Glare (1 Viewer)

The biggest problem I have with optics is glare. I don't know if I am using the correct optical term, but what I mean is the problem of being in a relatively bright place and looking in the general direction of the Sun. What happens is that I get a foggy look, sometimes so extreme that I can't see anything.

In my very limited experience some binoculars and scopes are horrible and some are excellent. None of this 90% of the best business.

I seem to be always running into this problem. Yesterday I had a Red Tailed Hawk cruise right over my head at 30 to 40 feets and then land in a tree 50 yards away. I could barely see it through my B&L Discoverer 8X42 Porro's, but I could see it to some extent. I am sure that if I had the same thing happen to me in Nov. to April with not leaves on the trees and all the light colored leaves on the ground it would have been much worse. I have had rifle scopes (Burris and Weaver) that show nothing but a bright yellow fog if you look within 20 degrees of the Sun in November.

The only optical instrument I have ever looked through that really minimized this are Leupold rifle scopes. These scopes have a reputation of being mediocre optically but you can see things clearly through them even when looking in the general direction of the Sun.

To me glare control is the most important feature of any optic to be used outside, but rarely mentioned by anyone reviewing optics. When it is mentioned, it seems to be an afterthought. Is there any place I can find comparison of different binoculars with respect to this problem. Is the problem solely controlled by internal "baffleing", whatever that is?

To me, worrying about resolution in arc seconds is absurd if you have even moderate glare problems, which makes it difficult to see any detail f you are looking in the general directlon of the Sun into a woodsy area. Many of the birds in my area have the annoying habit of landing in trees with no regard for the fact that they are in between me and the general direction of the Sun!

By the way, my B&L Discoverer's do very well the streetlight at dusk test. Its that annoying Sun and woods problem the is their downfall.

In my experience "glare" is nearly always caused by an internal reflection which appears at or near the edge of the exit pupil. Typically in binoculars the cause is a lack of effective baffling at the edge of the objective, the edge of the focusing element or the first aperture of the prism cluster. You can see it as a bright crescent of reflection at the edge of the exit pupil if you hold the binoculars away from your eyes. It's easy and cheap to get this right. Amazing that it often isn't done well, even in expensive binoculars. It's usually less of a problem in large exit pupil optics because the light from the edge of the exit pupil may fall harmlessly on the iris rather than enter the lens of the eye in bright daylight.

Here's an example. This reflection comes from a bright sky with the binocular pointed into a dark area. In the binocular image it looks like a fuzzy half moon of unfocused light covering the lower part of the field.

This is an interesting topic to many I suspect (including myself). I agree with Rip that loss of image quality when looking toward sun and/or other brightness is a key and understated issue with optics. I also agree that there seems to be a lot of variation between makes and models in regards to the issue. (FWIW - I believe I've noted a consensus here that Leica is the master of glare control. My experience confirms this notion as well.)

There seem to be different types of image problems related to this issue. Sometimes, it is a bright "glare", sometimes there is just a loss of contrast, or loss of sharpness and/or foggy image, etc. Is there a difference between "glare", "flare", "stray light", etc, or are they all the same basic problem?

APS

A curious producthttp://www.camouflage.com/howardswork.php about wich I haven't any experience. In any case the angular space the sun makes "difficult for binoculars" depends on the optics you use. My 8x32SE suffers more than the 8.5X42EL as I experience day after day. The underlying theory wich explain it is unknown for me.

I went to store yesterday to check out some binoculars. I have found that many binoculars, from $50 to $1000+, have a common crescent looking spot next to the perfectly circular exit pupil in the center. Please see the picture below. It is on the right side of the exit pupil. While using a relatively expensive pair (close to $900) with this problem, I didn't see any glare or flare, whichever way you want to describe it.

I am wondering what is causing this and how come I didn't see much optical quality degradation with this apparent "defect". Any advice is greatly appreciated.

Thanks

APSmith said:

There seem to be different types of image problems related to this issue. Sometimes, it is a bright "glare", sometimes there is just a loss of contrast, or loss of sharpness and/or foggy image, etc.

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Is there an emoticon for pickyness?

The resolution (sharpness) doesn't change as the contrast is reduced but the acuity does.

Of course the effect is the same ... you can't see the damn bird properly.

Is there a difference between "glare", "flare", "stray light", etc, or are they all the same basic problem?

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It seems a lot of people on this forum use these terms interchangeably though they aren't the same problem.

I'd group "glare" and "stray light" together as a general reduction in contrast coming from light that outside of the desired image.

You can verify this by using a hand to screen the light from falling on the objective. I notice this with some of my glasses (e.g. Minolta Compact) in overcast skies but it's much less of a problem in sunny skies. In cloudy skies there are more directions the light can come from to hit just "right" and spoil the contrast. THe effect is as Henry describes it an overall washout of the image with a brighter crescent, in this case at the bottom of the image from the clouds above.

Of course glare also has some other common meanings

http://en.wikipedia.org/wiki/Glare_(vision)

"flare" is a different problem. It's related to the reduction in contrast in the dark parts of the image from bright light inside the image e.g. looking for plumage details in a bird sitting on a branch with sky or bright cloud behind it. With more flare the light gets scattered between the lens and is noticed in darker parts of the image reducing contrast (and so acuity).

Lens and prism anti-reflective coating are the techniques used for reducing flare. The better the AR the less the flare. In less well coated lenses you'll see flare as bright spots and rings.

