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alan potts

More reports on Televue eyepieces

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Nice one you two. I may well try and come to SGL 9, but I will be in the dog house for a while.

Nice link John, I will mark that one and read it a few times. I knew what coma looked like and I must have a M?N with supressed coma. I would have thought if it were going to be there it would raise is ugly head in an Ethos. Maybe that like pixie that is inside each Televue that you told me about is working extra hard.

Alan

Edited by alan potts

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A star party here, I just turned the field over too.

John.

A point that you makes about coma on a Mak/Newt, I think the adverts say coma free, I have never seen any and the stars at the very edge are sharp. My understanding of coma is you get a comet sort of shape, if that is so I have never seen it on any magnification with any FOV, could it be going faster than this could cause it. The scope is sold mainly as an astrograph and photos I have seen from others show very good star shape (though croping could be in the mix). I seem to make a habit of using scopes designed for photography for visual..

Going back to the focal reducer, I guess if the scope speed is 6.3 then it is a 6.3 scope but it would be interesting to know if the other unwanted baggage invites itself along for the ride.

I will learn some of the crater on the Moon as it seems popular. At the moment with it being close to full I don't observe even though it is clear most of the time. Oh how I recall my first large scope up in Hull, it was 3 months before I could use it after it was finished.

Alan

Alan this may help :grin:

http://www.lunasociety.org/atlas/

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Surely focal length is just focal length. Most SCTs have a primary with a focal ratio of F/3 or F/2, it's the secondary mirror that adds most of the focal length.

Another example would be using a x2 powermate - it doesn't add anything except magnification. More precisely, it doesn't do anything other than increase the focal length of the scope.

With exceptions (C9.25, C14, new Meade f/8 scopes, undoubtedly more...) SCTs tend to have f/2 primaries and f/5 secondaries. I can visualise those as differently curved mirrors focussing the light on different points. It's the funky lens stuff I'm scratching my head with :eek:

Going back to the focal reducer, I guess if the scope speed is 6.3 then it is a 6.3 scope but it would be interesting to know if the other unwanted baggage invites itself along for the ride.

Lucky my shift doesn't start til later, I'm prolly going to waste the morning looking this up...

All I can imagine, in simplistic terms, is that the focal reducer has some final element that is slightly concave and brings the light to focus sooner/shorter than before?

Anyhow, f/6.3 is f/6.3 right? Still not a stiff enough test for some of the more hardened optics nuts around here, but good enough for me :D I'm not sure which corrector you have Alan, but the Celestron reducer flattens the field too. It be interesting to experiment with that on the back of your Mak, although I'd expect the baffle tube ultimately restricts your max FOV.

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Dunk,

It is the coma free optic that got them into hot water. The reducer is also meant to flatten as well.

I was only really asking out of interest, I don't want to put an additonal optic in the path , it will only be making any faults more testing to work out, is it the scope, is it the eyepiece, no it's superman.

Alan.

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