Owling and ED glass (1 Viewer)

Peter Audrain · Nov 12, 2018

I have gotten interested in birding around sunset, because—owls! And I don't own any ED glass binoculars, but I have read, in discussions of their benefits, that in principle ED glass improves low-light performance.

My question is: How much?

One way to make this question answerable is to compare the advantages of ED glass to the advantages of more aperture. For instance, which of these two pairs of binoculars, the Minox BV 8x56's (which don't have ED glass), or the new Olympus Pro 8x42's (which do), would you expect to work better during the 45 minutes after sunset?

Minox BV 8x56's (a P.D.F.):
https://www.minox.com/fileadmin/downloads/produktinfos/sportoptik/MINOX_BV_8x56_Product_Information_EN.pdf

Olympus Pro 8x42's (also a P.D.F.):
https://www.olympus-europa.com/site/en/b/binoculars/professional_binoculars/pro_binoculars/8x42_pro/index.pdf

Thanks so much in advance for any thoughts about how the advantages of ED glass come across in low light.

Peter

F88 · Nov 12, 2018

Peter Audrain said:
I have gotten interested in birding around sunset, because—owls! And I don't own any ED glass binoculars, but I have read, in discussions of their benefits, that in principle ED glass improves low-light performance.

My question is: How much?

One way to make this question answerable is to compare the advantages of ED glass to the advantages of more aperture. For instance, which of these two pairs of binoculars, the Minox BV 8x56's (which don't have ED glass), or the new Olympus Pro 8x42's (which do), would you expect to work better during the 45 minutes after sunset?

Minox BV 8x56's (a P.D.F.):
https://www.minox.com/fileadmin/downloads/produktinfos/sportoptik/MINOX_BV_8x56_Product_Information_EN.pdf

Olympus Pro 8x42's (also a P.D.F.):
https://www.olympus-europa.com/site/en/b/binoculars/professional_binoculars/pro_binoculars/8x42_pro/index.pdf

Thanks so much in advance for any thoughts about how the advantages of ED glass come across in low light.

Peter

Personally I don't think ED glass makes a world of difference.
As far as the 8x42 vs the 8x56 I would say the 56 would work better regardless of non ED vs ED. I also think that a 42 would get the job done.

Canip · Nov 12, 2018

Peter,
Here is my two cent.
„ED“ in an optical context means „extra-low dispersion“. ED glass is used in optical instruments because it has a lower dispersion factor than other kinds of optical glass, resulting in a reduced chromatic aberration. Lower chromatic aberration (often abbreviated CA) improves sharpness and contrast.
ED glass only has advantages in low light performance inasmuch it has a better transmission rate, but I am not sure this is the case with all kinds of ED glass.
For your purpose, i.e. low light observation at dawn or dusk, possibly in various lighting conditions and against all sorts of backgrounds (forest / forest edge / etc.), two other factors appear more important in my view than the use of ED glass:
- excellent stray-light suppression (stray-light can seriously affect the quality of the image)
- excellent anti-reflection coatings (this, together with high quality glass, results in a high transmission figure)
This is what you should focus on in your search for a good low light binocular.
By the way, for the specific use at dawn or dusk, I would go with something like 8x56 rather than 8x42, because of its larger exit pupil which should prove useful in low light.
Canip

jring · Nov 13, 2018

Hi,

transmission rates for ED glass are not a lot different than "normal" optical glass. The main advantage is that with ED glass and a well chosen partner glass one can build a doublet objective with quite low chromatic aberration - one would have to use three normal elements in order to reach that level of CA. Or one can build a triplet objective with ED elements an reach true apochromatic behaviour.

But I don't see any use of ED glass for twilight performance. Please don't confuse ED glass with the HT glass used by Zeiss - the latter is indeed high transmission and might help a little bit.

But once again, during twilight, aperture rules supreme! The 8x56 format is popular among the shooting folks for a reason!

