QHY247C Offset Problem

A place to report problems and bugs in SharpCap
Forum rules
Please read about Troubleshooting USB Issues before posting.

*** Please do not post license keys - please report any problems with licensing to 'admin' by PM ***

Please include the following details in any bug report:

* Version of SharpCap
* Camera and other hardware being user
* Operating system version
* Contents of the SharpCap log after the problem has occurred.
[If SharpCap crashes, please send the bug report when prompted instead of including the log]
Post Reply
eseavey
Posts: 51
Joined: Thu Jan 18, 2018 3:39 pm

QHY247C Offset Problem

Post by eseavey » Sun Jun 16, 2019 4:58 am

Robin,
I am helping a friend with his new camera, and we are coming across a problem with the offset. When I set it to 40, the image is gray and the histogram is at 40%. I attached the logs for you. Connecting the camera through ASCOM does not show this problem. Do you know what is happening?

Eric
Attachments
Capture_00001.Histogram.csv
(293.67 KiB) Downloaded 15 times
Capture_00001.CameraSettings.txt
(750 Bytes) Downloaded 28 times
QHY247C Offset Problem.txt
(74.39 KiB) Downloaded 15 times

User avatar
admin
Site Admin
Posts: 3254
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: QHY247C Offset Problem

Post by admin » Sun Jun 16, 2019 9:30 pm

Hi,

I feel a bit like I'm asking about the Emperor's new clothes here… Why would you set the offset to 40 if that gives you an image that is too bright? There is no real magic value for the offset control on any camera – you just pick the smallest value that nicely separates the histogram peak of a dark frame from the left-hand side for your selected exposure and gain settings. If I remember rightly, for a lot of qhy cameras the offset seems to be applied before the gain, which means that you need to pick different offsets at different gain values.

Cheers, Robin

User avatar
turfpit
Posts: 887
Joined: Mon Feb 13, 2017 8:13 pm
Location: UK
Contact:

Re: QHY247C Offset Problem

Post by turfpit » Sun Jun 16, 2019 9:59 pm


eseavey
Posts: 51
Joined: Thu Jan 18, 2018 3:39 pm

Re: QHY247C Offset Problem

Post by eseavey » Mon Jun 17, 2019 7:20 am

I use offset of 40 because it is what I use for my QHY224C and QHY168C cameras. I selected 40 using this table: https://www.qhyccd.com/index.php?m=cont ... =31&id=199 Now I am seeing their starting Offset is 200 with the QHY247C

I did not use that table last night, however, I did see that when connecting using ASCOM, the default offset was 79. It was in the same ballpark as the offset I was using for my cameras so I guessed that that was some recommended starting value. The offset sensitivity with the QHY247C seemed very sensitive. Especially compared to the ASCOM controls that pop up in a new QHY window in Sharpcap.

Eric

User avatar
turfpit
Posts: 887
Joined: Mon Feb 13, 2017 8:13 pm
Location: UK
Contact:

Re: QHY247C Offset Problem

Post by turfpit » Mon Jun 17, 2019 1:09 pm

Eric

In 2019 there have been 12 updates to the qhyccd sdk. This could make the older information in the tables obsolete.

What I have been doing to establish a reasonable offset value for DSO imaging is for a given gain: try an offset value and take a bias frame looking for a centralised histogram (or at least the min value being > 0). If histogram not central, then adjust offset and repeat. If an SDK changes, then I recheck my offsets for the gain settings I use.

[Note: for lunar/planetary I set offset=0 (or lowest value available).]

bias-frame-with-reasonable-offset-setting.JPG
bias-frame-with-reasonable-offset-setting.JPG (109.1 KiB) Viewed 334 times

Interestingly the bias frames from my Atik CCD and Canon DSLR (both of which offer no offset adjustment as this is taken care of in hardware) look just like the image above (centralised histogram).

Dave

Post Reply

Who is online

Users browsing this forum: No registered users and 3 guests