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Low light performance (1 Viewer)
- Thread starter RobConnel
- Start date
AlanFrench
Well-known member
You'll probably get some opinions, but everyone is using pretty darn good coatings on high end stuff these days, and I suspect the differences are nothing to fret about. I'd be more concerned with the fit and feel in your hands. Which feels best to you?
Clear skies, Alan
Clear skies, Alan
AlanFrench
Well-known member
JCJ said:
Best fit, or best coatings <G>.
They are supposed to be good.
Clear skies, Alan
I think they all have good coatings, especially swaro and zeiss. For some reason zeiss on avg. always seem brighter than the others. I have owned about every bino made by these 3 for the last 10 years or so(except 12x) and zeiss is usually brighter. Not that I like them better, they are just brighter. Maybe its their a-k prisms. I don't really care for their fit as much as the other 2. But this is subjective, I like them all.AlanFrench said:
AlanFrench
Well-known member
JCJ said:
I've often wondered if apparent field has an influence on perceived brightness. Is comparing binoculars of the same power but different apparent (and true) fields bias the results?
One thing I look for is companies that say the coatings are carefully matched to the glass types. For best results you can not simply slap the same coatings on each lens.
Clear skies, Alan
Wehr
Well-known member
AlanFrench said:
Hi Alan,
this was done years ago to compensate the yellow, red or green color of some glass types. Today coatings don't care about the glass types but are all optimized for the deep blue part of the spectrum, because all glass types still swallow up UV and with it a small amount of visible blue.
Different color reflections on the coated surface say nothing about the range of optimization, it depends only on which layer is the last on the entire package.
Walter
AlanFrench said:
FOV has a big influence on perceived image, the brightness and power perceived in my opinion. I think a larger field not only makes something appear brighter but also closer. Most coatings used by todays major companys are very simular. Where you get your variations is in the glass types, even within the same brand. Thats why you can take say 5 of the same bino, 7x42 leicas for example, and chances are their lenses will vary in color. One may have a green hue, another a reddish, a purple, a yellow, or maybe a violet color. The are hardly ever the same color. The coating reacts different with different glass types. Each batch of glass usually has subtle differences, so they try to tailor coatings to match the type of glass to give them all a simular result. A good test to determine whether a particular bino is coated as precisely as another is to look directly into the objective lens as you would a mirror. You should not see yourself. If you can, then some light is being reflected back at you instead of being allowed to pass through your bin.
zeiss
Scientific analysis (third party) proves zeiss flourite coatings are the way of the future. Nothing can compare currently to their ability to see through shadows in dim light.
However, I still like the ergonomics of another brand, swaros. However overpriced, rapidly becoming abandoned, resented, et all. They still have to fit my hands all day long. Bottom line.
Best of luck.
Scientific analysis (third party) proves zeiss flourite coatings are the way of the future. Nothing can compare currently to their ability to see through shadows in dim light.
However, I still like the ergonomics of another brand, swaros. However overpriced, rapidly becoming abandoned, resented, et all. They still have to fit my hands all day long. Bottom line.
Best of luck.
AlanFrench
Well-known member
Wehr said:
Walter,
That wasn't the issue I was writing about. For maxium transmission, the coating should be taylored to the particular glass it is being used on. For maximum transmission, a coating should be designed for the indices of the glass being coated.
For instance... "At Leica, high-performance broadband coatings are applied that are tailored specifically to the types of glass that are being used."
I am not sure what you mean by "optimized for the deep blue part of the spectrum." The general goal of glass and coating selection is to maximize transmission across the visual spectrum. It is probably a good thing - and no accident - that our eyes are less sensitive to blue and red light, which represent the portions of the spectrum less well controlled by refractive optics (including our eyes).
Clear skies, Alan
Wehr
Well-known member
AlanFrench said:
Hello Alan,
Taylored coatings were a big deal in the days of 1-4 layer coatings with only magnesium oxid.
Since the big four are all using multi-layers (12-40+) with materials like ZrO2, Al2O3, SiO2, TiO2, Ta2O5 (with lamda/4, lamda/5, /6, /7,...) and so on, using Ion Beam Sputtering or other methods followed by laser beam or ion beam compression, they all reach the same transmission of up to 99,6% for each glass-air surface with a very smooth light transition from air to (any kind of) glass and vice versa.
With these techniques indices of glas are no longer problematic. Some kind of tayloring is done by keeping the layers in specific order and by using specific material. They do it all the same way - therefore it makes no sense to talk about it. And last but not least, stressing the dark blue and violet part of the spectrum compensates the light absorption within the glass, which leads to a colour-neutral performance.
This is the way how coating is done today by the big four (and it is very expensive). The best proof that they do it all in a similar way is, that they all reach the same degree of transmission (speaking of losses through reflection not absorption!). So, nowadays coating is not the big deal, but absorption. You can hope to reach an increased transmission of 1% for the intire binocular by only improving the coatings. But less absorption may recover 5-7% of todays losses within the glass way.
That was the issue I was writing about and don't let me be misunderstood.
Walter
henry link
Well-known member
Walter,
A very interesting post. I recall long ago seeing an absorption figure for generic "optical glass" of 1% per inch and I beleive on another thread Alan posted a link to a Japanese optical glass maker with specifications that were a little better for most types. I would guess that in binoculars most of the absorption occurs in the prisms and that the total glass thickness for most binoculars might be 100-150mm. I would be very interested to read any further information you have about this.
