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Old 28-12-2008, 01:58 AM
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QHY8 and pixel size/focal length

HI all!

After playing around for a while with my Canon 40D I am now considering the purchase of a CCD!
I'm missing colors on all the emission nebulae around galaxies arms and such with my non modified Canon!

So here's the question:
Since I am imaging at 800 mm or less, smaller pixel sizes should be used right? 5.7 or 5.4 um would be ideal, correct?
What are the effects of bigger pixels, such as the QHY8 at 7.4 um?

Would you recommend going with a QHY8 for my Pentax 125 SDP? IS there anything else out there that has the same CCD area of the QHY8 or my Canon 40D?

Also, I'm using a Mac with PHD Guide and Nebulosity for imaging acquisition!


Thank you!
E.
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Old 28-12-2008, 05:17 AM
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Well bigger pixels means more light falls on them. In general you should try to have your pixels covering about 1 to arc sec of sky. Smaller then that your wasting pixels. Bigger then that and you can get square stars.
try this calc to see what happens http://www.astrovid.com/ccd_calc.php
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Old 28-12-2008, 07:23 AM
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Hello E.
I have never understood, nor taken the time to analyze those pixels to focal length rules.
If it helps, my QHY8 works well with the likes of my 10" 5 newt (1250mm focal length), but has worked equally well with an FS102 (800mm focal length), and is at the moment going very very well with my 80mm triplet (without reducer 480mm and with reducer about 380mm focal length).
Great camera for the money.
Gary
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Old 28-12-2008, 07:31 AM
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Thank you Kenny and Gary!

Gary, do you have some images you took with the QHY8 ?
I'm shooting with the 40D, but I'm already tired of CMOS and noise!
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Old 28-12-2008, 08:13 AM
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Sure E, I have e mailed a few to you, and there and gazillions of them on this site, as the QHY8 is a popular camera here.
Gary
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Old 28-12-2008, 09:07 AM
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Thanks!

Anyone else?
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Old 28-12-2008, 06:26 PM
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Assuming perfect seeing, tracking etc, you want the Airy disc to be twice the pixel size to get the full theoretical resolution of your scope. This is what you would aim at for lunar, planetary etc. However, in practice, the seeing is unlikely to be better than 1-2", so 1" per pixel is probably the best you are going to get in terms of resolution. On the other hand, you may be more interested in capturing dim stuff than getting resolution, in which case larger pixels would be the go
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