Photo Method for Showing Color Bias and Light Transmission (1 Viewer)

[henry link]

Ron and Ed have done some amazing work with the raw images from my first efforts at this test. Without their analyses I wouldn’t have understood the need for very careful control over the angle of light, evenness of illumination and the exact position of the crops. I have no ability to generate the numbers and charts they can do, so I am concentrating on trying to achieve better reliability and consistency in the original test photos. I continue to hope this test can provide a simple and direct way to make a visual comparison of binocular color bias and light transmission that the eye will instantly recognize, just like comparing paint swatches. The color part seems to be pretty easy, but light transmission accuracy and consistency are hard to achieve. It’s a continuing process. I’ve thought of a few refinements since I made the images in the photos below, but I’m going ahead and posting them as examples of the best efforts to date.

I made a trip to a dealer who is very tolerant of my geeky testing and stocks some models of the (so called) alpha brand binoculars. They allowed me to set up a test in the parking lot. It had to be in direct sunlight, but I’ve tried my best to produce evenly illuminated crops of the same area of the paper in each binocular. In every binocular’s color swatch I had to crop out a bright upper left corner, so I suspect the main culprit in unevenness was a spot of glare on the paper itself, which was imperceptible to the eye.

The left image shows a comparison of four binoculars: Leica 8x42 Ultravid (upper left), Zeiss 7x42 FL (upper right), Nikon 8x42 LX-L (lower right) and Swarovski 8.5x42 EL.
The right image shows a comparison of a Zeiss 7x42 FL (top) and a Zeiss 8x32 FL. I thought that one would be interesting since the optical design and coatings of those two are nearly identical except that the 7x42 uses an Abbe-Koenig prism and the 8x32 a Schmidt-Pechan.

Naturally I have my own opinions about what I see in the images, but I would be very interested to hear what others see in them first (and of course inscrutable charts and numbers from Ron and Ed will be most welcome also).

 

[mooreorless]

Hi Henry, I have been following most of this and I hope you don't mind me saying what I see with my monitor. The first images I see both on left Leica and Swaro are very close and looks slightly grey bias, the right upper Zeiss Fl is white the right lower is red bias"Nikon". Second image top white and lower slight grey. I tried to do this without remembering where the images were for each binocular.
Thanks for taking the time to do this.:t:

Regards,Steve

 

[ronh]

I once had occasion to radiation-damage antireflective layers of magnesium fluoride on glass (related to protective covers for solar cells on satellites), and then measure the loss in transmission vs wavelength in the damaged spot. It was easy to see a spot having only 1% transmission loss in the visible. From that, I would estimate the difference between the AK and SP FLs to be about 1%. I think it's said by Zeiss to be 2%.

This is a very sensitive test, so sensitive that it could lure somebody into becoming overly fixated on trivial transmission differences. Hey, that's a compliment!
Ron

 

[Surveyor]

Henry,

I first tried to get a feeling of color shift just by visual appearance as you requested. My estimates for Slide 2 were that the shift from the background of the two left swatches either were down in transmission or had a shift towards the red end of the spectrum and since I knew the characteristics of the two binos, I estimated a shift towards red but could not tell how much. Looking at the top right swatch, I estimated a shift from the background in the blue-green direction; I was able to cheat a little here since I know all these models are within a few percent of each other in transmission. The bottom right swatch I estimated as having less transmission and a greater shift in the red direction than the two left swatches.

Then I went back through them, measuring the RGB values as previously described with the following results:


Background average of 8 samples=227.5,229.375,231.5
Leica 8x42 Ultravid value=215,215,215 and shift=241,239,237
Swarovski 8.5x42 EL value=215,215,215 and shift=241,239,237
Zeiss 7x42 FL value=215,219,218 and shift=241,243,240
Nikon 8x42 LXL value=212,213,208 and shift=238,237,229

This leads to the following estimates of transmission and color shift:

Leica 8x42 Ultravid = transmission 95%, shift 30 degree, S=2 (orange)
Swarovski 8.5x42 EL = transmission 95%, shift 30 degree, S=2 (orange)
Zeiss 7x42 FL value= transmission 96%, shift 100 degree, S=1(light green)
Nikon 8x42 LXL value= transmission 94%, shift 53 degree, S=4(orange-yellow)

Note that the saturation number may end up being analogous to value of intensity along the dominant wavelength in CIE colormetry i.e. the Zeiss only shift 1% in the light green direction, while the Nikons shift 4% in the orange-yellow direction. This is only a thought and needs further investigation.

