Sunday, September 6, 2020

Celestron FirstScope - Eyepiece Tip

A good eyepiece for the Celestron FirstScope
based on the condition of the secondary
diagonal mirror and the low focal ratio is this
Aspheric eyepiece with a wide diameter lens
that lets in maximum light.
Celestron FirstScope - Eyepiece Tip

The photos show two eyepieces, one that works well and one that does not work well. For the best images, a good eyepiece will have a wide diameter lens combination which gives a large field of view.

This eyepiece has a very small
diameter lens and difficult exit
pupil, which causes a number
of problems with the short
focal length and diagonal
secondary mirror compromise
on the Celestron FirstScope.

At top, the photo shows an aspheric lens combination, which is a simple arrangement to pass the largest amount of light - a good combination for a 2.99-inch telescope.

Aspheric eyepieces are also light weight, and come coated with a black interior and antireflective coatings. The barrel is threaded for filters and was successfully used with a threaded 2x Barlow and a threaded .5x Focal Reducer.

Also noted is the entire set of aspheric eyepieces have larger lens diameters compared to other designs such as Orthoscopic, Plossl, etc. Aspherics also have the advantage of high performance and lower cost.

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