Does higher power demand fancier optics? (1 Viewer)

[OPTIC_NUT]

Just to ballpark the figures and refer to a less "specious google"(?) ref, here are classic empirical
and a modern theoretical figures:

http://www.tazz.ch/PDF/Visual acuity and its measurement.pdf
Dept of Opthalmology, U.California.)

"
Robert Hooke reported the first systematically documented measurements
of the visual power of the human eye. He realized that two stars must
be separated by more than 30 seconds of arc to be detected as
two independent light stimuli.
"

"
Theoretically, the maximum resolving power of the human
retina could be derived from an estimate of the
angle of approximately 20 seconds ofarc because this
represents the smallest unit distance between two
individually stimulated cones
"
(at the center of the fovea)


----------------
So we may have a range to investigate around, that is, more or less than 20-30 arc seconds (Best).
Not only that, but this range appears to have survived from 1647 to today, and also to match eye theory
into the 21st Century. Seems fairly non-spurious.
-------------------


The issue with lines is....how wide a line, its edges compared to the gap, etc.
Gaps in solids, like the opening in the letter C are mentioned.
An interesting shape would be two thick black block areas with a small white gap between them.
Detecting the gap well would signify two edge-widths, actually. The acuity decay fills in
that gaps from both sides. So a gap of 60 arc-seconds would be the best performance.

I understand the thing about 'peak acuity' being at a meter. Since most people's eyes
are not corrected perfectly at a distance and can vary, you cannot achieve best acuity
under normal coricumstances. You would need a gadget past your corrected eyes with very finely
adjusted extra correction.


--------
OR...if we assume fine binoculars exceed the human eye's resolution by a wide margin,
we could simply focus those and factor them in.

But....that (binoc resulotion far exceeding eyes) means that the standard "tapered bunble of stripes"
on the resolution charts should do for checking the eyes. OK....looks like an empirical
measurement strategy is nominated.

 

[OPTIC_NUT]

Somebody'd done some checking, albeit in 2006:

http://www.cloudynights.com/item.php?item_id=1410

4 models, using the chart, 100 to 200 arc-seconds,
noticing tripod vs. handheld resolution.


The 8x40 Swift gets to 97 arc-seconds handheld, 154 arc-seconds mounted.

"... essentially no difference between the 10x50 and the 8x42.
And there was not much difference even with the 12x50,..."

Same limits, almost. Put another way, you reach a limit the extra power cannot get you past.

 

[elkcub]

You might be interested in a somewhat more general analysis done by Daniel Vukobratovich in 1989. He's the same guy who co-authored the 2011 SPIE Field Guide to Binoculars and Scopes, where the concept of efficiency (E) is also discussed. Notice in Fig. 1 that the hand-held curve reaches an asymptote of about E ~ 6.7 with increasing magnification.

Ed Zarenski's CN article has particular merit for examining different methods for steadying the binoculars.

We've discussed this topic on BF several times.

Ed

 

[OPTIC_NUT]

That's a fascinating article.
Looks like the main point is the severe effect hand tremor has on performance.
...and the severe rolloff in extra performance as the power goes up.
I should keep working on making my shoulder stabilizer less clunky to set up.

The article does differ from the Cloudy Nights observations
in the the performance limit of high power is purported to be mainly a
function of shake, whereas in the Cloudy Nights observations,
the high power reaches a limit on the tripod as well.

So...that edge limit mystery continues.

 

[bh46118]

At low magnification does a person shake the same amount as when viewing at higher magnification, the lower mag making the shake less visible ? Or when viewing at a higher magnification, does your ability to see the shake more clearly cause an exacerbation of the shake ?

 

[OPTIC_NUT]

At low magnification does a person shake the same amount as when viewing at higher magnification,

Right: the shake is the shake. ...the same, likely.

the lower mag making the shake less visible ?

Yes, but there seems to be some extra effect.

Or when viewing at a higher magnification, does your ability to see the shake more clearly cause an exacerbation of the shake ?

