Bushnell's custom line with UV filters - how is this done? (1 Viewer)

Over the years I have come into possession many Bushnell Custom binoculars which claim they have UV filters installed. How is this accomplished? Is there an internal lens similar to camera UV filters? Anyone in Bird Forum land that has knowledge of this?

John

My assumption as always been that the AR coatings were adjusted to reject UV light, but that's just an assumption.

John,

I have an old Bushnell catalogue which has the following two entries about "Squint-Pruf" filters in the Customs and Rangemasters;

"'Squint-Pruf' front lenses block reflected glare from water, snow, sand and haze."

"The electric-blue color of the objective lenses reveals built-in 'Squint-Pruf' filters that block reflected glare from water, snow, sand and haze"

Like peatmoss, I think it's probable that "Squint-Pruf" filter is marketing speak for a coating with aggressive UV rejection applied to the front and perhaps the rear objective lens surfaces. Using that coating through the whole binocular would probably cause an unacceptable color bias from too much rejection of blue/violet wavelengths.

Henry

. Several of the Olympus small reverse Porro prism binoculars have large stickers saying that they are UV protected.
I don't know if this still occurs with the present production Olympus models.

What I did like was that some of these Olympus binoculars had extra wide-angle eyepieces. Again I don't think they make them any more.

I sure that Bill Cook will chime in about UV blocking properties of glass. More than a year ago he said that a certain thickness like 5mm block UV light waves.

It was good to hear that looking through binoculars does not contribute to cataracts, though the glare from the sun does when the binoculars are not shading my eyes.

Rob.

John Dracon said:

Over the years I have come into possession many Bushnell Custom binoculars which claim they have UV filters installed. How is this accomplished? Is there an internal lens similar to camera UV filters? Anyone in Bird Forum land that has knowledge of this?

John

Click to expand...

John,

AFAIK are these assumptions pure marketing mambo jambo.
UV wavelenghts are filtered out of any binocular because of the thickness of that glass which filters the UV wavelenght.
Taken in consideration the complete length of the light going tru a prism getting up side down and reversed it's complete bs.

Jan

. However, when dealing with damage to the eye, the research seems to suggest that the near blue wavelengths are the most damaging.

So I suppose it depends which wavelength one is talking about.

It may be that the binoculars marked with UV stickers, actually are reducing the near blue wavelengths.

So it may not be only advertising hype.

I'm not sure how much viewing with binoculars generally in daylight affects cataracts.

The UV filters (and other "UVC" filters) are always on the outer surface of the objectives.
Right, throughout would be too much. But also, why allow a frequency with much higher
scattering on dust bits and walls to enter in the first place?

It's simply layers designed to reject violet a little and UV a lot, like the response of any
band-pass filter. Interference in coatings is always bandpass filtering. In the original single-layers,
violet and UV are rejected far more than the red end, because the violet end is extremely
prominent in haze over hundred yards.

If you lose a little blue, a bit more violet, and lots of UV, things far away don't actually look yellow,
because in fact your distant image is already 'violet-shifted' to start with. Your eyes also
automatically adjust color sensation, as they must to cover morning and dusk lighting.

People using 4mm and up for exit pupils should beware of bright backgrounds with
super-transmission lenses. Your eyes are being aged quickly, just like looking at
bright things without the lenses. You don't realize it as much because your AFOV is
not the same as the unaided eye. Also, blue and violet diminish your light sensitivity
more.

Here you can read some about UV and optics...

http://www.naturfotograf.com/UV_IR_rev05.html#top_page

Thanks for that Binoseeker.