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  1. #1
    holmburgers's Avatar
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    Experiments with RGB-colored screens... a la Dufaycolor & Autochrome

    Hi y'all,

    So I've posted a thorough explanation of what my proposed method is on the "autochrome recipe" thread and another older thread "restarting my autochrome experiments....". But I felt bad about hijacking these more historical discussions and thought I should just create a new thread to share my experiment/plan.

    The goal is to recreate the look of autochrome & dufaycolor photographs. Instead of attempting to reproduce these methods exactly, which were developed 103 years ago, I figured there had to be some modern methods that would be much easier.

    I came up with the idea of using slide film to record the reseau, RGB-colored screen, by photographing a white TV screen (RGB elements of equal amplitude) TV screen.

    Then, thru pin registration, this screen will be attached to ordinary panchromatic b&w film, exposed, separated, reversal processed and re-registered.

    Voila!

    Naturally, the irony is how retrogressive this technique is... using color film to make a reseau only to permit making another color picture on b&w film. .....doesn't bother me a bit though....

    So, after going thru all the theoretical steps, I've moved to the practical steps, namely, calculating magnifications. However, I've come up against some problems.

    To make a .05mm TV pixel (approx.) equal to a .005mm autochrome starch we need a magnification of 1/10th. Take a 12"x16" TV screen and 4x5" film and my calculations say that the TV can't fill the whole frame at that magnification. SOO either we have to sacrifice resolution or find a higher-definition screen.

    I haven't done the math yet, but perhaps a 1080 hi-def screen would do the trick. As I don't have one ($), a computer monitor is probably the next best thing.

    However, this got me thinking about lens/film resolution. I haven't done a ton of looking into it yet, but it seems like 60 lp/mm is about the limit of resolution.(??) That equals .017mm per line pair.

    Would it be fair to say that it's impossible to reach the resolution of the autochrome starch grains with a typical lens/film combination? I thought that making a reseau thru optical means would be significantly easier, and indeed it is, but at a cost I guess.

    I would appreciate any input on my calculations & in determining the maximum resolution available by the method I've outlined. Either way, I'm still going to attempt this.

    Thanks!

  2. #2
    holmburgers's Avatar
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    Took a couple pictures of a TV last night using EPP 4x5". I found it surprisingly difficult (at least on this set) to get a clean, blank image on the screen w/o the channel number or "no signal", etc. I had to hook up a DVD player just to get it to stop flashing at me.

    I ended up using a relatively dark screen and exposures at f/11 were 60 and 90 seconds. That's giving a 2/3 stop increase for reciprocity failure and 1 stop for bellows factor. I'm concerned with reciprocity failure and how it might affect the color balance.

    Therefore, it has occured to me that I need to use a bright white screen, which will mean shorter exposure times. Also, while looking thru a loupe and adjusting the color balance on the TV set, the phosphors didn't change color at all. So, it appears that I need a signal before I can actually manipulate the balance. The blue looked signficantly weaker than red & green did to my eye.

    Where can one find a pure white television signal? How about creating one, any ideas? You wouldn't realize how rare such a thing is until you need it!

  3. #3
    holmburgers's Avatar
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    good call on signal generators, maybe i can find some cheap somewhere. but hey, this stuff is still analog

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    Photo Engineer's Avatar
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    It is so difficult to do that using a color dot matrix printer is much easier.

    PE

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    What about using a digital camera to shoot a white background,
    then hooking that up to the tv monitor?

    I cannot even begin to do the math, but large screen (outdoor) displays are another option... you might get them to give you a white screen for a few seconds before their broadcast begins

    Or just make your own...
    get ahold of some unneeded white... (or black!) studio Background Paper and
    spend the summer painting teeny tiny RGB dots on it.
    When your finished, stand back and shoot it.

    Are these good ideas, or do I need some more sleep?

  6. #6
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    I'll put my two cents in here ... To create a white screen, you can always find a camcorder, small security camera, etc. that has TV output, and trick it into overexposing so far that the screen goes pure white ... maybe shine a flashlight into the lens at close distance?

    Why not shoot a computer screen (CRT or LCD) instead?

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    Quote Originally Posted by holmburgers View Post
    However, this got me thinking about lens/film resolution. I haven't done a ton of looking into it yet, but it seems like 60 lp/mm is about the limit of resolution.(??) That equals .017mm per line pair.

    Would it be fair to say that it's impossible to reach the resolution of the autochrome starch grains with a typical lens/film combination?
    You're not hoping to reproduce the aliassing problems the Bayer-pattern filters in digi-thingies create, are you?

  8. #8
    holmburgers's Avatar
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    I like htmlguru's idea... I have an old VHS camcorder, I could see what can be done with that. But actually, you raise a great point about using a computer monitor. That would completely simplify this signal generating portion of it. Just open up Windows paint... voila! That's brilliant.

    However, can anyone comment on my concern about resolving power? At what point will I simply not be able to resolve the pixel elements?

    And no, I'm not hoping to reproduce any aliassing problems, but we'll see what I get !

    I realize a dot matrix printer would work, but I don't have one, and it wasn't my idea, so what do I have to gain?

    I like the idea of painting a wall.... NOT! I'm not that zen! But I did have the idea of planting my backyard with three flowers that produce RGB, and then taking a photo of them for my screen at the peak of bloom. Groovy, eh?

    Thanks for all the input, the slides are on their way to the processor, so I'll report back once I see them.

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    I'm surprised that QG has not suggested that you stop working on this tricolor approach!

    PE

  10. #10
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    Howdy everyone!

    Alright, well I got back my 4x5 slides and I have to say that I'm optimistic, at least for my 1st attempt.

    There is a very pronounced blue cast in the reseau, which is odd since I thought the blue TV "pixels" looked pretty weak on the ground glass. Can anyone comment on typical color shifts that result from reciprocity failure? Lemme guess.... blue?

    To the unaided eye it appears fairly continuous, though I'm sure the aperture-plate pattern from the TV will be apparent in the resultant photograph. Either way, I see red, I see green & I see blue; which in my book spells "additive color synthesis".

    The attachments show the whole slide and then a close up. The scans look pretty miserable; it looks better in person.

    Next step is pin registration (*cough cough*, office hole punch) and reversal processing. I think I might send a couple tests off to dr5 just because my darkroom is in tatters at the moment and I've never done reversal processing. Plus, photo formulary is still down.

    Anyways, just wanted to share an update.
    Attached Thumbnails Attached Thumbnails reseau scan for apug.jpg   reseau closeup for apug.jpg  

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