Not seeing the shake more clearly, exactly....more like, the speed of the shake
(how fast a point on the view zips back and forth across your retina)
makes it hard to track the movement and compensate for it.
As I found out with the laser pointer, your eyes are always subtracting a
huge amount of shake, but it looks steadier to you than it is.
Making the shake 'bigger' should actually make it easier for your cortex to figure it out,
but the shaking (in rods/cones per second) is faster. At some point your optic cortex
can't keep up. As an extreme case, I can hold a 40x spotting scope by hand,
and I can barely figure out what's there, even if I focused it on a tripod beforehand.
My brain just can't stitch the picture together from all the shaky images.

Also, your eyes can only capture about 20 frames/second
(so flicker-free monitors have to run at twice that).
A lot of shake will cross a big distance frame to frame, and it gets
hard to figure out (in the cortex) what happened.
(just another way of saying it)

If you put the binoculars in a binocular tripod adaptor,
you see things much sharper, but when I do that with 10x
I only see a little sharper than 7x. Now...that part is something different
(that I'm not sure about). You can keep going to 200x with a telescope,
but that has a much longer barrel (even with the same aperature up front)...
...so I'm thinking that is part of the problem...the relative length.

 

[elkcub]

At low magnification does a person shake the same amount as when viewing at higher magnification, the lower mag making the shake less visible ? Or when viewing at a higher magnification, does your ability to see the shake more clearly cause an exacerbation of the shake ?

Your question (statement?) is a good one. There may be a visual-motor feedback that would lead to an 'observer induced oscillation.' :t:

However, I would also expect to see considerable variation between individuals due to grip, stance, instrument weight, muscle tone, hold duration, etc.

Ed

 

[WJC]

Your question (statement?) is a good one. There may be a visual-motor feedback that would lead to an 'observer induced oscillation.' :t:

However, I would also expect to see considerable variation between individuals due to grip, stance, instrument weight, muscle tone, hold duration, etc.

Ed

Boy, Ed, I thought Peter's list was geeky. I don't think it can hold a candle to BF! I'm glad I just had to fix the suckers.

The sad thing is that so much of our whines, dreams, opinions, and speculations are virtually useless--barring any ego pumping. The telescope maker gets to decide on: aperture, configuration, focal length, focal ratio, baffling, smoothness of surfaces, types and magnifications of eyepieces, and more.

If we want--need--an instrument that's better in some way . . . we have to BUY IT!

Cheers,

Bill :hi:

 

[NDhunter]

Boy, Ed, I thought Peter's list was geeky. I don't think it can hold a candle to BF! I'm glad I just had to fix the suckers.

The sad thing is that so much of our whines, dreams, opinions, and speculations are virtually useless--barring any ego pumping. The telescope maker gets to decide on: aperture, configuration, focal length, focal ratio, baffling, smoothness of surfaces, types and magnifications of eyepieces, and more.

If we want--need--an instrument that's better in some way . . . we have to BUY IT!

Cheers,

Bill :hi:

Bill:

This is from the recent press release from Zeiss about the new Victory SF 42 binoculars.

"Unlike conventional binoculars, the focal point of the lens was shifted further back towards the eyepiece. This makes it possible to support the VICTORY SF on the head, for comfortable, relaxed viewing over extended periods of time."

Could you comment on how the length of the focal point
can make changes in what we see ?
Does longer make things better or not so much.

Also, if you or some others know how some binocular models compare in focal length.

I have not seen much discussion on this topic, and now Zeiss has promoted this feature in their big blast on their new uber binocular.

Jerry

 

[henry link]

Jerry,

I think that was a garbled way of saying that the focal point of the objective lens falls within the SF eyepiece rather than in front of it. That's because the eyepiece almost certainly has a negative field group (similar to a Barlow) placed in front of its focal plane as in the EL SV.

Most of the simple binocular objectives I've measured have had focal ratios between f/3.6 and f/4.2. I think some of the compound objectives in binoculars with internal focusers have effective focal lengths that are even faster, approaching f/3.2. Most binocular objectives have alarming levels of aberrations at full aperture, which are made visually acceptable by the low magnification. In addition those of us who use binoculars during the day benefit from our pupils closing down so that we only see the aberrations generated by the rays from of the central part of the objective that can actually enter the eye.

