|
The spreadsheet doesn't come up when you click on it so I can't read it.
By the way what is an RCC1? A corrector of some brand?
I have imaged galaxies extensively with BRC250 (10 inch) and Microline 8300.
I currently use CDK17 and Proline 16803. I have used the ML8300 on the CDK17 for galaxy imaging and it did not work well. The smaller pixels at 3 metres focal length merely meant far less resolution and more effect of the seeing. It was interesting to see just how much it cost in detail in galaxy images. A lot. But then you are not looking at 3000mm focal lengths. The Proline 16803 however is a beautiful match.
Clearly a higher QE camera will outperform a lower QE camera but there are other factors that enter in. The 694 has very small well capacity so overflowing pixels especially on fast systems will mean stars will bloat easily. There are not many images on the net from a 694 but the few that are there have really large stars in them. There is a galaxy image on the Starlight Express site and another and both have distractingly badly oversized stars. So I don't know if this is operator error (poor focus, lousy scope) or shocking seeing (the small pixels will get kicked around more) or small wells of the chip? More images will make it clearer as it gets used. It does have great potential as a camera sensor. I am not sure how you got the 694 was $1200 more? Which 8300 camera were you comparing that to?(most are considerably more expensive than Starlight Express 694).
I would disagree with your analysis that 10 inch is optimum. That does not match my experience at all. My CDK17 leaves my older BRC250 for dead for galaxies. All the very best galaxy images are from 20 inch RCOS scopes. Are you sure a 10 inch F4 is only slightly slower than a 12 inch F3.8? I find that hard to believe as it has something like 30% more light
so why only less than 10% faster speed? There must be a calculation or assumption error there. Its a good idea to quantify this but I think you still have to realise this is theory and it would be easy to overlook something and at the end of the day looking at others images and seeing what they used if its an image you like is based on the actual not the theoretical and therefore more likely to succeed. I think the conclusion should be more about which focal length is optimum for your area and you get the largest aperture you can afford to match that. There are plenty of good 10 inch GSO RC images around but they aren't as good as large aperture scope galaxy images.
Small well cameras are more susceptible to bloat on fast scope systems. So that would mean shorter subexposures to compensate which in turn is not ideal for faint galaxy imaging.
The seeing calculation refers more to focal length than aperture. Long focal length scopes need good seeing and larger pixels. Aperture is still king and having good seeing is still a very important factor (Martin Pughs Sierra mounted CDK17 images are about as good as you see anywhere).
The best 10 inch scope shots I have seen (not many were galaxy shots though) were from the discontinued RCOS 10 inch astrograph by Roth Ritter (google his name and you should get his site).
I had a lot of fun with my Takahashi BRC250 and Microline 8300 though and it did work well for galaxies but as I say my Proline 16803 on CDK17 is a far better combo.
A light sensitive narrow field of view camera makes a lot of sense with a large aperture fast Newt design that tends to flex easily. I think Mike's setup will be hard to beat without seriously large and very expensive gear.
10 inch is probably a tad small for galaxy work in my experience and you would be stretching it to get enough light no matter what F ratio configuration (F ratio myth, CCDs are linear in performance unlike film). At the end of the day its all about aperture and QE of the chips and matching pixel size to focal length and shooting with a setup that will perform in your local seeing and light pollution.
Greg.
|