A and B focus points are moving

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BlindPilot
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Joined: 09.06.2014 17:37

A and B focus points are moving

Post by BlindPilot »

Hello,

I am photographing objects using panoramas [ 25 to 50 views] with focus stacking. I have the demo version of HR for Windows. What happens is the following:

1) if I use 2, 3, 4 slices on the focus stacking all works fine and the result is great.

2) if I use 5, 6 slices[have not tried with more] I find that at the end of the panorama [a total of 25 to 50 stacks] the near and far focus points [A, B] have moved toward the camera quite a bit rendering the work useless

Is this a limitation of the demo version or a known bug? any possible solution?

Thanks for your attention,
Manuel
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Stas Yatsenko
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Re: A and B focus points are moving

Post by Stas Yatsenko »

Hello Manuel,

It's most likely that you're observing the imperfection of the lens drive. Slack and slip in the mechanism causes the A and B points to drift when the lens makes a lot of movements. Every movement usually turns out to be slightly less than expected due toi slip, and over a lot of shots this error accumulates significantly. Some lenses have much more slip than others.
BlindPilot
Posts: 13
Joined: 09.06.2014 17:37

Re: A and B focus points are moving

Post by BlindPilot »

It is strange that after finishing 25 stacks of 4 slices A & B points have not practically moved while, with 5 slices, you can see, by looking at the files, that the A & B points have moved, bit by bit form the first stack, acumulating a significant displacement at the end of stack 25.

Are most focusing motors open loop, without any feedback system to control slipage and play?

Thanks for your attention,
Manuel
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Stas Yatsenko
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Re: A and B focus points are moving

Post by Stas Yatsenko »

Yes, that is weird that there's such a difference between 4 and 5 shots. I can't think of an explanation.
I'm not aware of design specifics of the lens drive and control algorithms, but with some of our lenses slippage is very obvious. Not so much with some others.
BlindPilot
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Joined: 09.06.2014 17:37

Re: A and B focus points are moving

Post by BlindPilot »

Do you know if there is any slippage between the manual focusing ring and the lenses? If there is no other solution, I am thinking on driving the manual focusing ring with a microcontroller, a stepper motor and a toothed belt.

Thanks,
Manuel
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Stas Yatsenko
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Re: A and B focus points are moving

Post by Stas Yatsenko »

No idea, but there usually seems to be some slack in the ring. And now I'm not convinced the issue you're observing is caused by mechanics.
You could try experimenting with different lens orientation (horizontal, upside down etc). If there's a difference in focus movement - then we know it's a mechanical issue.
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