Warming Filters and Digital W.B.

My apologies if this has been covered before: here is a question a photo buddy and I have been going

around about, perhaps members will weigh in with their experiences:

 

Let�s say that you have a D200, or any other digital camera with an auto white balance function. You

attach an 812 or 81A or B warming filter to the lens and take a picture with the camera in Auto White

mode. Does the picture warm up?

 

My friend says yes. I say no, because the camera�s auto white function would subtract the warmer element

of the light and balance out to whatever it was going to be in the first place.

 

What really happens, and why? (This is also a � assed way to ask if there is any point in investing in a

�warming� polarizer, or just a plain vanilla one).

 

Thanks!

IMX, auto WB does get fooled by a warming filter. Until I started shooting digital I used Nikon Conversion A2 (same as 81A) on all my lenses as warming and protection. This worked well with Velvia and Provia but not so much with E100VS (which has an annoying habit of turning red at the slightest excuse).

 

However, after getting a DSLR I immediately noticed the shots *without* a warming filter have better out of the camera color balance in JPEGs (I shot JPG+RAW). With the A2 filters D70 showed a tendancy to underexpose and greens had a dull-yellowish tint with a very slight hint of red (nothing that you couldn't correct in RAW processing). I transitioned all warming filter to exclusive film shoots and started using Nikon L37C or B+W UV MRC F-PRO for my digital shoots. So far so good. Not that now auto WB behaves itself all the time, but relatively more consistent results.

 

"if there is any point in investing in a ýwarmingý polarizer, or just a plain vanilla one"

 

I'd say a plain vanilla one. Why lose whatever additional small amount of EV due to warming filter loss? Effect of pol cannot be easily duplicated in photoshop, but warming effect can be applied very easily.

If you use a color compensation filter with auto white balance it will shift the color of the photos. I read about this in Tom Hogan's D70 e-book and tried it out. It is useful when shooting indoors around incandescent lights, since an 80A shifts the light to roughly 4500 Kelvin, which is a range the auto white balance meter can handle much better than the 2500 to 2800 K of incandescent bulbs.

 

Does rob you of a few stops though.

 

Hope this helps,

 

Justin

If you set the WB manually to where you want it, then the warming filters will give the desired

effect. I don't have a dslr, but on my canon A510 I always set the white balaence to

something other than AWB if I'm using a coloured filter (or in this case, orange coloured

sunglasses). Excellent results can ensew.<div></div>

OK, how about the right answer?

 

You do not shoot a DSLR (especially a Nikon) through a warming filter unless you are shooting under very cool light sources, such as an overcast day.

 

The RGB filters and amplifier gains of a DSLR are typically set to produce about the same signal level when shooting neutral gray under 5500K sunlight (for Nikon) or a color temperature of about 4000K for Canon. When you make the image warmer than this (either by using a warming filter, or by using a warmer light source, such as incandescent light or candlelight) all you do is decrease the green and blue signals in relation to the red signal. So, the camera increases the overall exposure (because green has the highest overall contribution to the exposure metering) causing the red channel (unaltered by the filter) to blow more easily, resulting in blotchy yellow highlights. The attenuated blue channel gets more noisy.

 

If you want a warm picture, warm it up in post processing, or through the preset WB feature of the camera.

I agree with Joseph. Basically use a filter to balance the light - use a cool filter if the light is warm and warm filter for cool light - so that all color channels get proper exposure. Do the special effects in post processing.

I 2nd Joseph.

CCD's work in a completely different way to photo-chemical film. coloured filters merely alter signal processing in a way that the ccd was not designed. Without wanting to sound condescending, digital cameras are a whole new ball game and the best thing you can learn is how to manipulate colour using WB settings. I am slowing making the use of WB second nature, and my images require less and less correction (or adjustment) day by day.

If you want the effect of a light warming filter with the D200, i have found that AutoWB -2 gives great consistent results.