ND Filters & White Balance

Snapper73 said:
By the way did you and Gary shoot any medium format stuff when up in Scotland ;)
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We, well, "I" did, yes :D I shot a few rolls of velvia and provia 100F, as well as shooting garys with FP4. Gary needs a good slapping for not using it! I used his MF more than he did, and I have my own!
 
By the way, this thread is crazy. In the highlands, we all saw the effect of either A: using a filter on a scene, or B: Increasing the exposure. B was only possible due to A. I suspect it will only increase saturation in certain situations, mainly where there is a lot of light movement and changes (ie, sunrise and sunset).

Needs more testing.

Gary.
 
AliB said:
Using long exposures the light has more of a chance to reflect and refract within a scene and perhaps by using long exposures this is where the "Colour washing" comes in especially if the blues and greens are being held back or not recorded but the reds are...............

Ponders...........
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Long exposures won't have any effect on C, that's pretty much constant so reflections/refractions won't change.

But as Gary says, at sunrise/set the sun is moving pretty quick and the colour temp will change quite quickly too and I suspect these are key factors. Use a long enough exposure and you should even start to notice motion blur on the shadow :)
 
Blapto said:
Well, that's the issue. You're rejecting a hypothesis without any evidence to confirm or deny it and purely based on some sort of gut feel.
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Blapto, don't you start ;)

But if you must, and you think that the colour casts we're seeing with ND filters is because of some camera-induced IR effect, rather than the extremely likely probability that the filters are simply not neutral, then I will happily entertain that debate when we have establshed as fact that these ND filters are indeed neutral.

Until that position exists, I am with Gary - this thread is crazy.

"You're rejecting a hypothethis without any evidence to confirm or deny it purley based on some sort of gut feel." Without any evidence? What?! How much do you need. It's here, and on numerous other threads. It comes up all the time. Just look at this photo of filters posted earlier; what does your gut instinct tell you?

EdBray said:
I have two types of filter Kood and Cokin, the Cokin filters definately have a magenta cast compared to the Kood versions, this can be seen with the naked eye never mind on the sensor.

Straight jpeg out of camera, white balance corrected from paper before placing the filters. Cokins top, Koods bottom!

IMG_7294.jpg


I realise this does not have anything to do with the long exposure change in colour just the difference between makes of filter.
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HoppyUK said:
Blapto, don't you start ;)

But if you must, and you think that the colour casts we're seeing with ND filters is because of some camera-induced IR effect, rather than the extremely likely probability that the filters are simply not neutral, then I will happily entertain that debate when we have establshed as fact that these ND filters are indeed neutral.

Until that position exists, I am with Gary - this thread is crazy.

"You're rejecting a hypothethis without any evidence to confirm or deny it purley based on some sort of gut feel." Without any evidence? What?! How much do you need. It's here, and on numerous other threads. It comes up all the time. Just look at this photo of filters posted earlier; what does your gut instinct tell you?
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As far as I can tell, IR light wasn't excluded from the test that EdBray did. It doesn't prove anything. I don't trust my gut instinct because it's not proof.

Looking at the histogram for certain parts of that photo, yes, the Cokin filters permit more, higher frequency red light and the Kood filters permit more higher frequency blue light. That doesn't prove anything either way. Besides, I can use the histogram tool on that sheet of paper to find parts which have a similar shaped histogram to parts of the individual ND filters.

I'm not saying that the filters are or aren't neutral, I'm saying that you're wrong to completely accept or reject a hypothesis without any evidence.

1246512524.jpg

Have a look at the centre of the crosses, what does your gut tell you? Now look at the histograms or crops for just the areas in the centre of the crosses.
 
Guys - I did a little more investigation last night with my cokin filters. There's a big learning curve here for me

For the biggest effect I restricted myself to the P154 NDx8 and the P121S Grad NDx8. Shooting was approx 8:30 last night, so the sun was starting to lower. I shot the sky and a white card, both in direct sunlight and in shade. Family pressures meansd I didn't get time to try the custom white balance but I hope to repeat this today. I used both my Canon 50D with 24-105 lens and 400D with kit 18-55.

Direction of shooting the sky made a big difference. 180 degrees away from the sun gave the least purple effect, shooting towards the sun, but so the sun was just out of viewfinder, gave the most. Ok no surprise their perhaps as they'll be more red/orange light in that direction.

The white card test was interesting, showing a definite increase in red when the filters were applied.

What was noticeable to the visible eye is on their own the filters appear gray, but stacking them instantly produces a huge magenta colour cast and explains my shot of the boat. I was stacking filters to get the long exposure for milky sea and grading the sky down to get an even exposure.

Shooting towards the sun explains the sky/cloud shot I posted earlier. I think that was with the NDx8.

Hopefully I'll find some time this morning to play with a white card test.
 
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