Glare, flare, internal reflections and veiling??? Someone care to explain? (2 Viewers)

All,

Some terms I'm hearing used to describe binocular shortcomings... glare, flare, internal reflections, veiling, ghosting, haze, and stray light. Are these being used to describe the same thing? or are they very different phenomena? I've heard of a few others, but they are escaping me at the moment... (well into a bottle of red at the moment... of course, I only do this for the health benefits). B

Feel free to jump in with your .02....

CG

I think thaey are personalized, but there are patterns in the terms:

Glare: seems to be used somewhat generically: you notice that nearby
out-of-field light disturbs the view with extra light.

Glare can also be something bright actually in the field spilling over into
something dark next to it. I have a ~25 yr old roof monocular where that happens.
Resolution is fine, but then it breaks down near sunny, contrasty situations. This may happen
due to bits of dust in the ocular or inadequate coatings/dust on the prisms.


Flare: often mentioned as noticeable light streaks or flashes in or near the image
field. The "ring-of-fire" effect at the edge, from lights or the sun,
a light-splash across a zone.

Internal Reflections: this is just some lack of internal absorption that is presumed to
aggravate the results things and diminish contrast. Someone feels this is a
root cause or factor in those effects.

Veiling: mostly covers my main peeve. I call is 'hazing', but it's a widespread milky
light leakage that spoils proper contrast and color saturation in the image.
You could get it from off-axis sunlight, or in winter, from bright diffuse snow
light pouring into the objectives without being filter by an iris or flat black walls.

Ghosting: at least the eyepiece/telescope-derived term, can refer to reflections
inside the optics that cause you to see faint de-focused images of internal parts.

Haze: likely my term for "veiling": diffuse milky background that spoils the contrast.

Stray Light: big general term for all confounding light types.

I've posted many times on this subject, so I won't re-hash everything. Here are the basics of what I've found from examining binocular interiors under the conditions that cause these things.

Nearly everything that is called glare, flare, veiling glare, haze, etc. is caused by glancing reflections from lens edges or the metallic surfaces of objective lens cells, focusing lens cells or prism shelves. The left photo below shows an example of what that looks like - a fuzzy haze of light overlaying the image, sometimes looking like an unfocused crescent moon near the edge of the field. The middle photo shows the cause - objective lens and focusing lens cells inadequately baffled against a very bright off-axis light. In this case the source of glancing light is so bright that it even causes some back reflections from lens surfaces (the colored reflections) and lights up every dust mote on a relatively clean objective lens. The only reflections that contribute much to the fuzzy haze on the image, however, are the bright ones coming from the bottom edges of the lens cells (blown-out from overexposure in the photo).

Occasionally there are similar reflections coming from the edges of eyepiece lenses or spacers between the eyepiece fieldstop and the eye. They can cause a ring of defocused reflections in the black area just outside of the image field, but not typically within the FOV.

The right photo shows ghosting in a binocular. In this case the ghosts are the dim "triangles" scattered around the field. They are duplicate images of the brightest parts of the very bright halogen lamp light source on the left. We birders don't see much ghosting under daylight conditions, but it can be a problem in astronomy for a few bright objects like the Moon, Venus or Jupiter. It's caused when a glass surface reflects forward to another backward facing glass surface and then back to the eye.

Another reflection problem I've noticed mentioned happens when there is a bright light source behind the observer, which reflects from the eyepiece glass backwards into the eye.

I think the term "ghosting" should be limited to what it really is. As for all the the other glare/flare terms, I prefer "veiling glare", but the term used is less important than understanding the causes.

Good answers all, and Henry's photos really drive it home.

Ron

Was the Graf Spee a Pocket Battleship, Battleship, or Battle Cruiser? It depends on who you ask. Also, some very experienced folks in different countries use the terms differently.

There was once a LARGE antifreeze spill on the way to Bellingham, WA--as the sun was going down. Some radio reports indicated the liquid was GREEN; others YELLOW. Who was right? Or, more precisely, at what point does yellow become green--or vice versa?

This has to do with PHOTOPIC vs SCOTOPIC sensors.

It's the old "What constitutes a 'GOOD' binocular."

Back in my hole, now.