Wikipedia has a good article (with pictures) on lens flare

http://en.wikipedia.org/wiki/Lens_flare

But bins with flare are great for UFO hunters

http://valuca.piczo.com/LensFlare

Perhaps there should be a birdforum glossary (in the wiki?) that defines each of these terms.

Or does that seem way too organized

EDIT: rereading the wikipedia article I see they define flare as unwanted light in the image from reflection or scattering in the optical elements and then say "When a bright light source is shining on the lens but not in its field of view, lens flare appears as a haze that washes out the image and reduces contrast.". I guess we just need to get people to define their terms. Or at least use the phrase "stray light" for that type of problem.

Of course if we use "barndoors" on our bins then the problem will go away. THis is a bit of a joke but adding len shaes (made from black pipe) to the ends of the objectives you could easily reduce this problem.

And "veiling glare" is yet another term for it as shown (and measured) by this rather excellent page (and not because he uses the terms "flare" and "glare" the same way I do).

http://www.imatest.com/docs/veilingglare.html

Veiling glare is stray light in lenses and optical systems caused by reflections between surfaces of lens elements and the inside barrel of the lens. It is a strong predictor of lens flare— image fogging (loss of shadow detail and color) as well as "ghost" images— that can degrade image quality in the presence of bright light sources in or near the field of view. It occurs in every optical system, including the human eye.

Lenses with low flare have been traditionally known for their excellent color performance. Color saturation is higher, especially in shadows. Low flare may be as responsible as sharpness for the exalted reputations of some classic Leica and Zeiss lenses. Even though lost color saturation and contrast can be recovered with digital processing, lenses with low flare will always have an edge in quality.

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I wonder if flare (i.e. dark image detail in a bright image) is another area where a porro prism bins can beat roof prism bins at a lower cost by reducing the number of air/glass transitions? Or do modern multi-layer AR coatings make this a moot point?

I never know what to call these various scattered light phenomena, but I hate them too. This spring, we were going to watch some owls and their young at dusk a lot of evenings. They were living in a hole in the side of a rocky canyon wall, and we had to look towards the setting sun, at the dark cliff wall. Bright sky was either within or just outside the field of view, and we were trying to see owls inside the dark hole, and as they moved about on ledges. This was very difficult lighting for these kinds of problems.

The very best of my binos, in fact nearly perfect in this regard, was a Fujinon FMT-SX 7x50. My wife's 8.5x42 Swaro EL and my 8x42 Leica Trinovid BA were quite good but not as good, with the EL edging the BA a tiny bit. MUCH worse was a Fujinon FMT-SX 10x50. Once my wife forgot her bino (!!!) and was harshly punished by having to use the Nikon 8x25 Travelite that lives in the car. You could not see a cotton picking thing for the glare in that one.
Ron

I experience glare/flare or whatever on a monocular I purchased. Although the inside was painted matt black at low angles it appears no longer matt and there is a lot of light reflection even on a black surface.

I lined the inside of the monocular with a black felt which performed much better then the paint.

On telescopes they use baffles along the tube to suppress reflections.

I suspect that the better binoculars also use baffles and have a better quality matt paint/material on the inside.

SG6 said:

I experience glare/flare or whatever on a monocular I purchased. Although the inside was painted matt black at low angles it appears no longer matt and there is a lot of light reflection even on a black surface.

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Even a matte black painted surface will reflect around 1% of the light hitting it. At specular it might be even more.

So if you need a black target you need a "black hole" -- not a supermassive star but a black box with a hole in it and light absorbent (scattering) material inside away from the hole as a real "black" target. See the link I posted on measuring veiling glare above.

SG6 said:

I lined the inside of the monocular with a black felt which performed much better then the paint.

On telescopes they use baffles along the tube to suppress reflections.

I suspect that the better binoculars also use baffles and have a better quality matt paint/material on the inside.

Click to expand...

Usually they do this by modifying the inside surface of the optical tube so it is no longer flat and so no longer can generate specular reflections that go down the tube. Or they can do as you did with the felt and put in a material that absorbs a lot of light but doesn't generate a specular reflection. The light that isn't absorbed is scattered over a hemisphere (2π steradians).

For example, you can cut grooves inside the optical tube that have a sawtooth shape with the long side pointing down the tube. In a telescope design the short side might even be highly reflective (the best way to get rid of stray light is to reflect it out the entrance of the tube. That may or may not work with a lens assembly at the end of the tube. The shape has to be optimized so stray rays can't take an different route to get to the eye.

e.g. http://www.freepatentsonline.com/5189554.html

You also see this on porro prisms (and roofs I supposed) with a stop at the entrance of the prism to cut down stray light getting beyond that point. Baffling the sides of prisms helps too (so stray light can't bounce into them on a face that's not suposed to get light).

A S&T article shows how you can do this on a Newt. Interesting to look at just to see how many different places need some baffling when cleaning up a inexpensive Newt.

http://gmpexpress.net/~tomhole/baffling.pdf

Once again doing the design work properly is the key and is the sort of effort that gets puts into an expensive scope or bins though I think the cheaper ones could do better than they do. But then you wouldn't by the more expensive products.

Last night I was testing some bins against stars and Jupiter's moons with a bright moon in the sky just 10° from Jupiter. That test really showed up the difference in stray light handling of the four bins I've been looking at. It's a lot easier to see stray light I suspect the worst of the bins (a Vortex Hurricane 8x28) was suffering exactly the sort of bounce of the optical tube you describe - with a great crescent of stray light on the opposite side of the image from the moon.