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PHD Guide Image Brightness

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#1 John Miele

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Posted 04 March 2013 - 06:48 PM

Just tried my new QHY5-II Mono camera for guiding last night for first time. I had it mounted in my ST-80. Even at 1 second exposures, the guide image in PHD was very bright and looked way overexposed. The contrast between stars and background was poor and washed out. I have not guided in a while, but I recall my older QYH5 based Kwiq-guider behaved similarly but not as bad. Are there settings in PHD to improve the contrast and darken the background? I cannot find any. It was so bad that I am half way considering stopping down the ST-80 to increase the focal ratio and maybe darken the background that way. I did find a camera gain setting and will fiddle with that next time...Thanks...John

P.S. I know it will get asked and the answer is...No...I did not ever get it to guide due to unrelated issues I had actually run across before and forgotton about in my time away from guiding :foreheadslap:...

#2 Mike7Mak

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Posted 04 March 2013 - 07:06 PM

There's a slider somewhere in the PHD window that varies the contrast of the guide image.

#3 John Miele

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Posted 04 March 2013 - 08:15 PM

Well whatdayaknow! Thanks Mike. I can't beleive in all the times I used PHD I never noticed that slider :tonofbricks:! I'll try it out next chance. Thanks again!!...John

#4 Harel_Boren

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Posted 06 March 2013 - 05:11 PM

I think you may solve this by shooting darks for it. It's an automatic process in phd.
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Harel

#5 JoseBorrero

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Posted 07 March 2013 - 05:14 AM

If the camera is binned, also increase brightness.

#6 astrovienna

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Posted 07 March 2013 - 09:13 AM

How bright were the guide stars? If I understand correctly, PHD adjusts the display brightness depending on the stars. Bright stars will give you a dark background. Adjusting the slider will help, but faint stars will still have a bright background. The background doesn't affect the guiding at all, however.

Kevin

#7 Tandum

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Posted 07 March 2013 - 10:00 AM

There is also a gain control for the camera in ascom setup before you connect.

#8 John Miele

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Posted 07 March 2013 - 03:32 PM

I actually did take darks the other night :confused: and it was still very bright and washed out. The stars themselves were hard to pick out from the background. But I must have done something wrong because this camera is known to work well. I'm going to try again tonight and will adjust that gamma/contrast slider and/or the camera gain to see what works best. Thanks for the replies from everyone and I'll report back...John

#9 AstroScience

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Posted 07 March 2013 - 11:55 PM

John, what version of PHD you use?
QHY is the same camera as Orion SSAG and i think i know what's the problem.

#10 John Miele

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Posted 08 March 2013 - 08:41 AM

Hi Sergio,

I'm using the latest version from the Stark Labs website.

I tried again last night. I had used Procyon as an alignment star so it was in the QHY5's FOV. I immedatley noticed the background was much darker and the star field looked more contrasty. I moved the gamma/contrast slider a bit and got a very pleasing view. Then I slewed to my target galaxy which had no bright stars around it and the view became all washed out again. I was able to move the slider almost all the way to the right and the few stars in the field stood out well enough to lock on for guiding but I did get some starmass warnings that periodically flashed on and off. I used 2 second guide exposures and a dark frame. So it looks like when there is a bright star in the field, PHD does perform somy type of auto adjustments on contrast which can be augmented with the slider and you get a nice dark and contrasty background. But when you only have faint stars in the field, it's difficult to darken the background and get good contrast. I don't think this is anything unique to using the QHY5-II. I have not guided in a while, but I remember my old Kwiq-guider doing something similar...John

#11 astrovienna

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Posted 08 March 2013 - 04:11 PM

You can always get a reality check on the star with Tools>Star Graph (or something like that). This shows a cross section of the star, which helps me predict whether that star is really usable by PHD.

Kevin

#12 Peter in Reno

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Posted 08 March 2013 - 05:11 PM

Just to be clear about this. PHD does NOT use the gamma slider you set for PHD to detect the stars. PHD detects stars however the programmer (Craig Stark) set it. Gamma slider is there for each user to view the stars on the computer monitor. Changing the gamma slider points has no effect for PHD Guiding.

Peter

#13 John Miele

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Posted 09 March 2013 - 12:41 PM

Thanks Peter. I was wondering a bit about that very question. Had another session last night and while my guiding performance was not as good as I wanted, PHD worked well and locked onto the guide stars with no trouble...John






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