Twilight Viewing (2 Viewers)

Hi. I have a pair of non HD Ultravid 10X42 binos which serve me very well for bird watching. However, we have started getting hedgehogs coming to the garden at dusk and I am looking for a second pair specifically for low light viewing. I can't justify a pair of Ultravid 8x50s or similarly priced binoculars but I am considering a pair of Trinovid 8x50 BAs. As far as I can tell the advantage of the Trinis is the 50mm lens and the increased exit pupil size, and for the Ultravids, the better coatings. Looking at some of the birdforum posts indicates that the Trinis would be a bit better in low light conditions, so my question is, how much better? Is it worth getting them for watching wildlife and birds at dusk - how much longer would I be able to view things? If it is an extra 5 mins over the Ultravids it isn't worth it but if it is, say, an extra half hour it might well be. Thanks.

Hi Tricky, and welcome.
Depending on your pupil size, the 8x50 should be better.

The amount of twilight depends on the time of year and your latitude.

Unlikely to get anywhere near 30 minutes, and I am an astronomer, not an experienced birdwatcher.
The birdwatchers might have an idea, but I'd guess 5 to 10 minutes maybe.

Also one should know the close focus distance of the binocular to be sure the hedgehogs are in focus.

Tricky,

Not a straightforward question to answer.

I appreciate that many birdwatchers head for home when the light is low enough to dilate their pupils to about 4mm, so your UV 10x42 ticks that box. In birdwatching terms, you might get another 5 to 15 minutes with a 5mm EP depending on the season, in terms of light level, but that is not the only consideration. Whereas the light might be red at sunset, it is often strongly blue in the hour or so after, which doesn't play to the older Leica's strengths. Perhaps Swarovski and Zeiss vie for the top spot, but many more modest pairs do quite well. Once you get to moon light or the glow from street lights the ability to distinguish colour will have faded. You would need as much exit pupil as your age can manage, but it would be a mistake to sacrifice magnification if you can help it. A 10x56 appears to work best for me, but a 12x50 still did better than an 8x42 by moonlight in a direct comparison. For the amount of low light usage I do I couldn't justify spending a lot. My £300 10x56 serves my needs pretty well. I suspect the Swaro SLC might be a fraction better.

Good luck,

David

I think you would have to compare side-by-side under your circumstances to be sure if the 8x50 will work noticeable better than the 10x42.

If your eye pupil can dilate to 6.25 mm and if it's dark enough, you will get 120% more light with the 8x50 (39 vs 18 in relative brightness).

The variation in maximum dilated pupil size is significant.
Even at the age of 69 it might be as large as 7.5 mm.
So what works for others might not work for you and vice versa.

http://lasikcomplications.com/images/pupil_size_chart(Mar2011).jpg

HI,

The UVHD 10X42 is a nice binocular. IMO you'll have to really step it up to get an appreciable difference in viewing time and quality at dusk. Personally, I'd stick with the 10X magnification. I'd go up in objective size to 54-56mm AND i'd PREFER to have a binocular to have A-K prisms. So basically that includes the Swarovski SLC 56mms, Zeiss Conquest HD 56mms, and Zeiss HT 54mms. You also may find a used Zeiss FL 56mm around. The Conquest HD 56mm is probably the most bang for the buck...probably not a whole lot more money than the Trinovid BA you mentioned but should be a better binocular overall for low light viewing.

You might check out the Meopta B.1s as another option.

Does anyone have experience of the
Leupold ProGuide BX-4 12x50?
It is in the current ProGuide range
(around for more than a year now I think)
replacing Mojave ProGuide BX-3 (dropping 'Mojave').
Its low-light ability is praised in
user reviews at online retailers' sites etc.
Thanks! Adhoc

I was hoping to keep things simple, but it sounds like I need to explain things further. ;-)

I'm sure most have heard of the Twilight factor, but I guess fewer understand what it really means. It was derived from a study by Zeiss scientists to determine the limit of acuity in low light for different magnifications. It doesn't tell you anything about how bright the scene appears, only the level of resolvable detail. Twilight in their terms is not the limit of colour vision (photopic) that would provide the full stop for most birding, but more akin to moonlight levels, when hedgehogs are most active.