Henry

 

[OPTIC_NUT]

Most of the simple binocular objectives I've measured have had focal ratios between f/3.6 and f/4.2. I think some of the compound objectives in binoculars with internal focusers have effective focal lengths that are even faster, approaching f/3.2. Most binocular objectives have alarming levels of aberrations at full aperture, which are made visually acceptable by the low magnification. In addition those of us who use binoculars during the day benefit from our pupils closing down so that we only see the aberrations generated by the rays from of the central part of the objective that can actually enter the eye.

Thanks: that puts it together, wraps it around to the top posts.
It ties into a number of your previous posts and the observations...brilliant!

One thing you are implying is that the error is about the same high or low power
but the low power makes it less visible. That seems to be shown
in those arc-sec charts...

I am assuming that the main reason the ratios are so short is
consumer pressure to keep the length down on a hand-held gadget.
They are shorter than FOV alone demands.

Perhaps a possible reason for high-powers that don't deliver
the expected extra sharpness would be: they wouldn't sell many at the longer length.
They can sell telescopes long enough for extra detail, but that's with tripod.
An f/7 10x50 with a monopod would be nice. Doubt they would sell, though.

 

[OPTIC_NUT]

I did a little experiment today. I took the longest 10x50s I have,
the Selsi "Luminous", out to an orchard where an art show was going on.
I met a guy from my lit group with a pair of Diamondback 10x42s.
The day was bright with puffy clouds, enough to probably narrow the
pupils for both pairs. I used a monopod I made from an adjustable
roller-painter arm (much easier to make and adjust than home-made).

They were close at 200 yards on the treeline, but the Selsis could find the
feather color banding on an eagle riding a thermal over the highway cloverleaf
1/2 mile away (when it flared wings to catch the next plume). The Diamondbacks,
while better all-around closer in, just saw the silohouette. That is a
tremendous distance, mind you. They were both kind of pointless without
the monopod.

I'm going to go with
---the f/ratio dominating sporting binoculars' resolution,
(take a look at astonomical binoculars: they are much longer for the same aperature)
---and that being thus about the same with low and high power,
---and that resolution is far more like 100 arc-seconds (1.5 arc-minutes) than 1 arc-second
for the binoculars we always refer to. I think there is no way spending money alone
can get over most of the f/ratio distortion problem.

All this also jibes with my early resolution and depth of field testing with stopped-down objectives.
It all makes sense now. Some into eagles might want to look into astronomical binos, unless
the tripod drags things down too much. It's a tough decision.

One thing I wonder about: could they make folded-length (Mak) binoculars of
reasonable size for hand-held? That might kick things up to f/6 or f/8, cause major
improvements in resolution. You still would have shake to deal with, though.

 

[OPTIC_NUT]

Found some very nice work..

It all runs to some limits, though...ends up always a bit over
the human eye resolution of 60 arc-seconds apparent:

Some great measurements, involving Henry, Holger, and Professor Edz:

http://www.cloudynights.com/ubbarch...ge/0/view/collapsed/sb/5/o/all/fpart/all/vc/1

So we see...there isn't much difference in apparent resolution between super Alphas and mid-priced,
the actual resolutions are 5-10 arc-seconds, and the overall results are around 100 arc-seconds (apparent).

It seems you just run up against the human eye....maybe you could increase the binoculars length to
give you a bit more, but you run up against your own limits. It was fun adding a baffle to the front so I could
use a 10x40 with a better f/ratio, and it worked well, but I can see that's the limit. To see a lot more of the
eagles I would have to go to 25x100, and that's a monster that needs a sturdy tripod, probably my Bogen.
Total weight might go from 2 lbs. to 20. Stretching to a higher f-number at 10 might get you from 90 arc-sec to
just 60 apparent, but that's not spectacular.

You just need bigger glass and higher power. Your basic astronomicals.
Sport binocs are tweaked for practical human limits and there is little or no resolution difference from middle to super.
It would be wasted. There are other
things to work on.