Green/Yellow filter question: filter factor ??

[Joao]

Hello
I have a light green/yellow filter that came with a Industar 26 M.
The inscription on the filter ring shows Æ C-17 (first letter before the C is a cyrillic "zhe") and 40,5 X 0,5 together with what seems to be a Lyktarino logo (the "C" inside a sort of triangle with curved sides).
My question is what is the "filter factor" of this filter - or, in practical terms, how much do I need to change in f-stops ?
Thank you in advance
Regards
Joao

 

[rbiemer]

I have one of these filters and when I am shooting with my Bessa and J-8, the meter generally indicates around 1 stop more. If I'm using a hand held meter, I sometimes forget to make any adjustment and my negs still look pretty good. I primarily use Kodak BW400CN film which is very forgiving of exposure "errors".
Rob

 

[daveywaugh]

2/3 of a stop I believe.

 

[Joao]

Thank

Thank

Thank you for the answers, 2/3 to 1 it will be. I will test some shots whithin this narrow range .
Regards
Joao

 

[Marel]

What I generally do is just meter (either with a handheld meter or a metered camera) with and without the filter in front of the meter, and note the difference in exposure. Then you'll know exactly how to adjust to that particular filter.

 

[Joao]

What I generally do is just meter (either with a handheld meter or a metered camera) with and without the filter in front of the meter, and note the difference in exposure. Then you'll know exactly how to adjust to that particular filter.

It makes sense !
Thanks
Joao

 

[oftheherd]

At http://www.jackspcs.com/filters.htm I found the below which might be of value.

#11, X1 (060)
A light yellow-green filter which corrects panchromatic film to tungsten eye response. Differentiates green tonal values in landscapes and reduces distant haze.
The filter factor is approximately 2.

#12 (099, Schott OG 530)
A yellow filter with correspondingly greater effect than the #6 and #8. The #12 filter is "minus-blue," meaning it absorbs virtually all light of blue wavelengths.

#13, X2 (061)
A yellow-green filter is similar to the #11 filter, but stronger. Yellow green filters darken blue sky values and shadows, as well as red subjects, and lighten foliage somewhat (green filters in general may have less effect on foliage than expected, partly because of the reduced sensitivity of panchromatic films to green.) The #13 filter applies a strong "correction" to panchromatic film under tungsten illumination. A green filter is recommened when using Kodak Tech Pan to photograph scenes which contain foliage.
The filter factor is approximately 3.

At http://photo.net/black-and-white-photo-film-processing-forum/009Rgw I found this which may be of value.

Yellow-green (e.g. #11) historically was the "standard" B&W filter in Europe, while yellow (e.g. #6 or #8) was the "standard" in the US (at least in Kodak's view of the world, altho the German-made Kodak Retina came with a green filter). With the old orthochromatic film, yellow had less of a speed penalty than yellow-green. Older US books also recommend yellow-green as the appropriate "correction" filter for red-sensitive panchromaic films under tungsten light. Early (pre 1955 or so) panchromatic films came in widely varying spectral responses; part of the difference in filter popularity may have been different spectral responses of early German panchromatic films vs Kodak ones.

Scott McLoughlin , Sep 11, 2004; 02:25 a.m.

Thanks for the background and history! I'll give one a try.

Jim Vanson , Sep 11, 2004; 02:29 a.m.

Scott a couple of things to mull over:

A K2 yellow or yellow/green (#11) have a filter factor of about 2. That means you are going to loose at least 1 stop of light. Can you afford that?

...

 

[Godfrey]

What I generally do is just meter (either with a handheld meter or a metered camera) with and without the filter in front of the meter, and note the difference in exposure. Then you'll know exactly how to adjust to that particular filter.

Most modern meters are a bit more sensitive on the red end of the spectrum, so when using this technique for orange and red filters, your filter factor will be a little less than it ought to be while green-blue filters will be a little more than it ought to be.

My usual tactic is to do this for a given film and then run a test to see what the actual results are like, then mark the filter for what I perceive as the best exposure compensation number.

G

 

[Rob-F]

I think the "0.5" marked on the filter may suggest a filter factor of 1/2 stop (that may or may not actually be the case).

Because filters freely pass their own color, while holding back the complementary color, the correction required really depends on what you are photographing. If you want to photograph a yellow-green object against a blue sky, using a yellow-green filter, and you want to darken the sky while having no effect on the object, you would use no filter factor at all. The filter will freely pass the object of its own color, while holding back blue, which is the complement of yellow.

Films vary in their sensitivity to color, and that will affect the filter factor. I find that blue sky comes out darker with Delta 100 than with, say, FP4 or Tri-X.

So take Godfrey's advice and do some testing!

 

[tjh]

I think the "0.5" marked on the filter may suggest a filter factor of 1/2 stop (that may or may not actually be the case).

I would think that that the 0.5 following the diameter of the filter is the pitch of the filter thread.

Tom

 

[Rob-F]

I would think that that the 0.5 following the diameter of the filter is the pitch of the filter thread.

Tom

Could be. 40.5 x 0.5 certainly could be the complete spec for the thread. I have some Hasselblad light yellow-green filters, though, in bayonet mount, that are marked 0.5 for 1/2 stop.

Try several bracketed exposures, Joao, on your favorite subjects, with your favorite film. It's the only way to know for sure.