Joachim

paddy7 · Nov 13, 2018

Also, bear in mind how old you are! If your pupil cannot dilate any more than around 5mm, an exit pupil of greater than that won't be much advantage: pupil-limited, rather than optics-limited!

wllmspd · Nov 13, 2018

Coatings and exit pupil size will make the most difference, it’s not as if any optical glass has poor transmission, though you will lose some light depending on the optical path lengths involved. When it gets proper owly dark, you’re going to have to switch technology or seriously eat a lot of carrots.

PEterW

Peter Audrain · Nov 13, 2018

Thanks, Joachim. That makes sense, that reducing CA doesn’t have very much at all to do with increasing transmission, which is what I want—to see any details at all, after a certain part of dusk. I saw an internet reference to ED glass helping with ‘low-light performance,’ but I suspect that author was just throwing around every buzzword he could think of.

I would guess the anti-reflection and phase coatings are likely to be pretty comparable on, e.g., the two binoculars I mentioned—with one a little more expensive, but the other a little more recent—so the big difference in aperture should make for a dramatic difference in brightness. I have seen surprising statements about just how much coatings can affect transmission rates, but I think aperture alone is likely to be the differentiator between the kinds of binoculars I am considering.

Of course, there’s always the fact that 8x56’s weigh nearly twice as much! It’s sad that 7x42 or 7x49 and non-‘marine’ 7x50 pairs have gone so thoroughly out of style.

Peter Audrain · Nov 13, 2018

Thanks, Peter W., that seems like an apt summary. I have a five-pound bag of carrots in the fridge right now, though I hadn’t thought about them before as the key to my owling evenings! But whatever works, amirite?

Peter Audrain · Nov 13, 2018

Paddy, I have to go to the eye doctor soon, and I think I really will ask him to check my dilation, so I know with some accuracy what I’m working with. I wonder whether really hard-core amateur astronomers are ever tempted to give themselves dilating eyedrops before a night’s observing?

Peter Audrain · Nov 13, 2018

Joachim, when a specification sheet says, for instance, ‘9 elements in 7 groups,’ is it possible to tell from that how many lenses are in the eyepiece?

It’s a shame that things aren’t made much more explicit by sports optic manufacturers.

Binastro · Nov 13, 2018

If one wants to see low transmission glass, poor coatings and possible vignetting, try an old, 12 to 15 years maybe, Bresser Porroprism 15x60 binocular.
The glass in my two samples is clearly grey.

I think that WW2 Barr and Stroud used best Scottish sand with impurities in the glass, also grey. Nothing better was available. Ross also used locally made glass.
Some Chinese glass followed the same tradition.

The performance of the eye is so poor at say 9mm dilation, I doubt that astronomers use drops.
However, some have used bottled oxygen particularly at high altitude dark sites. To great advantage.
Hyperventilation may help but made me giddy, so I stopped doing it.

Peter Audrain · Nov 13, 2018

Best Scottish sand! At one time, surely a selling point.

I’m happy we live in a time unhaunted by international supply problems and stoppages of trade in vital components for consumer goods on the order of the period of the world wars. So far. Sorry, I was just on Twitter, and I think it darkens my tone.

I had no idea about the oxygen! I wonder if the World Series of Birding should disallow performance-enhancing techniques, like oxygen inhalation. The amount of caffeine alone already carried in those vans is surely unbelievable.

jring · Nov 13, 2018

Peter Audrain said:
Joachim, when a specification sheet says, for instance, ‘9 elements in 7 groups,’ is it possible to tell from that how many lenses are in the eyepiece?

It’s a shame that things aren’t made much more explicit by sports optic manufacturers.

Hi,

in binoculars it's most probably a doublet objective (more often than not air spaced, although cemented does happen) - that makes two elements in two groups for air spaced or two in one group for cemented. So if we have a pair with external focusing (like most porro pairs), the rest is going to be the eyepiece. In case of internal focusing there is usually one movable group used for focusing.

