Did I buy a dud?

[nobby2 (Neil)]

Recently I purchased an f4, 8 inch 800mm reflector second hand. It was not a known brand to me "Precision"
After laser collimating, cleaning etc I am still getting a secondary or ghosting image on the edge of Jupiter and I wouldn't describe the stars as pin sharp. Tending to be slightly elongated.
The star out of focus test produces an even glow each side
but not what you would call spherical rings?
I have since read a review which stated that this scope was a Chinese model not known for quality and probably not using a parabolic mirror. I have since found the GS website www.gs-telescopes.com with what looks like the exact f4 scope although in this case it expressly states the quality of it primary (parabolic) with multiple coating etc.
SO
Do I own a fake?
Do own a poor quality older model?
Are these known issues with an F4, 800mm?
Has anyone had any dealings with a similar scope?
thanks

[h0ughy (David)]

hard to say laser collimating doesn't align your optical train and you still may need that done, then re collimate? can you post some pics of the scope and the mirror? maybe someone else can comment

[Shiraz (Ray)]

the GSO f4s have pretty good optics and would definitely show a ring structure each side of focus. An "even glow" sounds like you might have a spherical mirror and the elongation could be either astigmatism or slight mis-collimation.

found something called a "Precision Optical F800203EQ1V-A" which may be what you have. If so, it is not a GSO. It is described as a "refractor", which may indicate that the importer was not too clued up on optics - maybe they fitted spherical mirrors to keep costs down? - scary thought, but possible.

Before you write it off though, check that the main mirror is not under tension from a protruding adjustment bolt, that the main mirror clamps are not tightened right up (they need to be floating just above the mirror surface) and that the secondary mirror is still firmly held in place.

Maybe also take a few pics of it from various angles and post them as Dave suggests.

[Satchmo]

The thing about cheap scopes is that complete duds can still slip through . I encountered an Orion 8" GOTO ( with GSO mirror ) out in the field at a festival one night that was obviously a spherical mirror.. the images were so bad you couldn't get any kind of clear focus even at low power and the star test was shocking . The owner had bought it second hand and didn't know any better- never looked through any other scopes. I advise him to join an astro club . He thought the Moon looked impressive . So its always a case of buyer beware.

[Shano592 (Shane)]

Is the GS brand the same as GSO brand?

If it is anything like this scope:

http://www.productreview.com.au/p/pr...203eq1v-a.html

I will suggest that it will have a spherical mirror.

There is another way to test this. In a lot of the bottom-end Chinese scopes, they have a corrector lens in the focusing train, between the eyepiece mount and the secondary mirror.

If you like Neil, you can PM me and I can swing by and take a look. I live close by to where you are.

EDIT: What you are describing sounds very much like the 6" Chinese one that I first bought. Everything looked like it had a comet tail on it, and no amount of fine adjustment would remove it. I ended up pulling it apart and giving it a good clean up, but the aberration was still there, due to a spherical mirror.

Just click on my name at the top of this reply, and choose the Private Message option.

[nobby2 (Neil)]

Thanks to all
Much appreciated.
Shano592 has offered to have a look. Will report on results over next days

[Shano592 (Shane)]

Hi Neil,

Got your PM, and replied to you.

[nobby2 (Neil)]

After shano592 and i had a look and endless attempts to align i resolved the issue in the best way. I sold it (very cheap) and expect to purchase a new 8 inch dob from a reputable dealer and make. Lesson learn't !