Hi there, I have a co-worker who is looking to sell a telescope. I am thinking of buying it, but thought I'd get some advice here first. The telescope is currently much better than anything I have now (which isn't saying a lot :-). It's a Bushnell Voyager, a pretty standard equatorial-mount newtonian. I believe the primary mirror is 4". She's willing to sell it for about $100. I don't get out observing much these days, but perhaps a better scope like this would encourage me to do more. Any advice? Is this one of those drugstore types to avoid? Thanks, Dan Hanks
Hi Dan: The scope was reviewed in S&T some years back, and as I recall, had some problems. The focuser was too tall for the secondary mirror size, causing vignetting. What this means is that the telescope only uses about 3" of it's mirror. I also seem to recall that the mirror was not fully parabolized, but my memory may be faulty on this score. If you have access to an S&T index, look up the article. On the other hand, if it gives pleasing images, (try it first!), offer what you think it's worth. $100 is too high, in my opinion. Chuck Hards --- hanksdc@plug.org wrote:
Hi there,
I have a co-worker who is looking to sell a telescope. I am thinking of buying it, but thought I'd get some advice here first. The telescope is currently much better than anything I have now (which isn't saying a lot :-). It's a Bushnell Voyager, a pretty standard equatorial-mount newtonian. I believe the primary mirror is 4". She's willing to sell it for about $100.
I don't get out observing much these days, but perhaps a better scope like this would encourage me to do more.
Any advice? Is this one of those drugstore types to avoid?
Thanks,
Dan Hanks
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Since I've not got much experience with 'nice' scopes, what should I be looking for? Is there something I'll see that will indicate that the scope is vignetting? Or will the image just not be as detailed as it could be were the scope using all of its mirror? What things might I see to indicate that the mirror is not fully parabolized? I'll be testing it out tonight, so of course that will probably be the real test--if it's enjoyable to use. -- Dan Hanks On Thu, 2 May 2002, Chuck Hards wrote:
Hi Dan:
The scope was reviewed in S&T some years back, and as I recall, had some problems.
The focuser was too tall for the secondary mirror size, causing vignetting. What this means is that the telescope only uses about 3" of it's mirror.
I also seem to recall that the mirror was not fully parabolized, but my memory may be faulty on this score.
If you have access to an S&T index, look up the article.
On the other hand, if it gives pleasing images, (try it first!), offer what you think it's worth. $100 is too high, in my opinion.
Chuck Hards
--- hanksdc@plug.org wrote:
Hi there,
I have a co-worker who is looking to sell a telescope. I am thinking of buying it, but thought I'd get some advice here first. The telescope is currently much better than anything I have now (which isn't saying a lot :-). It's a Bushnell Voyager, a pretty standard equatorial-mount newtonian. I believe the primary mirror is 4". She's willing to sell it for about $100.
I don't get out observing much these days, but perhaps a better scope like this would encourage me to do more.
Any advice? Is this one of those drugstore types to avoid?
Thanks,
Dan Hanks
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http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy
__________________________________________________ Do You Yahoo!? Yahoo! Health - your guide to health and wellness http://health.yahoo.com
--- hanksdc@plug.org wrote:
Since I've not got much experience with 'nice' scopes, what should I be looking for?
The best advice I could give would be to attend some star-parties, and look through other people's scopes. This allows you to make a decision BEFORE you spend any money. Most people are too happy to let you look through their telescopes. Also, most reputable dealers will give you return priveliges if the scope you actually buy turns out to be a dud.
Is there something I'll see that will indicate that the scope is vignetting?
This isn't a precise, exact answer, but when you look through the focuser without an eyepiece, with your eyeball dead-center, you should be able to see the entire primary mirror without moving your eye around. If the edge of the mirror isn't visible, there is a probable vignetting condition.
Or will the image just not be as detailed as it could be were the scope using all of its mirror?
Not a loss of detail, but a loss of brightness that you can't detect, because you don't usually have a non-vignetted comparison telescope side-by-side.
What things might I see to indicate that the mirror is not fully parabolized?
Short of a Foucault or Ronchi test (performed on the optical bench or with a special Ronchi "eyepiece"), the image will be soft at high powers, when known telescopes of high-quality are giving sharp, detailed images at the same time (to eliminate poor atmospheric conditions as a variable).
I'll be testing it out tonight, so of course that will probably be the real test--if it's enjoyable to use.
Good luck, Dan, let us know what you find out. Chuck __________________________________________________ Do You Yahoo!? Yahoo! Health - your guide to health and wellness http://health.yahoo.com
On Thu, 2 May 2002, Chuck Hards wrote:
Is there something I'll see that will indicate that the scope is vignetting?
This isn't a precise, exact answer, but when you look through the focuser without an eyepiece, with your eyeball dead-center, you should be able to see the entire primary mirror without moving your eye around. If the edge of the mirror isn't visible, there is a probable vignetting condition.
Is this something that can be fixed by adjusting the position of the secondary mirror? I noticed that you can adjust the "depth" of the secondary mirror (i.e., closer to or farther away from the main mirror) on this scope. Would that fix the vignetting? Thanks again for your help here. -- Dan
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