For more than this you would need a cutaway or xray image of some kind.

For your owling I would recommend a pair with as much magnification as you can hold steady (try 10x) and as much exit pupil (and thus aperture) your eyes can use.

If mobility is not an issue, a well mounted 5 or 6" f8 or f7 astro refractor with a 40 or 50mm EP is your best bet...

PS: german ace pilots preferred blackberries for improved night vision... worth a try and if it doesn't help with the eyes, at least they're yummy...

Joachim

paddy7 · Nov 13, 2018

Without complicating things too much, it will also depend on what owls you are after. The truly nocturnal will be on the wing at night i reckon - if you go too big optics-wise, this could be a hindrance. I've spotted Scops Owls in Bulgaria with 8x32FLs - same with Pygmy Owl at twilight/dusk. Crepescular and diurnal species like Barn and Short-eared are no problem with whatever.....depends what you're planning i guess....
My life's birding ambition would be to see a Great Grey flying over a snowfield at dusk...dreamt it once....

Peter Audrain · Nov 13, 2018

I’ve just been reading up on the basic eastern North American owls, and Great Horned Owl and Eastern Screech Owl should be simplest. I’m sad that Barn Owls will likely never happen for me. A dream of the Great Gray Owl—what a wonderful dream that must have been!

The Great Horned commutes from its roost to a favored high perch in the hour or two straddling sunset, and does almost half its hunting then—another 45% around sunrise, and about 10% in the dead of night.

The Eastern Screech Owl I should most readily see in daytime, sunning in a roost hole. Though apparently they’re pretty easy to lure, day or night, and do do some crepuscular hunting, they seem to be more of a dark-of-night-and-flashlight kind of owl.

So I guess my main hope in New Jersey is to locate a good Great Horned Owl who I can watch working from his perch in the hours around sunset. I just want to see as much detail as possible when I do. They breed so ‘early’—during the mid-Atlantic midwinter—that I’m hopeful about finding a nest as well.

dries1 · Nov 14, 2018

I agree with what Joachim said regarding the suggestion of 10X. I was out at sunset into the early evening tonight, it gets dark here on the east coast at 1700. I had a very good 8X42 with a 8 and 10X56, and for me I loved the views with the 8X56, but the 10X56 is the true glass for the night. For some the only drawback of this aperture is the weight. Either one would be better than any 8X42.

Andy W.

Troubador · Nov 14, 2018

Andy and Joachim are dead right. On the Isle of Islay recently we overlooked a sea bay and 10x42 cut through the gloom like a knife and the high quality 8x42 I had with me, one of my favourite instruments. just couldn't do it. A bigger objective would only make this advantage even bigger, providing you are willing to carry the weight and bulk of course.

Lee

wllmspd · Nov 14, 2018

I would suggest using a thermal scope. Owls are masters of blending in, especially when it gets dark and stuff all looks the same, unless you are lucky to see them flying in the open. Normal night vision won’t help much due to this too. As owls are warm and their feathers can’t hide this fact.... should be easy to spot wherever they are hiding. Not cheap, but more of a dead cert for spotting.

Peter

Peter Audrain · Nov 14, 2018

Peter,

I was like, Hold on, is that really a thing (IR viewing)? And I guess it is! Currently browsing around to see if anything’s improved, or cheapened, since this blogger’s last posts:

http://infrared-birding.blogspot.com/p/welcome-to-infrared-birding.html

What an enjoyable wrinkle!

I had fun doing call-and-response with two Eastern Screech Owls last night, seeing nothing. I think I am basically hoping for a sunset profile of a Great Horned when it flies to its hunting lookout. I don’t think I deserve new binoculars until I can at least localize one to that extent.

wllmspd · Nov 14, 2018

Being in a park with light pollution (especially when cloudy) would give the chance of viewing outlines against the sky.... I have heard owls a number of times, but never seen one...

peter

Owling and ED glass (1 Viewer)

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