Odd lens coatings
Posted 08 April 2013 - 08:27 PM
My Bushnell Powerview 16x50 have a greenish coating. Not the deep green multicoating, but more of a reflective mirror coating. Looking through these bins, gives a slight red cast but not as strong color cast as the ruby ones.
My Pentax UCF-M 8x21 compacts also have a green coating. The view has a slight red cast, but lighter than the above.
What other odd coatings have you seen?
Posted 09 April 2013 - 03:19 AM
Posted 09 April 2013 - 06:16 AM
Possible reason for color cast is the degree of lens correcction. An apochromatic lens is color corrected to 1/8000 of the focal lengths of the color range. An achromat is correccted to only 1/2000 and in fact lesser achromats may be corrected to 1/1800. Lenses can be manufactured to be balanced far more towards one end of he color spectrum than another. Some lenses give a blue appearance, some give a strong red appearance, opposite ends of the spectrum. Focusing can change the color only slightly, but never remove it completely, simply because the lens is not corrected well enough to eliminate all color.
Posted 09 April 2013 - 11:37 AM
It was a pocket compact model,labelled Day&Night 24x25.
The actual magnification was around 12x,not 24x.
The coatings "melted"(kind of peeled)off the lenses after I'd carelessly left them uncovered on the dash board of a hire car in Gran Canaria in blazing hot sunshine and temperatures of around 100 degrees F.
I've seen binoculars with brownish/amber coatings too,but can't remember the models.
Posted 09 April 2013 - 04:56 PM
This is the best explanation I've read about how and why anti-reflective coatings affect viewing color: http://www.allbinos....dex.php?art=160 .
That's good information. It explains why I see a slight yellow tone to the view through my Nikon 7x35 AE and Oberwerk 15x70. It is most noticeable when the daytime sky is in the view. It is really not an issue to me, just something I noticed.
Posted 09 April 2013 - 06:12 PM
Posted 09 April 2013 - 11:24 PM
One lens is clearly a red / magenta hue and the other lens is clearly a green / blue hue.
I believe those were manufactured back in the 1950's to watch 3D movies at drive-in theaters from the back row.