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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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  • \$\begingroup\$ 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! \$\endgroup\$
    – MrUpsidown
    Oct 6, 2022 at 9:05
  • \$\begingroup\$ 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. \$\endgroup\$
    – xenoid
    Oct 6, 2022 at 9:10
  • \$\begingroup\$ 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. \$\endgroup\$
    – MrUpsidown
    Oct 6, 2022 at 9:15
  • \$\begingroup\$ Checked on Amazon, all the bulbs for projectors that give a CT are 3300K, so that should settle this part of the problem. \$\endgroup\$
    – xenoid
    Oct 6, 2022 at 9:37
  • \$\begingroup\$ 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. \$\endgroup\$
    – osullic
    Oct 6, 2022 at 10:06

3 Answers 3

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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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    \$\begingroup\$ Yes, probably overthinking it. Setting a custom WB from the diffuser should be enough. \$\endgroup\$
    – 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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Slides are basically meant to be viewed with a slide projector, so you should find a light source of 3200 K and you should set the white balance fixed to halogen light source.

5000K will give a wrong colour balance. Moreover, 5000K light has much weaker reds so the reds will not appear properly saturated, no matter which white balance you set in the camera (and no, 3200K light + 3200K white balance is not equivalent to 5000K light with 5000K white balance).

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