Exposure compensation for small apertures

[Dan Fromm]

Right, right, Dan, I’m not saying the mechanism is the same, I’m asking whether the shutter opening slowly relative to the overall shutter speed (eg if it takes 1/1000 to open and 1/1000 to close and you selected a 1/500 shutter speed, such that the aperture has just enough to open to open and close, rather than offering a large fraction of exposure time being fully open) isn’t but in fact another mechanical vignetting effect — different from the one you mention (now induced by the shutter creating the vignetting) but that in fact compounds with it when you shoot wide open at extreme shutter speeds.

Thanks for asking again. You're concerned about shutter efficiency, which has been addressed well earlier in this discussion.

[Kiwi7475]

Right, except that my question (still) is whether it will create a radial effect due to the position of the shutter within the lens. Or will it be a uniform under exposure across the entire film area. That was my original question.

[JohnF]

Many apologies, I misread the information. It is a reduction of exposure required as correctly pointed out in the thread. I agree, it is an irrelevant though interesting point as regards real world natural light large format photography. I have really enjoyed reading the replies.
I am using the 7th Edition of View Camera Technique. Book extract with charts of compensation not published for fear of copyright infringement.

[Michael R]

Right, except that my question (still) is whether it will create a radial effect due to the position of the shutter within the lens. Or will it be a uniform under exposure across the entire film area. That was my original question.

Uniform. Imagine opening the diaphragm in a lens from a small aperture to a larger one and back down again, and what you would see happen to the image on the ground glass/image plane as you do this.

[BrianShaw]

Many apologies, I misread the information. It is a reduction of exposure required as correctly pointed out in the thread. I agree, it is an irrelevant though interesting point as regards real world natural light large format photography. I have really enjoyed reading the replies.
I am using the 7th Edition of View Camera Technique. Book extract with charts of compensation not published for fear of copyright infringement.

I think the Fair Use Clause permits limited reproduction for academic purposes, which this probably is because nobody is seeking profit from Stroebel’s work, but I respect your position.

Does Stroebel’s table look like this? Post 4 in thread 'Leaf Shutter Efficiency Compensation'

https://www.photrio.com/forum/thread...nsation.17444/

[JohnF]

Caution to the winds!

[BrianShaw]

Interesting. A rather complicated table, though. If I read it correctly, Stroebel is generally consistent with Kodak except Stroebel works in units of 1/4 second and Kodak in units of 1/3 second.

Oddly... in many, many years of photography this compensation has not been a problem for me except when using flash bulbs.

[Jody_S]

The reason for the exposure compensation at small apertures vs. wide open is clear when using fast shutter speeds, what interests me is the other factor which is increased depth of field at fastest apertures.

You're composing and shooting with the lens wide open, but shooting at say 1/400 gives you a variable aperture exposure starting and ending with a pinhole, and only reaching full aperture momentarily in the middle of the exposure. Your effective aperture for the purposes of depth of field may end up being 2-3 stops smaller than what you thought you were shooting at.

[Bernice Loui]

If larger lens apertures are needed for sheet film/LF view camera images, apply neutral density filter to move the shutter speed down as needed.

Given the types of images made using a view camera with sheet film, high shutter speeds (1/500 to 1/125 sec) is extremely questionable.

Back to the "red herring" again, this question might be of intellectual-academia curiosity. In real world sheet film image making, does any of this uber shutter speed discussion apply_?_


Examples of sheet film images made at f22 or smaller lens aperture with a shutter speed of 1/500 second or so outside of specialized scientific and similar images_?_

Bernice

[Michael R]

Your experience makes sense to me. After all the compensation is 1/4 stop or less until you get to 1/250s, ie not something to worry about.

Interesting. A rather complicated table, though. If I read it correctly, Stroebel is generally consistent with Kodak except Stroebel works in units of 1/4 second and Kodak in units of 1/3 second.

Oddly... in many, many years of photography this compensation has not been a problem for me except when using flash bulbs.