focus stacking question

[bs0604]

If I am going to take a series of images for focus stacking is there any rule of thumb as to whether I should use a low or high f stop?

 

[Overread]

It depends on how you shoot and on what you want.

If you're on a tripod or other stable setup then you can choose a wide or a small aperture depending on the effect you want. Note that the wider the aperture you choose the more frames you will need to take, with very wide apertures this can make getting all the frames needed a bit tricky if you're doing the adjustments manually as with a very thin depth of field you can more easily miss out a frame. A smaller aperture makes getting the needed overlap much easier.

If you're shooting handheld I would suggest a smaller aperture since its even easier to miss out a frame.

Note that if you use a very wide aperture you can get an odd effect which is where because the wide aperture gives a very small depth of field and as such you get a fast fall off into blurring. However when you focus stack you get an odd looking photo because you end up with a very strong line between an area of blurr and a sudden jump into detail. One way to mitigate this is to vary the aperture so that the apertures you use for the first few and last few frames are smaller (thus more depth of field) whilst those in the middle are wider. This lets you create a more natural fall off of sharpness when the photos are stacked into a final version.

Note that typically most people tend to choose sharp apertures between around f4-f8 for focus stacking if preservation of sharpness is the most important aspect. Smaller than f8 and diffraction starts to kick in and wider and you're typically shooting near or at the maximum aperture for the lens (f2.8 on most macro lenses*) and as most lenses perform their best stopped down one stop.

There is also a method where you keep the focus point the same and take two photos, one at a sharp aperture such as f8-10 and then take a second photo at a much smaller aperture. Allowing the user to merge the effect of a wider depth of field that say f18 or f20 gives, with the sharpness of a wider aperture.




* Note if you shoot Nikon then f5.6 will be your reported maximum aperture on most macro lenses. This is because the Nikon setup takes into account the effective reduction in aperture used by most macro lenses to get to their closer focusing distances. Canon and other brands also use the same optical methods, but their cameras often don't report the effective aperture change. This tends to mean that, in practice, if you're comparing macro photo settings of a Canon user to a Nikon then the Canon user is able to shoot a stop wider - in actuality they are not, it just appears that way because of the settings. Similarly the Nikon user can shoot around on stop smaller before diffraction softening becomes too extreme - again in actuality the points are about the same its just the difference in how the apertures are reported to the user.

 

[480sparky]

I would use the aperture that gives me the sharpest image regardless of the DOF.

 

[bs0604]

thanks. I am using a nikon d800 and a 105 mm Nikon lens and will always try to use a tripod. Looks from your posts that f5.6 would be right

 

[480sparky]

I never use generalizations and others statements as to which aperture is sharpest for my lenses.... I test each one I own. My 105 Nikkor micro is sharpest at f/11 and 16, followed closely by 5.6 and 8, then 22. F/4 is acceptable, with 2.8 and 32 unusable.