Henry, you might clarify one point. My colormetry work starts with a known value and mathematically arrives at the native color point of the bino. I am assuming that you intend to estimate the shift from whatever background is present, instead of a fixed value. I went towards the shift perspective since it looks as if it matches most perceptions better.

Now on to Slide 3. Visual inspection leads me to think there is a color shift of either orange or yellow from the background with a small transmission loss in the bottom swatch compared to the top (more about this later).

The measured parameters were:
Background average = 228,228,232.5
Zeiss 7x42 FL value = 219,221,218 and shift =245,247,239
Zeiss 8x32 FL value = 213,215,212 and shift = 238,240,233

Resulting in:

Zeiss 7x42 FL transmission (Luminance) 97.1% shift 75 deg. S=3% (yellow-green)
Zeiss 8x32 FL transmission (Luminance) 94.9% shift 77 deg. S=3% (yellow-green)

At this point, something I have been thinking about seems to become more obvious. This method is not measuring transmission, but rather the luminance of the swatch and would, therefore, be dependent on the aperture and transmission, maybe not an indication of true transmission.

Henry, you seem to be controlling direction and intensity very well for an outside, illuminated flat sheet. How are you doing it??? This appears that it is going to be a valid test for comparisons done under the same conditions at the same time. It may even carry to independent status under more stringent conditions, but that may negate the simplicity sought.

I have never done any formal testing of the Zeiss FL series, so I am not familiar with what bias I would perceive in the view.

I, also, tried to stay within the confines of RGB, at least to the limit of my understanding of that system since I almost never use it. Ed will need to verify my RGB perceptions (I hope I did not mess them up to bad).

Best
Ron

 

[henry link]

Ron,

Thanks for all your work, again.

The first thing I notice is that the background color and FL crop from the two slides don't generate exactly the same RGB numbers. I don't understand that since they are the very same images transferred from iPhoto to PowerPoint, though I may have resized and reshaped them slightly differently once they were transferred. Should we just expect some small differences in each transfer or should I avoid any resizing or shaping?

As far as controlling intensity, I had to resort to very small crops (about 1" square) inside a 4" square I had penciled onto the background paper. I found I could see small differences in intensity within a crop by transferring a duplicate of it to PowerPoint, then juxtaposing the original and duplicate with different rotations and overlaps. I moved and adjusted the crops until I finally found a crop of pretty even intensity. Then I tried to match that with the same area on the background. Quite a pain in the rear.

Today I tried something different, which is illustrated in the slide below. I used the controls in iPhoto to brighten the four "alpha" binocular samples so that they all approximately match the background brightness which leaves only the pure color bias visible, like the smile of the Cheshire Cat. The iPhoto control of "exposure" assigns numbers to the increases. I don't know what the numbers actually mean, but this is what was required to bring each binocular up to approximately the brightness of the background: Zeiss FL-.09, Leica Ultravid-.13, Swarovki EL-.15, Nikon LX-L-.17.

Also, thanks Ron and Steve for the visual impressions. I think the Zeiss, Nikon difference is a pretty good test for red/green color blindness. And thanks, Ron #2, for the compliment only a true optogeek could appreciate.

Henry

 

[Surveyor]

Henry, the problem with exact matches of the RGB numbers is that I am averaging an area to get the value and even trying to pick the same area (in the above case I used 50x50 pixels) you will get a difference of a couple of counts. I do not have the time at the moment to redo the last Slide you posted, but I did crop an area out of the Nikon, Zeiss and Background of the last slide and process with the online software I listed in Post #17 (since this is an online script, I think it will work with Macs). I cropped a large section of each patch to a separate jpg and loaded that into the program.

Look at the top three rows, the h, s and v rows and, also, notice the color wheel plot on the left of the page. Note how when sampling the patch the RGB values range in color and amplitude of various widths. The upper left box with a saturation value directly below shows the average hue. The total deviation from white is the fourth row, HSV value. The RGB values are below that, but it is hard for me to visualize them.

At the moment, I do not see this as much of a factor since we are looking for a shift from the background to the inter-optic patch.

