Re: [Paddlewise] Tasco Binoculars

From: "Steve Holtzman" <sh_at_actglobal.net>

> The eye relief is 17 mm but I found it
> is more comfortable to not roll the eye cups down and just sort of push my
> glasses up slightly.
> 

I've noticed that there is considerable variation in the degree to which
binocs are able to "overfocus".  That is, the infinity point for someone
with normal or corrected vision is not the end of travel for the focus
control.  They often focus past that point.  That means that those of us
that are nearsighted can sometimes focus past the normal infinity point
and use them without glasses!  

Over the years I've found that most 7x50s seem to top out at correcting
for something like a -3 or -4 diopter.  I once tried a pair of 16x50s
that corrected to about -6 and standard Carton Alderblick 10x40 (or so)
that just barely made -6 (I require -6 so that's how I know - I once
borrowed a pair of CAs on a beach in Baja for stargazing and with a little 
straining, had wonderful views of the southern sky that's not visible up 
here in the Great White North).  I find that in the small aperature range 
of roughly 7x20 to 10x26, they tend to correct around -4 to -6.  My 
Bushnell 8x25 Anglers are close to -6 so I can more or less use them 
without my glasses.  Note that -6 is the extreme and -4 is more typical.

I haven't found a strong correlation with anything that can guide you
on how much correction you can expect, though magnification _seems_
to matter - the higher the magnification, the more correction possible
as a crude rule of thumb.  There may be an inverse correlation with
price - the expensive binocs seem to have tight tolerances and don't
often allow much focus beyond infinity (the CA example aside).
This is definitely a YMMV situation.

So, if you wear glasses, this might be an additional feature to look
for when trying out binocs.  If they can correct so that you can use 
them without glasses and you don't mind pushing your glasses up, the 
eye relief becomes less important.  Significantly, if you want to use
the binoculars for astronomy in the evenings, the ability to use them 
without glasses makes stray light much less of a problem.  The latter 
is why I made this a priority for me (when paddling I use contact 
lenses, so correction is not an issue then).

Mike
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