Henry
A very interesting post. I recall long ago seeing an absorption figure for generic "optical glass" of 1% per inch and I beleive on another thread Alan posted a link to a Japanese optical glass maker with specifications that were a little better for most types. I would guess that in binoculars most of the absorption occurs in the prisms and that the total glass thickness for most binoculars might be 100-150mm. I would be very interested to read any further information you have about this.
Henry
With my limited knowledge and if I remember what I was told at a Bird Fair, I understand that it is not only coatings that play a part in low light performance (a major part, but not all). My understanding is that for low light use the Abbe Koenig roof prism used by Zeiss in some of their binoculars enhances low light performance when compared to a mirrored surface roof prism. The modern day dielectrical layers used on mirrored roof prism has increased transmission (through the entire binocular, as well as the prism itself). Apparently one company has improved its transmission considerably Vs its previous model, by approx 4%. False / Stray light can also play a part, apparently 2% is good, but some are down to between 1-1.5% across the spectrum.
AlanFrench
Well-known member
Wehr said:
Walter,
I agree that coating technology has put even one on pretty much an even footing, so it is not much of an issue.
I still don't understand your point about the blue and violet. I looked at the transmission data for BAK 4 on the Schott glass map and it is still extremely high at the blue end of the spectrum. Our eye's loss of sensitivity in the blue is far, far greater than the slight difference in transmission. Also, if coatings have transmissions in the upper 90 percent range, how can you do much to emphasize the blue? I am sorry, it just makes no sense to me.
Do you know specific glass types used in binocular prisms?
Clear skies, Alan
Wehr
Well-known member
AlanFrench said:
Hello Alan,
you are right with BAK 4, but it is usually only for prisms. There are different materials used for the lenses (would lead to far to talk about), but all these glasses suffer from some loss at the visual blue end of the spectrum, because they absorb UV. Missing blue makes all colours yellowish. Our eye's loss of sensitivity in the blue is not the point. With that loss, our brain judges colours to be natural. Using binoculars shall lead to the same result. So there must not be an additional loss caused by the glass (brain is very sensitive regarding deviations from what it thinks is natural). Not to forget, light more and more becomes blue at dusk. With the mentioned measures low light performance is increased best. Good example is Zeiss with their new FLs. With the FLs they practice this kind of coating in a rather extreme way, and on my impression they lose a bit of contrast in daylight. In daylight I personnally prefer a slight yellowish characterization, because it increases contrast by blocking a portion of the blue straylight, when observing in the mountains or at the sea.
Walter
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AlanFrench
Well-known member
Wehr said:
Walter,
The longest light path is in the prisms, so it seemed like the sensible place to look first. I just looked at Schott BK7 and F2, which are frequent ingredients in achromats. Again, the difference in tranmission in the deep blue does not seem to be of any significance.
Out of curiosity I also look at the abnormal dispersion (ED) glasses. They all had even better transmission in the blue than did the normal glasses.
Clear skies, Alan
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AlanFrench
Well-known member
For folks who want to rummage through some optical glass, here are links for Schott and Ohara...
http://makeashorterlink.com/?G1322186B
Click on the glass map.
http://www.oharacorp.com/swf/catalog.html
Select from the glass map.
Clear skies, Alan
http://makeashorterlink.com/?G1322186B
Click on the glass map.
http://www.oharacorp.com/swf/catalog.html
Select from the glass map.
Clear skies, Alan
RobConnel said:
I would include Nikon!
Somewhere on BF there is a list of % transmission for various binoculars. I think the best were Nikon SE and Zeiss Victory (FL?) which reached ~96%. Zeiss claim ~96% in their techie bumf. The 'worst' of the premium bins were Swarovski EL at about 84% IIRC. I seem to recall that Leica were closer to the Nikon/Zeiss than the Swarovski. However, those figures are probably peak measurements, rather than averages over the visible range, and manufacturers sometimes change and improve coatings on existing bins as the years go by, so the figures are not necessarily up to date.
Transmission is not everything though as the Nikon HG range do not transmit as much light as the best, but the contrast is very high which largely compensates. In my experience performance in low light depends on both transmission and contrast.
As someone else said, I'm not sure the differences between the best are that significant. Maybe someone with direct experience in low light can contradict me.
Leif
Wehr
Well-known member
Leif said:
Hello Leif, do you mean overall transmission?
To not render further discussion completely useless, we should avoid using such numbers without further precision. None of the trustworthy companies ever claimed an overall transmission of 96% for their binoculars. I recall only one case of bullshit with Fujinon (Fujinon claimed 95% for a while, in the meantime they repent their sins). Zeiss for example claims 90% as a standard, which is outstanding and much more faithful. They also don't talk about "overall" transmission.
Transmission and contrast performance of binoculars cannot be separated (MTF!) and cannot be affected from outside - not in low light and not in daylight.
Only contrast perception of the observer's eye (or better: brain) varies with atmospheric conditions and how the binocular handles these conditions. The latter depends mainly on the chosen glass components and the transmission graph, which can easily be influenced by the optical coating. The eye needs a good MTF of coarse structures during direct observation, whereas a photographer needs it in the fine structures too.
Walter