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Stackshot Issues & Partial Solution
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mawyatt



Joined: 22 Aug 2013
Posts: 1383
Location: Clearwater

PostPosted: Fri Nov 04, 2016 4:28 pm    Post subject: Reply with quote

mawyatt wrote:
Smokedaddy,

Thanks, I have been looking at something similar. The one you identified has a 2mm thread pitch, whereas the Stackshot rail has a 1.59mm pitch, and the Wemacro has a 1mm pitch.

However now I am not so convinced these industrial grade rails are that much better than the ones that Stackshot or maybe Wemacro offer, especially with the off axis tension concept mentioned. They will handle a larger load, and have more travel, but may not be much better in short movement uniformity with little image shift. I don't require precise location, nor repeatability but do require very little image shift.

Johan at Extreme Macro evaluated the Wemacro system, and Beatsy has posted some very nice images at 1 micron steps. These confirm that 1 micron steps are possible with these rails, but I may require tighter control of image shifts that they do because of my chip subjects.

I am shooting at 20X with 2 micron steps as shown here and will be going to 50X at 1 micron steps soon, so any image shift will just get amplified more.

If I had the $, or my company would pay, I would just get a really precise expensive rail...but that is not the case.

Anyway, thanks for the pointer, if you find a 1mm pitch rail please let me know.

Best,

Mike


BTW I should probably mention like most here I do this at my home and out of pocket, so don't have the luxury of a lab and proper budget.

MJKZZ (Peter) is looking into these eBay industrial rails in another thread, and posting his progress with his new setup which si quite nice I might add!


Last edited by mawyatt on Fri Nov 04, 2016 4:34 pm; edited 1 time in total
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Smokedaddy



Joined: 07 Oct 2006
Posts: 1097
Location: Phoenix, Arizona

PostPosted: Fri Nov 04, 2016 4:33 pm    Post subject: Reply with quote

Here ya go ... but NEMA 17(?) .... 100% Positive feedback too. <g>

http://www.ebay.com/itm/PBC-Linear-Motorized-Actuator-Guild-Stage-1mm-Screw-Nema-17-PRICE-DROP-/161762592285?hash=item25a9cd461d:g:lycAAOSwNSxU721S

-JW:


Last edited by Smokedaddy on Fri Nov 04, 2016 4:52 pm; edited 1 time in total
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mawyatt



Joined: 22 Aug 2013
Posts: 1383
Location: Clearwater

PostPosted: Fri Nov 04, 2016 4:40 pm    Post subject: Reply with quote

JW,

Wow, that looks very promising indeed!! I never came across this offering, never was any good at searching, can't even find my keys!!

Thanks so much for pointing this out!!

Best,

Mike

Edit,

Took a good look at this and the PBC Linear site. It's 515mm long which is much too long for my setup. The Stackshot rail is 200mm including stepper motor. I'll point Peter to this though.
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Smokedaddy



Joined: 07 Oct 2006
Posts: 1097
Location: Phoenix, Arizona

PostPosted: Sun Nov 06, 2016 10:31 am    Post subject: Reply with quote

Well here's one with about a 3 1/2" stroke.

http://www.ebay.com/itm/THK-KR2001A-150L-Singlne-Nut-block-with-Cover-1mm-Precision-linear-actuator-/201537136834?hash=item2eec8ca8c2:g:72QAAOSwvgdW3is1

-JW:
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Charles Krebs



Joined: 01 Aug 2006
Posts: 5800
Location: Issaquah, WA USA

PostPosted: Sun Nov 06, 2016 3:12 pm    Post subject: Reply with quote

mawyatt wrote:
Charles,

What is your opinion of the WeMacro rail, Beatsy seems to like it and his results are outstanding.

Don't have one, but I do have one coming, along with a separate 400 step motor (0.9 degree.step). I plan on using the motor on microscope focusing blocks.

Have you thought of adapting a microscope focus block? Something like this:
http://www.ebay.com/itm/OLYMPUS-BHMJ-COARSE-FINE-FOCUSING-BLOCK-/222093700788?hash=item33b5d0eeb4:g:UnsAAOSw1DtXGOlp

I use couple of the BHMJ blocks right now for various set-ups.

