Why Doesn't Coating Color Effect Image Temp?

[Scott Rosenberg]

just some more late night ponderings... this one for the optics guys amongst us.

some of my lenses have really nice ruby coatings (Sironar) whist others have blue/green (Fuji EBC) and still others have violet/indigo (MC Gold Dot Dagor).

i was wondering why the colors in the coatings don't cause a shift in the color of the image, as would be the case if a colored filter was placed in front of the lens.

thanks,
scott

[Paul Fitzgerald]

Just a guess,

What you see on the glass is reflected white light that has part of the spectrum canceled by the 1/4 wavelength reflection of the coating, not the light transmitted thru it. The glass looks clear, the filter looks colored.

Now for a second cup of coffee.

[John Cook]

Scott, I thought it kinda does, just not so much as you'd notice without really looking for it. (Does that sentence make any sense?)

I have friends who use Nikkor LF lenses exclusively, because they say these lenses are better color-matched as a complete line of products than some of the competition.

Nothing will run up the price of a catalogue faster than a bunch of color transparencies intended to be printed on the same page which don't balance with eachother. Perhaps this is no longer a problem in the digital age. But in my day, it meant the difference between one big ganged separation vs many individual seps, each diddled-with to make match the balance of the others.

[Mark Stahlke]

Maybe it does.

I notice that it's usually the German lenses that have a magenta coating. The Japanese lenses typically have a greenish coating. Some folks claim that German lenses have a cooler color rendition and Japanese lenses are warmer. If the front coating is reflecting a minute amount of magenta or green light, would that explain the claimed differences in color rendition?

Disclaimer: This is pure speculation and could easily be completely incorrect. But it's a nice theory, isn't it?

[David Vickery]

Hello,
The coatings have no effect on the image forming light rays. The modern coatings are very efficient at helping to reduce the flare and reflections of non-image forming light. The different colors reduce specific wavelengths of light. These coatings have no effect on the color of the film image except in that they increase the contrast by reducing the flare, which may allow for more color saturation, etc. depending on the circumstances of exposure.
Furthermore, I believe that the idea of different sets of modern lenses producing a different overall color on the film may be largely another Myth. I am not saying that it is impossible, just that it would require Extremely tightly controlled film, film exposure and film processing to prove it. Everything about color film, from manufacturing, age, transportation conditions (heat), storage, exposure, processing---this may be the biggest variable, etc., has an affect on the final color cast of the image on that film. I think that it would be very difficult for the average photographer to control all of the variables tightly enough to say that a given set of modern lenses produces an overall image color.

[John Cook]

David, I'll buy everything you said.

But just for the record, the studio to which I alluded purchases its Ektachrome all in one emulsion number, direct shipped from Albany through a local distributor. Upon arrival at the studio it is placed directly in a freezer, except for a few boxes which are tested for color balance.

Each individual flash head in the product setup lighting scheme is read with a Minolta color meter and balanced to the others at the final power setting with Roscoe stage gels. Then, when they all match, an over-all reading is made and Sinar CC filters are placed on the rear of the camera lens to balance the film emulsion to the set's Kelvin temperature.

All film is processed within an hour of exposure by the studio's in-house Kodak Q Lab, using tightly replenished automatic dip-and-dunk machines. Each run is monitored with a densitometer and Kodak-exposed test strip from the freezer. The dry transparencies are viewed on a calibrated Macbeth light table.

I would tend to believe these folks just might know of what they speak. The lithographers don't have many complaints. Or it could all be baloney designed to fool the art director...

[george jiri loun]

Paul, you're right. It is the same as if someone wondered - how come when I take from inside a lake a picture of a stick put in it the stick is right when looking at it out of the water I see it broken...

[paulr]

John, it's true that different lenses render color differently (although pretty slightly differently with modern lenses). It's very unlikely that this has much to do with visible differences in the color of the reflected light from the coatings. A lot goes into color balancing a lens, including matching the glass choices of different elements.

A Schneider technician told me that Asians actually tend to see colors slightly differently than Europeans, which accounts for the general slight differences between German and Japanese optics--it's not so much an esthetic choice as it is everyone seeking a slightly different interpretation of neutral.

[francisco_5406]

If little green people from Mars made film and lenses, we would see their products optimized for pleasing green fleshtones.

Asian skin looks much better than Caucasian skin on Velvia. Probably the same for Asian versus Euro lenses. The urban legend is that Kodak always judged its products fleshtone response by Caucasians on an overcast day in Rochester, New York.

John, I too remember the days of adding a 0025CC Y or M Wratten to a batch of film. But now, thanks to that wonderful little "grey balance" eyedropper tool in Photoshop, I only filter for 2000 degree color shifts!