What filter factor should be used

[NeverSummer]

Please advice the question. I have Cokin red (003) filter. According to producer specification the factor is 3 1/3 EV. But if I use spotmeter (Sekonic L508) the factor of the filter is float value depending on certain scene (I meter without the filter and through the filter and get the EV difference). And this value is about 2.1-3 EV (in most cases about 2.3 EV). So the question is – that figure should I trust – official documentation or metering through filter? Firstly, I thought that the metering through filter is right way but someone told me spotmeters have different spectral sensitivity and the density of the filter measured by densitometer and therefore I should use the documentation value. Unfortunately at the moment I can not make a test so please pass your opinion.

[Joanna Carter]

If you use a spotmeter to measure through the filter, you will get different readings, dpending on the colour of the subject that you are reading. Meter a red object and you will get much less filter factor than measuring a cyan subject; that is the nature of light.

The standard exposure compensation for a red filter is normally 3 stops in daylight, less in tungsten, but what you use depends on the effect that you wish to photograph and under what lighting conditions.

[ki6mf]

If you do measure through the spotmeter you do not have to worry about what the factor is or the quality of light. For that exposure you will get the proper reading and can forget about the filter factor.

[NeverSummer]

I work with daylight. Mainly in forests, mountains and ocean shore

[NeverSummer]

If you do measure through the spotmeter you do not have to worry about what the factor is or the quality of light. For that exposure you will get the proper reading and can forget about the filter factor.

I am worrying about such thing if the spotmeter has integral sensitivity and I measure through color filter the spotmeter reading my be incorrect because the spotmeter may react differently the certain light wave length.

[Joanna Carter]

I work with daylight. Mainly in forests, mountains and ocean shore
Then why do you want to use a red filter? To darken skies? Don't forget that anything blue or green like water reflecting sky, the sky itself and green foliage will also tend to darken.

As I said, you need to determine the look and feel you want from your image. If you don't allow for the full filter factor, your sky will appear very dark but thigs at the red end will be less affected. If you allow for more than three stops, then the sky will appear more "normal" but reddish things will appear brighter than normal.

It depends on what you want to achieve.

[Joanna Carter]

I just did a quick experiment withe my digisnapper - I took an exposure reading for some red and yellow lilies in our garden, then I added a red filter.

If I allow the full 3 stops, I get an image where the flower heads are totally blown out but the foliage is "normal". To get the flowers to look "right", I had to reduce the exposure factor to a mere 1 stop. and the foliage looked darker but still with some detail.

[Brian Ellis]

A red filter is IMHO a poor choice whenever green foliage makes up a significant part of the photograph (as in many forests, some mountains, occasionally even the sea shore). A red filter will darken the foliage to a point that it can become black, which you normally don't want. I think a medium orange filter is a better compromise if the idea is to darken the sky but still retain some detail in the foliage.

I've used all sorts of different methods for metering with filters and finally ended up just using the manufacturer's filter factor. The problem with spot meters and metering through a filter is as Joanna says, the reading you get will vary depending on the color of the spot you're metering and of course you aren't photographing just one spot. Then there's the problem growing out of the fact that the meter and your film aren't equally sensitive to the same colors. And on and on.

There is no perfectly precise way I know of to meter an outdoor scene with any b&w filter. The filter factor is simple and is about as good as any IMHO. And b&w film has enough latitude that you're highly unlikely to be so far off that you can't made a good print from the negative.

[Chauncey Walden]

Gordon Hutching's filter factors would be a good guide. You meter through the filter then make adjustments for certain filters like plus one stop for a #21 and two stops for a #25 or #29. This will ensure adequate shadow detail.

[Joanna Carter]

Gordon Hutching's filter factors would be a good guide. You meter through the filter then make adjustments for certain filters like plus one stop for a #21 and two stops for a #25 or #29. This will ensure adequate shadow detail.
Maybe, but for shadows in which colours?

[NeverSummer]

If I allow the full 3 stops, I get an image where the flower heads are totally blown out but the foliage is "normal". To get the flowers to look "right", I had to reduce the exposure factor to a mere 1 stop. and the foliage looked darker but still with some detail.

So .. If we speak in term of 'normal' exposure I should be guided by producer specs, but bear in maind that i can lose or too strong change some tonalities. For example pure red will be blown and blue sky or water will be almost black but rest of the scene will be exposured 'correct'. Is it right?

[Capocheny]

Hi Neversummer,

I'd suggest you go out and shoot a few sheets of film... of the same subject with the filter on the lens.

Measure through your meter at the subject matter. Look for a subject matters with greens, reds, and blues in it. Add 1 stop, then 2 stops, then 3 stops additional exposure.

Lastly, take another shot of the above scene with the manufacturer's suggested filter adjustment.

Process the films and compare the results. Look at the effect of the filter and exposure compensation on the different areas of the images. This should give you the answers to your questions. It's a good learning process.

Me? Like Brian, I usually go with the manufacturer's recommendation.

Cheers

[Chauncey Walden]

Joanna, maybe it's different on your side of the pond, but over here, the shadows are mostly blue light;-)