Light Gathering 7X50 Marine and Victory 8x42 HT (1 Viewer)

Buying when I get home:

I'm currently in Swaziland using a Zeiss Classic Marine 7x50 on safari. Very satisfactory results, clarity, awesome in low light, headed to South Africa on Friday. Lovely viewing dawn/day/dusk. As an aside, the moon is the brightest white here (at 4,000+ feet altitude) I have ever seen.

Here's my question: If when I return I buy the new Victory 8X42 HT, will the new HT's increased light gathering capabilities make them as bright as my 7x50 Marines, or is that asking too much of 42's at 8X. Or, should I look to Victory 8X56 FL's which will certainly be even brighter still.

Final question, will the 10X56 Victory FL's be as bright as my marine 7X50 Marine Zeiss?

Thank you so much.

Glad you're enjoying the 7x50.

There are two parts to image brightness: the transmission of light through the binocular, and how much light your eye can take in or how big your pupils are.

Among the binoculars you have mentioned, the transmission probably won't differ more than 5%. If your pupils could expand enough to take in all of the the 7.1mm exit pupil of your 7x50, then the brightness difference between it and the 5.2mm of the 8x42 would be the square of the ratio of those diameters, 1.86, for a brightness difference of 86%. So, if your eyes can do that and it is dark enough for them to actually do it, the pupil effect will greatly overwhelm the transmission differences.

But the pupil effect is often not that great. In daylight, the pupils will be around 2-3mm in diameter, so the larger exit pupil loses all of its brightness advantage, and the more transmissive binocular will appear brighter. This is one reason that daytime birders so highly prize binoculars with even a little bit better transmission, like the Zeiss HT--in good light, transmission is the whole story. As dark approaches, your pupils will expand, but just how is impossible to predict, since it depends on the particulars of your eyes and just how dark it is. Maximum pupil size generally gets smaller with age, but there's a large variation among individuals. So, there's just no easy answer to your question without some measurement of your pupil diameter under the darkest conditions that you want to observe, or directly comparing binoculars in low light. A measurement isn't too hard, but I won't go into that here.

Image brightness isn't everything--magnification also contributes to how much information you get out of an image. But by low light and high light, the difficulties and rewards of high magnification are no different, and I would not recommend buying a high magnification binocular just for low light use.

FWIW, my eyes open up to almost 6mm in complete darkness, but only to 4mm in twilight where I can still see to measure my pupils by holding a mirror and ruler up to my eyes. I can see an 8x32 peter out while it's plenty bright for many songbirds to still be around. I am a stargazer too, and often observe in full darkness. I like higher power binoculars, just a personal preference, as I find I can see more detail with about 10x and am usually willing to put up with the increased shake and reduced field of view to get that. So, it shouldn't be hard to believe that my #1 is the 10x56 FL, as it rings all my optics bells at once, and is compact, lightweight and easy handling, for a 56mm (little joke there, I just like hugeness I guess). But I also like my 7x50 for low light--the very large exit pupil and low power give a very pleasant and relaxing experience as you know. And, a good 8x42 is not bad at all. I have used one often for observing owls until it was too dark to see them, and the long periods of watching without rest favored the light weight of the small binocular.

You might try to get to one of these big box outdoor stores around closing time and take another binocular out in the parking lot to compare it with your 7x50.

Ron

DeeDubya,

In the practice of viewing, there can be more to it than just brightness. Leaving aside optical field quality and distortions, some of those things can be Field of View, Depth of Field, Objective size, Magnification, hence Exit Pupil size, and Twilight Factor, etc.

One of the first questions to ask is what's your low light, or dark adapted exit pupil size? (This broadly correlates with age, and decreases from ~7mm+ at 20 years of age, pretty linearly down to ~4, or 5mm at 70+ years of age or so. Some people more, some people less). This compares with a daytime (in bright light) exit pupil size for just about all folk between ~2 - 4mm, depending on age. You'd have to measure yours to get more data of use to you.

Obviously larger Objectives, and larger Fields of View, pull in a larger light cone, which is beneficial in low light, and by and large trump relative brightness and transmission parameters . Also the transmission %, and colour balance, along with field quality will have an effect on 'apparent brightness', up until the larger factors of environmental light, and your corresponding exit pupil size take over.

