Achromat Question

I hate to break up the very informative and interesting thread regarding Apos, lens types and coatings. Thanks for the great discussion.

I have a more basic question. The only refractors that I have ever looked through or owned have been a TV Genesis SDF and a TAK FS-102 and an Orion 80mm ED (the last two I now own and use regularly). I have never looked through an achromat!!! However, these larger achromats, primarily made by Synta, are very tempting becaue of the aperture/cost ratio. Is the performance of these low end scopes so terrible that even a 6" achromat pales in performance in comparison to a 4" Apo on the planets and the moon?? Or will a 6" achromat (like a Konus or Synta) reveal more planetary detail despite the chromatic aberrations?

Perhaps I've been spoiled by only having experience with some very good refractors.

Ed Kessler

Ed,

I own a Meade AR-6 and have also looked through a TV-101 and TV-102 owned by other people. I think it is fair to say the extra 2" aperture does provide more resolution but it can not provide the degree of clarity seen in any true APO. The principle culprit is the color abberation effect, even when using a minus violet filter. No matter how many ways you cut it a portion of your light is going to be out of focus.

The other issue is lack of consistency in Synta refractor quality. With APO's you pretty much know what you are going to get. With achromats it's a crap shoot.

I enjoy my achromat very much and tend to use it often during club public viewing events to avoid the cool-down problems inherent with my SCT.

Ed, If you already have the FS-102 I personally do not think a 6" achromat is going to impress you much. You will probably notice the disadvantages before you note the extra resolution.