|
Doh!
I have found further information on my collimation problem and a reply on an overseas forum seems to sum up things. It isn't good news for anyone with a short tube 'scope
Re: Will it work?
What you have is a Jones-Bird design reflector telescope. It uses a spherical mirror rather than the more expensive parabolic mirrors used in a regular Newtonian reflector.
The Spherical mirror in combination with a Barlow/Corrector lens inserted into the focuser's draw tube is what gives you the total focal length of the telescope.. You "do not" want to remove that barlow/corrector. If you do, you will have all kind of spherical aberration problems. You wouldn't even want to use that mirror in a longer OTA. It won't work without the correction of that barlow/corrector lens, or some kind of corrector plate on the end of the OTA. Then you would essentially have yourself something similar to a SNT if you did that.
Jones-Birds are a cheap design, made cheap to reduce the cost of manufacturing in order to increase profit margin.. They are notorious for collimation problems.
My roller coaster ride didn't end there though. I then found a Mead 5" 1000mm fl mirror on e-bay yesterday and thought about a full rebuild with that and a long tube. A-Ha, I thought, I can beat it!
I investigated still further but it turns out that Meade uses the Bird-Jones approach as well on a number of problematic models and replacing a spherical mirror with another spherical mirror isn't going to do much. So....it turns out that I can't beat it.
At the moment, the thing is sitting over in the corner mocking me. I bought it as a compact solution for use on holidays in the country and it is fine for looking at the moon but will never give me even a half decent look at the planets by the look of it.
I think they say a man needs to be able to know when he is beaten.
Steve
|