[Wavytone]

I suspect you're going to be disappointed by the lenses from SurplusShed, f/2.8 is way too fast for a doublet to be any good visually. OK as a condenser - which is what such lenses were made for - but not as a small telescope (ie. a finder). What you should be looking for is a doublet around 60mm aperture at f/5 (300mm focal length).

I've looked at their site before and yes the stuff is cheap... but not much practical use, which is why I refrained from suggesting it.

There is another alternative - old camera lenses - I have two from my ancient SLR which i use as finders. Both are OK at low power with an old 20mm Erfle eyepiece, but they aren't diffraction limited (not even close off-axis) so useless for higher power:

- a 135mm focal length f/2.8 telephoto, it gives about 7X and a very bright field of view, excellent as a finder.

- a 500mm f/8 mirror lens, which gives 25X with the same eyepiece. It's useful for projecting the sun, the resolution is good enough for that. Aperture about 60mm and overall length about 100mm, so it's very compact.

You can find similar lenses for next to nothing in auctions.

Sigma made a 600mm f/8 mirror lens which as I recall gave fairly good image quality as a telescope; if you find one it would probably serve well as a guidescope.