P3D Re: Viewing with vs. without lenses

["Greg Wageman" <gjw@xxxxxxxxxx>]

From: Bruce Springsteen <bsspringsteen@xxxxxxxxx>


>George said, after pointing out that free-viewing is often yields tiny
>details, false sharpness, stretch:
>>>>
>I know many people enjoy freeviewing stereo prints and
>claim that this viewing method has many advantages...
>"zero magnification", no stretch, no chromatic aberration,
>no distortion due to the lens, etc.  Freeviewing has one
>big advantage:  You don't depend on a device to see
>stereo.  But if you have a viewer on hand, why would you
>freeview?
>>>>
>
>I agree with this question, but with the stipulation that it be a good
>viewer - not some plastic lorgnette.


As someone who enjoys parallel freeviewing, I have to take exception.
As was pointed out recently (again), I believe most recently by Mr.
Klooswyk, us near-sighted folks can parallel freeview at extremely close
distances.  I just checked my own measurements.  Without my eyeglasses
(another advantage!), I can sharply parallel freeview a stereo card 8
inches from my nose.  I measured one of our stereoscopes, and it
positions the card 6.5 inches from my nose when focused through not one,
but *two* sets of lenses, since I must wear my distance correction
prescription eyeglasses in order to focus the stereoscope (which as we
know places the image at "infinity").  My myopia is not extreme, so I
suspect there are many, many people in a similar situation.

The difference in magnification between 10/8 = 1.25 and 10/6.5 = 1.5 is
not that great, and the lack of two sets of glass more than compensates
for any "loss of detail" from the slight decrease in size.  (And the
possibility exists that people with even more extreme myopia could get
better magnification without a viewer than with!)

So before you guys go making grand generalizations about the supposed
advantages of viewing through glass, make sure you take into account all
of the factors.  George's contention that one should use a viewer anyway
seems to be based solely on magnification, but I don't agree that a
quarter of a power (in my case) is going to make a huge difference.  It
certainly is not going to make as much difference as seeing without
ordinary glass, as only the best stereoscopes are achromatic.

Please note that this applies only to images which have already been
enlarged!  Freeviewing 35mm stereo slides is not nearly as rewarding as
viewing them through a good achromatic, lighted viewer, with 5x or more
magnification.

     -Greg W. (gjw@xxxxxxxxxx)