Quote:
Originally Posted by ausastronomer
Larry you have picked the best of the best in terms of 6" refractors and compared it against one of the worst 11" telescope designs going; in terms of visual performance. As I said in another thread, SCT's make poor visual instruments for several reasons. Very large central obstruction (33% plus), the thermal cooling issues caused by the closed tube design and the corrector plate; and the additional air to glass surfaces over a newtonian, namely the star diagonal, the corrector plate and in many cases a focal reducer. On top of that these are mass produced telescopes with fast F2 to F2.5 primary mirrors and the optical quality of a great many of them is downright poor.
Try comparing your 6" AP refractor to my 10" SDM (Suchting mirror) or my 14" SDM (Zambuto mirror) on a night of decent seeing and see how they it fares.
I have had my 18" Obsession to 1075X on the Moon and Saturn and my 14" SDM to 800X on the same two targets. The 14" Zambuto would go higher under ideal conditions, but I dont have the eyepiece/barlow combinations to go any higher, without stacking barlows. Try 800X plus with a 4" or 6" refractor and see how nice the image holds up.
Honestly, to think that a 4" refractor is the best choice as a visual telescope for someone who is only going to have one telescope, considering that 90% of what we observe usually are DSO's which benefit from greater aperture, is 1970's thinking at best, or the thinking of someone who needs to sell a Takahashi refractor IMO.
Cheers,
John B
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I would not argue with someone of your undoubted knowledge, John. But frankly I would not want to be bothered with the constant collimation adjustments required with newtonians.
Back in the '80s my 1st scope was a Meade 2120LX3 and I bought an 80mm Meade (Mizar) refractor as a second scope.
I have not owned anything but a refractor since-I just love the pinpoint star images they produce,and the superior contrast that comes with having no secondary obstruction.
These days I cannot manage a large scope, so I have restricted myself to a 4" apo-but I am happy with it.
Cheers
Laurie