I’m using HF very successfully in conjunction with a Stackshot rail, a Z9, twin SB900 flashes at very low power to achieve 1/10,000th approx effective shutter speeds, a Mity 10x + tube lens optics, and with everything bolted down, to create very solid flawless insect images. I’m generally using step distances about 3-5Mu, so my HF stacks are multiple hundreds of .nef images.
Question: Has anyone carefully tested and gathered data on the effects of even smaller step distances on stacked image quality?
I assume there’s something akin to “diminishing returns”… as step distances get smaller and create larger image-to-image DOF overlap.
Obviously deeper stacks take more processing time, etc.
With the Mity 10x LWD I’m using my DOF is about 7Mu,if I’m reading the Mity spec sheet correctly.
But I’d be interested to know if there’s any kind of actual -negative- effect on stacked image quality from using a step distance that’s down around 1Mu, which is the bottom limit for my HW.
Or… does stacked image quality continue to get (even very slightly) better as step size decreases?
Thanks for any data/testing/guidance.
Is there hard data on optimal step distance?
Re: Is there hard data on optimal step distance?
There's a lot of information out there on this. I think when you go beyond x10 objectives you are into issues with image resolution and diffraction and the like because of the size of the sensor pixels. Allan Walls on YouTube is a good source of info. Similarly Micael Widdel.
Re: Is there hard data on optimal step distance?
You shouldn't shoot a lot more photos that needed with your actual DOF, that might make the result less sharp. We recommend a 30% overlap between photos. This is a rough number and it doesn't matter if it's 60%, but taking multiple times more photos than needed by the 30% rule - that could degrade the result.
Re: Is there hard data on optimal step distance?
thank you both, catherine and el48tel for your tips and suggestions.
im familiar with allan walls. will revisit him.
i realized, belatedly, that there’s a super simple way to test this empirically…
i’ll shoot a deep stack at a very small step size… 1 or 2Mu…
then just run HF a few times…keeping everything else constant of course…
but selecting every image, every other, every third…
and then compare stacked image results side by side by side.
will do…and post results here:)
thanks again
im familiar with allan walls. will revisit him.
i realized, belatedly, that there’s a super simple way to test this empirically…
i’ll shoot a deep stack at a very small step size… 1 or 2Mu…
then just run HF a few times…keeping everything else constant of course…
but selecting every image, every other, every third…
and then compare stacked image results side by side by side.
will do…and post results here:)
thanks again
Re: Is there hard data on optimal step distance?
Just been looking back at my hand scrawled notes. My best guess is 8 to 10 micrometres steps. There’s a large number of tables and calculators on line. My interpretation is that sensor size is a factor as much as anything. Diffraction is an issue with high density sensors. Numerical aperture is a factor. If you stray from the design tube length it does strange things to the optical quality. I use 160mm tube length objectives but if you extend the tube much beyond this to have greater magnification the quality falls off markedly. Although going shorter to lower the magnification doesn't seem to make as much difference. I use an old Sony A77 body on a StackShot. I have an adaptor to convert the alpha lens mount to RMS thread for the objective. I can send you details of the guy who makes camera to RMS adaptors.
I use a Fujifilm body with extension rings and in camera focus stacking for lower magnification stuff. Or screw in close up lens over main lens on that body.
I've tried the Sony with bellows and reversed enlarger lens too for about x4 to x10 again on the StackShot.
I use a Fujifilm body with extension rings and in camera focus stacking for lower magnification stuff. Or screw in close up lens over main lens on that body.
I've tried the Sony with bellows and reversed enlarger lens too for about x4 to x10 again on the StackShot.
Re: Is there hard data on optimal step distance?
thanks el48tel.
i just shot a ~500 image stack of the fine hairs above the eye of a fly...
i shot the stack at 2Mu steps...Mity 10x + DCR 150 + 180mm tube, on Nikon Z7...
then processed in HF B/1/1 three times...selecting "every image," "every other image," and "every third image"...
ie effectively 2Mu, 4Mu and 8Mu steps.
the 3 HF focussed stacks were very nearly identical.
only by pixel peeping at 200x.. could i see extremely minor differences, with the 4Mu very very slightly better.
under normal viewing at 100%, all 3 stacked images were entirely identical.
i was expecting to see some visible stack quality degradation at the 8Mu effective step distance, but i did not.
i'm slightly puzzled by this result, since i believe my setup at described above should produce a 7Mu DOF, which should mean 3.5Mu of focus, straddling each focus point.
and if ~30% image overlap is a suggested target for best stacking results...i would think that 8Mu steps would be visibly worse.
Based on the above... do you think I'm missing something...or that my physics+arithmetic are off?