When you did that last manipulation, it really brought out the red and green, at least on my monitor.

 

[elkcub]

With reference to Post #21, as Ron mentioned the various areas are not quite uniform. The following RGB readings, therefore, are estimates of an average value.

Four section panel:

Background 227, 228, 232 (blue bias)

Upper Left 216, 216, 216 — 8x42 Ultravid
Lower Left 215, 215, 215 — 8.5x42 EL

Upper Right 218, 220, 217 — 7x42 Zeiss (slight green)
Lower Right 215, 212, 207 — 8x42 LX-L (slight red-green)

The two section Zeiss FL panel:

Background 227, 228, 232 (same blue bias)

Upper 218, 220, 217 green bias, (2% greater transmission?) — 7x42 FL
Lower 213, 215, 212 green bias — 8x32 FL

Comments about color tint are based on the RGB weights, but also correspond to my subjective impressions of the various swatches in the panels.

The way I tend to think of this is that the background models daylight, perhaps as seen by the eye, and the various swatches tell us how this is modified by the instrument. This is the work of the optical transfer function for each instrument. So, for example, the Ultravid and EL filter out some blue to produce an equally weighted RGB, whereas the FLs, and LXL change the bias from blue to green or red, respectively. With the appropriate rotation matrix, these values could be represented in HSV format that Ron prefers, but the information content remains the same.

Ed

 

[elkcub]

Then I went back through them, measuring the RGB values as previously described with the following results:


Background average of 8 samples=227.5,229.375,231.5
Leica 8x42 Ultravid value=215,215,215 and shift=241,239,237
Swarovski 8.5x42 EL value=215,215,215 and shift=241,239,237
Zeiss 7x42 FL value=215,219,218 and shift=241,243,240
Nikon 8x42 LXL value=212,213,208 and shift=238,237,229

This leads to the following estimates of transmission and color shift:

Leica 8x42 Ultravid = transmission 95%, shift 30 degree, S=2 (orange)
Swarovski 8.5x42 EL = transmission 95%, shift 30 degree, S=2 (orange)
Zeiss 7x42 FL value= transmission 96%, shift 100 degree, S=1(light green)
Nikon 8x42 LXL value= transmission 94%, shift 53 degree, S=4(orange-yellow)

Ron,

I'm having a senior moment. Don't follow how you arrive at shift values in RGB. I understand the H-shift in degrees when comparing two hues.

Ed

 

[Surveyor]

Hi Ed;

Hopefully I haven't derailed myself with the RGB. What I did was divide the patch R, G and B by the Background R, G and B and multiply by 255 so I could directly compare with the white value of 255,255,255. Example, the Leica and Swaro came out 241,239,237 compared to 255,255,255 white for both luminance and color shift.

Best,
Ron

 

[henry link]

Thought I would post one more image which shows some interesting changes in the color bias of the Zeiss FLs since they were first introduced. The photo below shows a 8x56FL from about 2 years ago (upper left), the 7x42 FL I tested at the dealer last week (upper right), the Leica 8x42 Ultravid from the same test (lower right) and an early production 8x42 FL from 2004.

To my eye it appears that the early FL had a more neutral appearing color bias which more closely resembles the Ultravid. I noticed the slighty greener bias in the 8x56 FL when I first bought it. It's an early example of a LotuTec coated FL and my suspicion fell on that as a possible cause. It's also possible that an unrelated change in the coatings was made to extend high transmission further into the blue/green for a better match with peak eyesight sensitivity in low light. Whatever the reason, it appears that recent FLs have a greener bias than early ones. On my monitor the new 7x42 appears obviously greener than the 8x56 from two years ago.

 

[elkcub]

Hi Ed;

Hopefully I haven't derailed myself with the RGB. What I did was divide the patch R, G and B by the Background R, G and B and multiply by 255 so I could directly compare with the white value of 255,255,255. Example, the Leica and Swaro came out 241,239,237 compared to 255,255,255 white for both luminance and color shift.

Best,
Ron

Hi Ron,

I think you're right on track. You expressed the observed R, G, and B values from the binocular-plus-camera as a proportion of the R, G, and B values obtained from the camera alone. When these proportions are taken of pure white (255, 255, 255) it models the binoculars' (pure) color shift. Of course, this assumes constant proportionality, which makes sense.

