Light Transmission [Archive]

ksbird/foxranch

Wednesday 2nd August 2006, 02:47

I don't know who paid for these tests, but the PDF's make interesting reading.

http://www.carson-optical.com/Light.html

John I included this info in the opticsplanet link and it shows the equiva;ent of color sensitivity in binoculars, that would correspond to "evenness" of color output in a photographic light source. Since none of the spectral sensitivity curves for any of the binoculars in the list is "even" or "flat" (flat being ideal), every one of these binoculars either adjusts reality by "coloring" what the viewer sees, or they function best in various applications (which is what Steiner proposes by making the same format of binocular [eg. 8x30] with various coatings so they each have different spectral throughput curves. It also points out graphically what I was saying about how the colors we see when we look at the colors of light reflected back to the "looker" represent color which has been reflected "back out" of the lens system and thus, ... do not reach the viewer's eye.

Briefly

both Pentax 8x42s have a smooth spectral curve in the blues, greens, and are still okay in the yellows and then in the oranges they becomes less able to transmit and in the reds they almost act like a blocking filter. This binocular blocks IR allot and some reds would seem to be muted if not missing.

The Bushnell Elite 8x42 is the opposite of the Pentax above, transmitting reds and oranges really well but is weaker in the blue/violet spectrum.

The Steiners seem to have a pretty smooth spectral response curve although it is strongest in the longer wavelengths like red and yellow and weakest in the blue violets.

The Bushnell Legend has poor response in the blue/violet range and peaky sensitivity in the middle range (like yellow).

The Leupolds have a response/sensitivity color spectral curve similar to the Steiners bieng weak in the upper blue/violets but reasonably smooth everywhere else.

The Nikon Monarch ATB 8x42 shows a spectral response/sensitivity transmission curve similar to the Pentaxs but the blocking/filtering-out effect in the reds is not so pronounced in the Monarch as it is in the Pentaxs.

Assuming these tests to be fair and honest, 99% of the reason why the curves look like they do is because of the type of glass, lens cement and coatings used.

What is interesting is that according to these test curves a Carson binocular has the best overall balanced image, color-wise compared to all these other well-known brand binocularss. The blues are a bit peaked and the low red range is reduced enough so it blocks IR, but even though the curve shows a definite long-wavelength-bias, the Carson binocular is the best of the bunch and most clearly matches the curve of "available light" at midday in the middle lattitudes on a clear, dust free day with no air pollution, at standard temperature, pressure, and humidity. In other words if there were cheap artificial light sources with a similar output curve, matching the Carson transmission curve, photographers would like it because it would work really well with film (and likely video too).