Re: Horizon 4x loupe review

[rlrylander@xxxxxxx]

Greg Erker wrote (Re Horizon 4x loupe):

> Hi gang,
>
>   I got my loupe this morning. The bad news
> is that it doesn't have nearly enough coverage
> to use as a MF stereo viewer lens. The square
> base is roughly 2x2" and that is all you can see
> with it. There is no extra coverage to see into
> the corners.
>

I've found that cheap binoculars are a good source for inexpensive
achromats.  I recently bought a Bushnell 7x35 "Falcon" binocular on sale
for $18.95.  This is no Zeiss or Swarovski, but it has a pair of  ~150mm
focal length x 37mm dia. achromatic objectives with a simple (MgF2) AR
coating.  The lenses were ideal for a chimney magnifier I made for a 4x5
camera - all but the very corners of the viewing screen are visible.

Besides the objectives, you get a couple of Kellner eyepieces, rubber
eyecups and the porro prism assemblies (without the objectives or
eyepieces: an inverting, hyperstereoscope?).  Not a bad deal for < $20.
The binoculars are made in china and when disassembled remind me of a
Seagull camera without the shutter.

I've also cannibalized a cheap Vivitar monocular for its 80mm focal
length x 22mm dia. achromatic objective.

The down side is that you cannot accurately predict what the objective
focal length will be from the binoc specs - magnification only tells the
objective to eyepiece focal length ratio.  Field of view, eye relief,
type of eyepiece, etc. don't really help.  The best guide is the
physical size of the binocs (keeping in mind the folded path through the
prisms).  For magnifier or viewer applications, the focal length usually
isn't critical anyway.  Shorter focal length objectives can usually be
found in "wide angle" designs.

It's always surprises me that a complete assembly can cost less than the
parts within - try to buy an achromat from Edmund for < $10 (even
"experimental grade").