Bill

After all the cleanings and range-testings, I tend to think of it
more in terms of the source. Nicotine film is fascinating...looks smooth
and only slightly yellow on the surface, causes a uniform smoke haze from molecular
scattering. The contrast loss in many recent binocs is a bit blotchy and subtle
but it messes up looking into shadows. Fortunately, about 1-2 yrs ago the makers
started taking front suppression seriously again. The "ring of fire" problem was in a lot
of 8x40s but quieted down a year or so ago. About the time I started wishing for
better irising it filtered into the products again. There are still shiny plastic ribbed
moldings that they should just cheaply sand-blast but that's in lower cost models.
Many roof units I tested today had 2-stage suppression up front...a far cry
from 3 years ago.

In a nutshell, I think the fuss about stray light will go down now as the makers
add proper front end work to all models.

Bill,

Thou speaketh in parables, but your point, I believe about subjectivity and navel contemplation, is well taken.

But...wouldn't an enemy sub captain have the common sense to surface against the rising or setting sun, make a quick sighting and fire a torpedo? Surely the suppression of these effects was highly desirable, for survival on that boat, lit so plain in the periscope's view.

That's how birds treat me, anyhow. Except for the torpedo.

Ron

Now that's some poetic parable-wielding! We were just watching 'Red October'
last night. I think you mean....what about sensible use of the widget?

The winters here (NE Massachussetts) can have a lot of brilliantly-lit snow-pack under
a shady canopy, though. It's hard to duck-n-cover from that. I was despairing the
leakiness of roof binoculars, and then, more appopriately, the lack of good old-school
front irising and flat-black wall coating, and my antique binoculars were beating the
pants off the newer stuff, but now the tide is turning, and yesterday I saw about
a dozen pairs, mostly roof, with two-stage light suppression, a 2-step iris/tunnel
and then a ribbed cone. Some binoculars from the middle period, say 2006-2012,
benefit a lot from a hood, not just for strong direct light but for strong diffuse like
snow-pack. Old Bushnell Customs and high-power Selsis have amazing contrast
under such lighting.

But...the 'back-to-the-future' trend in front irising is well underway now.
What I saw from Vortex, Carson, Nikon, and Leupold yesterday shows...they get it.
What's brightness without contrast to make it into information?

ON,

Glad tidings indeed! Recent and exalted binoculars such as the Zeiss FL and worse, Swarovision, are not so hot in this department. They say the Zeiss HT has done something about it. But how did baffling, which had been perfected, become a lost art? I can believe your old Bushnell and Selsi get it right although I haven't used those. I like the Leica Trinovid in this way.

Ron

I can only guess they thought the finer coatings made worries about stray light
a thing of the past. Two problems with that I can think of: 1) any tiny dust mote or nit
lights up with all the ricochets from glossy surfaces, and 2) multicoatings reflect like
crazy well off-axis (as you can see looking at the light show from outside).
They might have also assumed that more light overcomes a lack of contrast.
Amplifying noise only makes it worse, though. Worse with increasing brightness
in this case.

This kind of thing happens a lot in the specialized modern world, like the insulation
standards for moisture barriers that actually caused the house mold crisis. It assumed
absolute perfection in sealing the walls. The codes have since been totally redone.
Doctors might fix one thing and cause another if they don't check with others.
You have to design for lifetime and for the whole system, not just the day of manufacture
and ideal cases. Without some baffling, you could be cleaning all the time or to
ridiculous levels to keep the noise out.

I have yet to see the beautiful pitch-dark lamp black interiors of the oldies,
but we're getting there.

My experience with glare problems is different from O_N's. I haven't observed any general pattern of worsening or improvement through time. Some old binoculars have better glare resistance than others and the same is true for new ones. I use a controlled lighting set up, so I can compare glare resistance consistently and I use a magnifier to examine the binocular interior from the rear under the test conditions that produce glare. The cause is not difficult to identify. It's always a bright spot or ring of glancing light at or near the edge of the exit pupil, like the one photographed in post #3. It can happen in binoculars that look well baffled from the front, when the baffling is not properly sized or positioned as is surprisingly often the case.

I seldom find glare to be so poorly handled that it's a deal breaker, but here are a few suggestions if you are very concerned about it.

1) Buy a Leica binocular. In my experience the Trinovid BA/BN and Ultravids have very effective baffling.