Of importance is the performance of you own eyes. As the light levels drop, does your focal accommodation rapidly diminish? or retain a goodly portion of daytime ability? Likewise, is your low light vision riddled with aberrations, such as astigmatism, or does it stay fairly sharp? (Given that the eye works in different ways for bright, normal, and low light situations).

Can you handle the lower image stability of higher (10x) magnifications? In which case, you may be able to convert some of that Objective size, (and Exit Pupil size) into higher magnification at the expense of lower Exit Pupil size and "ease of view" (the magin of error for keeping the eye centered within the Exit Pupil area - larger ones are handy f'rinstance when being bounced around in a truck trying to view a subject).

Relative Brightness is defined as (Exit Pupil diameter in mm) ^squared. ie:-
7x50 = 51
8x56 = 49
10x56 =31.4
8x42 = 27.6
10x50 = 25
8.5x42 = 24.4
10x42 = 17.6

Twilight Factor is defined as the square root of (Objective size in mm x Magnification), and is a measure of a binoculars low light capability. ie:-
10x56 = 23.7
10x50 = 22.4
8x56 = 21.2
10x42 = 20.5
8.5x42 = 18.9
7x50 = 18.7
8x42 = 18.3

So you can see that the formats with the highest Relative Brightness are not the ones with the highest Twilight Factor. For most adults, the 5.25mm Exit Pupil of the 8x42 format would be a minimum size, then work up from there - 5.6mm of the 10x56, or 7mm of the 7x50, and 8x56 ..... maybe around the ~5mm size of the 8.5x42, or 10x50, if you are much older. It's an individual thing as to which qualities you prefer more, and which work for you in the type of viewing you will be doing. You really have to try for yourself and see.

I feel the 10x56 is probably a good compromise for all but the very young. If the image stability, FOV, and DOF, and EP size, suit both your eyes (focal accommodation, pupil size) and viewing style, then go for that (with the higher TWF).

If you want a smaller, lightweight option, then the Zeiss 8x42 HT (especially, with it's 95% transmission, and high blue spectrum levels) will certainly keep you in the running with the big jiggers until about 2/3 of an hr after sunset.

I think the 7x50 option really only comes into it if you need the greater eye placement margin of error afforded by the 7mm Exit Pupil size, and extra DOF of the 7x format - often though the AFOV's are comparitively narrow.

Otherwise, if you really need a 7mm EP, go for the 8x56, though these 7mm EP's really only benefit brightness-wise about 3/4 - 1hr+ after sunset at your latitudes. Of course as Henry detailed there's a host of reasons why they are better in brighter light too - but that's up to you to decide the value of that.



Chosun :gh:

ronh said:

..... FWIW, my eyes open up to almost 6mm in complete darkness, but only to 4mm in twilight where I can barely see to measure my pupils by holding a mirror and ruler up to my eyes. I am a stargazer too, and often observe in full darkness. I like higher power binoculars, just a personal preference, as I find I can see more detail with about 10x and am usually willing to put up with the increased shake and reduced field of view to get that. So, it shouldn't be hard to believe that my #1 is the 10x56 FL, as it rings all my bells at once. But I also like my 7x50 for low light--the huge exit pupil and low power all gives a very pleasant and relaxing experience. And, a good 8x42 is not bad at all. I have used one often for observing owls until it was too dark to see them, and the long periods of watching without rest favored the light weight of the small binocular....

Click to expand...

Howdy Ron - I see that you said most of that while I was a typin' !

Also, that the fire still burns bright for the 10x56 flame! :kiss:

How do you find the twilight performance of this bin for you, particularly with regard to the 10x's shallow Depth of Field?

The reason I ask is that my eyes have been copping a lacin' recently, and I'm finding even 8x DOF pretty shallow after the sun goes down. I might just have to pack my eyeballs off to the gym for a workout!


Chosun :gh:

Chosun,

The 10x56 is the best twilight performer that I have used. Although my eyes are probably not taking in the full exit pupil in those conditions, some combination of eyepiece design and the somewhat largish exit pupil make for a view that does not flicker when I glance around the field, as I experience with most 5.0 or 5.2 mm exit pupils. It's the same feeling as with a 7x50. I suppose 5.6mm is enough for me.

