Low light binocular (1 Viewer)

JabaliHunter · Jun 29, 2011

First of all, let me apologise if one of my earlier threads offended anyone's sensibilities. It was not my intention and I'll tread more carefully in future.

I joined this site to learn more about binoculars, specifically models suitable for low light wildlife viewing.

I feel that my current pair of 10yr old Swarovski 10x42 ELs are not quite right for me. I think it is because of the 4.2mm exit pupil, but also the relatively narrow field of view. Yes I can see the shakes in the 10x too, but am usually able to support them if necessary. I don't know if I either need to drop magnification or go bigger on the front end, or both.

I will certainly try the Zeiss 8x56 T*FL. It has a wider field of view, bigger exit pupil and lower magnification, so ticks all the boxes above. I note Henry Link’s extensive review of the benefits of large objective and long focal length binoculars too. But it is pretty much the same weight as carrying around a full bottle of wine!

The Leica 8x50 HD would also give a large exit pupil and lower magnification, but no wider field of view than my 10x42. I am not technically astute enough to know whether similar large objective/long focal length benefits would also be achieved with this model. I suspect that for the latter, the focal length is not long enough...

A 5-5.25mm exit pupil seems fairly ubiquitous and I could achieve that with a wide field of view in say an 8x42 Zeiss FL, Leica HD or 8.5x42 Swarovski EL; or in a 10x50 EL with a narrower field of view (same as a 10x42EL). I suppose only trial and error will tell me if I prefer a larger exit pupil or not.

It has also been suggested to me that the colour bias of different binocular models may have more of an effect than increasing exit pupil size above 5mm, something I haven't looked into yet!

I will admit to feeling a bit lost in choosing an appropriate pair of binoculars. I have been talking to various shops but they are not much help. Nowhere that I can find seems to have the models that I want to see in the same place. But they all helpfully point out that I won't be disappointed with whatever I choose!

Any advice, comment or observation welcome.

Thanks in advance.

henry link · Jun 29, 2011

Let me just add to the confusion. The image quality advantages of large aperture binoculars I mentioned paradoxically apply only in daylight when the outer part of the exit pupil can't enter the eye. In very low light, if your pupil is dilated enough to accept the whole exit pupil, then all the aberrations from the entire objective lens come flooding in. Nearly any large binocular, including the Zeiss 8x56 FL, has pretty awful aberrations at full aperture. Just as bad or worse are your own eye's aberrations when they're fully dilated, so often a small exit pupil binocular will look dimmer but sharper in low light just because it cuts off the light to the outer part of the eye's low grade lens and thus improves your eyesight acuity.

typo · Jun 29, 2011

Last winter I spent a very dull and misty afternoon trying out some low and mid-priced 8 and 10x42s . It might have been a fairly wasted exercise as all the colours seemed muted in the gloom and the mist was blurring everything. Not my idea of birding weather. However, with one pair I discovered there were cows grazing in the next field, which were invisible using the other pairs. I've tried the same pair since in good light and seen nothing remarkable as an explanation. I'm guessing the difference was in the transmission curves or something, but what and how I have no idea. How the alphas compare under the same conditions, I'm not sure, but perhaps others do.

David

Roadbike · Jun 29, 2011

Since the 10x bins are shaky try an 8x42. That alone should provide a big improvement in image quality and your ability to observe in dim light. I have yet to find a single shop with all the bins I'm interested in trying, so you will probably have to do some shopping. Part of the fun in my opinion.

brocknroller · Jun 29, 2011

henry link said:
Let me just add to the confusion. The image quality advantages of large aperture binoculars I mentioned paradoxically apply only in daylight when the outer part of the exit pupil can't enter the eye. In very low light, if your pupil is dilated enough to accept the whole exit pupil, then all the aberrations from the entire objective lens come flooding in. Nearly any large binocular, including the Zeiss 8x56 FL, has pretty awful aberrations at full aperture. Just as bad or worse are your own eye's aberrations when they're fully dilated, so often a small exit pupil binocular will look dimmer but sharper in low light just because it cuts off the light to the outer part of the eye's low grade lens and thus improves your eyesight acuity.

Nearly all, but not all, at least not this one, according to allbinos the Docter 8x56 Nobilem is nearly distortion free. Of course, you pay for that by getting a smaller FOV. But that's always the rub, isn't it?

Some wise sage once said that binoculars are a collection of compromises, take your pick.

http://www.allbinos.com/81-binoculars_review-Docter_Nobilem_8x56_B_GA.html

Brock

P.S. I found the Zeiss Jena 8x50 Octarem excellent for watching wildlife in low light. I used to watch owls, nocturnal flying squirrels, possum, rabbits, racoons, and other nocturnal critters. It could really soak up the photons. It was as if a small flashlight were shined on my subjects.

