ND filters - colour cast

**Master Splinter** · 19th January 2016, 09:06 PM

Actual accuracy will depend on how much effort you put into deciding on your white point. A selection done at whatever size it opens in Photoshop at will of course be different to one where you zoom in and sample an individual pixel.

Whether or not either of those is a 'true' representation of how the scene would be perceived by a human eye is an entirely different matter, and really if you want to go to that level of accuracy, you need to shoot a colour reference card each time you change location or the sun goes behind a cloud.

Once you've got your shot of a Macbeth colour card, you can then go and calibrate an accurate adjustment value for that set of images - this will give you a more robust solution (that will also take account of different response of the RGB sensors at long exposure times) than any set of filters could achieve.

**Sawdust Maker** · 20th January 2016, 02:34 PM

Mick (Optimark)

That expodisc looks interesting. approx $50 US, when's father's day?

Mr Splinter

thanks

**Optimark** · 20th January 2016, 03:09 PM

Originally Posted by Sawdust Maker

Mick (Optimark)

That expodisc looks interesting. approx $50 US, when's father's day?

Mr Splinter

thanks

It is interesting, and it isn't interesting. This depends upon your camera and the ability it has to acquire a specific Kelvin reading. For instance: my friend with his Olympus reflex camera body, has the ability to specify any kelvin reading (colour temperature). It may be that the correct colour temperature required to work with the receptors in one camera to get the correct temperature is, say, 6975 K. This is what my friends camera is able to do, this is important.

My wife, on the basis of our friends camera, purchased an almost exact same Olympus reflex camera, unfortunately the successor of our friends camera, which is what she purchased, had a modification that disabled that function. She can only specify kelvin in multiples of 100 generally, and then, only either side of accepted norms like Tungsten, candle light, midday sun, Moon light, and strangely, Polar light; presumably so these cameras will work well down at the South Pole.

So, if you are interested in one of those Expo Discs, ensure that your particular camera can come up with a stepless (actually not quite stepless, but near enough) colour temperature measurement reading that it can apply that reading correctly to your in-camera computer.

Maybe there is someone near you with an Expo Disc to try?

Another way is to go to a physical shop with one of these Expo Discs and place one in front of your camera and do a colour balance measurement, then take a few shots and look at the little picture on the back of your camera. This will literally only take a few minutes, but take your instruction book with you. There just may be some quirky set of button pushing required to access this free colour temperature setting ability, which can be insanely difficult if you don't know what buttons and in which sequence to push them in.

Mick.

**Sawdust Maker** · 26th January 2016, 04:02 PM

Looked at the manual, seems I can set from 2500K to 10000K in 100K increments

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