Which control glare better porro's or roof's? (1 Viewer)

St. Elmo · May 26, 2015

Despite some inherent flaws that caused a parting of the ways, I used to get dangerously close to the sun with the my Leica Ultravid (non-HD) 10x42.

OPTIC_NUT · May 26, 2015

Going through a pile of vintage binoculars to see which had 'veiling glare',
I found two pair with very noticeable issues. When I looked inside, the normal
2nd stage of the baffle tunnel was not there. The threads for tunnels were there
and I was able to find fitting parts in my parts pile,
resulting in zero glare...and better contrast as well.

I don't know if they were left out in manufacturing or in a prior cleaning,
but that's a possibility when you see this issue.

"
In my experience exterior hoods are only effective against this kind of glare if they are quite long. The geometry of the situation is pretty simple. The bright lens cell reflection that causes veiling glare occurs on the opposite side of the lens from the offending light source, so a hood has to be long enough to shadow the opposite side of the lens from the source. If the problematic light source is 30º off-axis then the length of the hood needs to be about 1.5 times the objective diameter, if the light source is 15º off-axis the length of the hood needs to be about 3 times longer than the objective diameter.
"
---The assumption behind this geometry is that there is nothing at all between the objective and
the lit surfaces. I don't think I have any binoculars with no baffle tunnel at all. A short hood merely
minimizes the area the stray light splashes on.

When you shine a light in, surfaces appear to be in a line, but the effect of the lenses on what you see
hides the fact that they are not. For example, the front tunnel appears to be a straight tube, but it
in in fact a steep taper. Proper design of all the diameters keeps the stray light from ever reaching
the eyepiece. If you need a very long hood, you have no baffle tunnel at all. There are binoculars
with too-short tunnels, so it's possible...

denco@comcast.n · May 26, 2015

OPTIC_NUT said:
Going through a pile of vintage binoculars to see which had 'veiling glare',
I found two pair with very noticeable issues. When I looked inside, the normal
2nd stage of the baffle tunnel was not there. The threads for tunnels were there
and I was able to find fitting parts in my parts pile,
resulting in zero glare...and better contrast as well.

I don't know if they were left out in manufacturing or in a prior cleaning,
but that's a possibility when you see this issue.

"
In my experience exterior hoods are only effective against this kind of glare if they are quite long. The geometry of the situation is pretty simple. The bright lens cell reflection that causes veiling glare occurs on the opposite side of the lens from the offending light source, so a hood has to be long enough to shadow the opposite side of the lens from the source. If the problematic light source is 30º off-axis then the length of the hood needs to be about 1.5 times the objective diameter, if the light source is 15º off-axis the length of the hood needs to be about 3 times longer than the objective diameter.
"
---The assumption behind this geometry is that there is nothing at all between the objective and
the lit surfaces. I don't think I have any binoculars with no baffle tunnel at all. A short hood merely
minimizes the area the stray light splashes on.

When you shine a light in, surfaces appear to be in a line, but the effect of the lenses on what you see
hides the fact that they are not. For example, the front tunnel appears to be a straight tube, but it
in in fact a steep taper. Proper design of all the diameters keeps the stray light from ever reaching
the eyepiece. If you need a very long hood, you have no baffle tunnel at all. There are binoculars
with too-short tunnels, so it's possible...

Interesting that the design of the baffling is important as well. Coatings would seem to make a difference also.

OPTIC_NUT · May 26, 2015

Baffling is critical, at least in terms of covering all your bases.
If you slice out what you don't need early on, the design doesn't have scattering all through it.

Coatings can reduce some lens scattering, but that's a secondary source, and any
dust or film on multicoating can light up the 'Hi-Q filter' multicoating represents off axis.
Which is to say, short of a clean-room environment, multicoating doesn't take kindly to age.
A Takumar SMC lens, for example, can look great to the eye but have some grey level that
needs another cleaning. A little nicotine or out-gassing from within....the layers 'glow'.

The thing is, that little ring is never supposed to be lit to make the veil, or if it is hit,
it's supposed to be very thin and absorbtive, almost invisble even when lit.
That's how a 1950s field stop works, with its carbon-coated thin diaphragm.
The irises before the prisms are supposed to be beveled, not straight cut.
I'm talking about a hood helping a design that falls short, not entirely replacing it.

Either there is something to be gained when that glare happens, or its a serious desgn flaw.
If you find a long hood helps, that's really just slicing away some of a cone, cutting the whole
path down to protect something that shouldn't see that light or isn't shaped right.

henry link · May 27, 2015

OPTIC_NUT said:
---The assumption behind this geometry is that there is nothing at all between the objective and
the lit surfaces. I don't think I have any binoculars with no baffle tunnel at all. A short hood merely
minimizes the area the stray light splashes on.

When you shine a light in, surfaces appear to be in a line, but the effect of the lenses on what you see
hides the fact that they are not. For example, the front tunnel appears to be a straight tube, but it
in in fact a steep taper. Proper design of all the diameters keeps the stray light from ever reaching
the eyepiece. If you need a very long hood, you have no baffle tunnel at all. There are binoculars
with too-short tunnels, so it's possible...

The assumption behind the geometry is that the objective lens cell IS the "lit surface" and that there is nothing at all between that "lit surface" and the eyepiece. In every case of veiling glare involving the objective lens cell (which is most cases) that's exactly why the veiling glare is visible to the eye, whether there are "baffle tunnels" or not. Ineffective or only partly effective internal baffling is a common design flaw, which is why the veiling glare complaint comes up over and over.

OPTIC_NUT · May 27, 2015

Looking at this from common ground:

I will say....I do agree and understand how
having excess exit pupil allows the eye to cut the 'rind off the orange',
throwing away the veiling glare the the prism artifacts, etc. You are
stopping down the entire path with your eye.

However, there are many binoculars, especially in the misty past
of Japan, that gladly tossed the junk out before it got to your eyes.
Your eyes are by no means the only thing that can cut off that trash.
There are many opportunities to do so in the gadget. It involves sacrificing light
to achieve contrast, and I support that choice over the blind craving
for transmission alone. It may be that I am discussing a world of baffling
I have seen many times and you rarely see.

I'm not sure, but it seems you must admit there are better and worse binoculars
for this glare at the same power and aperture. Some designs miss the mark by a lot,
some by a little. If you don't own many variants at the same PxA, try a big shop's counters.

Which control glare better porro's or roof's? (1 Viewer)

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St. Elmo

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