Aperture (f-number) stacking?

A forum to ask questions, post setups, and generally discuss anything having to do with photomacrography and photomicroscopy.

Moderators: rjlittlefield, ChrisR, Chris S., Pau

kit1980
Posts: 124
Joined: Thu Aug 18, 2016 11:14 pm
Location: Bellevue, WA, USA

Aperture (f-number) stacking?

Post by kit1980 »

What if instead of changing focus plane, we change the aperture, and then merge the photos with usual focus stacking software? I think this may result in increased depth of focus without introducing diffraction artifacts to the part that is in focus, with "main" part that really in focus to lead the viewer to.

I have this idea for some time, but haven't really tried it. Have anyone tried this? Does it sound it can work?
Omax microscope with Nikon CF objectives
Olympus OM-D E-M10 Mark II camera
http://sdymphoto.com/

Lou Jost
Posts: 5943
Joined: Fri Sep 04, 2015 7:03 am
Location: Ecuador
Contact:

Post by Lou Jost »

I also have been thinking about that, but with an eye to using shots at successively larger apertures all in the same stack, using the initial small-aperture shots to fill in the parts that are usually washed out by haloes from edges that are in front of them.

rjlittlefield
Site Admin
Posts: 23561
Joined: Tue Aug 01, 2006 8:34 am
Location: Richland, Washington State, USA
Contact:

Post by rjlittlefield »

kit's idea should work OK. Taking a few shots with smaller apertures is a well established way of finishing stacks, to make the background less blurred without affecting the in-focus slab.

--Rik

ChrisR
Site Admin
Posts: 8668
Joined: Sat Mar 14, 2009 3:58 am
Location: Near London, UK

Post by ChrisR »

Kit - I played around with that some time ago, after finding I got more detail from a smaller aperture, where it was otherwise hidden behind out of focus haze. That was happening in steep sided depressions, where the sides caught the cone of light when using a wider aperture.

Alignment problems arose:
one is that stacking software usually goes through an alignment phase. You have to make sure they're all aligned the same, - or not at all;
even when you do that, closing an aperture often shifts the focus a little, which is confusing;
and detail from a small aperture frame will sometimes appear in a different place from were it is on a sharper, large aperture frame.

The upshot was that I had to exclude almost everything from the small aperture frames. It was only the one at the back end of the subject (as Rik explained) and just parts here and there, when there was a detail obscured by OOF blur which the stacker had left behind.
Chris R

Dalantech
Posts: 694
Joined: Sun Aug 03, 2008 6:57 am

Post by Dalantech »

rjlittlefield wrote:kit's idea should work OK. Taking a few shots with smaller apertures is a well established way of finishing stacks, to make the background less blurred without affecting the in-focus slab.

--Rik
I've seen shots there the last frame was taken with the lens stopped down, and it looked really good. Those sharp transitions between what's in and out of focus are distracting, but stopping down the last frame smoothed it out.

ChrisR
Site Admin
Posts: 8668
Joined: Sat Mar 14, 2009 3:58 am
Location: Near London, UK

Post by ChrisR »

Yes, it can be good wherever you aren't doing a complete stack. You need something like 3-4 stops down though, so a lot more light. Then edit out anything from the image which is sharp from in front of that last slice.
Chris R

Lou Jost
Posts: 5943
Joined: Fri Sep 04, 2015 7:03 am
Location: Ecuador
Contact:

Post by Lou Jost »

Here is where I think it would pay off to stack a series at steadily increasing f-stops, each over the whole range of depth that was desired, rather than tacking on one very different image at the end.

Example- Single shot at f/32, a couple over the whole range of interest at f22, then the whole range at f16, then the whole range at f11, etc, all in the same stack so the slices get draped on properly to a single consistent master image, so that any haze from out-of-focus edges will be rejected or minimized or easily removed in retouching.

I have never tried this though, don't know if it will work.

ChrisR
Site Admin
Posts: 8668
Joined: Sat Mar 14, 2009 3:58 am
Location: Near London, UK

Post by ChrisR »

Yes it did work where there were those"deep depressions". I think the only post I did about it was the first- http://www.photomacrography.net/forum/v ... hp?t=20238


Some lenses improve contrast a little on stopping down as well, which can male things look better even if there's strictly speaking, less resolution.
Chris R

Post Reply Previous topicNext topic