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Can I assume that slides are somehow designed to project proper colors when illuminated by a lamp with a specific color temperature? If so what temperature was that? 3200K?

When I digitalize slides I use natural light as a light source, so is there a way I can evaluate the color temperature of that source (that can be slightly altered by the diffuser behind the slides), for instance by taking a picture of the diffuser without a slide?

I of course assume that by knowing the two color temperatures I can correct the digital capture to better approximate the intended colors...

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  • I thought checking color temperature of slide projector replacement bulbs might be a good idea and 3300-3500K seems like the most used values, whenever the information is available and that is not very often!
    – MrUpsidown
    Oct 6, 2022 at 9:05
  • Good idea. I took 3200K because that's the CT of most halogen bulbs, and I remember that projector lights where whiter than standard lights.
    – xenoid
    Oct 6, 2022 at 9:10
  • And for evaluating the color temperature, there is a variety of sensors available, from professional devices to smartphone pluggable devices. If you use natural light you must be closer to 5000-6500K.
    – MrUpsidown
    Oct 6, 2022 at 9:15
  • Checked on Amazon, all the bulbs for projectors that give a CT are 3300K, so that should settle this part of the problem.
    – xenoid
    Oct 6, 2022 at 9:37
  • I assume a sensible thing to do is to photograph slides on a light box / light table, which generally have a colour temperature around 5000-6000 K.
    – osullic
    Oct 6, 2022 at 10:06

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Kodak does not specify viewing conditions for their slide films. Fuji specifies ISO standard (D50/5000k) for the transparency viewer (table) used. But that is not a slide projector; they do not specify a projection temp. And I am unaware of any E6 white paper that does specify the projector characteristics.

E6 film is not known for color accuracy. Actually, the primary attraction of slide film is/was it's color inaccuracy... the particular "look" or saturation they added to a scene.

So really, what you are wanting to do is record the slides as neutrally/accurately as possible... whether the slides were accurate at the time, or if they even still look as they did when taken, doesn't matter much (i.e. each viewing condition/environment will affect the result).

For consistency purposes I would probably set a custom white balance by taking a picture of the diffuser w/o a slide for each batch/session; but even that is probably overkill.

This is the relevant section for Velvia 100 Pro. enter image description here

This is the closest relevant section for Kodachrome 64/200. enter image description here

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  • Yes, probably overthinking it. Setting a custom WB from the diffuser should be enough.
    – xenoid
    Oct 9, 2022 at 20:44
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The Kodak Carousel lamp is 3300 thru 3350 K. Slide copy film was balanced for Tungsten A 3200 K. Industry standard for viewing color prints is 5000 K with a color index of 95 or greater.

That being said, I don't think the illumination of a side matters much because the human eye-brain has an involuntary system that white balances our vision. Additionally, the modern digital camera will white balance.

If I were tasked to do this, I think 5000 K with color index of 95 wins out.

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