Orthochromatic Response Curve

[Machinbird]

Hi everyone. Does anyone have a good link to a color response curve for orthochromatic film as used in WWI? I'd like to be sure the response curve is not what is now called Monochromatic film. See example below (taken from a radiology film site) I suspect the "Blue Film" line corresponds to monochromatic film, and the "Green Film" line corresponds to modern Orthochromatic film. Also, does anyone have any idea if filters were used in WWI to better balance color response of the film?

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Just multiply micrometers times 1000 on the color scale to match with nanometers on the response chart.
Had an idea while watching a video of Voss turning the propeller on 103/17. An area of the cowl that had been in shadow was now in sunlight. By measuring the actual change in density that occurs in the area of interest and knowing the response curve of the film, you should be able to make some conclusions about the general color of the surface. You could probably do the same thing by measuring the change in density across the shadow line on a photo assuming you knew that the color did not change in the area of interest.
What I expect is the non-linearity of the film color response to different colors of light will point out the color, or at least eliminate the possibility of certain colors.
Say the color is red. The "orthochromatic" film should have negligible response to red and in or out of sunlight, red will be a dark color. With yellow, there should be a stronger response to sunlight and yellow should brighten up more than red would between shadow and sunlight.
Problem with this is I'm not really sure where the WWI orthochromatic film drops off. Have I missed anything obvious?

[Dan_San_Abbott]

Machinebird:
Thank you for the explanation, between you and Jan, I am getting a better understanding of color response to orthochromatic film.
I can see the posibilities of more precise color determination by measurement of the grey tones on a photograph. And of course I understand that you must have an idea of what the color may have been. This could be quite useful.
Merry Christmas,
Dan-San

[Sreiko]

I have something like this in attach.

[jumpinjan]

Originally Posted by Machinbird

...An area of the cowl that had been in shadow was now in sunlight. By measuring the actual change in density that occurs in the area of interest and knowing the response curve of the film, you should be able to make some conclusions about the general color of the surface. You could probably do the same thing by measuring the change in density across the shadow line on a photo assuming you knew that the color did not change in the area of interest...

I really have a hard time following your idea. The difference of an object in a shadow vs. in sunlight is the illuminosity difference. I see no color discriminate information that one can pull out.
Here is an old picture (that I posted here before) of a typical spectral response curve for an ortho film. This looks much like what you posted (Yes, you don't want the monochromatic)

By the way, your impression that colors will follow the curve will only apply to the colors found in the spectrum (pure colors at full saturation). The complex colors to include browns & magenta & purples and colors with tonal components will not act that way (and are not found in the sprectum). If a red has some tone to it or not as saturated, it will not be black but a gray level will be apparent. Also, the "Gamma" needs to be adjusted (contrast) to get the gray levels in line. This is especially critical when comparing two photographs (of the same object), whose Gamma are way different. You need to compare apples to apples, and so I find an object that should be the same color (like the grass) and set the contrast so that object's gray levels are as close as I can discern it to be.
Did I loose you?

Sreiko:
Your ortho emulation is a bit off, the yellow should be a dark gray. This is a quick & dirty emulation that I made and those colors are not a good choice to represent the spectrum. You included magenta.

Jan

[Sreiko]

Jan- this is not my presentation at all. This is taken from the site where is one man demonstrated possibilities of the grayscale conversion of the image editing software. Things with the images are more complicated then we are talking about. It is not just only about the basic physical properties of the film but also parematers and conditions under which the image was taken. There really need deep analyse to get any info about the color from b&w. Also quality of the photo sensitive layer many decades ago was not much high.

Only way to get color from b&w image is to have additional info about the color used and material used.

[Machinbird]

Well, I'm greatly relieved that someone was willing to comment on the "idea". Let's see if I can spread some understanding of the possibilities and the limitations.
Jan, you have brought the most cogent questions, I'll try to address them as best I can.
The orthochromatic color response curve starts off as relatively linear in the violet-blue end of the spectrum and continues at that approximate level until the knee at the green-yellow part of the spectrum and then rapidly drops off in the yellow part and is essentially gone by the time we get to orange. Anything further to the right is not seen by orthochromatic film except as a dark surface. The area I expect the proposed concept to yield some color information is in the non-linear part of the curve around yellow, and (by elimination) red
Points to the left of the knee should be analyzed by conventional gray level analysis. Points to the right of the knee may yield information from sunlight/shadow analysis. Points beyond the film color response would be categorized as reds.
As you see, I am strictly talking wavelengths and not perceived colors. I think you will also see that yellows are not likely be be saturated on orthochromatic photographs since the bluer colors will saturate long before the yellows. Reds will never saturate.
The analysis I envision will primarily use a single photograph and you would compare brightness of a shadowed area against a homogeneous adjacent sunlit area and get a light to dark "ratio". The normalization criteria might be as simple as ensuring the rest of the photo was properly exposed. You would be looking for areas that show relatively low absolute brightening in sunlight compared to shadow. The results could be hidden if there is a bluish "tone" mixed with the color, In that case you would probably get a relatively high brightening effect.
Jan can you see the possibilities? I appreciate the time you took to respond.

Dan-San, If it helps other members of the forum understand the subject of orthochromatic color response better, it's worth the effort. I'm glad you found it useful.

Sreiko, When I was doing preliminary investigation of this idea, I found the thread you had written earlier and considered it helpful. Thanks for your work.

[Sreiko]

Sreiko, When I was doing preliminary investigation of this idea, I found the thread you had written earlier and considered it helpful. Thanks for your work.

I writte about this before... To be honest I have almost forget about it. Glad that you make first researched step here on Aerodrome.

Some time ago I have talk with my very good friends about the problems with black and white materials, weather conditions, exposure, focus, lenght. Start point was the image of Yak-3 in flight where stars was almost white and they are actually red and could be almost black or medium grey. Also we talk about the some light grey color which look very dark on some images and the same airplane on other look almost pale. Thanks to the archive data and close view at image it was know that it was not overpainted and it wear the same light grey color.

The subject we threat here are real labirint and hope that we will not lost inside.

Keep on good work.... no matter of possible answer or not