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StackShot and Bugslabber

 
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Lindaavitt



Joined: 18 Dec 2017
Posts: 23
Location: Austin, Texas

PostPosted: Thu Feb 01, 2018 12:25 pm    Post subject: StackShot and Bugslabber Reply with quote

This forum is a wealth of information. I just tried my first sub-stack with Bugslabber, and it's fantastic. So much better for editing!

One StackShot question. I've been using the auto-distance mode, where I mark the start and end points. I always mark it a little farther on either end than I think I need.

How reliable is the StackShot about going to the exact designated starting place and ending at the designated stopping place? It seems like it has stopped short of getting to my designated starting place. (I hope that all made sense.)

Am I missing the mark or is it possible that StackShot is a little off?

Thanks!
Linda Cool
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rjlittlefield
Site Admin


Joined: 01 Aug 2006
Posts: 18794
Location: Richland, Washington State, USA

PostPosted: Thu Feb 01, 2018 12:47 pm    Post subject: Reply with quote

The problem that you're having is due to "backlash". There's a little bit of mechanical play in the screw and nut that causes the carriage to reach slightly different positions depending on which way it moved to get there.

The simplest and most accurate solution is to always approach the start and end points from the same direction, both in setting the endpoints and in shooting the stack.

Typical workflow is to position the carriage to some distance before the intended start point, then move forward, mark start, move forward, mark end, then move backward to someplace before the marked start, so the rail moves forward again to reach the start point and begin shooting.

If you're using the StackShot controller that is built into Zerene Stacker, then there is automated support for this approach. On the Configuration tab, just set the "Prerun distance" to something like 1 mm, which is comfortably larger than the rail's actual backlash of around 0.2 mm. If your optics have very short working distances, say with some microscope objectives, then be careful to avoid the possibility of running the lens into the subject.

It is also possible to calibrate the rail's actual backlash, but this approach is less accurate because of slight nonlinearities and rotation that also occur around reversals in direction. See the procedures at http://zerenesystems.com/cms/stacker/docs/stackshot/backlash if you want to do the calibration.

--Rik
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Lindaavitt



Joined: 18 Dec 2017
Posts: 23
Location: Austin, Texas

PostPosted: Thu Feb 01, 2018 2:00 pm    Post subject: Reply with quote

Thanks, Rik. I'll do that. Your directions are very clear.

I've read about backlash, but was never quite sure about what it meant.

Linda
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