Beginner question on camera aperture

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AIMP
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Joined: Sun May 29, 2016 5:33 am

Beginner question on camera aperture

Post by AIMP »

There's plenty of information how to calculate effective aperture, but i can't seem to find anything on how should you choose your camera aperture in macro photography. That's probably because the question is too basic.

For example if i'm taking a stack of photos on CANON 20MM f/3.5 MACROPHOTO using lens aperture of f/3.5, with canon auto bellows at 5x magnification and Canon EOS 700D camera, which has the lowest aperture setting of f/2.8. Doing everything on automated stacking rail. Continuous studio lighting, ISO100 and controlling the lighting with exposure time setting.
Should i set the camera aperture equal to the aperture of the lens (f/3.5), or should i set it to lowest possible at f/2.8, since DoF is not a problem with automated stacking rail, or pick any option between lens aperture of f/3.5 and effective aperture of f/21 to get the best quality photos for the stack?

rjlittlefield
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Re: Beginner question on camera aperture

Post by rjlittlefield »

The question is not too basic. In fact there are some subtle aspects.

For focus stacking, standard advice is to stop down as far as you can, while maintaining the sharpness that you need. This will give you the minimum number of frames in the stack, while also minimizing stacking artifacts.

However, that phrase "the sharpness you need" admits at least three common possibilities. Some people want the sharpest image they can get, period, some people want to run wide open to get the best background bokeh, and some people can live with reduced sharpness because of their intended use for the images. If your goal is the sharpest image you can get, then there is no substitute for testing the lens at a variety of apertures to see how quality varies with f-stop setting. At 5X, it is likely that the sharpest aperture will be wide open or stopped down just a little bit. On EOS 700D, even effective f/21 at wide open is still well into diffraction territory. If you can live with reduced resolution because, say, your goal is to make 1000 pixel images for an identification key, then probably you can stop down a couple of notches and apply heavy sharpening in post-processing. Again, the best approach is experimentation because results can vary with the subject, lens, illumination, and your skills at postprocessing.

One aspect of your question puzzles me. If the lens that you're talking about is the one described at https://www.closeuphotography.com/canon-macrophoto-20mm-lens , then as far as I know that's a manual aperture lens in which the camera has no control and not even any awareness of what f-number the lens is using. If that's correct, then the only effect of changing the f-number on the camera is to possibly confuse its metering system. This situation frequently arises with other lenses on various adapters. Standard recommendation is to set the camera as wide open as it will allow, because that tells the camera that the taking aperture is the same as the viewing/metering aperture.

Make sense?

--Rik

AIMP
Posts: 5
Joined: Sun May 29, 2016 5:33 am

Re: Beginner question on camera aperture

Post by AIMP »

rjlittlefield wrote:
Sun Jun 27, 2021 9:32 pm

One aspect of your question puzzles me. If the lens that you're talking about is the one described at https://www.closeuphotography.com/canon-macrophoto-20mm-lens , then as far as I know that's a manual aperture lens in which the camera has no control and not even any awareness of what f-number the lens is using. If that's correct, then the only effect of changing the f-number on the camera is to possibly confuse its metering system. This situation frequently arises with other lenses on various adapters. Standard recommendation is to set the camera as wide open as it will allow, because that tells the camera that the taking aperture is the same as the viewing/metering aperture.
Yes, i manually set lens aperture for f/3.5 and always use it at that and camera doesn't have control or any awareness of the lens, but changing the f-number on the camera still has an effect, because photos are getting darker when i'm stopping down via camera settings.

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