To get an idea of what this tint (241, 239, 237) looks like one can use the RGB calculator at: http://webdeveloper.earthweb.com/repository/javascripts/2001/06/48571/hex.html. In HSV terms this comes out to (21, 4, 241). (Unfortunately, the calculator only produces .tiff files, which BF doesn't accept.)

But, our calculations don't quite agree. Using your RBG numbers I would calculate the binoculars' transmission as 215/229.45 = 93.7%, where 229.45 is Sum(RGB)/3. Also, the calculator's HSV is 21 deg. not 30. What am I missing?

The basis for my RGB preference is that it is essentially the Young-Hemholtz theory. A good summary of this and the many normalizations and transformations later developed by psychologists and CIE can be found in "Optics" by Freeman and Hull. http://books.google.com/books?hl=en...X&oi=book_result&resnum=1&ct=result#PPA368,M1 Unfortunately, the whole section on colorimetry isn't available to read on the Internet, but at least some of it is. (I bought the book some time ago.)

Ed

 

[elkcub]

Thought I would post one more image which shows some interesting changes in the color bias of the Zeiss FLs since they were first introduced. The photo below shows a 8x56FL from about 2 years ago (upper left), the 7x42 FL I tested at the dealer last week (upper right), the Leica 8x42 Ultravid from the same test (lower right) and an early production 8x42 FL from 2004.

To my eye it appears that the early FL had a more neutral appearing color bias which more closely resembles the Ultravid. I noticed the slighty greener bias in the 8x56 FL when I first bought it. It's an early example of a LotuTec coated FL and my suspicion fell on that as a possible cause. It's also possible that an unrelated change in the coatings was made to extend high transmission further into the blue/green for a better match with peak eyesight sensitivity in low light. Whatever the reason, it appears that recent FLs have a greener bias than early ones. On my monitor the new 7x42 appears obviously greener than the 8x56 from two years ago.

Henry,

Here's what I get:

Background 229, 228, 232 C= Sum(RGB) = 689

UL 219, 221, 220 Trans= 660/689 = 95.79% 8x56FL
UR 218, 220, 216 Trans= 654/689 = 94.92% 7x42FL

LL 218, 218, 218 Trans= 654/689 = 94.92% 8x42 Ultravid
LR 216, 216, 216 Trans= 648/689 = 94.05% 8x42 FL

Again, there is some variation in each panel. Transmission values are too close to tell apart by eye, IMO. Ron can elaborate on color shift, but I would say the early FL and Ultravid are more "neutral" in the sense that they produce white from daylight. And, yes, the newer ones have a greener bias — good eye!

Ed

 

[henry link]

Thanks for the measurements, Ed.

I should have mentioned that in order to compare the results of the earlier test of the 8x56 and 8x42FLs to the test of the 7x42 FL and 8x42 Ultravid done at a different time and place I had to resort to equalizing the background "exposure" values for the two tests in iPhoto and then applied the same equalization to the crops. Changes in the angle of the sun cause the test brightness values to wander. I may have cooked up a fix for that. I plan to glue an object to the edge of the paper and trace its shadow with pencil. Then all subsequent tests will be set up for the sun's shadow to match the tracing. Then, of course I still have to get the binocular optical axis perpendicular to the paper, something I've just been eyeballing so far.

The biggest surprises for me in the light transmission numbers that you and Ron generate are how very high they are and how closely clustered. In this last test, for instance, I have no trouble seeing the difference in brightness between the FL and the Nikon LX-L by just looking through the binoculars, I would have guessed it's between 5-10%, closer to 10%. The tiny differences your numbers indicate are not something I expect to be able to see at all. From published tests I would have guessed the FL would have transmission around 94-95% (440-450nm), the Ultravid and EL around 89-91% and the LX-L maybe 86-87%.

I was also very surprised to see the closeness of the Ultravid and EL in both color bias and light transmission. They look like they could be two samples of the same binocular.

Henry

 

[elkcub]

Thanks for the measurements, Ed.

I should have mentioned that in order to compare the results of the earlier test of the 8x56 and 8x42FLs to the test of the 7x42 FL and 8x42 Ultravid done at a different time and place I had to resort to equalizing the background "exposure" values for the two tests in iPhoto and then applied the same equalization to the crops. Changes in the angle of the sun cause the test brightness values to wander. I may have cooked up a fix for that. I plan to glue an object to the edge of the paper and trace its shadow with pencil. Then all subsequent tests will be set up for the sun's shadow to match the tracing. Then, of course I still have to get the binocular optical axis perpendicular to the paper, something I've just been eyeballing so far.

