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PGW Steve
professor emeritus
Reged: 10/03/06
Posts: 632
Loc: Winnipeg, Canada
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The 20DA is legendary as an astro DSLR for its red performance and low noise. Now with the sensor improvements, and daytime capable live view of the 40D and all around tech improvements how do these two stack up? I'm interested in what is lost and what is gained in a 20DA vs. 40D modded camera specifically image quality, sensitivity and noise.
I have one other question about custom white balance.
I set custom white balance on a Hutech 40DH, and take some daytime pictures, all looks good. Now it's dark and I want to shoot some nebulae. Do I delete the custom white balance data, or leave it set as I had for daytime?
Thanks in advance 
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dvb
different Syndrome.
Reged: 06/18/05
Posts: 3038
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I found this thread from the Yahoo digital_astro group interesting. This fellow preferred the results with his 20Da to his 40DH -- he seemed to find the latter was overly sensitive to light pollution compared to the 20Da. Can't say I've read of anyone else with this complaint.
http://tech.groups.yahoo.com/group/digital_astro/message/109557
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Strgazr27
Vendor - Deep Space Mods and Composites
Reged: 10/04/04
Posts: 6984
Loc: StonyHill Observatory
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I don't think it's as drastic as moving from an unmodded 20D but there are a few somewhat significant differences. The Hutech 40D will offer better response in the red end of the spectrum. If the difference is similiar to that of a Hutech 20D vs the Da it's a pretty big increase.
The only difference in the liveview function is the ability to move the selection area around the FOV. This cannot be done with the Da which requires the focus star be centered in the FOV for best results.
Noise seems to be as good if not better with the 40D. You also get the step up to the DIGICIII Chip as well as 14bit processing. The 40D also seems to be a bit better "Sealed" to the environment than the 20 or 30 series is.
Would I consider the move to a 40DH if I owned a 20Da? Most likely as to get the same sensitivity to Ha with the Da you'd need to Mod it yourself or have it done. If your going to pay to have it done than why not just spend a bit more and make the jump?
JMO's
CS's
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Bobby
StonyHill Observatory
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Samir Kharusi
scholastic sledgehammer
Reged: 06/14/05
Posts: 988
Loc: Oman
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Quote:
Now it's dark and I want to shoot some nebulae. Do I delete the custom white balance data, or leave it set as I had for daytime?
Thanks in advance
No, just leave the Custom White Balance as you used it for Daylight shots. ImagesPlus then allows you to retain this daylight white balance throughout your post processing, if you so wish, ie have colors appear as they "should" to human vision, except for the boosted H-alpha. These "correct" colors are of course not necessarily what you are used to see in astrophotos, eg the sky background is toffee, rather than reset to grey as everyone and his brother-in-law does these days. But most people are happy to set the sky background to grey and retain "correct" (human vision) colors on the brighter portions. At least that is the generally accepted practice these days...
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Strgazr27
Vendor - Deep Space Mods and Composites
Reged: 10/04/04
Posts: 6984
Loc: StonyHill Observatory
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Quote:
These "correct" colors are of course not necessarily what you are used to see in astrophotos, eg the sky background is toffee, rather than reset to grey as everyone and his brother-in-law does these days.
I would consider this true only to a point. If one is shooting from a dark sky site, than the sky should not be a toffee color and I have personally seen the difference in my shots taken at my property vs my house. The difference being Mag 7 skies there to Mag 5 skies at my house.
I agree that I see a lot of clipped black points to make the sky background more dark than it really is but I don't think it is a trend that is new.
I could be wrong 
CS's
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Bobby
StonyHill Observatory
Skywatcher EQ6 Pro (On it's way)
AT 130 F/6 Prototype
Royce 10" f/4 Astrograph (Under Construction)
Self Modded 40D
70-200 F2.8 L IS
SSAG
YAHOO TMB 130SS Group
Astronomy Technologies Yahoo Group
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Samir Kharusi
scholastic sledgehammer
Reged: 06/14/05
Posts: 988
Loc: Oman
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Hi! The most "correct" colors you can have at the current state of technology development are probably the colors you get with Daylight White Balance in an unmodded camera. The camera makers have spent countless hours researching how to make their cameras replicate human vision as closely (and as pleasingly, not necessarily the same) as possible. So, to see what the "correct" color of the night sky is, just shoot the sky at a dark site with any digicam to mid histogram with Daylight White Balance (!) and look at the back of camera LCD. Toffee! Never grey. You can get grey if you use Auto White Balance, because that setting simply resets the white balance of the majority of the frame to grey. Still unconvinced? See this. Actually I read somewhere that even in near-Earth orbit the sky is still toffee from all the hydrogen and oxygen out there. What if we go far, far out in space? I suspect still ditto, from all that Hydrogen Alpha. Hydrogen is practically everywhere, as all those new astropics from Gendler continue to amaze us. I get the feeling that if we shoot 30+ hours integration in almost any direction we will find oodles of red H-a nebulosity. At least the trend seems to go that way. Of course, even I hate a toffee backdrop to my astrophotos. So I make my sky backdrop a greenish blue, rather than grey. Neither is more valid or less valid scientifically, just whatever pleases you 
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