A 400 step motor driving that will get you 0.5 micron steps without even getting into micro-stepping! I have no idea how the "wobble" would compare to a StackShot or the WeMacro... but if in good condition I would imagine it should be pretty good in that regard.
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mawyatt



Joined: 22 Aug 2013
Posts: 1383
Location: Clearwater

PostPosted: Sun Nov 06, 2016 4:46 pm    Post subject: Reply with quote

Smokedaddy wrote:
Well here's one with about a 3 1/2" stroke.

http://www.ebay.com/itm/THK-KR2001A-150L-Singlne-Nut-block-with-Cover-1mm-Precision-linear-actuator-/201537136834?hash=item2eec8ca8c2:g:72QAAOSwvgdW3is1

-JW:


That rail looks just like the one Peter is using over on his "Finally built my dream focus stacking setup" in Equipment Discussions. Hopefully he will see this and respond. If I could get the adapter for mounting a standard NEMA 17 stepper, and top mounting plateI might give it a try

I'll add a note on Peter's thread.

Thanks for pointing these rails out,

Best,

Mike
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Saul



Joined: 31 Jan 2011
Posts: 1100
Location: Naperville, IL USA

PostPosted: Sun Nov 06, 2016 5:52 pm    Post subject: Reply with quote

Charles Krebs wrote:
...Don't have one, but I do have one coming, along with a separate 400 step motor (0.9 degree.step). I plan on using the motor on microscope focusing blocks. ...A 400 step motor driving that will get you 0.5 micron steps without even getting into micro-stepping! ...

I'm using 400 step motor (0.9 degree.step) on my both vertical (with Labophot)
http://www.photomacrography.net/forum/userpix/1489__DSC2738PMN_2.jpg
and horizontal (Del-Tron) setups:
http://www.photomacrography.net/forum/viewtopic.php?p=192376#192376

On the Labophot step is 0.5 micron without micro-stepping. Del-Tron - 2.5 microns.

Quote:
... have no idea how the "wobble" would compare to a StackShot or the WeMacro... but if in good condition I would imagine it should be pretty good in that regard.

Did not notice any "wobbling" (but I'm using my DIY controls). My question is - is possible in the WeMacro software to change motor step size ? Their software is based on 1.8 degree step... In this case I could use in my setup.
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austrokiwi1



Joined: 14 Sep 2014
Posts: 338

PostPosted: Thu Jun 29, 2017 11:33 am    Post subject: Reply with quote

Seems I was repeating this thread with my recent post:

http://www.photomacrography.net/forum/viewtopic.php?t=34601

I will try the rubber band loading however it will be a bit of a challenge as my rig is verticle( I will work somethign out) I realized there may be another iissue going on. the problems were worst over the last week when were were having 28-33 degrees C heat each day. I wonder if different metal expansion rates made the problem noticeable( to me)
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Cameras' Sony A7rII, OLympus OMD-EM10II
Macro lenses: Printing nikkor 105mm, Sony FE 90mm F2.8 Macro G, Schneider Kreuznach Makro Iris 50mm , 2.8, Schnieder Kreuznach APO Componon HM 40mm F2.8 , Mamiya 645 120mm F4 Macro ( used with mirex tilt shift adapter), Olympus 135mm 4.5 bellows lens, Oly 80mm bellows lens, Olympus 60mm F2.8


Last edited by austrokiwi1 on Thu Jun 29, 2017 9:08 pm; edited 1 time in total
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Saul



Joined: 31 Jan 2011
Posts: 1100
Location: Naperville, IL USA

PostPosted: Thu Jun 29, 2017 12:54 pm    Post subject: Reply with quote

austrokiwi1 wrote:
... I realized there may be another issue going on. the problems were worst over the last week when were were having 28-33 degrees C heat each day. I wonder if different metal expansion rates made the problem noticeable( to me)


I do not have backlash issue in my setups (unless i did not notice it). Hard to believe that it happens because of the metal expansion ... Maybe controller or it's driver is somehow overheated and started "losing" steps ? I had a similar case when used wrong Hz in my DIY controller.

Does it happens in the beginning of the stack ? Did you try Rik's advice:
http://www.photomacrography.net/forum/viewtopic.php?p=214369#214369

BTW, your link does not work
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austrokiwi1



