Home Forums Hunting & Shooting Hunting Optics Binoculars: Light transmission results

www.carson-optical.com/Light.html

Here are som results from a light transmission test.
For dark and dusk, wavelenght numbers from 500-550nm are the most important, but I'am not sure how to read these numbers. For use in dusk and dark, light transmission is very important, but not the only important factor. Colours, contrast and sharpness are also important. And can be the reason why two binoculars with equal light transmission (500-550) in % can give different results when actual tried with your own eyes.

The color spectrum is extremely important to providing top notch low light performance. Coatings that enhance the blue spectrum perform best in low light conditions.

Thanks for the link............

I would take a stab at this if I knew what it is that you are asking. Are you asking about the significance the visible color spectrum (400nm-700nm) or why that particular range, 500-550 is important to understand. I'm pretty sure I can be of some help.

Well the results in % are the average light transmission from 400 to 700nm. I would like to know the lowest or average light transmission for each binocular from 500 to 550nm in %.

Most binocular lense coatings, broad band coatings, will peak light transmission in the neighborhood of 550nm which is generally in the green wavelength of color. The charts you are probably referring to will indicate transmission values from 400nm (purple) at a lower percentage, say 60% as an example, to 700nm (red) at say 60-70% with a peak at 550nm at 90% with the higher grade binoculars. At the middle of the visible color spectrum is where the human eye is most color sensitive in daylight, which is most likely why manufacturers readily advertise light transmission values at 550nm. If you took the "average" percentage of transmission it would probably be somewhere in the neighborhood of 80% for good bino's to perhaps 85% for the top of the line bino's. The key or goal for lense coating technology is to have a more evenly distributed light transmission across the visible color spectrum. Hunters will often benefit from lense coatings that allows more blue light to be transmitted due to the eye's sensitivity to the color blue at dusk or night time. That's a whole different conversation regarding the photo receptors in the human eye that are active in daylight that are different from those active in night or scotopic vision. I hope this sheds some light, no pun, on your question.

Thanks I appreciate your answer.

I have one more question, as we know maximum pupil exit is 7mm when we are young. About 6mm when we are 40 and less when we get older.
Last night I tried two riflescopes. One 4 years old Swarovski 2.5-10x56 and one brand new Zeiss Conquest 3-9x40. Both have a light transmission at 93% (info. from Swarovski and Zeiss). When I put both of them at 6x, then the Swaro would have a light "beam" (I 'am not sure what to call it)of 9.33mm and the Zeiss 6.66mm. I'am over 40 years old so in theory I would have no use for a lightbeam over 6mm.
But the Swarovski was significally brighter than the Zeiss.
Is the explanation that the Swarovski have clearer, sharper optic with a better contrast. I asume 93% is correct for both scopes?

One person here on 24hourcampfire says for example that Leupold XII or XIII have over 90 % light transmission so they must be just as good as euro optics with over 90%.

But in my opinion light transmission don't tell the whole thruth about how good a scope or binocular is in darkness.

I suspect what happend is the actual magnification of the Swaro was higher than that of the Zeiss. Magnification is far more important in twilight performance than how much light a scope transmits.
If you want to test your night vision or lack of it, set your Zeiss scope at the highest magnification you can and work down as you must to still see an image as it gets darker. If you make it down to 8X, then your eye can open to a 5mm exit pupil. If it gets darker and you can still see an image at slightly under 6X, but not with more magnification, you may still have the ability of use a 7mm exit pupil. But if you can't go that far, you will simply loose the image and no magnification setting will work. E

It is not just a bright image that makes a scope good for low light use. You are on to the answer when you observed a clearer, sharper image with the Swaro. I have said on many occasion that quality glass and lense coatings provide a higher level of resolution and contrast. This is why I believe as we get older, we see more of a benefit from high grade glass/coatings as a scope with an exit pupil of over 5-6mm is not necessary or useful to the human eye. Light transmission stats make nice conversation. High grade optics speak for themselves.

