Strange effect when using 3 stacked ND filters

[hil26]

Wanted to get a slower shutter speed today during an outing in some snow.

Put ND8 and a ND4 in the Cokin holder but still not slow enough; borrowed an additional ND8 but image had a really bad red tint to it. Before fitting the additional ND8 tone of image was OK.

ISO was 100 and no settings were changed apart from exposure.

Anyone know why?

Dave

[Benchista]

I suspect the balance of light you're exposing for has more IR as a result of blocking more visible light.

[beejaybee]

I suspect the balance of light you're exposing for has more IR as a result of blocking more visible light.

I suspect you're probably right; dye-in-glass filters almost always transmit strongly in the infra-red, whatever colour they are and however dense they appear to be to the eye.

Try adding a dichroic infra red blocking filter.

[LargeFormat]

Try leaving the lens cap on