Hi all,

I'm looking at increasing the optical zoom of my Powershot A70 and 
wondering if anyone has had any experience/comments.

At the moment I've made up a mounting plate so that I can attach a 8 
times magnification monocular to the front of the camera. It works quite 
well, but the biggest problem is that sometimes 8 times magnification is 
too much.

What I was thinking is to use some of my old SLR lenses as the objective 
lens of my own telescope. If I could get a -25mm lens (or something 
similar) and mount that between the SLR lens and the camera then that 
should form a telescope, with magnification F/25 (where F is the focal 
length of the SLR lens). Since I've got SLR lenses ranging from 28-400mm 
then that should give a nice range of magnifications. Obviously it would 
require some mounting brackets and a little bit of playing around, but 
that should all be fairly easy.

I've had a go at the basic idea by using a 50mm and 28mm SLR lens 
back-to-back and it seems to work okay, giving about double 
magnification, but obviously the image is inverted because that is with 
2 positive lens. If I can get a negative focal length as the "eyepiece" 
lens then that should avoid the image inversion.

So...anyone know where to get a strong (~25mm) negative lens cheaply, or 
has anyone else got any ideas?

Cheers,
Steve