Teacher suggests warming filter

I may have the kelvin number wrong, it may be 6000 or 6500, but I think you need to test without flash. I looked at your test and it looks like the WB is moving in the wrong direction. The warmer the gel was, the cooler the measured WB by the camera.

I'm not sure how a camera would correct for the white balance of a color filter over the lens. The WB setting on the camera corrects for the color of the light source reflecting off the objects that the camera sensor is seeing. Assuming the sun as a light source, full spectrum light strikes the objects and the object's color determines the color of light reflected towards the viewer.

However with a colored filter over the lens, you are filtering the incoming wavelengths of light from all objects in the scene. An orangish (warm) filter would filter out more wavelengths in the green/blue/purple range from reaching the camera sensor. With that color information not reaching the sensor, how would one correct for that missing information? Say the filter was a saturated yellow, then wouldn't any blue objects show up as black ?

Bearmann wrote in post #16675130
I may have the kelvin number wrong, it may be 6000 or 6500, but I think you need to test without flash. I looked at your test and it looks like the WB is moving in the wrong direction. The warmer the gel was, the cooler the measured WB by the camera.

OK did some more tests. I initially did them under some fairly bright Cree 2700k LEDs but I applying CTO's pushed the temp out of the range that the camera's AWB and Lightroom can handle. I then did a shot with a blue gel instead. AWB did increase the color temperature in response.

I also ran some more tests with the CTOs but with the flash off-camera and triggered with a simple radio trigger so there could be no communication between the flash and camera. AWB applied a lower color temperature as the gels got stronger, as you might expect.

So it looks like the AWB does indeed attempt to correct for the presence of colored gels/filters. But, after correcting white balance and exposure, the shots are NOT identical in terms of color rendering. I've shot under these LEDs before and never been happy with the results. Colors just don't pop and skin tones look off. The funny thing is that the shot with the blue gel actually looks better after correction than the shots without gels.

You use a UV filter which is worthless to a digital camera, it's no worse than what that teacher recommends.

circles_of_confusion wrote in post #16675144
I'm not sure how a camera would correct for the white balance of a color filter over the lens. The WB setting on the camera corrects for the color of the light source reflecting off the objects that the camera sensor is seeing. Assuming the sun as a light source, full spectrum light strikes the objects and the object's color determines the color of light reflected towards the viewer.

However with a colored filter over the lens, you are filtering the incoming wavelengths of light from all objects in the scene. An orangish (warm) filter would filter out more wavelengths in the green/blue/purple range from reaching the camera sensor. With that color information not reaching the sensor, how would one correct for that missing information? Say the filter was a saturated yellow, then wouldn't any blue objects show up as black ?

Fluorescence aside, it doesn't make any difference if you filter out part of the spectrum before it strikes the subject, or after it is reflected.

circles_of_confusion wrote in post #16675144
However with a colored filter over the lens, you are filtering the incoming wavelengths of light from all objects in the scene. An orangish (warm) filter would filter out more wavelengths in the green/blue/purple range from reaching the camera sensor.

Purple is not a colour associated with a single wavelength; violet is.

It is reaching the sensor - a colour temperature shifting filter like an 81A does not completely remove any wavelength, because blackbody radiators are wide spectrum radiators. There is just less of it, so you have to increase the values to compensate. You end up back where you were, except for increased noise in the channels which had to be increased in software.

If the filter passed only a narrow spectral yellow, then yes. Commonly used yellow filters for black and white photography just attentuate other colours somewhat, e.g. yellow darkens the sky. A yellow filter used for B&W is not a warming filter.

I used to carry warming filters for all my lenses... when I shot film. Still have some of them, though they are mostly packed away.

I don't use them for digital. AWB cancels out some or all the effect of a colored filter. Emphasis on the word "some". A colored filter still can have some effect, but it's unpredictable on a digital camera when using AWB. If using a Custom WB, that will cancel out the filter's effect completely, except possibly in the case of an extremely strong filter.

A much more accurate and consistent method of "warming" an image is to use Warm Cards to set a Custom WB. These precisely colored targets "fool" the camera into producing a warmer image in a predictable and accurate way. Warm Cards have been used for digital videography for many of years, but work equally well for digital still photography. They aren't just for warming, either. There are cooling cards correction cards in the full set, too. Or you can make your own from colored cardboard (the problem will be finding correct, muted, pastel tones for the effect you want).

However is you "warm up" your images, you still have to be a bit careful. IMO many portraits are overly warmed giving the person a jaundiced look.

Finally, if you aren't working with a well calibrated computer monitor screen, forget it. Any adjustments you're making are too apt to be wrong.

Can anyone tell me why "warming up" is not possible, even more desireable, and cheaper by adjusting the color temperature or color tone manually in DPP?

Abu Mahendra wrote in post #16677172
Can anyone tell me why "warming up" is not possible, even more desireable, and cheaper by adjusting the color temperature or color tone manually in DPP?

Not easily, as that is how most would do it. I can see that for some who rely on in-camera processing alone use of filters may offer a more "transparent" method.

maverick75 wrote in post #16675265
You use a UV filter which is worthless to a digital camera, it's no worse than what that teacher recommends.

I only use the B+W UV filter because I have a 1 year old son, and young nieces and nephews around a lot. They always seem to get within striking distance of my camera when I least expect it. So as much as it may be wishful thinking, I use the multi-coat UV filter in the hope that the filter will get scratched before my lens does.

Abu Mahendra wrote in post #16677172
Can anyone tell me why "warming up" is not possible, even more desireable, and cheaper by adjusting the color temperature or color tone manually in DPP?

You are correct, but if you like the slight warming, as I do with high altidude landscapes, crystal clear skies and puffy clouds, why add warming in post if a filter can add something pleasing to me up front?

John from PA wrote in post #16678050
You are correct, but if you like the slight warming, as I do with high altidude landscapes, crystal clear skies and puffy clouds, why add warming in post if a filter can add something pleasing to me up front?

Because it's quicker and allows a variable effect.

hollis_f wrote in post #16680498
Because it's quicker and allows a variable effect.

Perhaps, but I would also offer that the manner in which I shoot landscapes out west might be significantly different than the vistas offered in the UK. I remember a winter of hosting some people from the UK many years ago who were quite impressed that you could see actually the sun in January. I do realize you have your sunny days, as my family traces to the Kent area, and I have visited the UK on many an occasion. But when I am at a 5000 foot elevation, 43 deg north latitude (as opposed to 51 deg N), catching the early morning sun in a stark blue sky, I find the warming effect of the Moose Polarizer useful. You are almost 500 miles north of me, so it is not unreasonable to anticipate a different shooting situation. I'm not saying I mount an 81A and leave it on all the time, just when the subject needs some warming.

Internet suggests another teacher