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03-15-2014, 07:27 AM   #1
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Focus stacking

I do a fair amount of close up using focus stacking.

I was wondering if it would be possible for Pentax to use the AF adjustment to do "auto focus bracketing"? Maybe it could be implemented with a firmware upgrade? It could make stacking a lot easier, using it in conjunction with mirror lock up on a tripod.

It could also be another Pentax "first".

03-15-2014, 07:37 AM   #2
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Good idea.
I made a motorized device to rack the Pentax bellows -M with a resolution down to less than 0.1 mm for a similar effect. Used with Pentax K-01 and Oly M43 which don't have shaky mirrors.
Then a script to automatically align and stack the tiffs. I put a thread about it some time ago in DIY
03-15-2014, 07:59 AM   #3
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You might try multi-exposure, but it may not give a result as sharp as you'd like. But I assume you'd rather have it make micro focus adjustments in the bracket; that would be an awesome Pentax first.
03-15-2014, 08:41 AM   #4
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I would love this for copying slides (where the film is often warped).
There are two ways I can think of specifying how you want to focus across the frame. One would be adding the ability to specify more than one focus point. The other simpler way would be to specify a virtual depth of field, maybe specified as an f stop. That way you could have the lens aperture set for optimum sharpness yet have virtually f64 for instance.
I think with the new FLU card, it might be possible to do it now (with a bit of software), since it is possible to define the focus point via the FLU card. A bit of software could shift the focus between shots. Probably would not be nearly as fast as an in-camera implementation though.

03-15-2014, 04:18 PM   #5
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I'm not sure how well this could work - wouldn't the change of focal point also change the magnification relative to the other frames in the bracket?
03-15-2014, 04:35 PM   #6
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QuoteOriginally posted by Hornet Quote
I'm not sure how well this could work - wouldn't the change of focal point also change the magnification relative to the other frames in the bracket?
It's done manually all the time. Why wouldn't it work if the camera does it on it's own?
03-15-2014, 05:11 PM   #7
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My understanding of focus stacking is that one wants the magnification (=focus distance) to remain constant hence the reason focus rails are used to move the whole camera relative to the stationary subject. Another example is a microscope - the whole optical system is moved up or down relative to the subject to move the focal plane.
03-16-2014, 07:10 AM   #8
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QuoteOriginally posted by Hornet Quote
I'm not sure how well this could work - wouldn't the change of focal point also change the magnification relative to the other frames in the bracket?
I admit my understanding of image stacking is fairly limited. Perhaps the stacking software has to resize the images to make them align?

03-16-2014, 07:22 AM   #9
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QuoteOriginally posted by Hornet Quote
My understanding of focus stacking is that one wants the magnification (=focus distance) to remain constant hence the reason focus rails are used to move the whole camera relative to the stationary subject. Another example is a microscope - the whole optical system is moved up or down relative to the subject to move the focal plane.
The stacking software automatically scales each image to fit. It also corrects for any misalignment. The auto alignment is good enough even to make good for handheld macro shots and you are careful enough. What it cannot correct for is perspective changes if there is too much lateral movement between each frame.

The focus bracketing should be quite easy to implement in firmware. If they were to make it shoot at 8 FPS and preferably without lowering the mirror between each shot it would make handheld macro photography much more practicable.

I've been thinking for some time of making something myself with a stepper motor coupled to the focus ring, probably much like what wombat2go describes except that it would adjust the focus ring of the lens rather than the bellows extension. Probably the day after I get round to actually making it Pentax will release a firmware that does it in camera.
03-16-2014, 05:42 PM - 1 Like   #10
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software like Zerene Stacker will "compensate" for subtle change of perspective with ordinary macro lenses. I use it all the time. That being said, using a focusing rail and moving the camera body does provide for a better stack. Here is a link to a stack I did last summer using a bellows and moving the body:



here is a stack I did recently using a "normal" camera lens (i.e. changing focus manually between shots):



In both cases, Zerene Stacker did the trick admirably.

Michael
03-16-2014, 06:34 PM   #11
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QuoteOriginally posted by lister6520 Quote
I've been thinking for some time of making something myself with a stepper motor coupled to the focus ring, probably much like what wombat2go describes except that it would adjust the focus ring of the lens rather than the bellows extension. Probably the day after I get round to actually making it Pentax will release a firmware that does it in camera.
no need for anything as complicated or as prone to introducing vibration as a stepper motor. a regular dc brushed motor with a dpdt switch and a gear box to slow it down will do. just add a raised bump to one of the gears to repeatedly trigger a roller switch wired to a shutter release, or use an encoder disk.
03-17-2014, 07:52 AM   #12
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QuoteOriginally posted by maltfalc Quote
no need for anything as complicated or as prone to introducing vibration as a stepper motor. a regular dc brushed motor with a dpdt switch and a gear box to slow it down will do. just add a raised bump to one of the gears to repeatedly trigger a roller switch wired to a shutter release, or use an encoder disk.
You guys have some great ideas. I'm thinking one of the ancient floppy disk drives I have stashed away would be sturdy enough for a focus rail, but I would have to make the steps finer.
03-17-2014, 08:08 AM   #13
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The microfocusser I made presently holds the lens fixed and moves the camera.
But thinking about it on this thread, it might be better for the microfocusser to move both the camera and the lens.
That is, in the interest of keeping the images in the stack all of the same height.
?
03-17-2014, 01:25 PM   #14
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my tests convinced me that keeping the lens in the same location provided the best, most consistent results when using stacking tools like Zerene.
That being said, Zerene does a very good job when keeping the body fixed and simply changing the focus on the lens -- you just have to work the image a bit more in post to soften the inevitable "halos".

YMMV

Michael
03-17-2014, 04:18 PM - 1 Like   #15
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Having the camera bracket AF (via the AF adjustment or other more direct means) would be pretty cool.

I hope you guys have been donating to Shodan, who is currently working on Pentax firmware hacking

https://www.pentaxforums.com/forums/6-pentax-dslr-discussion/250555-resurrect...e-hacking.html
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