I don't notice the depth of field seeming any different in low light. Mainly, everything's just.....darker.

Ron

Ron and Chosun,

I don't think the relationship between light levels and depth of field is particularly straightforward and probably varies quite a lot with age and other factors. Conventional theory suggests that as the pupil dilates the DOF should reduce considerably and visual acuity should improve. In fact visual acuity decreases a lot, typically 10 fold at the limits of photopic (daylight) vision, so what we perceive as the limits of acceptable sharpness changes with it and may actually stay the same or even increase.

I notice a pronounced decrease in DOF for instance when the sun is suddenly hidden by cloud on an otherwise sunny day. When it drops to twilight levels my impression is that it improves again but in fact I'm seeing significantly less detail so defining the DOF limit with less discrimination. I switch from my usual 7x36 to a 10x56 in twilight as it offers the best combination of apparent detail and DOF of all the format's I've tried. Others eyes may come up with a different answer.

David

Ron, David - thanks for your thoughts, and info on DOF in low light.

I find that my DOF takes a substantial dive during twilight (or peering into deep, dark shadows) if I've been concentrating on a computer screen at a fixed distance all day. In fact it takes a day or two of "nature acclimatisation" before I get any meaningful DOF back.

As well as a "darker" view, I would also say I experience a "cruddier" view, in low light.

This acuity deterioration in low light seems particularly worse after staring at aforementioned computer screen. My screen is 1280x800 resolution, @60Hz, and 32bit colour. I have the brightness turned down to 60% (the least the crappy AR coatings will allow, without eyestrain inducing reflections taking over), and always used in a well lit room. In low light, aside from general "mush", I'll often see what looks like millions of little fireflies flickering in Red, Gold, and Geen-Blue, @60Hz, and in a regular Million pixel matrix. Anyone else plagued by this, or have any tips, or solutions? |8.|

Apart from that (or maybe because of that), I find a 10x56 preferrable to a 7x50 in low light, despite my pupils opening up to at least 7mm - now if I can just find a "lightweight" one, or an affordable bearer to tote it around for me safari guide style :king:



Chosun :gh:

Thanks so much folks, that was incredibly informative. This is my first internet access since my original post, so I enjoyed reading the tutorial.

I was at Gander Mountain before I left for South Africa, and the only high end glass they had was a Zeiss 10X42 HT - which if I understand your posts will be excellent in light when my pupils don't benefit from a bigger mm.

My final safari's were last night at Kruger Park, and my "Far Lookers" (what binoculars are called in Afrikaanse is twee‐ogig, or, far lookers) did just great giving my incredible detail in distant shadows other less expensive glass on the ride didn't provide.

Thanks again, head back tonight.

ronh said:

Chosun,

The 10x56 is the best twilight performer that I have used. Although my eyes are probably not taking in the full exit pupil in those conditions, some combination of eyepiece design and the somewhat largish exit pupil make for a view that does not flicker when I glance around the field, as I experience with most 5.0 or 5.2 mm exit pupils. It's the same feeling as with a 7x50. I suppose 5.6mm is enough for me.

I don't notice the depth of field seeming any different in low light. Mainly, everything's just.....darker.

Ron

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I agree, Ron. The 10x56 FL is simply a light-vacuum. Abbe-Konig prisms give Zeiss a decided edge in light transmission - even the newer Swarovisions are no match. My 60 year old eyes can no longer see any advantage to a 7mm exit pupil vs. 5.6. I have never done a side- by-side between the Zeiss FL 8x56 and 10x56 - that would be an interesting comparison for low-light supremacy.

Awesome help. One issue partially eludes me from the excellent material above: Twilight Factor.

While the math is straightforward, this seems to be an at least somewhat subjective measurement that seeks to reveal how much detail you can see in twilight conditions, and it tends to favor magnification.

For instance, Chosun reports a TF of 7x50 binoculars as 18.7, and the twilight factor of 10x50 binoculars as 22.4. Eye age aside, why the superior TF for the 10x50's though the 7x50's have a 7.1mm exit pupil, and the 10x50's only a 5.0mm exit pupil?

Is this because, and here's what seems subjective, is this because the increased magnification presumably makes up for the decrease in brightness in "twilight conditions" (when the eye is not yet fully dark-adapted)?