The biggest surprises for me in the light transmission numbers that you and Ron generate are how very high they are and how closely clustered. In this last test, for instance, I have no trouble seeing the difference in brightness between the FL and the Nikon LX-L by just looking through the binoculars, I would have guessed it's between 5-10%, closer to 10%. The tiny differences your numbers indicate are not something I expect to be able to see at all. From published tests I would have guessed the FL would have transmission around 94-95% (440-450nm), the Ultravid and EL around 89-91% and the LX-L maybe 86-87%.

I was also very surprised to see the closeness of the Ultravid and EL in both color bias and light transmission. They look like they could be two samples of the same binocular.

Henry

Hi Henry,

A basic question, I think, is the validity of what we're doing. By that I mean, how do our inferences from simple pixel values correspond with refined spectral transmittance measurements of luminous flux? At best, I would guess they are a gross approximation, which hopefully retain ordinal relationships, i.e., A > B > C, etc. For several reasons I can think of its probably too much to expect the scaling to be linear. Ron, no doubt, might comment more about this.

Ed

 

[Surveyor]

Ed,

Sorry to be so long getting back to you but I am having computer problems at work and have to deal with the stuff that pays the bills first. Concerning post #31, I am glad I did not stray too badly. About the difference in the HSV, I think this probably concerns settings of the converters. I have attached a jpg of the calculator I use and for HSV I use the format 0-360 degree for H and 0-100% for S and V. The converter I use will allow me to select from 6 formats for HSV. From the results you show, I think your calculator may default to 0-255 counts for all three values (21/255=30/360, 4/255=2% and 241/255=95%). The difference we have in T% or luminance is that you are using the straight RGB values and I used the CIE luminance value, or L in the Lab definition. The numbers will track in the relative sense, but does point out the need for a good protocol definition.

Henry, ED;

Like Henry, I am surprised by the high values for the assumed T%. At this point, I am thinking what we are seeing is an average of three lens systems, the bino, the camera and the CCD photosites. We are probably also getting an electronic gain figure from the camera program that charges the CCD for a given exposure setting. If this is indeed the case, I think the T% values are more along the lines of a random distribution and are going to be undependable for the use intended, but this is strictly conjecture at this point.

Based on the procedures I have to go through when doing transmission measurements, I am going to assume that a simple transmission estimate is fairly unlikely. Controlling directionality and intensity setup take far longer than actually doing the measurements. For instance, a tightly collimated beam with a maximum dimension of ½ the aperture and preferably less controls directionality. Anyone who has tried to collimate a visible light beam down to close to laser dimensions will understand the problems. Controlling the intensity is a set of problems all their own.

I have attached a jpg of three of the binos referenced (although 20mm versions) that show the levels we should be getting close to but I have never had the chance to test any of the FL range. The values Henry referred to would be typical peak values. The average values for the range of 380-780 nm would be:

Ultravid=76.05%
Swaro=69.77%
LXL=79.78%

For the photopic range of 500-600 nm (I assume camera sensitivities peak in this range, but do not know that for fact):

Ultravid=88.7%
Swaro=87.8%
LXL=85.6%

The color difference is another story. These appear to be tracking very well to me. As Henry noted the difference between the Swaro and Ultravid is very close to the same. Look at the transmission curves and this is confirmed, the shapes are remarkably similar. The colors from the color test were very close also, the color temperature only differed by 11K. You can see the red bias in the LXL plot, very consistent with Henry’s photos.

Still, a method that deserves more study and experimentation.

Best to all.
Ron

 

[elkcub]

Yup, that makes sense. The calculators can be scaled differently within the same measurement framework.

But, I suspect that the computed GRB transmission values were also distorted by Henry's iPhoto correction of the "exposure". This may very well have had a disproportional impact on relative magnitudes because the upper numerical boundary is 255. Of course, I can't prove it.

Henry: In #33 did you really mean 440-450 nm?

Ed

 

[rjwims]

Why did this thread die?

Seemed to be moving along nicely...:-C

Thanks