Telescope Reviews: Re: ED glass in binoculars

All that technical information above may well be true for telescopes, which have larger aperture objectives and can be pushed to high powers; however, I've owned several small 8x and 10 ED porros (44-50mm) and tried one of new Chinese ED roofs, and every one without exception had less chromatic aberration than my non-ED bins, including my Nikon SEs.

I could look at a crow against a bleak, winter's sky with the 10x ED bin and not see any color fringing on axis and even a bit off axis.

I had about a dozen bins at the time, and had them all outside in my backyard to compare, and they all produced some level of CA in that high contrast situation.

The worst of the bunch produced a colored halo around the crow while the best showed a thin green line on one side of the crow and a thin purple line on the other side.

I suspect that with the ED porros, all the ED elements were made by (or for) Vixen despite them being used in bins branded "Celestron," "Eagle Optics," and "Swift". So that doesn't provide a wide sample of ED glasses. And none listed Abbe numbers.

I don't know who makes the ED glass for the Chinese open bridged clones. I've tried only the Promaster so far, but hope to try a Zen Ray soon. Those ED glasses might also be made by the same Chinese manufacturer.

So I am admittedly dealing with a small sample of ED glass, but then again, how many companies are there that have made ED glass for bins?

For daytime use, there is another advantage of ED glass that is often overlooked (or at least not written about much on CN, though it's literally hard to overlook for daytime use), which is that colors are more intense, and you can see more shades and gradiations of the same color.

For example, in a non-ED bins, you can barely make out the subtle differences in shading between dark and lighter reds in a male Cardinal. In an ED bin, you can detect those subtle differences.

Colors really "snap" in the ED bins I've used compared to most of the non-ED bins I've tried, though I must mention that the dozens of layers of advanced coatings on premium roofs such as the Nikon LX produce about the same color depth as the ED bins.

There are other qualities such as a more robust build, better fit and finish, and a smoother, faster focuser that make the LX better than the cheaper Chinese EDs, but image-wise, the difference is small.

I could be that the Chinese ED bins use lead glass like the LX. I could be mistaken about that but lead seems to be a common contaminant in Chinese products and the Chinese don't abide by the stricter environmental standards that the US and Europe does in this regard.

Or could it be the use of ED glass corrects the skewed image tint of the lead-free glass?

For whatever reason, the color palette in the Chinese ED bin was not skewed warmer like I've typically seen in lead-free glass bins.

The color tint seen through both the Chinese ED bin and LX look like what I see naked eye, only much more vivid.

That is, fire engine red naked eye is vivid fire engine red through the bins, not slightly orangey red.

You have to be careful to compare apples with apples (literally) when testing color, because nearby objects tend to influence what tint we see, as show in this chart:
tints of red

Note how the red squares near the dark squares look darker and the red squares near the light squares look lighter.

I can also use this chart to illustrate the differences I see in the SE vs. EII and LX vs. LX L (that is, lead vs. lead-free glass).

Dark reds through the SE and LX remain dark red and very close to what I see naked eye, whereas through the EII but especially the LX L, the reds have a lighter tint with a bit of yellow added.

The upside is that the warmer colors in the lead-free glass bins give the impression of the image being brighter.

However, in an actual color extinction test at twilight, the SE outperformed the EII by about 8-10 minutes, perhaps because of the slightly larger aperture or more efficient light transmission.

In daylight, the EII looks "brighter" to my eyes.

I didn't have the 10x42 LX and the 10x42 LX L at the same time, so I couldn't compare them at twilight.

The bins with lead-free glass I've tried also show more CA than lead glass bins of comparable quality. I suspect this has to do with the lack of lead in the glass.

"Even if lead-free glass material with an equivalent refractive index and Abbe’s number is developed, it is impossible to achieve the desired Apochromat performance especially for highest-grade objective lenses with a high aperture number when the anomalous dispersion degrades."

Here's the rest of the article:
Lead in optical glass

So the "ED craze" we are now seeing in roofs might be a result of manufacturers trying to reduce CA in their lead-free glass bins.

If you look back at reviews of the pre-HD/FL bins by Zeiss and Leica, you will see criticisms about excessive CA in the Zeiss Victory and Victory II and the Leica Ultravids (even in the Trinovid BN vs. BA).

I also detected more CA in the LX L than in the LX.

So while the color fidelity difference between high grade ED glass bins and high grade non-ED bins may not be that noticeable except in high contrast situations, the color saturation difference between the ED bins I've tried and non-ED bins, with the exception the Nikon LX, is quite noticeable.

For binocular stargazing, vivid color is limited to bright stars (most nebulous DSOs appear bluish-white, as do faint stars).

For daytime uses, ED binoculars can show you the entire spectrum of visible color.

Turn those ED bins on a Yellow Finch or a Cedar Waxwing or on colorful bed of flowers and be prepared for a "Wow" moment.

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B'rock, son of Grilka
Member of the House of Kozak
Klingon Poet-Warrior
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"The character of a Klingon poet-warrior is measured not only by the metal of his blade--but also by the mettle of his words."

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