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What am I doing wrong?
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Rikisub



Joined: 29 Jan 2013
Posts: 97
Location: Spain

PostPosted: Thu Jul 04, 2019 7:14 am    Post subject: What am I doing wrong? Reply with quote

Hi everyone! I'm back and I'm trying to improve my stacking set. Although I got some good results, there is something that is puzzling me: I'm working with a wemacro rail (which I think it is great), but when I start focusing, when I press forward, the subject "jumps" to the right, while when I press backward, it "jumps" to the left". I enclose a video where you may see what I mean. I think the problem is that the sensor plane and the subject plane aren't perfectly parallel. What do you think? the enlargement of the video is 10,9X. The lens, a Nikon BDplan x10. The camera is a Sony Nex -6. I think the subject shouldn't move. Any ideas to sort this out would be very welcome. Thank you very much in advance!

Here is the video:

https://drive.google.com/file/d/1W3zw2RqRDdIo26Rh7yGnDzpm7X0hZdtt/view?usp=sharing

My set is the following.
[url]IMG_1886 by Rickisub, en Flickr[/url]
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Luisifer



Joined: 05 Sep 2018
Posts: 49
Location: Czech Republic

PostPosted: Thu Jul 04, 2019 7:28 am    Post subject: Re: What am I doing wrong? Reply with quote

I think that it is thanks to torque of central screw plus backlash in linear guides on the sides.
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Rikisub



Joined: 29 Jan 2013
Posts: 97
Location: Spain

PostPosted: Thu Jul 04, 2019 7:31 am    Post subject: Reply with quote

Hi Luisifer, thank you very much for your answer, but I don't understand it well. Could you explain it better? How could I sort this out?
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Adalbert



Joined: 30 Nov 2015
Posts: 720

PostPosted: Thu Jul 04, 2019 7:39 am    Post subject: Reply with quote

Hello Rikisub,
Unfortunately I cannot see your video but I have already noticed such behavior in my rail.
If you change the direction the backlash is really big. It is a property of your rail.
In this case you can ignore the first photographs.
BR, ADi
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Luisifer



Joined: 05 Sep 2018
Posts: 49
Location: Czech Republic

PostPosted: Thu Jul 04, 2019 7:42 am    Post subject: Reply with quote

When the screw in the middle change the direction of rotation it moves (to the left or to the right, depend on new turning direction of screw) whole connected gear in this direction. Connected gear stop moving in X direction (left / right) after closing of backlash on side rodes. It should be possible to change it for example via changing of rodes spacing.
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Last edited by Luisifer on Thu Jul 04, 2019 7:45 am; edited 1 time in total
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Rikisub



Joined: 29 Jan 2013
Posts: 97
Location: Spain

PostPosted: Thu Jul 04, 2019 7:45 am    Post subject: Reply with quote

Thank you very much for your answers, I highly appreciate it.

Quote:
It should be changed for example via changing of rodes spacing.


What do you mean by this? Thanks a lot!
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Luisifer



Joined: 05 Sep 2018
Posts: 49
Location: Czech Republic

PostPosted: Thu Jul 04, 2019 7:52 am    Post subject: Reply with quote

Rodes on sides has some distance. It should help to set bigger distance, for example over underlaying of rodes ends. But it has to be done very carefully that balls running on rodes in housing will still runing and not to be pinched more than necessary.

(the worst case can cause crushing of balls)
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Rikisub



Joined: 29 Jan 2013
Posts: 97
Location: Spain

PostPosted: Thu Jul 04, 2019 7:55 am    Post subject: Reply with quote

Thank you very much again. Then, it might be easier just to discharge first shots then, or starting far from the real starting point and finishing the same way.
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RDolz



Joined: 28 Aug 2017
Posts: 74
Location: Valencia (Spain)

PostPosted: Thu Jul 04, 2019 8:09 am    Post subject: Reply with quote

Hi,

I have seen your captures on Fickr, ... they are very nice images.


Can you upload two photographs as perpendicular as possible to your setup and in the direction of the arrows?



(I'm sorry, I did not realize that I had not uploaded the image ... too many things simultaneously)
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Ramón Dolz


Last edited by RDolz on Thu Jul 04, 2019 1:00 pm; edited 1 time in total
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Rikisub



Joined: 29 Jan 2013
Posts: 97
Location: Spain

PostPosted: Thu Jul 04, 2019 8:15 am    Post subject: Reply with quote

Thank you very much to you all, I was completely wrong about the problem then.

Quote:
in the direction of the arrows?


Thank you for your kind words. However, I don't know what arrows you refer to . . .
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rjlittlefield
Site Admin


Joined: 01 Aug 2006
Posts: 19978
Location: Richland, Washington State, USA

PostPosted: Thu Jul 04, 2019 10:38 am    Post subject: Reply with quote

The left/right shifting effect is caused by the rail carriage rotating slightly when you reverse direction. The slight rotation of the carriage ends up moving the lens slightly left or right, which shifts the field.

The simplest solution is to always be moving in the same direction when you set the endpoints and shoot the stack. That is, back off before the start point before you do anything, then move forward to start, set the limit, move forward to end, set the limit, then back off again to before the start point, so that when you do start shooting, the rail will have to move forward again to reach the start point.

You may also be able prevent the rotation on reversal by pre-loading your setup with some elastic band (bungee cord, surgical tubing) placed off axis. This will work only if the torque produced by the preloading is enough to overcome the torque of the rail that causes the rotation when the elastic is not present.

--Rik
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soldevilla



Joined: 16 Dec 2010
Posts: 550
Location: Barcelona, more or less

PostPosted: Thu Jul 04, 2019 1:03 pm    Post subject: Reply with quote

I no sure where is your problem, but the three axes must be parallel, especially red and green ones.
Once the wemacro begins to push always in the same direction the play that this displacement allows is compensated and should not move laterally. My StackShot has the same problem, but discarding the first image, the operation is correct.

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Rikisub



Joined: 29 Jan 2013
Posts: 97
Location: Spain

PostPosted: Thu Jul 04, 2019 1:28 pm    Post subject: Reply with quote

Thank you. very much for your answer Rik, I know now what to do then.
Soldevilla, now I understand what you meant. Yes those three axes are paralel, you don't see them like that because of the perspective, but I line them (notice the bubble level on the left).
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RDolz



Joined: 28 Aug 2017
Posts: 74
Location: Valencia (Spain)

PostPosted: Thu Jul 04, 2019 2:21 pm    Post subject: Reply with quote

That's why I asked for perpendicular images, since I think I see the same thing that Soldevilla sees, ..
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Ramón Dolz
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Rikisub



Joined: 29 Jan 2013
Posts: 97
Location: Spain

PostPosted: Thu Jul 04, 2019 2:40 pm    Post subject: Reply with quote

All right, thank you!
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