2) Buy a large exit pupil binocular. Even when the baffling is not so effective the glare at the edge of a large exit pupil usually falls harmlessly on the iris of the eye. It may be there, but you don't see it.

3) Check out some cheap binoculars. Many inexpensive binoculars have good glare resistance as an accidental byproduct of poor design. Sometimes there are (apparently deliberately) undersized baffles behind the objective lens that reduce aperture and block the glancing reflections from edge of the lens (as well as a portion of the lens itself) or a prism cluster will be so undersized that its undersized opening accomplishes the same thing.

Strategies, in a nutshell ?

1) Come up with $1400
or
2) Buy some BIG nautical binoculars that always exceed you own pupils
or
3) Look for cheap happy accidents (not sure how to gather and pick those)

Not sure how to put all that together, but I found some wonderful visible improvements
at the Kittery Trading Post over the 2012--2014 period, at moderate prices,
especially in roofs.

Thanks guys... and I had been thinking of ghosting in TV image terms. Still learning...

CG

Ghosting was a bigger problem with advanced eyepieces and single coatings,
in the 70s and 80s mostly. The real thing (ghosting) is similar to TV ghosting,
but you are looking at your eyelashes and retina, etc. It's been rare since.
At first, they just 'didn't go there'. Now, quieter coatings make ocular design
more flexible. It will make cleaning trickier in the future, though.

Old thread, but I rather surf on an old one than to clutter the forum with even more threads.

Last few weeks I noticed with my Nikon mhg 8x42 internal reflections (flare? Two big light spots, red and green. And ghost? A tiny rainbow colored speck, each side gives the exact same effect in each eyepiece) when the sun is a bit sideways behind me. This was easily tracked down by coming from sunlight leaking by the sides of the eyecups.

First, as the thread topic, I'm wondering if this has its own terminology? I read some threads and sometimes someone starts to speak of stray light or internal reflections from back/sideways leaking in besides the eyes, and others flip over talking about flare by stray light in the objectives giving internal reflections. That's where the flare discussions seem focused on. The nomenclature seems vague and ambiguous, or isn't it? I'm a newbie at the tech aspects of optics, trying to learn, and English isn't my main language so maybe I'm just missing nuances when people speak about flare?

Secondly, I read many people use winged eyecups to keep stray light out from entering. That made me wonder if this phenomenon is something normally occurring and maybe even somewhat unavoidable? I never read about it in binocular reviews or read it mentioned much in bino talk nor do I remember noticing it before in my earlier Meostar.
Is it something taken for granted or overlooked, or found not so important as other aspects and easily solved by winged eyecups? Seems strange to me such an added solution would be thought as normal, and an internal solution inside the bins wouldn't ?

Hope you guys can help me develop my apprehension of all of this a bit, thank you! Sorry if I'm asking for familiar or silly stuff, one doesn't know what one doesn't know, now does he (whaaaat?!) B

To me, a ghost image is a fainter version of something bright in the view but it keeps the same shape and some of its details. Pretty easy to identify at night when looking at the Moon and everything else is just black sky - the ghost is then a fainter image of the Moon. A not too close streetlight works too.

Depending on the size of the ghost Moon you can identify if it comes from a flat surface (no magnification difference) or a curved surface (smaller or larger); depending on how it moves you might identify if it is internal to the instrument or if it is a reflection between your eye and the eye lens.

Henry (post # 11),
Thank you - that‘ good solid advice from you (as always).
In addition to the Leicas you mention, I would have added the Nikon EDG which in my experience controls stray-light better than most premium binos.

May I add my 2d's worth... Swaro 8x32 Field Pro, only 2 months old. Yesterday I experienced true veiling glare for the first time (sun about 15° above my view) but here's the odd thing... concentrating on the veil I could see my floaters quite sharply (I'm 73 so have plenty to spare!). Can anyone explain why they are visible?

I find the more plain/even/white/flat a view is, the more I become aware of my floaters & sinkers.
Looking at a white wall, the ceiling, net curtains, or the sky they are most obvious.
Looking at a contrasting jumble of shapes and colours they effectively vanish.

Thanks for that, it helps explain it. I also realised that the floaters are most obvious when the background is dark (e.g. trees) and the veiling glare is strong.