Filters anyone? (1 Viewer)

I've been trying to figure out for quite a why I prefer one pairs of binos under one set of conditions and different one in another. Probably obvious to many here but differences in transmission curves or colour balance appear to provide a big chunk of the answer. Just wondered if anyone else thought it was a good idea to be offered a totally neutral transmission pair and filter sets to modify the profile. Not an original idea I know, but it seems to have gone out of fashion. I've only found a few astro or marine pairs where it's currently offered.

At a basic level it's not uncommon for marine or 'tropical' pairs to have a lowish blue transmission, surveillance pairs to have a very strong peak in the green and for birding pairs to have a slight red bias (and sometimes a slight dip in the green). At least to my eyes these all provide a positive colour contrast balance (or sometimes contrast) benefit when used under appropriate conditions and are counterproductive under others. Some would see a totally flat 100% transmission as a technical ideal, I don't see it as a satisfactory solution on it's own. We've seen some pretty vigorous debates about perceived difference in models and brands. User tunable seems a reasonable way to go.

While my own bino collection is very humble but I've now spent quite a bit of time trying a variety of alphas trying to figure out which would suites me best (if I had the money). The answer appears to be.... that depends on the season, weather and time of day. So even the relatively small differences amongst the top brands I seem to register quite differently according to light conditions. Perhaps the most interesting result was that, at the weather extremes, the answer was sometimes none of them, a cheepie did a better job in emphasising contrast.

So would filters be the answer? I've not seen transmission curves for any of my pairs of binos, but at least to my eyes, I have a Bushnell with a slight red bias, a Pentax that appears to have green dip and a Chinese porro with a strong green bias. While far from ideal, using a swatch of theatre lighting filters from Lee Filters allows a fairly crude way of refining the view. I've found it's possible to substantially 'correct' the colour balance to somewhere close to neutral, and even enhance the colour contrast to close to my own preferences.

This lunchtime, the Pentax view seems 'neutralised' by filter 278 and enhanced by 159. The Chinese porro neutralised by 003 and enhanced by 279. Today I liked the Bushnell colour contrast as it is but the view is neutralised by 218. Under different conditions I've made different selections. You can look up the colours and spectra here.
http://www.leefilters.com/lighting/

As a foot note. In light of the ongoing debate over on the Nikon forum I do know the difference between contrast and colour contrast. My personal position is I am happy to use any distortion in the transmitted colour spectrum that helps me to distinguish birds from their surroundings.

Any opinions?

David

Color filters will of course selectively reduce the light transmission, so you are reprofiling the transmission curve to a different shape at a lower level. We know that works, as indicated by the universal use of filters in military glasses, although afaik the military only used yellow and gray filters. There may be much more available on this topic and hopefully one of the experts on this forum will chime in eventually.
However, I've not seen anything published that documents or ranks the effectiveness of various filter colors, or that attempts to do what you are doing, to discern which works best in which conditions.
Please keep us posted as your evaluation proceeds.

I much prefer neutral colors. I'm less concerned about acquiring a bird (under one particular set of circumstances) than I am about the colors of the bird appearing as close to natural as possible. Unfortunately, current glass and coating technology cannot achieve a completely flat transmission curve, so our choices are really between different departures from perfectly neutral. I'd be happy if all binoculars were tuned for the flattest possible transmission and had filters for task specific or just aesthetic purposes. I just wouldn't buy the filters.

Etudiant,

Those filters I used re-profile at a much lower level, but it seems inconsequential in good light. The choice to take them off for low light seems good to me.

Henry,

Simply advocating choice. At the moment it appears the manufacturers are making that choice for us, presumably based on some median preference in a particular market. I know you have reservations about the Allbinos data. One of the flattest transmission curves on there I've spotted is the Steiner Nighthunter.
http://www.allbinos.com/188-binoculars_review-Steiner_Night_Hunter_8x30_XP.html

Steiner don't bring that range to Bird Fairs. They bring the Skyhawk (which seemed to have the usual red bias) and other cheaper pairs. The reason I was offered was that the Skyhawk series had the colour balance preferred by birders.

David

David,

Yes, I've seen that Steiner review. Quite spectacular if it's true.

Henry

As David suggested, there has been US military work in this area. The attached 1992 NAMRL report deals with the development of an ideal military aviation sunglass, and the findings are very encouraging, at least for pilot detection tasks. Theoretically, at least, there is a ~5% increase in performance.

Those whose eyes glaze over at math can probably skip the formulas; however, please don't miss that the calculations necessarily incorporate the visual luminosity function. By and large, this paper is an excellent example of how the best human factors engineering research is conducted.

To accomplish the same optimization for combined sunglasses (i.e., filers) and binoculars, it would seem that one would only have to incorporate the transmission function of the binoculars into the equations. Unfortunately, though, since all binoculars have different transmissions, ideal filters would have to be developed for each one. (Sub-optimal filters should not be a problem. )

Ed

Thanks Ed,

An interesting article. I'm not sure "blue blockers" are going to be a popular birding choice. For a totally unrelated reason I made up some 'glasses' using filter 021 which is not so very different from their recommendation if I understood the paper correctly. The effect on perceived contrast was pretty dramatic but I wouldn't recommend it for nature watching. More subtle filters like 223 seemed a possible for bright days.

