Re: Horizon 4x loupe review

[Greg Erker <erker@xxxxxxxxxxxxxx>]

>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.

  That's a bargain for sure.

>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.

  Thanks for the hints.

  John B (or maybe it was John Ort) has stated that bino
optics have abberations in the objective that is correct
by the eye piece and vice versa. Don't know if this is true
or if they are small enough to be ignored in many applications
(like a chimney magnifier)

>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").

  The marvels of mass production (in 3rd world countries).

Greg