Joined: 14 Sep 2014
Posts: 338

PostPosted: Thu Jun 29, 2017 9:16 pm    Post subject: Reply with quote

Thanks I have fixed the link. The iissue does occur only at the start of the stack. It occurs in both directions ( with gravity and against Gravity) Last night I tried one suggestion After setting the stack I advanced the rail beyound the start point and that fixed the issue ( at least fof the one stack I tried). I still suspect heat may play a role. the mechanisim being different expansion rates between the screw and carrier making the back lash worse and therefore much more noticable.
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Macro lenses: Printing nikkor 105mm, Sony FE 90mm F2.8 Macro G, Schneider Kreuznach Makro Iris 50mm , 2.8, Schnieder Kreuznach APO Componon HM 40mm F2.8 , Mamiya 645 120mm F4 Macro ( used with mirex tilt shift adapter), Olympus 135mm 4.5 bellows lens, Oly 80mm bellows lens, Olympus 60mm F2.8
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mawyatt



Joined: 22 Aug 2013
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Location: Clearwater

PostPosted: Fri Jun 30, 2017 5:22 am    Post subject: Reply with quote

I always set the start and stop points from the same rail movement forward direction as Rik had mentioned in your other thread. This effectively removes backlash from the stacking equation. Another good procedure is to always set the stacking session beginning below the start point so the rail moves forward to the start point. I do this even with the THK KR modified rails which have no apparent backlash just to be on the safe side.

You may see signs of rail wobble as you move to higher magnifications, this is where the Off Axis Loading technique can help, plus it reduces backlash.

Best,

Mike
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concon



Joined: 01 Jun 2017
Posts: 87

PostPosted: Sun Sep 03, 2017 7:33 am    Post subject: Reply with quote

Resurrecting as I've been yanking my hair out daily over this issue. It started a few months ago after I began the dive into objective photography and needed a more precise step 3um - 1um. I've been over estimating the start and stop points to compensate, but even that isn't consistent- it just jumps 10ums+ forward on the first step, every time. It seems completely random how far it lurches forward and I often I have to pick the stop and stop point multiple times after seeing the first jump go right past where it needs.

I've seen the rubber band technique and have tried, but it didn't seem to help with the initial lurch- everything else about the setup is tight and working as I would expect.

Has anyone tried contacting Cognisys? Is there driver updating or maintenance that I should be doing to prevent or correct this?


Last edited by concon on Sun Sep 03, 2017 10:01 am; edited 1 time in total
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rjlittlefield
Site Admin


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

PostPosted: Sun Sep 03, 2017 8:08 am    Post subject: Reply with quote

Have you tried the technique of backing off and moving forward only, described at http://www.photomacrography.net/forum/viewtopic.php?p=214369#214369 ?

--Rik
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mawyatt



Joined: 22 Aug 2013
Posts: 1383
Location: Clearwater

PostPosted: Sun Sep 03, 2017 9:17 am    Post subject: Reply with quote

I don't think it's related to the Stackshot controller but more of the focus rail peculiarities. Might be stiction in the rail bearings or screw thread interface. As mentioned backing off a good distance certainly helps, if you are using Zerene to run the Stackshot controller, it has a backoff parameter you can set.

If you heavily load the rail this may help as well, worth a try. I've seen this behavior in the Stackshot and Wemacro rails, in both cases the heavy loading significantly helped.

This was one of the reasons I've adapted the THK KR20 linear actuators for high precision focus rail use. This device has almost no decernible backlash nor wobble I can detect.

Best,

Mike
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mawyatt



Joined: 22 Aug 2013
Posts: 1383
Location: Clearwater

PostPosted: Sun Sep 03, 2017 9:50 am    Post subject: Reply with quote

If you decide to try the THK KR20, it's relatively easy to make the mods and it works with the Stackshot and Wemacro controllers.

Peter at MJKZZ has a mod kit for the KR20 that includes a 400 step NEMA 17 motor. I believe the 400 step vs. 200 step motors provide a slightly better step uniformity because the motor specs typically call for about 5% step errors, so the 400 step motor has a potential 1/2 smaller absolute step error. This also reduces the micro stepping requirement for the controller by 2 for small steps, which again I feel is better. I have no evidence to support this, but just engineering judgment.

If you mount an ARCA rail to the KR20 base then it becomes very easy to remove/attach the rail and also slide the rail in the ARCA clamp for initial positioning. This works very well with the Wemacro Vertical Stand setup, as well as horizontal setups.

Contact Paul at Cognisys for a Stackshot connector so you can make a custom cable for the KR20. Zerene has parameters for rail thread pitch and stepper motor number of steps you can select. For the the same reason as selecting a 400 step motor vs. a 200 step motor, I would lean towards the 1mm pitch vs. 2mm pitch thread.

With a 400 step motor and 1mm thread pitch you get 2.5 micron steps and with 4 micro steps you get 0.625 microns per step.

Best,

Mike
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