QHY 247 offset problem

[brisguy]

I have been trying to determine the correct offset value to use with the QHY 247 and wanted to use the tools available in Sharpcap to help me. However, while collecting the data, it seems I discovered an issue with the ability of Sharpcap to control the QHY 247. Specifically:
1 - setting the offset value has no effect unless you click away from the entry field of the offset value
2 - even though I set the offset value and clicked in another field and saw the value change and saw the offset value change in the TIFF header, the mean value of the exposure did not change. This was on a 180 exposure. On an earlier 1 sec exposure, the change in offset WS reflected in the captured data.

Procedure:
1. Connect to the camera
2. set the gain and offset
3. After setting the offset value, do not click on any other field before taking an exposure (duration should not matter)
4. Mean value of the exposure will not change from a previous value of offset

OR

1. Connect to camera
2. set the gain and offset
3. After setting the offset value, click on any other field before taking an exposure (duration should not matter). The offset slider will move.
4. Mean value of the exposure will not change from a previous value of offset

Version 4.1.11591

[brisguy]

I should also have mentioned - I have FITS files that illustrate this issue. They show a initial set of 1 sec exposures with two offsets that clearly show the effect of changing offset while another set of 180 sec exposures shows none even though the FITS header shows a change.

[admin]

Hi,

the fact that changes made during the exposure do not take effect for the frame currently being captured is not really surprising I'm afraid. Manufacturers don't specify behaviour in this sort of situation in their documentation, so in most cases it is unclear whether such changes will take effect for the current frame or the next frame. Actually, in the case of QHY cameras, SharpCap deliberately delays sending control changes to the camera until the current frame has finished when the camera is in still mode as this works around a problem that was occurring when adjustments were sent to the camera during the exposure of a still mode frame.

The behaviour of typing text into one of the control value boxes is also as expected - you have to click away from the box (or use the <TAB> or <Enter> keys) to make the value get applied. This ensures that partially typed values are not sent to the camera (ie if you type 500, you don't want SharpCap to set the value to 5, then 50, then 500).

cheers,

Robin

[brisguy]

ok, I guess I understand the typing issue (could I also hit ENTER to make sure the value is active?), but the issue regarding when the change takes effect is confusing. In every case

[brisguy]

Sorry - overactive keyboard! Let me try again:

ok, I guess I understand the typing issue (could I also hit ENTER to make sure the value is active?), but the issue regarding when the change takes effect is confusing. In every case, I took a single exposure using the Start Capture function after making the changes and after making sure the changes took effect. Furthermore, the FITS header indicated the expected offset, but the data did not.

Would you also expect that?

[brisguy]

Also, I see that you already answered the ENTER question. Thanks

[admin]

Hi,

if you want to have exact control over which frame is affected by changes to settings like the Offset or gain then you need to have the caemra in still mode and also make all changes before starting the capture using 'snapshot', 'start capture', etc.

In live mode, the camera runs continuously and is always capturing frames to display.

Let's assume you are in live mode with an exposure of 60s and assume an exposure is already 50% complete when you change the offset value. As I mentioned previously, that setting change is not sent to the camera until the next frame starts. However that's an implementation detail of the camera that the rest of SharpCap doesn't know about, so from the point of view of the rest of the application, the change has been made. Now you press 'start capture', maybe with 20s of the frame remaining. The first frame saved as a result of capturing will be the one that was already started before you even changed the offset, so it will be unaffected by the change.

The fact that the wrong value is recorded in the capturesettings in this case isnt ideal, but at the moment I can't see a reasonable way to resolve that issue without making a large amount of code aware of the internal delaying tactics of the QHY camera code. That becomes unmaintainable when another camera brand does things a different way, or perhaps another brand does the same sort of delaying tactic inside the SDK itself - in which case SharpCap would be convinced that the updated value has been sent to the camera, but in fact it was being held for the next frame.

cheers,

Robin

[brisguy]

>In live mode, the camera runs continuously and is always capturing frames to display.

OK, I thought I understood how that worked, but apparently not. I *was* in LIVE mode, but saw that the output was not being stored until I started the Capture function, so I assumed the counter would start over when I hit Start. Seems like it should to me.

>The fact that the wrong value is recorded in the capturesettings in this case isnt ideal, but at the moment I can't see a reasonable way to resolve that issue...

Can't you query the camera status before writing the FITS header? I always wondered whether the FITS header was reliable, and would like to think that it is, but if it only represents the software status, that is concerning.

Thanks for your response and Happy New Year!