(I'm not sure if this is right area, but I think that this has more to do with lightning than color slides generally)

This is something that I have noticed first time perhaps around year 2003 and suffered since. The E-6 color slide films tend to have magenta color cast (varies from light to heavy) when the slide is exposed using hotshoe mounted flash. It's usually stronger with direct flash than with bounced flash.

This has happen since with other Nikons I have: FE2, F601, F100, ... And with different flashes (SB-25, SB-26, SB-28, Sunpak 120J, Metz 45 CL-4,...). With manual and TTL.

I haven't pay too much attention for this, as I have mostly used studio flashes and/or B/W films or colour negative films.

Until I recently begun to take more colour slides from normal family life which requires quite foten camera mounted hotshoe flash, even direct flash... Then I took this serious. I need better colors for my 'memory photos'.

My thoughts so far:
  • It could be developing error. But it's visible in the slides regardless of lab - and even in those that I develop myself
  • It could be the color of the flash. But why it occurs with all flashes (and when same flashes are used with digital, the result is neutral)
  • It's mostly visible when wall's (and ceiling) are white, but that probably just because it's easier to spot.
  • Can it be simply feature of the films - but if it is, why there's no CC filtration specified for flashes in the film's datasheets? At least Sensia, Provia, Astia, especially Velvia 50, Ektachrome E100G, Elitechrome 100 and 200.. they all suffer from this.
  • Why I am not seeing this with studio flashes? Perhaps the all reflectors/softboxes and the careful exposure gives more neutral result?
  • As the colour temperature of the flashes should be quite near to daylight (perhaps bit colder), then why photos taken outdoor does not suffer from this issue?
Is there anyone who has run to same problem?
If I cannot solve this otherwise, I guess the best solution is CC filter, but how to determine the correction?

Next I will take some photos with gray cards included, then I can at least get some readings with densitometer from something that I is known to be neutral.

Here's sample of Provia 400X, photographed on light table. These are taken with Nikon FE2, using TTL and giving one stop more exposure from the body to compensate light wall's that would otherwise fool the TTL metering.