David

Is there not a bias in this study from the setup?
It uses a bright background as its baseline.
Detecting targets against a blue sky may not a very good model for birding in brush or at dusk.

I think the paragraph below formula 15 acknowledges that. Any idea what the "spectral composition of the ground" might look like, or maybe more appropriately foliage etc.?

David

The photos below show what can happen when you try to enhance contrast for a specific task by fiddling about with the color transmission curve. In this case the very specific task is increasing the contrast between green and red book spines. The color transmission is manipulated here by using a sharp green filter that transmits lots of green, but very little red. That's the opposite of binoculars that have peak transmission in the red and this filter is much more severe than any binocular color bias, but the principle is the same. As you see the filter works beautifully to increase the contrast between the top and middle books, but the very same manipulation has the effect of greatly reducing the contrast between the middle and bottom books. Whatever you do to manipulate the color transmission for enhanced contrast under one set of circumstances will always come back to bite you somewhere else.

henry link said:

The photos below show what can happen when you try to enhance contrast for a specific task by fiddling about with the color transmission curve. In this case the very specific task is increasing the contrast between green and red book spines. The color transmission is manipulated here by using a sharp green filter that transmits lots of green, but very little red. That's the opposite of binoculars that have peak transmission in the red and this filter is much more severe than any binocular color bias, but the principle is the same. As you see the filter works beautifully to increase the contrast between the top and middle books, which had low contrast in unfiltered light, but the very same manipulation has the effect of greatly reducing the contrast between the middle and bottom books which had high contrast in unfiltered light. Whatever you do to manipulate the color transmission for enhanced contrast under one set of circumstances will always come back to bite you somewhere else.

Click to expand...

Seems that just like everything else in binocular design, transmission curves are compromises.
Still, the size of the effect in the study was pretty big, almost 20% range between the simple darkened sunglasses and the contrast enhanced glass. Is there a niche for a variable filter here that could allow some of that improvement without crippling the glass for normal use?

etudiant said:

Seems that just like everything else in binocular design, transmission curves are compromises.
Still, the size of the effect in the study was pretty big, almost 20% range between the simple darkened sunglasses and the contrast enhanced glass. Is there a niche for a variable filter here that could allow some of that improvement without crippling the glass for normal use?

Click to expand...

If one were to advance binocular technology by the inclusion of variable optimizing filters, this paper goes a long way to establish a visual performance basis for filter design/selection. In fact, the authors say:

The overall procedure developed in the present study may be applied to any of several different kinds of tasks where distant vision is crucial, that is, tasks that depend on detecting small differences in contrast between a target and a background. Spectral filters may then be specifically designed to enhance the target-to-background contrast differences and improve the performance of such tasks.

Click to expand...

Holger Merlitz has speculated about this sort of thing several times. As we know, some military field binoculars incorporated a mechanical filter array, although the purpose (visual tasks) it served, or how effective it was, doesn't seem to be well documented. In the case of birding tasks, however, I would think that hawk watching and pelagic birding come very close to what was optimized by these authors. Shore birding might be another.

As an engineering psychologist, I can't help but feel bitter-sweet about the Summary and Recommendations starting on pg. 22. One paragraph is worthy of note, which I'm sure fell on stone-deaf ears in 1992:

There is now a theoretical basis for considering the use of color in sunglasses. The effects of tinted lenses on color appearance and wavelength discrimination also need to be addressed. Studies of color appearance through colored filters are surprising —they consistently show that filters have little effect. In other words, objects seen through the filters tend to maintain their normal color appearance (38,39). Although this may at first be astonishing, it is consistent with the well known facts of color constancy. Again, the mechanisms for color constancy are not well understood, but the point is that there are reasons to reevaluate the common wisdom that colored filters are a hazardous disruption of normal color vision.

Click to expand...

Happily, however, it does support David's last reflection in the OP.

My personal position is I am happy to use any distortion in the transmitted colour spectrum that helps me to distinguish birds from their surroundings.

Click to expand...

Ed

http://www.roxoreyewear.com/

These sunglasses block wavelengths of the (green) sensitivity peak of the human eye, while keeping the other wavelengths pretty bright.
Theoretically, they'd be nice under green foliage to increase contrast against birds, but I'm still doubtful about that. I prefer everything to be as bright as possible.
They are primarily made for golfers.

Their Swedish homepage is quite crappy IMO, with useless marketing BS and silly links.
However, this does not imply that the sunglasses are crap.

Anyone here who tried them?

As a birder, I'd say any intentional filtering or bias is gonna mess up some ID's at some point. Give me neutrality and a minimum of CA and I'll take it from there.

Distinguishing birds from the background is seldom the problem; distinguishing subtle variations of color often is.