Just to keep it simple, I'll just illustrate if for a 5mm EP which might be the maximum for the average 65 year old.
7x = 15.7
8x = 17.9
10x = 22.4
12x = 26.8

It tells you that by moonlight, an average 65 year old would be about 70% better off in seen detail with a 12x60 than a 7x35, but there would be no difference at all in apparent brightness. Obviously individuals will have different maximum pupil dilation, and it doesn't give you any detail on the tradeoff at sub optimal exit pupils. My own pupils dilate to around 5.5mm a while an 8x42 looked brighter than a 12x50, I could see more detail with the latter.

Leica did a comparable study, but instead of acuity limit, they looked for the threshold for target detection. Like the Ziss study, it was conducted on young adult males. Holger Merlitz has published a paper describing how the results would be affected by the pupil reduction as we age. Although this is quite a different metric to the Zeiss study, it shows an even clearer benefit due to magnification. I won't try to extract some illustrative numbers from that paper but try to describe a comparison I did which convinced me of it's validity.

The view from my back fence is across a ploughed field to a small wood and hedgerow about 150m away. There was some moonlight, but at least part of the illumination was was from the street light glow of the town hald a mile away. I had to hand a 7x36, 8x42, 10x42, 10x56 and a 12x50. I started with the 7x trying to both determin the approximate level of detail I could see in the open, and also in the shadow of the hedgerow. I switched to the 8x and there was a slight improvement in detail, but to my surprise I could now see an animal moving. It might have been a dog or perhaps a muntjac deer I couldn't tell, but I rechecked with the 7x and I couldn't see it. Next the 10x42. The view was dimmer, but now I could see it was a fox. With the 10x56 I could not only see the fox, but also the rat it was hunting a few yards away. Again the view was dimmer with the 12x50, and the detail not as clear as the 10x56, but I could still detect the rat. I checked again and it was still invisible with the 8x42, and the fox invisible with the 7x.

Unless you are a 20 year old whose pupils still dilate to 7mm or more, based on the work of Zeiss and Leica and my own comparisons, I think you would be better off with a 10x56 than a 7x50..... when looking for hedgehogs by moonlight.

David

David, For long I have been a keen proponent of the 'twilight factor', and magnification for night viewing, in these forums, against strong opposition. I am happy to learn of this support from you--and Leica: I was only aware of the Zeiss formulation (though I never could find the original publication on the internet).

However, you have missed one important condition: the optical quality of the instruments has to be equal or close. I remember that an 8x42 Leupold Mckinley showed more detail than a 10x56 Barr-&-Stroud Savannah-ED at night. (I went for the B-&-S on praise by you for the Eden 10x56 and by another respected BirdForum member elsewhere for the B-&-S Savannah-ED 12x56.)

Adhoc,

As always, there will be various terms and conditions. The binocular transmission spectrum, particularly around 500nm, the spectrum of the illuminating light, the yellowing of the eye, and the optical resolution of the eye at full pupil dilation are just a few that spring to mind. As we always say, there is no real substitute for trying something for yourself.

David

David, on several occasions the same scene (differing with the occasions) was viewed by the same observer (myself) moments apart, so those last 3 factors (you give as examples) were constant. As for the spectrum, the Leupold (in good light) was actually "warmer", like Leica, the subject of this thread. I thought this difference at night was due to resolution and contrast, which in good light were better in the Leupold. At night I would guess that this applies not to small detail but to outlines (such as of your animals).

Adhoc,

You might have seen me mention that the Zeiss HT 8x54 appeared soft to some users as it was effective resolution limiting in good light. The Savannah 12x56 would have been designed to the lower ISO 14133-1 standard and it wouldn't surprise me at all to hear it was soft in good light. It' a quirk of the ISO criteria that the 8x42s tend to be a bit better. Low light is another matter. Our pupils dilate and our acuity drops. I would be very surprising if either of your sample was resolution limiting in low light.

I'm not totally sure we are talking about the same critera, and same light levels. I've tried do draw a distinction between photopic and scotopic conditions, where different rules apply. In the blue hour after sunset a warmer biased binocular may increase contrast, but reduce brighness for example.

Unfortunately I've not tried either of the models you mention, so I really can't comment on the specifics.

David

Thanks David. So, again, I think that how much I know and understand is enough, but... :'-(
BTW in that smiley the ' is supposed to be a tear, but not all fonts convey that well; it works better when slanted, still better when "teardrop shaped"

Tricky, I want to echo Chuck's recommendation to stick with 10x, and go for 56mm rather than only 50 since you already have a 42, and a high quality glass with AK prisms if possible. The SLC 10x56 I recently got also does very well in the bluer light of dusk, which David alluded to, as Zeisses also may. I prefer the view of the Swaro myself, but think you'll be favorably impressed if you try any of these at dusk.

