like 4x5. 35mm is a long, narrow proportion like 5x7 or 11 x 14. So that could also be part of the feeling that you are getting.

And you are not in macro territory if you are just doing a portrait. Unless you are shooting body parts like an eye, a nose or an ear only.

[Sheldon N]

A 305mm on 810 is the same as a 45mm on 35mm.

No, my original comments are correct. If you crop the edges of an image from a 35mm lens on 35mm film to share the same aspect ratio as 8x10, it's the same as a 300-305mm lens. Both have a roughly 37 degree vertical angle of view.

And you are not in macro territory if you are just doing a portrait. Unless you are shooting body parts like an eye, a nose or an ear only.

This is 8x10 film I'm shooting with. Just an eye would be ridiculous. A subject size of 8x10 inches (ie a medium tight headshot) is a 1:1 macro and would require 600mm of bellows from a 300mm lens. For my slightly looser portrait shot I had about 400-450mm of bellows extension with the 300mm lens. I had to put on the rear rail extension on my Kodak 2D to focus the shot. That's approaching macro territory for 8x10.

[Sheldon N]

As a side note, I just realized I can observe the phenomenon on the ground glass. If I point the camera out the window and look at the field of view on the ground glass while I add extension I can see the background get more magnified with a narrower field of view as it defocuses.

[ic-racer]

S
Does significantly extending the bellows into a macro territory alter the effective field of view of the lens? Or is this all in my head?

For certain. For example when you get to 1:1 your field of view is cut in half. For exampe the 300mm lens at 1:1 has the same angle of view on the film plane as a 600mm lens at infinity.

[Ari]

One thing I've noticed is that my lens seems to "feel" a bit longer in focal length than I would have expected.

If you crop the edges of an image from a 35mm lens on 35mm film to share the same aspect ratio as 8x10, it's the same as a 300-305mm lens.

These seem to be contradictory statements. The second statement leads me to think you no longer feel that the lens is too long, despite its normal-ish FL.
Mr Salomon was offering a reason why you might feel the lens to be longer than expected, and his math is bang-on.
8x10 has a diagonal of 312mm, so a 305mm lens would correspond very closely to a 45mm lens in tiny format.

[Sheldon N]

For certain. For example when you get to 1:1 your field of view is cut in half. For exampe the 300mm lens at 1:1 has the same angle of view on the film plane as a 600mm lens at infinity.

Awesome, that makes perfect sense! Thanks for the reply. That would mean that basically the lens has an effective angle of view based on the amount of bellows extension.

These seem to be contradictory statements. The second statement leads me to think you no longer feel that the lens is too long, despite its normal-ish FL.
Mr Salomon was offering a reason why you might feel the lens to be longer than expected, and his math is bang-on.
8x10 has a diagonal of 312mm, so a 305mm lens would correspond very closely to a 45mm lens in tiny format.

I guess I should have been more specific... it felt "long" when I'd set up a fairly close portrait with a decent amount of bellows extension. Out at infinity it behaves exactly as expected.

I have a really good natural sense of what that focal length would look like when shooting with an SLR, I can frame the shot in my mind's eye before pulling out the camera. So when I set up the shot with the 8x10 camera and focused, I was surprised to see how much narrower the field of view was than I was expecting.

Now I understand this was due to the bellows extension. With 8x10 the bellows extension comes into play much sooner than with smaller formats. I'd never really experienced this with 4x5 or smaller formats, and hadn't had it explained to me before.

[ic-racer]

Awesome, that makes perfect sense! Thanks for the reply. That would mean that basically the lens has an effective angle of view based on the amount of bellows extension.

The other neat optical property is that at 1:1 just about any 150mm lens made for a 4x5 camera not only covers 8x10 but also has the same angle of view on the film plane as a 300mm lens at infinity.

[Sheldon N]

That is very cool indeed.

Now does this principle apply to the finished image perspective as well? It seems like lots of people shoot 8x10 portraits with a near normal focal length and the images don't look nearly as distorted as one would expect.

[ic-racer]

finished image perspective as well?

That is only altered by change in subject to lens distance. Film format, aperture, focal length, etc have no direct effect (though they may cause you to alter your subject distance).