Weird spikes on old 80mm telescope

[skysurfer]

Nearly forty years (since Nov 1973) I have a Polarex spotting scope which I sometimes still use because of its ultimate grab&go capability.

I modded it years ago to replace the crappy turret + crappy Huygens eyepieces by a 1.25" diagonal which fits 'normal' eyepieces. Using a 13mm Nagler (38x) makes it a good 80mm deep sky viewer (but brighter stars show the spikes). Of course not as good as my Genesis.

But going beyond 50x power nasty spikes appear around bright objects and planetary observing is useless because of the spikes which destroy any contast.

Now I pointed thes scope to Arcturus and moved the focuser and filmed it, see here http://pix.northsouthsky.com/polarex-80-spikes.gif the result.

The objective is mounted with three metal pins :

http://pix.northsouthsky.com/polarex-80-objective.jpg

which might cause the spikes. I put some black felt over the metal pins with no avail.
Any ideas on this ?


BTW I consider retrofitting this scope with a new objective :

http://www.teleskop-express.de/shop/product_info.php/language/en/info/p4710_TS-APO-Refraktor-Objektiv-80-480mm-in-justierbarer-Fassung.html

but this costs me $440 and an aluminum adapter ring of M84x1 (thread on telescope) to M89x1 (thread on new TS objective) of about 5cm long to retain the same backfocus to be lathed.

Then this old one is refurbished to an APO.

Worthwile ?

[DavidU]

Severe astigmatism due to pinching of the objective in 3 places.

[skysurfer]

You mean deformations in the objective lens due to tension ?

[DavidU]

Yes, there is a lot of tension there for sure ! The objective should have something like a rubber ring gently pressing the objective pair into it's cell.
I adjust mine so there is a slight shake (audible rattle) when shaking the scope. Yours is so tight it risks damaging the lenses.

[bojan]

I second to this:thumbsup: