Yellow filter light loss.

[Steve_F]

I've just put a b+w mid-yellow on my M6TTL and intend to use a hand-held spotmeter. It's been a while but I had a re-collection that light lost, when measured was actually only 1/3 stop compared to b+w saying it's 1 stop.
An incident reading in steady light only differed by 2/10 of stop with the filter laying over the top of the retracted zone. M6 TTL couldn't tell the difference (only 1/2 stop meter accuracy) when metering with it on the same fixed area with and without the filter.
I've set the Sekonic h/held to ISO80 as I'm using 100 in camera and will adjust according to what I'm metering off.
Your thoughts, wisdom & experiences on this, appreciated, as always.

Steve.

 

[charjohncarter]

I use 2/3 stops, mine is a Y2 from Pentax, I also have a yellow Leitz 39mm yellow and it is the same. I would think they are medium yellow.

That would mean that on my hand meter I shoot 100ISO at 64, and 400ISO at 250. Good luck with it. I would not shoot a complete roll of 35mm film with the filter on until you have dialed in the difference between 'no filter' and 'filtered' with your development and printing/digital processing.

 

[Rob-F]

The amount of exposure compensation required depends on the color of the light passing through the filter. Filters freely pass their own color. Light reflected by a yellow object would attenuated only very slightly by the filter, due to its internal absorption and scattering. In that case, the 2/10 stop figure might be about right. There can be very little loss, just like with a UVa or skylight filter.

Now photograph something with a color (blue) that is the complement of yellow. The filter will hold back its complementary color, and the reduction in light can be considerable.

Next, consider a scene consisting of a yellow building with a blue sky in the background. We need only maybe 1/3 stop (or less) compensation for the building. The sky, on the other hand, having a color complementary to the filter, will be darkened to a greater or lesser extent, depending on how strong the filter is.

Now change the building to green or red, the split/complements of yellow. The building will be moderately darkened unless we allow a greater filter factor, of say, 2/3 to 1 stop for a #2 (Kodak Wratten #8) filter. And the additional filter factor (compensation) having been used, the sky will be less dramatically darkened than before.

As a general contrast enhancement filter, I use about 1/3 to 1/2 stop increase for a light yellow filter, 1 stop for a medium K2 cloud filter, and 1.5 stops for a dark (Wratten #9 or #12). This only applies with a hand-held meter. With the M6/MP I may trust the meter to make the correction. But if the subject is not yellow, and I want it to be darkened, then trusting the meter or mechanically applying a filer factor will defeat the purpose of the filter.

So there is no one-size fits all filter factor. The meter doesn't know what we are trying to accomplish.

BTW, the M6 meter is considerably more accurate than +/- 1/2 stop. If it were no more accurate than that, it would be useless with Velvia!

 

[Roger Hicks]

Dear Steve,

The actual light loss, sensitometrically determined with a neutral grey target, can vary from about 1/2 stop to about 2 stops, depending on the density of the yellow filter.

The measured light loss depends very much on the sensitivity of the meter cell, and the effective light loss also depends on what you measure: a blue sky will appear a good deal darker than a yellow daffodil.

In other words, (a) don't look for a precision that ain't there and (b) rely on simple empirical results (use whatever looks best) rather than trying to analyze too many variables, some of which are all but unknowable anyway.

The manufacturer's stated filter factor is always the best starting point, but even then, different films have different responses: an ortho film will have a very different response (more) as compared with a yellow filter from an extended red film such as Ilford SFX (less).

Cheers,

Roger