www.photomacrography.net :: View topic - Stackshot Issues & Partial Solution
www.photomacrography.net Forum Index
An online community dedicated to the practices of photomacrography, close-up and macro photography, and photomicrography.
Photomacrography Front Page Amateurmicrography Front Page
Old Forums/Galleries
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 
Stackshot Issues & Partial Solution
Goto page Previous  1, 2, 3
 
Post new topic   Reply to topic    www.photomacrography.net Forum Index -> Macro and Micro Technique and Technical Discussions
View previous topic :: View next topic  
Author Message
concon



Joined: 01 Jun 2017
Posts: 87

PostPosted: Sun Sep 03, 2017 10:31 am    Post subject: Reply with quote

rjlittlefield wrote:
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


I'm not really that interested in having another chord in the mix so I've been avoiding connecting the box to my computer/Zerene. I may be misunderstanding how to perform the the prerun you describe. When you say move the rail, are you meaning the camera on the rail, or the whole stackshot rail?

Currently I'll find where I want to start and end. Go way backwards, beyond where I'd even think about starting, set my start, move forward, and set my end (a bit beyond, but it doesn't seem to have problems stopping where I want it to).

I get no side to side wobble, and only have this forward lurching issue. Everything is connected via arca clamps so it's all modular and very easy to move around as needed- very tightened down as well- all secured to extrusion bars.

When I set my end point and move back and beyond my start point, I have the issue of it starting too far ahead initially, so no forward lurch, just not starting where I actually set it.


@mawyatt I'll look into the THK KR20. I've read a few comparisons between the two and have toyed with the idea of grabbing the kit off MJKZZ since reading about it on extreme-markro.uk.net. I'll also try overloading the rail as well for now!


Thank you both Smile
Back to top
View user's profile Send private message
rjlittlefield
Site Admin


Joined: 01 Aug 2006
Posts: 19327
Location: Richland, Washington State, USA

PostPosted: Sun Sep 03, 2017 10:45 am    Post subject: Reply with quote

No need to connect to your computer.

The technique is simple in practice but often seems difficult to describe & understand.

Quick summary is that you just make sure to always be moving in the same direction whenever you position to set a limit, and when you're actually shooting the stack.

A recipe goes something like this:

1. Back up far beyond your intended start point.
2. Move forward to your start point. Mark that as start.
3. Move forward to your end point. Mark that as end.
4. Back up far beyond your start point.
5. Move forward a little bit, but not as far as your start point.
6. Start the automated stack. The rail should move forward to the start point, stop there, take a picture, move forward, take a picture, and so on.

All of these moves are movements of the rail carriage, driven by the stepper motor, commanded by the controller.

Step 5 is not really required as an explicit action. I stuck it in to make the intent more clear.

This approach removes backlash as a concern.

Of course it's always a good idea to shoot a few extra frames at the beginning and end of stack, because that's much less expensive and annoying than to shoot the stack, start to process it, and realize that the limits weren't set exactly right.

--Rik
Back to top
View user's profile Send private message Visit poster's website
mawyatt



Joined: 22 Aug 2013
Posts: 1626
Location: Clearwater

PostPosted: Sun Sep 03, 2017 10:57 am    Post subject: Reply with quote

It just occurred to me that the lurch might be excessive backlash compensation, try and set the back lash to zero and see what happens, then in-between points.

Best,

Mike
Back to top
View user's profile Send private message
concon



Joined: 01 Jun 2017
Posts: 87

PostPosted: Sun Sep 03, 2017 11:13 am    Post subject: Reply with quote

rjlittlefield wrote:

...
1. Back up far beyond your intended start point.
2. Move forward to your start point. Mark that as start.
3. Move forward to your end point. Mark that as end.
4. Back up far beyond your start point.
5. Move forward a little bit, but not as far as your start point.
6. Start the automated stack. The rail should move forward to the start point, stop there, take a picture, move forward, take a picture, and so on.
...
--Rik


I'll give this a precise go. I feel like I do this- but maybe not as accurate/intentional, or maybe when I do it actually works as expected, ha. Just so I'm understanding- this should prevent the over stepping of the second shot right (first step beyond first shot at start).



mawyatt wrote:

It just occurred to me that the lurch might be excessive backlash compensation, try and set the back lash to zero and see what happens, then in-between points.


Hmm, not finding any settings like that on my controller; are you referring to the ZS setting? I've been avoiding connecting the box to the computer to minimize chord swing/vibrations).[/quote]
Back to top
View user's profile Send private message
rjlittlefield
Site Admin


Joined: 01 Aug 2006
Posts: 19327
Location: Richland, Washington State, USA

PostPosted: Sun Sep 03, 2017 1:21 pm    Post subject: Reply with quote

concon wrote:
Just so I'm understanding- this should prevent the over stepping of the second shot right (first step beyond first shot at start).

Yes.

Over-stepping of the second shot is classic behavior for what happens when you start the stack without going back to well beyond start after setting limits AND the rail happens to have a little less physical backlash than the controller thinks it does. In that case, when you start to shoot the stack this sequence happens:

1. Controller tells the stepper motor to move backward to what it thinks is the start position. Because the rail has less backlash than the controller thinks it does, the controller actually moves the stepper motor a little bit too far.
2. First picture gets taken.
3. Controller realizes that the rail direction needs to be reversed so that it can move forward to the second shot. It computes stepper motor movement as desired rail movement + backlash, but again, because the rail has less backlash than the controller thinks it does, this calculation ends up moving the rail too far. This is the long step between first and second shots.
4. For subsequent shots, controller realizes that the rail is continuing to move in the same direction, so backlash has already been taken out, so controller moves the stepper motor exactly as far as it needs to move. The sequence repeats, so that all subsequent steps in the stack are OK.

If the physical rail has more backlash than the controller thinks it does, then the first step will be too short. In extreme cases the first step, or even more, may be close to zero. Eventually the physical backlash gets taken up and movement becomes regular, but the start of the stack will be messed up. This case is particularly annoying because the actual starting position is probably not as far back as you intended it to be, so if you were tight on your start point, you're likely to lose the front of the subject.

Quote:
not finding any settings like that on my controller;

You're not looking in the right place. It's one of the Advanced settings that you reach by holding the CONFIG button for at least three seconds. Check your manual for details.

For some further insight, you might try reading https://zerenesystems.com/cms/stacker/docs/stackshot/backlash . Some of the details there are specific to Zerene Stacker, but the concepts are generally applicable.

--Rik
Back to top
View user's profile Send private message Visit poster's website
concon



Joined: 01 Jun 2017
Posts: 87

PostPosted: Mon Sep 04, 2017 4:00 pm    Post subject: Reply with quote

Got it and got it- I took the time yesterday to understand what was happening and think through the previous posts. I was able to perform the technique you described, though it took a few tries to nail it.

I was completely unaware of any advanced settings and will dive into them right now. I appreciate the knowledge and time!
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    www.photomacrography.net Forum Index -> Macro and Micro Technique and Technical Discussions All times are GMT - 7 Hours
Goto page Previous  1, 2, 3
Page 3 of 3

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group