Recap
A couple images from the past week. The moon was captured through a 120mm refractor telescope using a 10mm lens and a 2x barlow (effectively a 5mm lens). I think that's a magnification of 24x without taking into account the camera lens.
I've been reading photography books from the library and around sunset on Friday decided to experiment with camera settings and flowing water. Lucky me we have the pond's waterfall and plenty of frog models. In fact there was an audience of at least seven frogs (could have been more but you know how secretive they are).
The shot was setup with an exposure time of 1/25 of a second to smooth out the flow of water. F-stop of f/8 and focal length of 5.4mm using the A70's macro mode and no flash.
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I believe you mean "(effectively a 20mm lens)", as, if I remember right, lens length is roughly the distance from the viewing plane to the focal point of the lens, so 5mm would be wider than 10mm.
Actually it would be 5mm. With or without a barlow a 40mm lens shows more of the sky than does a 10mm. The downside is that there's less light with the 10mm.
A barlow "increases the effective focal length of an objective lens, thereby increasing the magnification." Which I copied from the excellent barlow tutorial below.
The nice thing about the barlow is that it effectively doubles the number of lenses you own. The 40mm is also a 20mm, the 25mm a 12.5mm, and the 10mm a 5mm.
http://www.astunit.com/tutorials/barlow.htm
That said I am far from the person to rely upon in such matters.
It still confuses me how much the focus point moves back after removing the star diagonal. Light origami.