Sponsored By:

Subject: Re: LX200 / Questar comparison
From: Thomas Roginski
Reply To: mapug@shore.net
Date: Sat Aug 19 03:29:49 1995

The answer is more involved than some of the statements which have been made.

There are three different issues here (assuming that we forget about the small size and portability of the Questar). One of these features is light grasp. I have used a loaner Questar on many occasions and have found it little better than my good 3" Unitron refractor on deep-sky objects. I went through the Messier list with the Questar or the 3" refractor next to my cheap 8" Newt reflector. There was no question at all. The larger 8" Newt scope was *very* much better at finding objects and viewing faint detail.

The second question of a telescope is resolution. There is no question that (for unobstructed telescopes) the resolution on double stars is a linear function of diameter. Because it is obstructed, the Questar was no better than my 3" refractor. The 8" Newt and my 10" LX200 can resolve much closer stars than either of the 3" scopes. It is necessary to have good seeing to allow the larger scope to resolve these close doubles.

The third question of a telescope is definition. While definition is a subtle feature, it is similiar to resolution of detail on a very low contrast target. This is where a small scope can make up some of the ground. It is necessary to train your eyes to see faint detail. I am a planetary observer of about 25 years experience and have observed with many types of telescopes in many seeing conditions. The Questar would out preform the 3" refractor and almost any 4" telescope I could find including a good 4" refractor my friend had. *At least with my eyes* on nights of good seeing the 8" reflector and my 10" LX200 are about equal and both out preform the Questar. Depending on the night, the 8" Newt might be better than the 10" SCT or visa versa. In this case note that I have said *with my eyes*. I have seen great drawings made with the Questar on Mars and Jupiter. I cannot duplicate these details. My wife who has very untrained eyes commented the first time she saw Jupiter with the 10" LX200 that *this was the first time she saw the bands on Jupiter*.

If we are to believe two recent issues of S&T which sought to resolve the matter of obstructed telescopes, we would believe that (assuming good optics) if you substract the diameter of the obstruction from the diameter of the telescope, you find the approximation of the resolution on poor contrast objects compared to an unobstructed telescope. In this case for the f/10 we have 10" - 3.5" = 6.5" or for the f/6.3 we have 10" - 4" = 6". In other words the 10" LX200 is about equal to a 6" refractor for low contrast detail. I agree with this. Neither the 8" Newt or the 10" LX200 is the equal on planetary detail to the 8" refractor which is owned by my club. The 8" refractor is impossible to transport and a 6" refractor also costs more than the 10" LX200.

I have not used some of these new super refractors with apochromatic objectives made by Meade and others. One of the planetary observers in our club has a 5" one and makes fantastic claims for its use on Jupiter and Mars. He is one of the best planetary observers that I know, but he made the same claims back when he used the Questor. I do not believe that a 4" super refractor will out perform the 10" LX200, and the 5" is much more expensive and only slightly easier to move around. Again I cannot comment on these refractors directly. The S&T article would indicate that the 10" LX200 would be better, but...

TOM (OWL1)

>> If you had a choice between an LX200 10" SCT and a Questar
>> 3.5" MCT, which would you choose? Questar claims their 3.5 MSC
>> will routinely outperform an 8" SCT.
>
>Tact task, here?
>