Hey guys,
After the problems I had with my 314e that ultimately led to me asking for a refund, I'd planned to re-evaluate the choice of CCD vs dSLR, which I've now done.
To my surprise, after articulating what was important to me, and assigning a weighting to each of those factors, then looking at what each option provided and the cost, it actually works out better "bang for buck" to spend more on a CCD. That's probably not news to you all, but honestly I was surprised.
Sine then, I'd planned on getting the Atik 314L+ (referred to as "314" from here on), which seems well regarded and is at the top end of my price range, so much so that I wouldn't be getting a filter wheel or filters for some time.
I've now done some reading on oversampling vs undersampling which has suggested that for my uses, the Atik 420 might actually be better, which was also very surprising to me.
First off, my primary interest is in shooting galaxies. I'm interested in photographing nebula also, but to a lesser extent. I'm shooting with a short tube refractor (600mm ED80) and I
think I typically have pretty good seeing. As I understand it a good dark site will have seeing in the area of 1", and given that I'm 15mins away from the nearest streetlight in a semi-rural area I think that a safe bet would probably be seeing half that good (assumptions for the win!).
Following is the main stats I've found on the cameras / sensors:
FOV
420: 40.84' x 30.76'
314: 51.44' x 38.43'
Resolution (w/ 600mm scope)
420: 1.51"/px
314: 2.22"/px
Peak QE
420: ~ 65% @ 500nm
314: ~ 65% @ 500nm
H-alpha QE
420: ~ 30% @ ~ 650nm
314: ~ 55% @ ~ 650nm
Read noise
420: 4 e-
314: 4 e-
Pixel resolution
420: 1620 x 1220
314: 1392 x 1040
Pixel size
420: 4.4
314: 6.45
Ideal pixel size
According to
this source, the ideal pixel size can be calculated as star size / 3.3, where:
Star Size = (Seeing * Focal Length)/206.3
I think a pessmistic assumption here would be a seeing of 3. So this gives me:
Ideal pixel size = (((3 * 600) / 206.3) / 3.3) = 2.64. Of course, a better seeing value would require even smaller pixels!
So, based off all of this I'm reaching the following conclusions: the 314 would be significantly better than the 420 in terms of FOV and sensitivity if my primary interest was in photographing nebula. The downside would be significant undersampling and lower image resolution.
The 420 has better cooling, a smaller FOV, peak QE parity, better matches my OTA and will require significantly longer exposures for nebula. Combining later with a focal reducer should give it a better FOV for wide-field nebula shots and offset the lower H-alpha QE to some extent.
Based on all of the above, I'm really feeling that the cheaper 420 is actually a better choice for me. Does anyone have any advice that might contradict this? If not, I'll probably order a 420 tomorrow.
Cheers,
Lee