Author Topic: QHY8 Off Centre?  (Read 2470 times)

Euan

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QHY8 Off Centre?
« on: September 26, 2009, 09:51:42 AM »
Hi all,

I have just got a QHY8 and I seem to get the same type of effect on my flat frames regardless of configuration. I've tried flats with no glass, an MPCC & 8" Newt, and a Televue TRF-2008 and ED80 scope

I've also tried spinning the QHY8 keeping the optics in place, but the result is always the same

Could the CCD be mounted incorrectly?

Thanks
Euan



Cyclop_si

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Re: QHY8 Off Centre?
« Reply #1 on: September 26, 2009, 10:25:58 AM »
My QHY8 flats looks similar.
« Last Edit: September 26, 2009, 10:57:24 AM by Cyclop_si »

QiuHY

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Re: QHY8 Off Centre?
« Reply #2 on: September 27, 2009, 05:56:37 AM »
Helllo,

           I think this is due to the thermal noise adding into the flat image. Please test Flat-Bias    and see if there is some change.
Because of the readout , the buttom pixel will wait more time to be readout so the thermal noise is bigger. All interline CCD(includes,
SONY's , and Kodak KAI series)  are effect by this thermal noise.

          You can also test high download speed and see if the center is moved.

Best regards,

Euan

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Re: QHY8 Off Centre?
« Reply #3 on: September 27, 2009, 06:20:09 AM »
Helllo,

           I think this is due to the thermal noise adding into the flat image. Please test Flat-Bias    and see if there is some change.
Because of the readout , the buttom pixel will wait more time to be readout so the thermal noise is bigger. All interline CCD(includes,
SONY's , and Kodak KAI series)  are effect by this thermal noise.

          You can also test high download speed and see if the center is moved.

Best regards,

Hi Qui,

Yes it does change with the download speed (see pic), I've tried subtracting bias from the flats but it doesn't change the position

Should I then use the fast download option?

Thanks
Euan



Hello,

          Maybe you flat light is too bright. For Interline CCD, the metal sheild of the vertical tranfer CCD may get some light transimission. So when you use slow readout , the light come into the vetical regsiter and cause some problem. Can you check a weaker light box?

Best regards,
« Last Edit: September 28, 2009, 02:12:43 AM by QiuHY »

MMys

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Re: QHY8 Off Centre?
« Reply #4 on: September 27, 2009, 08:04:10 AM »
NO, you should always use slow download mode for final imaging, because of lower noise !

You need not to deal with above described thermal gradient and resulting offset of brightest center because it is eliminated by calibration process. The same gradient is present in all calibration frames.
Vixen VC200L V.I.S.A.C., homemade Newton 185/610+Paracorr, Borg 77ED refractor,  optionally with EDF4 reducer, Modified EQ6 mount, Modified EOS 300D, QHY8 ccd camera, MII G2-8300 mono CCD camera, TVGuider.

Cyclop_si

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Re: QHY8 Off Centre?
« Reply #5 on: September 27, 2009, 10:13:16 AM »
So for max. performance the right approach is to take Offset and Light frams with slow speed and Flats with fast speed?

MMys

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Re: QHY8 Off Centre?
« Reply #6 on: September 28, 2009, 01:07:42 AM »
For final imaging (light frames and all calibration frames) always use SLOW readout. Fast readout is ideal for focusing, object framing and composition set-up etc...
Vixen VC200L V.I.S.A.C., homemade Newton 185/610+Paracorr, Borg 77ED refractor,  optionally with EDF4 reducer, Modified EQ6 mount, Modified EOS 300D, QHY8 ccd camera, MII G2-8300 mono CCD camera, TVGuider.