My first duff scope!

[Stratis]

Hi all,

Technically I'm not a beginner, I am the proud owner of a number of very beautiful telescopes, but something has happened to me that has made me feel like a beginner again, and I'd like to share my experience so that other fledgling souls to the hobby will not fall victim also

As the title suggests, I have bought a terrible, terrible telescope. Yes, on fleabay.

Everything looked so good.... £40 for a Celestron NexStar 80 GTL (no mount, just the OTA).... you hardly ever see a cheap classical refractor for a decent price anymore, Celestron always bundle them up with the motorised mounts to keep the price worth the shipping expense. I thought, a nice long-focus achromat would have been a fine instrument when I was starting out, why not convert it into a double-star or solar scope, maybe even a fun guidescope project for my big SCT?

Huge mistake.

Someone has been 'fettling' with the doublet lens on this scope; there are signs of frantic 'cleaning' on the inside surfaces (the ones that should never be exposed to air) of the Fraunhofer doublet, as well as what looks like silicon grease. It's been meddled with. The seller has admitted he didnt try it under the stars before passing it along.

Star shapes are abhorrent in every respect; bloated, flared, asymmetric... impossible to bring to focus in any eyepiece. I can only assume the lens cell is tilted somehow but it's so bad I don't even know how to photograph the aberrations...

Now maybe the 80GTL is a great beginner scope when its new and unsullied, but this one isn't.

Beginners beware the too-good-to-be-true awesome eBay deal! I believe this is maybe the 15th telescope I've bought in my life yet the first time I've ever truly felt it I'd gotten a dud (as opposed to just a bad design recipe like the 90mm Maksutovs....).

If it happens to you, don't give up! Return it, buy something better, keep trying!

Cheers,

Paul

[John]

Thats bad luck Paul

Are all 3 spacers in place between the lens elements ?. One was missing from a used TAL 100 I bought recently which creates coma.

Those long 80mm fracs are usually pretty idiot proof but if someone has been meddling with the lens who does not know what they are up to who knows what could have happened ?

[dweller25]

As John says - check the spacers and check the lenses are thr right way around too

[ronin]

Sounds like returning it is not an option so pull it apart and clean it, then reassemble "correctly".

Sounds like the lens may be incorrectly spaced, one may be at an angle and one or both could be orientated incorrectly.

Just get an inexpensive cleaning fluid - just sounds as if getting a more costly one is a suspect option.

Lens orientation is well documented on the net, spacing may be a bit more difficult, especially if there are no existing bits of spacer still hanging around to gain a measurement from. I would try 1/2mm or 1mm for the simple reason I have sheets of thin modelling ply of about that thickness.

[RLWP]

Sounds like returning it is not an option so pull it apart and clean it, then reassemble "correctly".

Sounds like the lens may be incorrectly spaced, one may be at an angle and one or both could be orientated incorrectly.

Just get an inexpensive cleaning fluid - just sounds as if getting a more costly one is a suspect option.

Lens orientation is well documented on the net, spacing may be a bit more difficult, especially if there are no existing bits of spacer still hanging around to gain a measurement from. I would try 1/2mm or 1mm for the simple reason I have sheets of thin modelling ply of about that thickness.

I'd go with this advice - what have you got to lose?

Richard

[laudropb]

Bad luck. I am very wary of buying second hand.

[damnut]

Sounds like a project, if you are able to sort the spacers, they can be as flimsy as a circle of very thin plastic bag type material you may come out with knowledge and a working scope. Stick at it.

[happy-kat]

Me too I see it as an opportunity to get that telescope observing right again and I have hardly any experience, why return it you may have a great scope there if you give it some fettle time.

[Dave Lloyd]

That's a great fiddle about project for 40 quid.

Presumably you'll set up a light bench to collimate the cell?

[xtreemchaos]

id look at as a challenge, just imagine how good you feel when you put the poor thing right. charl.