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Old 16-09-2017, 06:42 PM
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Paul Haese
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Paul Haese is offline
Join Date: Jan 2009
Location: Adelaide
Posts: 9,372
Originally Posted by gregbradley View Post
I am not totally convinced of these arguments. I have both types of scopes - the AP Honders 305 F3.8 1159mm focal length scope and a Planewave CDK
17inch 432mm aperture scope at 2936mm focal length.

The Honders is better at widefield. It can do galaxies well with small pixels (Sony 694 sensor) but I get a better result from the CDK. I have seen Peter Wards images with similar setups show the same results.

It may be more the aperture rather than the focal length but there is a point where large aperture is hard to physically handle without being in a more compact form like an RC or CDK etc. A 17 inch Newt would be very hard to handle and wind prone as well.

Perhaps its the old adage "aperture rules" at work more than the focal length but the 2 concepts are really intertwined.

Small pixel cameras come with their own baggage as well. Small wells, Sony
CCDs are more prone to fixed pattern noise too.

Let's look at this way. The RC12 with a 9 micron pixel sensor gives me an image scale of 0.76" per pixel. The Newt 12 with 5.4 micron pixels gives me an image scale of 0.92" per pixel. The Newt 12 image is smaller for any given target but so far it appears the resolution looks very similar to me. Both scopes are physically a similar size, in fact GSO used the same truss system for both scopes except they put a secondary cage on the top of the RC truss. So up to 12" I'd say the argument is null and void. Over that size then you have a point. I am not a fan of tubes in general and long tubes do get caught by the wind, so there lever arm and gravity to contend with. And; the point has been well made here, not many people can really afford a 30-50K OTA. If you have the money that is all well and good. I personally cannot afford an F8 CDK or RC over $10,000 so I needed to find a faster solution to the problem. I put a fast Newt on a great mount and I think once I have it firing it will produce similar results to both Ray and Mike. They both have the newer sensors but the results should be similar in resolution.

The long and short of it is, if you want to spend that sort of money on a scope, then go for your life. If you are happy with that sort of imaging speed, so be it. If you want faster you need to consider other options. Andy, I think if you look along the 10" newt path that should serve you well here. As Rob pointed out he has a 10 Newt and he gets good results. He has to do a bit of work to sort it out but now the results are coming forth.
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