CN FORUMS ARCHIVE Telescope Reviews: Refractor vs. Reflector ?

I believe baffles do make positive differences for deep sky and having conducted numerous observations with 12.5" and 16" Lightspeed Newtonians on deep sky has proven this. I also believe there are going to be some sacrifises though, if you wish to perfect both deep sky and planets. In other words, it's difficult to have your cake and eat it too. For example, Spectrum's IAD coatings. I believe these are the smoothest coatings for planets, end of story. But, on deep sky, they are simply not as bright looking. So you have a choice to make if you think you can notice the difference. Steve Kennedy, who is an expert on large aperture mirrors said he was noticing these differences himself. I told him I was not surprised. Some may argue that you can have your cake and eat it too, but that depends on what your definition of optical excellence is. I suppose it's both fortionate and unfortionate that the observing team has become very picky about how planetary images should look. I have had to be very careful not to let it interfere too much with my ability to simply enjoy the night sky itself.

Baffling is recommended for deep sky, but not needed for planetary observing and it's easily been proven. Conquering the thermals is one of the primary concerns of Grissom and Pons. The cooling used for truss designs vs. tubes has slight differences and I'll share them for those interested. In the tube design itself, the air flow from the fans is meant to keep it flushed. This helps prevent eddies at the primary, secondary and walls of the inner tube from occurring at all times.

Unfortionatly, the truss doesn't cool in this manner because the mirror box will not allow air to properly flow up, to flush out the secondary eddies as well. The truss will bounce the air around. This is the advantage of the tube. The tube itself actually behaves like a ventillation shaft, should eddies occur at the secondary. This is the reason we prefer to have all the air pushed up and forward. I've had long discussions about this and here are the conclusions thus far. I seriously had to make some changes to this 12.5" F-5 Starmaster. For those who may have missed these photos, I have shared them here.

Unfortionatley, some ATM's are not convinced or concerned that thermals are an serious issue. For example, take the 14.5" F-4.3 Starmaster. It's a wonderful scope however, it will be beaten by Grissom's and Pon's set up on planets everytime because they've covered every weakness that the Newtonian design has, including the spider. Some people may think these issues are a bit much, but they're not when comparing them side by side.

On the west coast, laminar air, flows from west to east. This is very important once you've seen the proof. A truss is more susceptible than a tube when body heat is crossing the optical path. This happens on the west coast because most truss's have their focusers placed on the right side and this is actually not right, excuse the pun. The focuser placement for west coast observers using a truss design, should be placed on the left side. When planets rise in the east and pass zenith, your body heat will always be down wind. All you have to do to varify which way the wind is moving, is to simply place your warm hands in front of the optical path and watch which way your body currents are flowing through the eyepiece while a bright star is racked out.

Imagine all your hard work on optics going to waist on planets because you neglected to address the issue of body currents crossing the optical path. The next issue is the fans. Some ATM's are convinced that fans placed at the sides should pull air into the box and exit out the opposite sides.

I conducted various tests to prove which method gave the best results. There were no doubts once the tests were concluded. I scrapped the original 12.5" Starmaster and started from scratch. Take in mind that I have to transport this thing to Wilson and this is the reason I'm using a truss, even though I like the tube better. It was optimized as close to Grissom and Pons's designs as much as possible. I'll soon share what was done.

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