Hell RD, you're pretty sharp good answer, as I have noticed the older that I have gotten the better the optics that I have needed. I have done a lot of research recently on this and your answer is exactly what I am finding................. <img src="/ubbthreads/images/graemlins/cool.gif" alt="" />
Great job............. <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

Loss of resolution is the result of less of the image making it through the optic intact. Therefore, if it can transmit a high percentage of the image, it is a simple step to focus that image. For a rifle scope, for instance, to have high transmision figures but not be able to focus that image would mean that the image suffered a loss at the end of it's journey. And that would be reflected in the percentage of light transmited. E

It is not that simplistic. Yes, the more of the image that is transmitted, or not lost, is important. However, in this instance, image resolution is what I believe Norwegian was trying to understand. Many companies advertise these high light transmission figures and that does not tell the whole story. Kinda like when you have compared bino's of various quality. I believe when you compared a high magnification Minox (15x, I think) to bino's of high quality and lessor magnification. IIRC, you felt, as do I, that there is no getting around high grade glass. You can magnify the crap out of a average image and it just reveals less and less to the user.You must increase glass quality to make use of the higher magnifications.

EXACTLY.......... <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

A well lit unresolved blob is still a well lit unresolved blob........ Aceman 2006

The more you magnify crap, the less crap you see.

Wow, those are some pretty scientific looking numbers! What the hell are they supposed to mean? Did it say that my Pentax 8x43 DCF SP were good or bad?

What numbers are you referring to? After I responded to the question I looked at the carson optical report that was referenced here. Light transmission reports/tests are but one factor used to measure how "bright" one binocular is compared to another. These numbers are captured usually by running light through a binocular (in this case) into a spectrometer which will calculate the percentage of light loss. It does not or cannot tell you what the image quality is which is the most important consideration. If you relied on the Carson tests you could be led to believe that their bino's are better than Pentax SP's. They must be awfully dam good if they are optically better than an SP. In other words, it's bullshit. The SP's are a great bino.

Thanks, RD, I'll take your word for it <img src="/ubbthreads/images/graemlins/grin.gif" alt="" />. I know I like them.

I am posting this cause I thought you might be interested, jwp. It started from a discussion regarding most important factors in light transmission. My efforts are not always in vain.


"Most important: the coatings on the lenses have nothing to do with "color correction". They reduce reflections, but they do not cure Chromatic Aberration, or change the angle at which any color of light is bent.

Second: there is no such thing as "white light." White is the sum of all colors. It does not exist on its own, and it is pretty much determined by the overall blend of the different colors and our brain's interpretation of them. That is, we "make" white light in our brains. Our brain has the original "auto white balance"...and can adjust our perception of white over a wide range of subtle shades of "off white." Which is the reason we have to have either auto or manual white balance on cameras...since they are much less forgiving of color bias than our eye/brain.

Most manufacturers measure transmission over the "visible spectrum" generating a curve that matches the transmission of each individual frequency (color) of light. They then might average those figures from the curve, or they might take the "high point" for their published figures, or they might select a particular color of light that they think is most important (in the green wavelengths generally, since that is the range the human eye is most sensitive to). There is no standardization for the measurement of transmission in the US. I think the European Union has such a measurement standard, or one in draft from at least.

Finally, there is only approximate correlation between the measured transmission of optics and their perceived brightness. Perceived brightness is a factor of the amount of energy coming through, but it also depends on the overall contrast of the image, the intensity or purity of the colors, and the particular color balance of the image. In fact, in my experience, color contrast is as important to perceived brightness as is transmission. In the end it is all about how much color and detail you can see in low light situations. A well baffled optic (that is one in which most of the reflected light is captured before it degrades the contrast of the image) with excellent color correction might well deliver better color and detail in dim light than an optic with great transmission (very little reflected light) but with poor baffling (so what light is reflected does, in fact, degrade image contrast), and poor color correction (so the colors are muddy to begin with). Only actual side by side tests can determine which optic performs best for your eye in the twilight.

Anyway, I am not sure this is of much help.

Keep up the good work in trying to educate folks to the realities of consumer optics.



Best regards,

Stephen Ingraham
__________

Birding and Wildlife Product Specialist
Carl Zeiss Optical, Inc.
Carl Zeiss Sports Optics Division
13005 N. Kingston Avenue
Chester, VA 23836 USA

Good post, Thanks.............. <img src="/ubbthreads/images/graemlins/cool.gif" alt="" />

Made perfect sense to me. Course he could be one of those "famous" Zeiss liars. <img src="/ubbthreads/images/graemlins/grin.gif" alt="" />

And only E could have exposed him............. <img src="/ubbthreads/images/graemlins/shocked.gif" alt="" />