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DIY Auto Focus Rail - Part 3: C'est Fini!
Posted By: AggieDad, 09-12-2018, 10:41 AM

The thing is done. Finally!

Two months ago (July 17) I announced to the forum (a device to keep me from procrastinating), my intentions to build my own automatic macro focusing rail. I then posted a couple of progress updates. Now, some 8 weeks later, "Big Stacker" is complete.

Although there are several DIY rails, complete with some instruction and a parts list, on the web, I decided to design and build my own. Why? I have absolutely no idea why. It was a crazy decision, but it sure was fun.

Here's how Big Stacker works. I enter the slice size (D.O.F.) anywhere from 0.01mm to 9.99mm and the length of the stack in whole millimeters from 1 to 9999mm. The program uses 80% of the entered slice size to create overlap of the images and calculates the number of images required to make the stack. The first move of the rail is to back up and return to zero to remove any possible slop in the screw drive. Each step of the stack includes delay to settle the camera, automatic firing of the shutter, more delay for flash recovery, and then move for the next step. At the completion of the stack, the camera is moved back to the start position.

I tried to keep everything simple without extras that really don't impact getting the basic job done. This kept the code and the wiring reasonably basic and eliminated potential problems. It moves, takes a picture, and moves again. That's all.

The linear screw rail has a pitch of 4mm per revolution. The stepper motor has a basic step size of 1.8 degrees, or 200 hundred steps per revolution. The stepper motor controller will resolve to 16 micro steps for each full step allowing for 3200 micro steps per revolution. I have tested my rail with a slice size of 0.01mm (actually 0.008mm after the 80% factor) with 125 slices for a 1.0mm stack. The result was a stack length of 1.04mm according to my trusty Harbor Freight digital micrometer, and that is more than accurate enough for me.

If you have a minute or so to waste, you can see Big Stacker in action in my little hand-held iPhone video. The slice size seen in the video is a rather large 4mm so the camera movement can be easily seen in the video. The K-5II's flash is used to visually show the camera actuation. This strictly a demo in fact the lens cap is still on the camera! My next step is to install the rail on my Studio macro setup.


If you are interested in what I did and how I did it, I can post more information.
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09-12-2018, 01:11 PM   #2
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Wow, that's inspiring.
Glad I've been following, you've done it.
09-12-2018, 01:18 PM   #3
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Cool!
09-12-2018, 01:23 PM   #4
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More info, definitely. Maybe a PDF document you can share

09-12-2018, 07:02 PM   #5
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Nice job!
09-12-2018, 07:28 PM   #6
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Great job, of course we want more details
09-12-2018, 07:43 PM   #7
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Excellent!
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