Sorry if my question lays in my own incomprehension of the principles. Thanks for your patience.

I am 53, and Ronh, Chosun, and other's posts would at this point have me hoping for Zeiss to announce a 10x56 HT. Can delay my next purchase until April when I will be on safari in two African countries again.

Thanks again folks.

. For astronomy it is mainly due to contrast with a much darker sky background with 10×50 compared to say a 7×50.
Stars about twice as faint are revealed with the higher magnification.

For telescopes higher magnifications reveal fainter and fainter stars in practice up to about 30 times per inch of aperture or even greater.
At much higher magnifications than this the atmospheric limitations takeover and no further gain occurs.

I presume that the twilight factor has also been found out empirically rather than from any theoretical calculations.

Initially, so-called theoretical formulae were postulated for the faintest star magnitudes, but these were quite inadequate and did not explain the much fainter stars seen in practice with high magnifications and also by skilled observers with excellent eyesight.

So now empirical formulae are used which match the actual magnitudes of stars that are seen from good observing sites without any light pollution.

Every time I have done low light resolution chart experiments, after I could not see any elements using what ever, when I walked up right after that I could make out some elements. With enough magnification, exit pupil etc., I never tried my 100ED set up at the same time.

I posted this complicated argument about the invalidity of the twilight factor, and edited it as I reexamined my thinking, and continued to edit it until the whole argument vanished in the mist. If some you witnessed this, I hope you were entertained!

Turns out, the more I think about it, the better I like the TF. Increased magnification never reveals as much more as the numbers would suggest, thanks to hand shake. And increased exit pupil doesn't help as much as you might at first hope either, because in many "low light" conditions most eyes can't take all of even a 5mm exit pupil. So, multiply these factors, but water it down by taking the square root--sound pretty reasonable to tell the truth.

Ron

Like Ron I've found TF a good guide to late twilight usefulness, but you still need a bit of common sense. A 10x56 does best out of the binos I've tried at 23.7, but my 12x46 (actual entrance pupil) at 23.5 is nowhere close. The 3.8mm EP is clearly limiting, but interestingly it's still better than my 7x36 with it's 5.1mm EP and 15.9 TF.

David

dwever said:

..... I am 53, and Ronh, Chosun, and other's posts would at this point have me hoping for Zeiss to announce a 10x56 HT. Can delay my next purchase until April when I will be on safari in two African countries again.

Thanks again folks.

Click to expand...

Zeiss has said that there are "GIANT" announcements coming next year, so you may?, possibly??, get your wish??? ...... :h?:

Visual acuity drops many-fold (David had a nice graph somewhere) around that "Purkinje shift" http://en.wikipedia.org/wiki/Purkinje_effect from "Photopic" (day) to "Scotopic" (night) vision, and as Ron finally, (sorry I missed the soliloquy!) concluded something like - there is a 'see-saw type balance' between magnification and brightness to give the best viewing result for the individual, that equations don't fully explain.

I say individual quite deliberately, as there are that many optical (spectrum transmission, etc), physical (age, condition, etc), eyesight (rod /cone make-up /efficacy, aberration characteristics, acuity maps, etc, etc) and processing factors at play - all with a large degree of variance - that it is very difficult to predict the view that you would prefer. For example, a dilating pupil allows more light, but the eye's aberrations also increase - maybe yours do significantly - maybe not. Maybe your visual acuity plunges - maybe it just drops, as light levels decrease. These are just two of the factors in determining whether brightness, or magnification help you the most.

Steve's suggestion of doing resolution testing at this time with different format bins could help you decide - though even this will have inaccuracies due to the possible lag in your pupils dilation /constriction, etc. It is also worthwhile to look at a variety of targets /distances /situations, at this time with different formats (mags <-> objectives), Fov's, Dof's, etc - to see what gives you the best view on actual subjects. As David discovered, even different formats of similar Twilight Factor numbers offer wildly different results. I feel that for myself, useful brightness begins around that ~5mm mark, and that my usual acuity (after computer screen bombardment, etc) could do with all the help it could get! Older folks, or those with better low-light acuity might think differently .......

Thus while TWF may not be the be-all and end-all, it's one of the few things we've got to objectively rank the binocular part of the human-bin optical system, before the subjective clouds come rolling in.



Chosun :gh: