Making usable a gift mediocre scope

[ingrast]

I was presented some weeks ago with a Celestron PowerSeeker 127 short tube newtonian telescope.

I have no observational background, neither owned or even peered through an eyepiece before, but have been acquainted with the trade for years through reading. This was the first chance to put to use whatever I may have learned about telescope use and issues.

This product belongs to the low cost could-have-been-made-better category, where cost cutting often unnecessarily spoils what cound have been a far better instrument.

- Mount. Shaky extruded aluminium tripod, wobbles at the slightest touch of the focuser knob. Fixed that filling the legs with mortar and fitting a wooden spreader to stress it open, much stiffer now only the mount elasticity itself is left, will look for further improvements.

- Eyepieces. Probably by far the weakest link, the supplied 5mm (Ramsden?) is mostly unusable due to lack of constrast and minimal eye relief. The 20mm unit (Kellner?) is moderately fair, but one cannot expect an about U$ 200 scope to come with a couple of eyepieces in the U$ 50 range or more, which is to be expected for decent muticoated Plossls to begin with. Add to this a 3x plastic body Barlow.

Planned upgrade is at least a better barlow and high power eyepiece (Celestron X-Cel range seems a good choice, hope to hear comments!), which will be a recoverable investment for eventual future telescopes, may be even a new 20 mm also.

- Assembly. Out of the box, the scope once assembled and pointed to Jupiter showed what even in my inexperienced eyes looked like gross miscollimation. After some testing and fumbling around, I replaced 2 of the collimation screws with a couple of longer bolts I fitted with knurled knobs and spring loaded between the mirror cell and back plate. This made visual collimation far easier in the darkness and prompted suspend the building of a laser collimator out of a scrap length of brass I had started. Will eventually finish it, but is no longer an urgent issue.

- Optical desing. This is a tough issue, the design is of the Jones-Bird type, i.e. a relatively fast spherical mirror, corrected and focal length extended by a doublet lens placed at the tip of the drawtube.

I have heard all sorts of negative comments about this scheme, though it seems they are mostly related with the actual execution of it in cheap scopes from general brands, rather than with the optical design itself.

Here I am in a quandry. I may choose to replace the primary with a quality paraboloid, replacing the tube itself if I want to keep approximately the same focal length (effective lenght that is, 1000 mm), or make a flex cell to deform the original primary (Sky&Telescope - Alan Adler Nov/2000). In this case, I may probably need to replace the inbuilt corrector-extender lens with a (better quality) barlow to remove the now unnecessary aspherical correction while keeping the focal length, or may be another approach I do not see now, or may be it is not worth in the end.

Whatever, I am enjoying quite fair views of the moon and Jupiter (can see the pale red spot with the 20mm eyepiece and barlow), and expect to hone my observational skills in the months ahead, wheather permitting!

Apologies for the long post.

Rodolfo

[scotastro]

You have certainly taken on a project to improve it. I have read the S&T article about distorting a mirror - looks interesting, but never had the nerve (or fortunately need ) to try it.

It is a shame that these scopes even exist, they are bought with such good intentions as yours was, but are just so bad.

Mike

[ingrast]

Yes, it is a project, and may be I enjoy as much (or more) working on it than actually observing!.

Whatever, I will keep reporting, and posting images both of the works and eventually shots taken through an adapter I built for afocal imaging, must work a bit still to get decent results.

Rodolfo