# The Diffraction Process of Colour Photography - Prof. R.W. Wood, 1900

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• 08-24-2012, 11:19 AM
holmburgers
Quote:

Originally Posted by gmikol
I just realized I left you hanging on this...

Assuming you want to make 4x5" images...

2750 lp/in (@ 4x5") --> ?? @ 600 lp/in (imagesetter film)
2750/600 = 4.583x reduction

4*4.583 = 18.333"
5*4.583 = 22.9"

Looking at the on-line price list of a service bureau in my area, they charge:

19 x 25 \$48.75
20 x 26 \$54.50
22 x 28 \$63.25

Hope that helps.

--Greg

...and...
Quote:

Right...exactly...a single master, generated at the native resolution of the imagesetter (600 lp/in works well for 2400 and 3600 dpi imagesetters). 3 different reproduction scales to get your rulings for imaging. BTW--Some can also image directly onto RC paper...it should support that resolution. And you have a reflective master to work with, instead of having to rig up a big backlight.
Revisiting this all-too-excellent idea today and have a few thoughts. So with a 600 lp/in screen of parallel lines printed on an ≈18.5"x23" paper, I have a master from which I can reproduce onto 4x5" film the appropriate line screens; 2750 lp/", 2400 lp/" and 2000 lp/". Furthermore, this master would allow one to make any frequency line screen, as needed, by simply changing the distance from which you are photographing it (the magnification factor).

My question is, what kind of lens is capable of doing this, and what kind of film? Would your typical process lens handle this? As for film, what about Arista Ortho Litho?
• 08-24-2012, 03:00 PM
Struan Gray
The heart of the matter: any lens capable of reproducing these gratings has to resolve clearly at least 100 lp/mm, and over a 4x5" field at that. Such lenses exist, but they're not cheap.

There is a huge support and service industry supplying chip-makers with photolithography tools and chemicals. One part of this is makers and suppliers of the 'masks' used to define the patterns which are then projected onto a photosensitive resist with the hugely expensive lenses I just mentioned. These masks are usually chrome on glass (or quartz) and are tough enough to be used for contact printing as well as projection printing.

One standard size is 5" square, which will have a large enough patterned area to contact print onto 4x5 film. Masks are specified according to the size and precision of the line features, and you pay for every step in quality, but your needs are at the low end of what is regular production, and you should be able to get masks made for a reasonable price. I used to typically pay €100 for this size and quality for one-off patterns, but I did the pattern design myself. You may be able to get a local university department to help you out (mask-making is also sometimes a routine service at high-tech incubator parks for startups) and pull the cost down further, or just help with design and ordering so that you avoid re-makes.

Such a mask would work well as a master, which could be contact printed onto lith film to make working gratings for print production.

I calculate that Wood's rulings produce coloured light at around 72-73° off axis. The viewer in the article you posted would either need to include a hefty wedge in the lens in front of the image, or have the peephole way off to the side, or (more likely) illuminate the image with collimated light coming in from the back at 72-73° off axis. The sun will work well if placed at the right angle, but a projected beam might be more reliable, especially in Rochester winters.
• 09-12-2012, 01:07 PM
holmburgers
Struan, I apologize for not responding sooner to your excellent post here.

The photolithographic masks you're talking about sound like a reasonable alternative to say Ronchi rulings and the like. I need to send some emails and find out what the manufacturers think of this application.

I wonder if there's not some way to make our own rulings cheaper and easier... Is it possible, for instance, to create line patterns with holography, or some kind of interference pattern? DCG is certainly capable of the resolution, but where does our image source come from?

I do like your idea of getting together with a university though, or perhaps it's possible that someone would be willing to "lend" their rulings for the purpose of contact copying.

I'm very curious to know how you calculated the viewing angle. Pray tell! :)

On a different note... I'm wondering if one could make a reflective version of diffraction photography. For example, what about etching onto a sheet of metal? Or, I guess, is it possible that these glass versions could be viewed via both transmission and reflection? Actually, when I think about a diffraction grating I recently handled, it was impossible to see the color by looking at the film; it had to be "projected". Hmmm... the physics is beyond me i'm afraid.
• 09-16-2012, 05:44 PM
CMB
Quote:

Originally Posted by holmburgers
...what about etching onto a sheet of metal?

Woods interference screens/diffraction gratings are similar to the "pellicles" used in one-shot cameras. The Devin-McGraw pellicles were made by pouring gelatin onto a ronchi grating (chrome on glass plate) and then stripped off when set. It would seem that an etched metal plate, as you suggest, would work as well.

BTW: The Frontispiece of A Handbook of Photography in Colours was the first published "natural" color photograph.
• 09-17-2012, 12:46 PM
holmburgers
Well that certainly does bode well for this idea. Utilizing structural colors is the most permanent kind of color we can make. In fact, fossils of beetles can still be quite colorful even after millions of years in the ground. UltraStable is good.. but this kind of color is epoch.

(pun intended... :laugh:)

That frontispiece you mention can be seen here... http://archive.org/details/cu31924031248119

My university library has an original copy of this book and it's one that really got me into this early color stuff. A very interesting read for sure. Cutting edge color photography at the turn of the century, before they had it all figured out.

Thanks for your comment!
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