Exposures Gone Wild

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johnpd
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Joined: Fri Jun 01, 2018 8:30 am

Exposures Gone Wild

#1

Post by johnpd »

I was playing with my new QHY5III-485C camera trying to see if I can get an image of a deep sky object. I initially set exposures at 20s. When I started exposures, the numbers were going all over the place. I might get 20s, I usually got 10s, and in one case I got 99s. I don't know what was going on. I have the latest Sharpcap 3.2 Pro. Any ideas?

JohnD
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admin
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Re: Exposures Gone Wild

#2

Post by admin »

Hi,

try enabling the 'Force Still Mode' option which puts the camera into still frame mode rather than video mode. This should work better for long exposures on modern QHY cameras. Another option is to try the SharpCap 4.0 beta, which has had a lot of work done on the QHY code that is not in 3.2

cheers,

Robin
johnpd
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Joined: Fri Jun 01, 2018 8:30 am

Re: Exposures Gone Wild

#3

Post by johnpd »

Hi Robin,

I think I have found the source of the evil. I am using a 15ft USB3 cable which was working fine. When I started a test inside I was getting all kinds of weird results when I started longer exposures. So I switched back to the much shorter standard QHY cable and everything started working correctly. I then again connected the longer cable to the camera and the other end into a powered hub. That worked fine. So I have to use the powered hub to get the camera to work properly if I want to use the longer cable.

I have another question. I tested stacking (without alignment) and noticed that the "last frame" time (4.7s) was less than the actual exposure time I had selected (5.2s). Is that normal?

Thanks,
JohnD
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Re: Exposures Gone Wild

#4

Post by admin »

Hi John,

ah, yes, long USB cables can introduce all sorts of unpleasant glitches. I've found from experience that about 3.5m is the longest you can expect to work reliably on USB3 without having to add a hub.

I've not seen the last frame time consistently go shorter than the exposure time on QHY cameras before (the last frame time is the time elapsed between the last-but-one frame and the last frame arriving at SharpCap). You might expect to see an anomaly there when changing exposure, but I would expect it to settle down after the next frame.

cheers,

Robin
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