At 45 oz., they are lighter than an 8x56, and they are so well balanced and the weight so widely distributed, and it provided very good thumb support that I did not find them fatiguing to hold for extended periods. In fact, the 36 oz. 8x42 HG tired my arms a lot quicker due to its concentrated central weight and lack of thumb supports.

Brock

ronh · Jun 29, 2011

Typo,
Tell us what it was man, cow in thick gloom big thing for me!

JabilHunter,
I agree with Roadbike, but will run on at length.

I am not as critical an observer as Henry, but even the likes of myself can see that a 4mm exit pupil craps out in low light. Quite a few observers have commented on this effect, although agreement is of course not universal. I see this effect easily with my 8x30 Fujinon FMTR-SX as the colors turn to shades of grey in evening light. I see it in my mighty 12x50 Leica BN: despite its monstrous "twilight factor", it dims out and loses aesthetic "punch" pretty soon around sunset. But 7x50 and 8x42 keep giving the "amazingly bright" view late into the gloamin' light. I don't think I have ever seen even one opinion that a 5mm exit pupil will not do all that can be done in low light.

My eyes open up to 6mm+ in absolute dark, so you'd think the 7x50 would seem to beat the 8x42 as badly as 8x42 beats 8x30, but that is not the case. Part of this I understand: I see 4mm appear to dim out early because my eyes open up to 4mm in surprisingly bright conditions, when I can still hold a ruler up to my eyes and measure my pupil with a mirror. But I have not done an experiment to measure how dark it must be for my eyes to cross the 5mm threshold. I can but speculate that their opening up to beyond 5mm takes a light level lower than I would actually try to birdwatch in. And I even like to go out and look for Great Horned Owls.

So, if your eyes work like mine and many people's, and you find 10x too shaky also, in addition to a 4mm exit pupil being inadequate in dim light, the solution seems simple to me. Replace the 10x42 with an 8x42.
Ron

henry link · Jun 29, 2011

brocknroller said:
Nearly all, but not all, at least not this one, according to allbinos the Docter 8x56 Nobilem is nearly distortion free. Of course, you pay for that by getting a smaller FOV. But that's always the rub, isn't it?

Some wise sage once said that binoculars are a collection of compromises, take your pick.

http://www.allbinos.com/81-binoculars_review-Docter_Nobilem_8x56_B_GA.html

Brock

P.S. I found the Zeiss Jena 8x50 Octarem excellent for watching wildlife in low light. I used to watch owls, nocturnal flying squirrels, possum, rabbits, racoons, and other nocturnal critters. It could really soak up the photons. It was as if a small flashlight were shined on my subjects.

At 45 oz., they are lighter than an 8x56, and they are so well balanced and the weight so widely distributed, and it provided very good thumb support that I did not find them fatiguing to hold for extended periods. In fact, the 36 oz. 8x42 HG tired my arms a lot quicker due to its concentrated central weight and lack of thumb supports.

Brock

Allbino's "distortion" just means pincushion. It has nothing to do with axial aberrations. In fact, none of the Allbino tests tells us much about full aperture axial aberrations. The catch 22 for actually seeing the full aperture aberrations of a 7mm exit pupil binocular is that your eye has to be open to 7mm. That means it's so dark and your acuity is so poor that you can't tell whether the binocular optics are any good or not. The only solution is to boost the binocular magnification until the exit pupil is small enough to fit inside your eye'e pupil at it's diffraction limited size of about 2-3mm. I can tell you that when the Zeiss 8x56 is boosted to 24x so you can see the full aperture aberrations it's not a pretty sight. But, strange as it may sound if you stop down the aperture to 30mm you will see a dimmer but much sharper and cleaner 24x image.

Henry

typo · Jun 30, 2011

Ron,

It was an Opticron HRWP 8x42.
http://www.opticron.co.uk/Pages/hrwp.htm
Some have suggested it may be the same or similar to the Minox waterproof porro. Obviously not in the same league as the big guys you've been talking about. In good light you might say it's very good for the price with a narrowish view, but why it was better than the roofs 2 or 3x the price in the mist/gloom I have no idea. But I wasn't comparing it to the top league pairs. They may have been good as well.

David

denco@comcast.n · Jun 30, 2011

JabaliHunter said:
First of all, let me apologise if one of my earlier threads offended anyone's sensibilities. It was not my intention and I'll tread more carefully in future.

I joined this site to learn more about binoculars, specifically models suitable for low light wildlife viewing.

I feel that my current pair of 10yr old Swarovski 10x42 ELs are not quite right for me. I think it is because of the 4.2mm exit pupil, but also the relatively narrow field of view. Yes I can see the shakes in the 10x too, but am usually able to support them if necessary. I don't know if I either need to drop magnification or go bigger on the front end, or both.

