#21  
Old 23-05-2011, 09:14 PM
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multiweb (Marc)
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Originally Posted by bmitchell82 View Post
I can see what your saying marc, and yes thats most likely right with the black points and white points changing though i beg to differ with the research that i have done on it.

Each program has a slightly different method of calculating statistics, a good test would be to run the same image though nebulosity and say maxim if they both come up with the same statistics then its how the programs interperate the drivers and settings. But i come back to ascom, if ascom isn't the main interface between drivers, control programs mounts and what not. Other wise ascom would need a driver for maxim, one for nebulosity and every other program.

When you do the calibration its not just setting the black and white point or getting the ADU above a cirtain number, its about optimising the CCD so that the pixel wells are actually getting everything that lands in there. the Black point that you talk about from my understanding is to get rid of the back ground noise and pixels that don't quite register as signal.

The Offset and gain are also affected by temperature so changing the temp will automatically change your settings, this might be the reason why your settings differ between programs as the QHY8 doesn't have TEC its just flat out like a lizard running from a big old wedge tail eagle! This is also the reason why i run at -25 deg C when my TEC is sitting at 40% duty cycle, because i havn't done the settings for -30 or -35 deg C

I do understand that not all ccds are the same but at the end of the day they arnt that different to each other and proper calibration will maximise your sky time!
No doubt you've done your homework. You're right I don't know what temp I take my pics at. My QHY8 is one of the first batch. When I get a regulated mono in the future I'll have to do my homework too. I'll come and pick your brain then.
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  #22  
Old 23-05-2011, 09:24 PM
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bmitchell82 (Brendan)
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I just did a test with Nebulosity and Maxim, theres a reasonable difference even within the same image so yeah pick one that is easiest to read, run with it
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  #23  
Old 23-05-2011, 09:41 PM
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Originally Posted by Logieberra View Post
When I take long exposures dark, eg 10mins with camera covered, why does it still look grainy like this? (
Maxim is screen stretching the image, see the 2 pointers, it is showing only what's between them.

Here's and old pdf on setting gain and offset on a qhy8.
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  #24  
Old 23-05-2011, 11:09 PM
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Best guide is here, takes a couple of minutes and works well in maxim. Scroll halfway down the page to see how to set gain and offset for these cameras. There is a similar one on the QHY website but can't find it right now but this is better in any case.

http://www.stark-labs.com/blog/files/GainAndOffset.php

Mark
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Old 24-05-2011, 05:21 AM
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Logan,

I agree with the comments above re your grainy image - turn off the screen stretch by un-checking the auto button or move the red and green sliders back out to the full range.

I'm not using Ascom to drive my QHY8pro - I'm using the Windows 32/64bit drivers. In Nebulosity I select QHY8pro - not ascom camera.
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Old 24-05-2011, 07:56 AM
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Logieberra (Logan)
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Thanks for your help guys. Lots of great info and some useful guides and links. This thread is a good resource for new CCD users out there.

Maxim doesn't have an auto screen strech button (it sounds easy in Neb2)... I'll have a fiddle with the red and green sliders and move them to the full range and see what happens...

And if the sky's clear this week I'll take an image or two and report back.

Logie.
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Old 24-05-2011, 09:14 AM
Hagar (Doug)
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Without reading everypost here, sorry. The grainy appearance is an artifact of the stretch routine carried out by Maxim and is not really indicative of the actual image. Maxim does a stretch on the image which allows you to see what faint fuzzy you are imaging. The output image will in most cases be almost black in it's raw state.
Programs such as CCD Stack also do a ddp stretch on the image for viewing only.

Craig Start has a nice detailed description of setting and forgetting Gain and Offset in the user manual for Nebulosity. I always ran my QHY8Pro at arround Gain=1 Offset = 125 without any problems.
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  #28  
Old 24-05-2011, 09:43 AM
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Im with you doug on the Maximdl, it can be a real arse that way when your trying to see what the data is. Nowadays I have that understanding and just screen strech the buggery out of the image to see the faintest data, then move it back to see if i have over exposed! The hardest thing is when you don't have a good SNR for a start (see dark nebs, flux nebs and the like) its nigh on impossible to figure your fuzzies

Good luck logan and I look forward to your first image with the 10+Cooled astro CCD goodness! Im sure you will be pleased with the outcome.
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Old 12-06-2011, 03:58 PM
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Boys, I've been fiddling with the QHY8 pro, but my issues with Alignmaster and Gemini 2 have overtaken all CCD progress...

But I did manage to grab a few crops of the butterfly cluster from the backyard, 90mm refractor, 4 x 5mins @ -15.

Thx for the help.

Logie.
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  #30  
Old 13-06-2011, 09:15 AM
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Gain-3
offset-116

use Maxim
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