Colours and brightness in binoculars
Lifelike colour reproduction and good brightness are essential qualities of a great binocular. Could I get a more objective view by photographing through the objectives of binoculars and then analysing the images in Photoshop?
Some questions I was really curious about: The green colour cast of the SF, the quite dark appearing view of the Nikon EDG, the awesome glow of the Leica Ultravid, and what is the colour difference between the 8x42 and 8x32 Ultravid - they look a bit different when using them...
I did some research about the CRI (colour rendition index) of light sources and after disappointing results with daylight, fluorescent light and halogen light with blue gel for daylight balance I was finally successful with unfiltered halogen light, which can have the highest possilbe CRI of 100 at a colour temperature of 3600K. This approach revealed subtle colour nuances and was consistent with my visual impressions when using the binoculars.
Setup - I moved one lamp to get a spotlight on the binocular for documentation, so that shade in the background appeared which was absent in testing...
Method: I took two 100w halogen Dedolights (high quality film lights) and lighted a simple white paper at 45 degrees from both sides (the same paper I had used with all other light sources). Binoculars had all been focused to infinity. I put the binocular´s ocular with eyecups screwed or folded down in a constant distance to the white paper (about 15cm) to insure brightness could reasonably be compared, and photographed through the objectives with fixed ISO, aperture and exposure time so no colour channel got clipped. A good alignment of the axes of the photo lens (Olympus ZD 50/2 on Olympus EM-1) and the binocular optics was essential but possible with a bit of practice. As the light intensity reflected from the paper was very high and distance to the test samples low I did not worry much about coloured spill light from the surroundings, and the halogens were the only light source in the room. I developped the RAW files in Apple Aperture, whitebalanced on an image of the white paper and applied these colour settings to all images.
Above is the Ultravid, below the Zeiss SF:
Can you see the difference? Not really. But wait.
The point is: Looking at white you will hardly see color casts, for a couple of reasons - the logarithmic nature of our vision which makes us rather unsensitive to brightness and colour differences in highlights which we can easily perceive in shadows and midtones. Moreover, we know highlights are generally white or should be white so our brain will strongly correct for this.
So yes, your white egret will look white even with the Zeiss SF.
When a hard-boiled binocular fan complained to me about grey harriers looking grey-green observed with the SF I realized that this fit with my experience -"it´s the midtones, stupid" - I really resent to watch the brown-grey bark of my apple trees with the Zeiss SF, they look weird, and my red bird house just looks subdued in colour, as red is weakened by the complementary colour cast of the SF.
Anyway, I lowered the brightness by a constant amount for all images, so that white would be mapped to a middle grey. I did not touch colour, just reduced brightness, as this makes colour casts more visible. I used the darkened image of the white paper as my reference grey as a background for the images.
This is what I got:
In the next step I zoomed into the images to get a pure colour and consistent brightness in the brightest, unvignetted central part of the image.
To be able to see even more clearly what is going on, let´s increase the saturation:
When arranging the images I started with the Habicht 8x30 for the most neutral colour. Next to it follow binoculars with a hint of green (the almost neutral DDOptics EDX) to a touch of green (Zeiss HT) to a distinct green cast (Zeiss SF). The Habicht 8x30 from 1961 has a terrifying green cast. You can already feel the heat of the Leica Glow in the Leica Ultravid 8x42 sample, it looks slightly warm and extremely bright, whereas the Ultravid 8x32 has a more reddish cast, which leads to the row of Nikon glass with just a touch of - Nikon typical? - red, with the EDG still being almost neutral. The vintage binoculars are interesting, too, the Zeiss West is comparatively bright but very yellow (its prisms are slightly hazy) and the Leitz Binuxit - although I cleaned it - is very dark and yellow-green.
Generally, brightness is difficult to rate, and for me the most important thing is the visible sparkle an Ultravid Plus and Zeiss HT have, but this is much more about beauty than about functionality. Even in beginning twilight, where brightness differences may be most important, I was not able to see more usable details with a Zeiss HT than with the quite dark Nikon EDG. In night vision, I see no differences at all.
Again, photographing through the objectives brought more evidence.
To my eyes Ultravid and SF look brightest here, with the EDG looking a bit darker than the HT. What happens if we turn this to black and white to block out the colour casts?
I am not sure about the validity of converting the colour charts into black and white to a) better judge brightness or b) even simulate colourless night vision. The sensitivity curves of our night vision receptors will surely not match the algorithms of the imaging software. Please mail me if you have any ideas about this.
Generally, the brightness differences are probably only a rough estimate with this method.
But it is probably fair to say Ultravid and SF look brightest here and the Nikon EDG looks quite a bit darker than the other 8x42s. Also I find the Nikon 8x30 E2 looks really dark, especially compared to its direct competitor, the Habicht 8x30, something that had disappointed me in the otherwise excellent Nikon SE 8x32, too. Looking at the vintage binoculars, the 1950s Leitz Binuxit is by far the darkest bino in this comparison, the 1961 Habicht 8x30 is still very dark, but the 1970s Zeiss West 8x30 looks surprisingly bright, especially compared to the Nikon E2.
My personal favourites colourwise at the moment are the Ultravid 8x42 HD Plus and the Swarovski Habicht 8x30. Generally I tend to prefer a hint of warmth in the colour cast which makes images look more pleasing when observing in bluish light.