I will certainly try the Zeiss 8x56 T*FL. It has a wider field of view, bigger exit pupil and lower magnification, so ticks all the boxes above. I note Henry Link’s extensive review of the benefits of large objective and long focal length binoculars too. But it is pretty much the same weight as carrying around a full bottle of wine!

The Leica 8x50 HD would also give a large exit pupil and lower magnification, but no wider field of view than my 10x42. I am not technically astute enough to know whether similar large objective/long focal length benefits would also be achieved with this model. I suspect that for the latter, the focal length is not long enough...

A 5-5.25mm exit pupil seems fairly ubiquitous and I could achieve that with a wide field of view in say an 8x42 Zeiss FL, Leica HD or 8.5x42 Swarovski EL; or in a 10x50 EL with a narrower field of view (same as a 10x42EL). I suppose only trial and error will tell me if I prefer a larger exit pupil or not.

It has also been suggested to me that the colour bias of different binocular models may have more of an effect than increasing exit pupil size above 5mm, something I haven't looked into yet!

I will admit to feeling a bit lost in choosing an appropriate pair of binoculars. I have been talking to various shops but they are not much help. Nowhere that I can find seems to have the models that I want to see in the same place. But they all helpfully point out that I won't be disappointed with whatever I choose!

Any advice, comment or observation welcome.

Thanks in advance.

How about these?

elkcub · Jun 30, 2011

Low-light viewing conditions (dusk and dawn) produce in intermediate state of visual adaptation between the extremes of photopic (daylight) and scotopic (night) vision. It is referred to as the "mesotopic" state and shares some of the attributes of both extremes. Unfortunately, it's hard to pin down target visibility under these conditions, since both the ambient light and retinal state are changing simultaneously. However, it is generally agreed that increased light gathering power and increased magnification tend to offset simultaneously the loss of image contrast and visual detail. A rule-of-thumb to balance these two factors is captured in the Twilight Factor (TF), where:

TF = (M x A) * .5 (i.e., the square root of magnification times aperture)

Note that for a fixed aperture (e.g., 50mm), increasing magnification produces a higher TF, and results in a decrease in exit pupil. On the other hand, for a fixed magnification (such as 10x), increasing aperture produces a higher TF, but increases the exit pupil. In other words, then it comes to twilight vision exit pupil size, per se, is ambiguous.

A further word on "twilight visibility" or low-light viewing. Under mesotopic conditions there is no way to compensate for the physiological changes that occur within the eye, and no way to produce a daylight scene with optimized optics. An ever increasing loss in visual detail and color sensitivity is inevitable.

Ed

RJM · Jun 30, 2011

Ed, I think I recall reading the Zeiss recommendation that a "low light" bino should have a minimum Twilight Factor of 17 AND a minimum Relative Brightness (exit pupil diameter squared) of 16. That roughly equates to the standard 8x40mm as the minimum size one should look for.

elkcub · Jun 30, 2011

Hi RJM,

I assume you meant 10x40, since the square root of 16 = 4.

(Or, maybe I read it wrong). That would correspond to a TF = 20. Quite a few configurations fall in the TF zone between 17 and 20, including the 7x42 BGATP, which has a TF = 17.15, and the 8.5 x 44 Audubon, which has a TF = 19.34.

Note that transmission efficiency can compensate for aperture to some extent, but not magnification. This becomes somewhat complicated by the influence of the observer's max. pupil diameter, so a rule defining the ideal configuration for everyone is elusive.

I tend to believe that the value of added magnification for twilight viewing is underestimated, although it might be a liability using the same binoculars under daylight conditions.

Ed

RJM · Jul 1, 2011

elkcub said:
Hi RJM,

I assume you meant 10x40, since the square root of 16 = 4. (Or, maybe I read it wrong).

No I am not mathmatically challenged. But is a mainstream 10x40 even made? I have only seen 12x40mm as the next progression in 40mm optics.

I tend to believe that the value of added magnification for twilight viewing is underestimated, although it might be a liability using the same binoculars under daylight conditions.

As do I. I also think Swift nailed the parameters for birding with their widefield 8.5x44mm Audubon . Unfortunately, my sample of their #820 ED had measured clear aperture of only 40mm!

elkcub · Jul 1, 2011

I guess the 10x40 that first comes to mind is the famous Zeiss BGAT, but there are others such as the Nikon Action and Zeiss Conquest, which are current. Many manufacturers made them in the past including B&L, Swarovski and Leitz (Trinovid).

Ed

soloflyfisher · Jul 1, 2011

JabaliHunter said:
First of all, let me apologise if one of my earlier threads offended anyone's sensibilities. It was not my intention and I'll tread more carefully in future.

Not offended at all--I thought your earlier thread was interesting and perfectly relevant to the binocular discussion. Personally, I would have allowed it to stand, though I can also understand why the moderators made the decision they made.

Low light binocular (1 Viewer)

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