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zoom percentage not working properly on S95

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Offline Mlapse

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zoom percentage not working properly on S95
« on: 11 / February / 2018, 06:11:45 »
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Hi all,
I was just getting pictures back from my S95 that is on a tripod screwed to the wall.

settings are done via ultimate intervallometer. zoom is set at 70%, focus @ infinity is on.

however pictures that were taken after a restart have a slightly different zoom factor.
if I look at the file information both have the same f-stop (4), zoom (13mm) and timing (1/500) but there is definately a visible difference in zoom.
I thought I might have distorted the camera position between the restart, but that does not explain the difference in zoom.
It looks like there is a small change in barrel distortion/angle as well: objects have width differences, lines that were straight got a slight curve..

does somebody know what is going wrong here? ....and possibly how to solve this.
« Last Edit: 11 / February / 2018, 06:52:43 by Mlapse »
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Online c_joerg

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Re: zoom percentage not working properly on S95
« Reply #1 on: 11 / February / 2018, 08:44:53 »

Is the image stabilizer or other focus settings (Safety shift) turned off?
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Offline Mlapse

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Re: zoom percentage not working properly on MY S95
« Reply #2 on: 11 / February / 2018, 11:13:05 »
IS is off and camera is set in P mode as far as I know safety shift is not possible, only in Tv or Av modes.
I just stopped and restarted the script without restarting the camera and the lens moved for a moment when I restarted the script. Although the lens was still in it's proper postion because I did not alter it when I stopped the script
I retried that a few times and sometimes it does rezoom/refocus more or less and sometimes not...I checked the camera's zoom/af settings and everything that can be off is off.

hmmm, sounds like it is a camera problem...because if it a setting problem I don't see what I missed.
« Last Edit: 11 / February / 2018, 11:55:10 by Mlapse »
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Offline reyalp

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Re: zoom percentage not working properly on S95
« Reply #3 on: 11 / February / 2018, 15:58:33 »
I assume you are using set_zoom() in a script to change the zoom?

If you post some example images, that would give us a better idea of how much things are changing.

I did some testing with elph130 and saw very little change (less than the ND example below), but I would not be totally surprised if cameras didn't return to precisely the same position.

Some other possible factors:
We have noticed that the ND filter being in or out has a very small effect on the image (see here https://chdk.setepontos.com/index.php?topic=13228.msg134454#msg134454) but it sounds like you are seeing something more significant.

Using set_zoom may change how the camera handles jpeg distortion correction. So if both manual zooming and set_zoom were involved, you might get different results.

CHDK attempts to reset the focus after you use set_zoom, but this may or may not happen depending on the camera. I think it will on s95. It  tries to do this even if the zoom didn't actually change (e.g. if the zoom is already at 70 and you do set_zoom(70) it will still try to focus). set_focus with identical values will not necessarily return to exactly the same position (e.g. if you do set_focus(1000), it might go to 998 one time and 1001 another.)
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Offline waterwingz

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zoom percentage not working properly on S95
« Reply #4 on: 11 / February / 2018, 22:16:54 »
Quote from: reyalp on 11 / February / 2018, 15:58:33
I assume you are using set_zoom() in a script to change the zoom?
OP mentioned using ultimate.lua, so that's a yes.

Quote
I would not be totally surprised if cameras didn't return to precisely the same position.
That seems the most likely.  Which will be a problem for ultimate.lua when it periodically restarts the camera.  Perhaps  inserting longer delays right before and right after set_zoom is called at script start might help?  I was also thinking about calling set_zoom(0) first to "recalibrate" the zoom motor mechanism?
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Offline Mlapse

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Re: zoom percentage not working properly on S95
« Reply #5 on: 12 / February / 2018, 04:05:50 »
Well, I don't suppose it is only a focus problem, but hereby 2 pictures.

4 minutes between shots, same f (set by camera/related to zoom),  and shutterspeed(set by camera), iso fixed at 400 in canon menu. ultimate menu: zoom set at 70% (13mm) focus @ infinity (on)...
in enhanched foto setting "override subject distance" is off (setting is not saved for camera startup)
both times camera was started using firmware update and started the ultimate script manually, did not set anything by hand .
shot from a tripod to rule out movement although the camera has moved slightly between shots...definately need a remote start

« Last Edit: 13 / February / 2018, 14:07:21 by Mlapse »
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Offline Mlapse

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Re: zoom percentage not working properly on S95
« Reply #6 on: 12 / February / 2018, 14:36:22 »
That seems the most likely.  Which will be a problem for ultimate.lua when it periodically restarts the camera.  Perhaps  inserting longer delays right before and right after set_zoom is called at script start might help?  I was also thinking about calling set_zoom(0) first to "recalibrate" the zoom motor mechanism?
[/quote]

maybe there should be a longer delay after zoom and before focus, that could help..is that line297?  sleep(2000)
I'll up it to 2500 and try tomorrow.
and set_zoom(0) first might help to get a standard startpoint if you have zoomed manually before starting the script or only stopped and restarted the script without powering down.

On former projects where I never used the zoom I haven't encountered this sort of distortion differences.
and it's a consumer camera so can we expect it to be perfectly accurate in zooming position?
« Last Edit: 12 / February / 2018, 14:44:51 by Mlapse »
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Offline reyalp

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Re: zoom percentage not working properly on S95
« Reply #7 on: 12 / February / 2018, 17:08:23 »
Quote from: waterwingz on 11 / February / 2018, 22:16:54
That seems the most likely.  Which will be a problem for ultimate.lua when it periodically restarts the camera.
Looking at the images posted, it seems like a much bigger difference than I would expect from this kind of thing.

Not sure what's going on here, but I don't think it's just normal slop in the zoom position.
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Offline Mlapse

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Re: zoom percentage not working properly on S95
« Reply #8 on: 13 / February / 2018, 04:43:07 »
I first thought it was the result of the camera position being slightly different.
But I have run a few test by changing the camera angle between shots by far more than on the 2 pictures I posted.
However the resulting differences in barrel distortion are a lot smaller than seen on these pictures and there is definately no difference in zoom.

Maybe it's the combination of slight reposition and slop in zoom that does this? I am as lost as you are to what made this happen.






« Last Edit: 13 / February / 2018, 05:02:22 by Mlapse »
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Offline reyalp

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Re: zoom percentage not working properly on S95
« Reply #9 on: 13 / February / 2018, 13:42:24 »
Quote from: Mlapse on 13 / February / 2018, 04:43:07
Maybe it's the combination of slight reposition and slop in zoom that does this?
I don't think so, it's a really big difference. If there were slop in the zoom, I wouldn't expect it to be more than an few pixels at the edge of the image. I didn't even see that much with elph130, though I had to do a fully USB controlled test to keep it stable.

Can you reproduce the problem consistently? If you can, I'd suggest shooting CHDK DNG and posting the full uncropped raw and jpeg. These will be too big for the forum, you can use a site like dropbox, google drive etc.

If you can avoid moving the camera, that would make comparison easier.

As I mentioned before, on thing that can happen is the software distortion correction can be set incorrectly in some cases. I don't know of a way it would end up different in your case, since the script is always setting zoom, but comparing raw should make it clear whether it's software or optical.
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