Mark

Just a small update of the filter experiments. Previously around midday, the Bushnell needed about a 5-10% cut in the yellow to red to give something close to a neutral colour balance. I did the test again shortly after sunset today. Much trickier to gauge in the cooler colour temperature, but the warm balance of the bins really over cooks the yellows in particular. A 20%-40% ( Filter 169-136) cut in the yellow was very acceptable improving the view dramatically, just leaving our red/purple leaved shrubs looking a little hot.

David

looksharp65 said:

http://www.roxoreyewear.com/

These sunglasses block wavelengths of the (green) sensitivity peak of the human eye, while keeping the other wavelengths pretty bright.
Theoretically, they'd be nice under green foliage to increase contrast against birds, but I'm still doubtful about that. I prefer everything to be as bright as possible.
They are primarily made for golfers.

Their Swedish homepage is quite crappy IMO, with useless marketing BS and silly links.
However, this does not imply that the sunglasses are crap.

Anyone here who tried them?

Click to expand...

Well I read thru the tech info and quite frankly I come away with the impression they are pushing ubiquitous AR coatings as an original idea. If anything most of the benefits they claim can also be had with polarized lenses.

On the otherhand, probably not much different marketing approach than with my brand. I wear a sunglass model from Swan in Japan that I can change lenses out for different weather conditions and activities. Mirrored polarized smoke for bright sun/beach/water/snow (useless with roof bins!) Lite amber for hiking in cloudy weather/dove hunting (excellent with bins!), and brown for everday use in the city.

Check pp47-48top of their catalog for explanations of the various tints.

RJM,

I really don't know much about the Roxor sunglasses. But the idea is based on very precise filtering, i.e. the tint of the lenses.
If they really are something special, they'd deserve a much better marketing where solid technical documentation could be had.

My Serengeti polarized AND photochromic AND antireflection coated sunglasses with sort of burgundy tint are quite nice, but don't see much use.
They seem to suppress the greens, too.

//L

Presumably a digital binocular would be able to implement such filtering more practically as well as all sorts of other features such as colour saturation and sharpness enhancement.
Guess the variables of colour bias of binocular glass, the ambient light as well as colours of subject and background all play a part. Maybe could do with a clearer definition of what is meant by neutralise vs contrast enhancement of a view? For example if viewing an LBJ swathed in glorious golden Autumn morning light can you describe what procedures you might you go through to achieve those objectives?

Example of colour cast removal and saturation increase "digital enhancement" attached (adapted from nice original taken by Richard Brown posted on following site recently :
http://merseawildlife.blogspot.com/)

Norm,

Generally on most cameras you can adjust the colour temperature to suite preference. Turn the orange light at sunset to something like the 'white' light of summer midday (~6000k). That could be an options for digital binos. For my own preference under bright conditions I feel I can better distinguish the detail on a bird and the bird from it's surroundings with a warmer balance, perhaps about 4000-4500k (preffered colour contrast). This seems to be close to what some binos offer, but then they can over accentuate the yellows and reds nearer to dusk, when a bluer balance would be advantageous. Just one thing that might be possible with filters. I Just used 'neutral' and a shorthand for a 6000k type balance, and 'enhanced' for a 4000k type balance. The experiment was a simplistic way to demonstrate, at least to myself, that the filter approach could be useful.

David

David,

I'm happy you started a separate thread on this subject. I agree with the basic tenants of your OP.

I prefer a "warm" bias for birding bins. However, as you pointed out, and as I wrote on the Nikon thread you referenced, different conditions can bring out the best or worst in the color balance of bins.

The idea of being able to manipulate the color balance yourself rather than having to switch bins is an intriguing idea and makes "hybrids" possible.

For example, an 8x32 FL/HG. You might like the CA control of the FL and the smooth but slower focuser (450* vs. the HG's 260*), but prefer the stronger red bias of the HG.

Through a combination of filters or a custom HG/FL filter that could add the light curve of the HG and minus the light curve of the FL, you could get the best of both worlds.

Henry's idea would be much simpler if it could be achieved. Then your filters could mimic certain preferred color balances w/out having to compensate for the color balance of the bin you're trying to modify.

I have a color filter set that I used with my telescope. They screw onto each other, so you can use multiple filters at once. I think there's also skylight filter in the set, and somewhere I have a pair of polarizing lenses, which I used to "fade in" and "fade out" with my old Super 8 camera.

After "crunch time" is over next week, I will try to experiment with the filters in different lighting and see what I come up with.

Adding optical elements will lower the light transmission, but high quality AR coatings on the filters would help.

A few binoculars, such as the Fuji FMTs have threads on the objectives for filters. These would be easier to experiment with. My filters were made to attach to the rear of threaded 1.25" telescope EPs. So I might have to make a mask to keep the filters from touching the binoculars' EPs.

Ed, Thanks for attaching the report. Have too many facts in my head right now about "human factors engineering" to read it now, but I will later (I'm writing about biomedical engineering).

Brock