How do people deal with Backlash with Stack shot?

[austrokiwi1]

I suspect there is a really simple answer to this but at the meoment I can't think of it. Over the last week I have had an irritating problem with my stackshot rail. it seems to occur when using very small steps. I set the start and end points accurately but when I start the run the stackshot rail misses the start point by an annoyingly large( this is relative to the step size). Distance. I suspect that it is due to backlash. what is the best way of managing this issue?

[mawyatt]

Check this out, helps with traditional backlash and stage wobble as I call it.

Best,

Mike

[austrokiwi1]

Check this out, helps with traditional backlash and stage wobble as I call it.

Best,

Mike

Missing link?

[mawyatt]

Sorry!!

https://www.photomacrography.net/forum/ ... ght=wobble

BTW, the best place to locate the Off Axis Loading is normal to the screw thread interface surface.

Best,

Mike

[rjlittlefield]

The off-axis-loading technique is a good one, particularly at very high magnification where it is important to minimize side-to-side wobble while the stack is being shot.

But for overcoming backlash, a simpler solution is to just back off an extra mm or so, then move forward both to set start/end and to begin the actual stack. The point is to operate the rail so that it never has to move backward with any precision.

Using the StackShot controller panel that is built into Zerene Stacker, this can be done automatically using the "prerun distance" setting, described at https://www.zerenesystems.com/cms/stack ... /stackshot . Quoting from that description:

"Prerun distance" allows you to specify a distance that the rail should “back off” before moving to the start position to begin shooting a stack. It will also back off before positioning in response to the "Go to Start" and "Go to End" buttons. The purpose of prerun is to guarantee that all types of mechanical slack have been removed before the designated position is reached. The main type of slack is backlash along the rail axis, but usually there is also a small amount of rotational backlash that can be important at higher magnifications. Be careful when using prerun at short working distances, to avoid running your lens into the subject. When moving to Start, the prerun position will be on the side away from End. To be safe, you should set Start to be farther away from your subject, and End to be closer. That way prerun will first move the lens farther away from the subject, then advance it toward the subject to reach the target position.

Using the StackShot's own controller box, the prerun technique can easily be done manually by moving the rail backward beyond the start point before setting start/end, and again before starting to shoot the stack.

It is also possible to address the problem by carefully calibrating the rail's actual backlash, for example using the procedures described at https://www.zerenesystems.com/cms/stack ... t/backlash . But I prefer the prerun approach because it also addresses the small amount of side-to-side twist that rails often exhibit as direction of movement is reversed.

--Rik

[austrokiwi1]

thanks the backing off worked