- quote -

Yes, I did measure the lens diameter only not the exit pupil.

- quote -

Excuse the delay. OK as far as the "exit pupil diameter" sitting 12-13 mm
behind the eyepiece. The question (puzzlement) is this. If I look at a
visual scene my 5mm scotoma occupies so much of my visual field.
Computable. But if I put the 7x's to my eye (blocking the good/better eye)
the view is much more enhanced. Much more than if I walked 7x closer, it
seems. The central field (5 degrees) is much more clearer. There is the
angular multiplication of course involved, but the scotoma just looks
reduced significantly. The low vision specialist is not considered now
since the better eye is better than 20/20. But the reduction of the scotoma
on the binocular (ok monocular) view is the question. Originally I had
thought there might be some principle of light magnification (more light)
involved that would enhance the central view. But I am gathering the answer
is no.

Thanks all for comments,
Don W.

WTF is Bev on about?

I will assume tha tyou are raving about Don's response about exit pupil
diameter.

I think Don got the wrong figures. He seems to be measuring the lens
diameter, not exit pupil.

The exit pupil, Don, is an optical point, in this case probably 12-13mm
behind the back of the eyepiece. It can be made longer or nearer
depending on what the designer wants to achieve. For example,
Eschenbach make low vision aids with exit pupils at 18mm to enable
spectacle wear while viewing with the telescope.

What is an exit pupil? This is the point that the light crosses that is
designed to be where your pupil sits when looking through the system.
If you are not at the exit pupil, then your field of view will be
smaller. The exit pupil if designed correctly and matches the pupils
size will transmit the maximum light possible (especially if the front
lens is a large diameter) which would produce the relative improvement
in brightness.

Don, if you are having issues, you would be well advised to see a low
vision expert and get some aids to give adequate viewing for the tasks
you need. Low vision aids are different from standard telescopes as
they are designed to be smaller and lighter in most cases so the can be
easily transported and stored in pockets. They are generally designed
to be used monocularly to achieve better magnification.

Best of luck

dr grant

Don,

On 3/13/06 10:54 PM, in article RMtRf.324$uu6.286[at]fe06.lga, "The Real Bev"
<bashley101+usenet[at]gmail.com> wrote:

- quote -

Yes. Wrong. Very often the exit pupil of binoculars is smaller than a dark
adapted eye. Bird watchers, for example, may want relatively high
magnification without the weight of large optics. Naval officers will want
to have "night glasses."

To estimate exit pupil size, take the diameter of the objective and divide
by the magnification. Thus the exit pupil for 7x50 is about 7mm. Note that
almost all optic sizes are measured metrically. I do remember control
drawings in which metric sizes wer converted to inches.

Bill
-- Ferme le Bush

Salmon Egg wrote:

- quote -

I would guess that all binoculars have roughly the same size exit pupil, the
main difference being in focal length and [big] lens diameter. Wrong?

--
Cheers, Bev
**********************************************
"I've had a Lucas pacemaker for years and have
never experienced any prob

On 3/13/06 8:41 PM, in article PPrRf.253$GM6.113[at]fe07.lga, "The Real Bev"
<bashley101+usenet[at]gmail.com> wrote:

- quote -

I am not sure what you are getting at because you did not quote the
pertinent part. IIRC, the binocular spec quoted by the original poster was 7
X 19, That makes the binocular's exit pupil SMALLER than the eye's pupil.
There is an inconsistency in the OP.

Bill

-- Ferme le Bush

Don W wrote:

- quote -

Why is the answer to the question NOT "Because the diameter of the binocular
lenses is bigger than the diameter of the lens of the eye"? Did my friend
really waste her money on that honking monster lens so she can take pictures
in near darkness?

Yeah, I'm testy today...

--
Cheers,
Bev
================================================== =====================
"Lord, grant me the serenity to accept the things that I cannot change,
the courage to change the things I can, and the wisdom to hide the
bodies of the people who pissed me off."

On 3/11/06 10:22 AM, in article
gzEQf.19659$NS6.16991[at]newssvr30.news.prodigy.com, "Don W"
<dwilgus[at]prodigy.net> wrote:

- quote -

setting the exit pupil for the system. With the eye's position at the
optimum spot, the exit pupil should have a diameter of 19/7=2.7mm. Most
binoculars do not fully utilize the calculated exit pupil. In any event,
getting maximum illumination onto the retina is not going to be the
limitation when there is a true permanent scotoma.

Bill

-- Ferme le Bush

- quote -

Yes, diagnosed as permanent scotoma, as far as I know.
Please see above reply for spec.

Thanks.
Don W.

"CatmanX" <drgrant[at]ozemail.com.au> wrote in message
news:1142049577.655414.79240[at]v46g2000cwv.googlegroups.com...
- quote -


This is the effect I am seeing with a conventional 7x binocular. The exit
pupil image enhancement math presently eludes me. The binocular is 7x, I am
just looking thru one one side, the scotoma side.
Entrance pupil diameter of binocular = 0.75 inch / 19 mm
Exit pupil diameter of binocular = 0.43 inch / 10.9 mm
Eye pupil diameter = 0.150 inch / 3.8 mm

The binocular is a Nikon 7x20 7.1 degrees.

So does the math agree with what I am seeing??
Thanks for any inputs.

Don W.

On 3/10/06 6:19 PM, in article
LsqQf.21129$tb3.7014[at]newssvr24.news.prodigy.net, "Don W"
<dwilgus[at]prodigy.net> wrote:

- quote -


You made a trick question out of your inquiry by leaving important
information out.

Are you talking about a permanent scotoma? How bi a field of view does it
cover? Do you have a diagnosis.

I had some similar problems which later turned out to be ocular migraine.
Fortunately the scotoma was temporary. Well, at least until I had a more
serious problem that I took to be a recurrence of the migraine.

Bill
-- Ferme le Bush