Thanks a lot:)
i just shot a ~500 image stack of the fine hairs above the eye of a fly...
i shot the stack at 2Mu steps...Mity 10x + DCR 150 + 180mm tube, on Nikon Z7...
then processed in HF B/1/1 three times...selecting "every image," "every other image," and "every third image"...
ie effectively 2Mu, 4Mu and 8Mu steps.
the 3 HF focussed stacks were very nearly identical.
only by pixel peeping at 200x.. could i see extremely minor differences, with the 4Mu very very slightly better.
under normal viewing at 100%, all 3 stacked images were entirely identical.
i was expecting to see some visible stack quality degradation at the 8Mu effective step distance, but i did not.
i'm slightly puzzled by this result, since i believe my setup at described above should produce a 7Mu DOF, which should mean 3.5Mu of focus, straddling each focus point.
and if ~30% image overlap is a suggested target for best stacking results...i would think that 8Mu steps would be visibly worse.
Based on the above... do you think I'm missing something...or that my physics+arithmetic are off?
Thanks a lot:)
Re: Is there hard data on optimal step distance?
If you don't see any signs whatsoever that the interval of 8 is exceeding the DOF (e. g. repeating stripes of less sharp pixels, where the "gap" between the images is), then maybe your actual DOF is larger than 8.
Re: Is there hard data on optimal step distance?
Waldenk I’d not doubt your figures or maths or physics. I’m probably at a similar state in the game. However your system is more complex than the one I’m using and might be the source of the miscalculation. I’ve been through my copy of Focal Encyclopedia of Photography, endless calculations and numerous websites. I too have suffered the heartache of not getting the image after hours of shots, hours of uploading and hours of stacking. Try using stacking in Photoshop. A 100 image stack takes hours. And I mean hours.
My basic understanding is that the key factors are as follows.
Effective aperture. Not easy with a microscope objective since it’s called numerical aperture. For most x10 objectives it’s 0.25 and equates to about f/20. You have additional optics inline. So that’s where I think one issue might be.
Magnification. This has to be the ratio of the diameter of the field of view to the diameter of the sensor. The physical optical corrections in the objective lens are made on the basis of a specific tube length or specific optical lens arrangement if the objective is of infinity design. All kinds of aberrations creep in if you try to push the lens beyond its design criteria.
Circle of confusion. Most camera and lens designers specify 0.03 inches. Leica specify 0.02 inches (?!?!).
The consensus for x10 objective is 8.7 micrometres.
My basic understanding is that the key factors are as follows.
Effective aperture. Not easy with a microscope objective since it’s called numerical aperture. For most x10 objectives it’s 0.25 and equates to about f/20. You have additional optics inline. So that’s where I think one issue might be.
Magnification. This has to be the ratio of the diameter of the field of view to the diameter of the sensor. The physical optical corrections in the objective lens are made on the basis of a specific tube length or specific optical lens arrangement if the objective is of infinity design. All kinds of aberrations creep in if you try to push the lens beyond its design criteria.
Circle of confusion. Most camera and lens designers specify 0.03 inches. Leica specify 0.02 inches (?!?!).
The consensus for x10 objective is 8.7 micrometres.
Re: Is there hard data on optimal step distance?
hi again el48tel and catherine,
i appreciate the additional info.
i have been getting very good results with my current optical setup, and of course HF9 for stacking..the latest HF release is terrific!
(here is a recent photo i took of a the eye of a hoverfly with bits of yellow pollen stuck here and there. its a large 30 meg file.)
https://drive.google.com/file/d/1KbTarR ... sp=sharing
i shot this at 2Mu steps (unnecesarily small) which resulted in a nearly 700 image stack.
i'm planning to move to 4-5Mu steps going forward.
the numerical aperture of my mity10x is .28, which yields, for me, an effective fstop of about f17.
i'd prefer a bigger fstop, to get further away from diffusion-land, but i can live with f17.
i suspect, as catherine points out, that with my DCR-150, my effective magnification is about 10.4x.
this might change my effective DOF, tho i think is would -smaller- than the 7Mu mity spec sheet value.
at this point tho i'm (needlessly) chasing a disparity of 1-2 micron DOF values which have zero apparent impact on my images.
so back to shooting!
thanks for both of your info...greatly appreciated:)
i appreciate the additional info.
i have been getting very good results with my current optical setup, and of course HF9 for stacking..the latest HF release is terrific!
(here is a recent photo i took of a the eye of a hoverfly with bits of yellow pollen stuck here and there. its a large 30 meg file.)
https://drive.google.com/file/d/1KbTarR ... sp=sharing
i shot this at 2Mu steps (unnecesarily small) which resulted in a nearly 700 image stack.
i'm planning to move to 4-5Mu steps going forward.
the numerical aperture of my mity10x is .28, which yields, for me, an effective fstop of about f17.
i'd prefer a bigger fstop, to get further away from diffusion-land, but i can live with f17.
i suspect, as catherine points out, that with my DCR-150, my effective magnification is about 10.4x.
this might change my effective DOF, tho i think is would -smaller- than the 7Mu mity spec sheet value.
at this point tho i'm (needlessly) chasing a disparity of 1-2 micron DOF values which have zero apparent impact on my images.
so back to shooting!
thanks for both of your info...greatly appreciated:)