Has Tricky001 made any progress with observation of hedgehogs in his garden?

I made an earlier post suggesting he might have a go at twilight observing with a 7x50. But after noticing this thread is part of the Leica forum, I deleted my earlier post -- not meaning to horn into the Leica users.

My experience of garden twilight observing occurs at a fence row 35-40 yards behind my home with one of two binoculars:


I use the 7x50 size frequently for this fence row observing at twilight. I get an additional 30 minutes at twilight (and dawn) by switching from a 8x40 or 10x50 to one of the 7x50's. The larger exit pupil makes a difference to my eyes at this time of decreased light.

I also use my 7x50 in heavy shaded woods -- hence the marketing name of "Foresta" for the Vixen 7x50.

Back to Tricky001 and the Hedgehogs in his garden. One influencing factor, in my opinion, is the distance from Tricky001's observing location to the Hedgehogs' foraging location in his garden.

I enjoy reading the Leica twilight optical research. Thanks for sharing.

If viewing at dusk IMHO, and you want the aperture, go with the mag, as David says, I can see much more with a 10X50-56 than a 7X50. If your pupil can really open to 7mm, then use a 8X56, still better than a 7X50.

Andy W.

Tricky:

fwiw, have put some effort forth in low light viewing from dusk well into the night over the years for general wildlife and owls in the birding sector. Have doubts that the 8x50 Trin would yield a significant advantage over the 10x42 Ultra. Different yes, advantage no. A half hour isn't likely to happen with handhelds betwixt like quality 42mm & 50mm, unless something is awry, imho.

Have also settled on the 10x56 handheld configuration specifically...for myself.

I don't manage a flock of binos, so to keep a lid on examples I just buy top drawer stuff to compare, at the risk of leaving money on the table.

I had great hopes for the 54mm Zeiss HT as I prefer the ergos and weight, but the Swaro 56mm AK prismed version of the SLC consistently showed better definition during a number of low light comparisons done over some months.

The 56mm version provide a notably better low light view than my 42mm glass on hand--enough to differentiate for me.

David(/Typo),
With ref. to posts #8 to #12 above
What possibility/ies can you think of
why that 8x42 showed more detail than that 10x56 at night?
Thanks! Adhoc

Adhoc,

As I indicated in #11 I don't really know enough about you, the binoculars, and the conditions when you did the comparison to have much Idea. What was the nature of the detail you were comparing and how dark was it? Do your pupils dilate to 5.6mm?

On the face of it, in terms of resolvable detail (Zeiss) the 10x should have had about a 20% advantage over the 8x (allowing for a bit of hand shake) at the tail end of daylight, improving to around 30% by moonlight. For the contrast threshold, it would again be about 20% at the end of day, increasing to 50-60% by moonlight. Both sets of figures assume that the transmission and other optical properties of the two binoculars are the same. In this case they are probably not, but even an aluminium versus dielectric mirror difference (?) shouldn't reverse that kind of advantage on it's own by moonlight.

You say the comparison was at night. The Zeiss and Leica calculation roughly hold for the 0.3 down to 0.003cd/m2 light range, which approximates to moonlight levels. If your comparison was instead at the tail end of daylight, say around 1-5 cd/m2 where there is still some colour vision, then under the blue ambient light after sunset I guess it's possible that a large difference in short wavelength transmission could make such a difference, but that's wild speculation. It's probably a combination of a number of number of things.

David

From the diagram found in the second link, you can see that an 8x50 seems to be more useful in twilight than a 12x42 for example (for contrast detection).
A 10x50 would have even more of an advantage at beginning of twilight but not when light level decreases even more. All this assumes that your eye pupil is large enough to utilize the full EP of the binocular. I guess that this is what makes the twilight factor fairly unprecise and dubious, since a 12x42 and 10x50 have almost identical twilight factor.

https://de.wikipedia.org/wiki/Dämmerungszahl

https://de.wikipedia.org/wiki/Fernrohrleistung

Link to diagram:

https://de.wikipedia.org/w/index.ph...utzleistung.jpg&filetimestamp=20150409085426&

I seem to remember that most of that second article was originally authored by Holger Merlitz, though it seems susequently amended by someone else. You can find Holger's complete paper, including the consideration of the older user, by diwnloading the link from Holger's website.

http://www.holgermerlitz.de/bino_performance/bino_performance.html

David