Are these filters too strong? Or, what filter factor is this, anyway?

I probably should have known better, but I ordered a stack of 40.5 mm filters (to fit the Jupiter 8 that came with my Kiev 4M) from a vendor in China. Red, orange, yellow, green, blue, and purple. No, I don't know what purple is good for -- minus yellow, I suppose, but it's not a true magenta.

Anyway, for three bucks a pop I should probably have expected this, but they aren't marked in any useful way (okay, the purple one has FLD, which I've just read corrects the green cast from fluorescent lighting and has a 2x or 1 stop filter factor -- only this one is way darker than the picture I found), just Blue, Green, etc.

The Red, Orange, and Yellow look pretty close to what I'd expect for contrast filters (3, 1.5, and 1 stop respectively), but the Green and Blue are pretty dark. I found a chart on Wikipedia, but this green looks darker than two stops and the chart doesn't even show a blue (what would I use that for, anyway -- simulating old blue-sensitive film?) other than one for correcting 3200K light to 5500K "daylight" with a 2 stop filter factor, and this seems darker than that (at least as dark as the red).

"Just meter through the lens." Um, no. I don't have anything with TTL metering that uses this filter size. And I don't know that a selenium meter will read correctly through a filter. I don't have a CdS meter with a good battery at present (got a regulator unit and lithium cell for my Honeywell Pentax 1/21 spotmeter on the way).

Can I trust my selenium Sekonic L-28/Studio S meter to read these filter factors correctly against a suitable reference light source?

I remembered there was a thread on this (spectral sensitivity of meters). Maybe use the meter to get the range to test and expose some test shots on film to check.
I have a Juipter 8 also, but did not realize it is 40.5, guess I never tried to put a filter on it. But it turns out most all the Horseman 6x9 lenses I have are also 40.5, so I have the Horseman 40.5 to 55 adapter that came with the kit.

https://www.photrio.com/forum/threads/comparing-spectral-sensitivities.93891/

Except for the FLD, these filters lighten/darken certain colors when captured on Black & White film.

What they do, and their filter factors are listed in this article.

http://www.fineart-photography.com/bwfilter.html

Donald Qualls said:

Can I trust my selenium Sekonic L-28/Studio S meter to read these filter factors correctly against a suitable reference light source?

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Hi, no, I don't think so.

I think that what I might do, just as a rough guide, is to lay all the filters out on a light table - one with known spectral qualities - and photograph them all in one shot. If you had a densitometer, and if you knew the response curve of your film, you could estimate the filter factors from that. Lacking that you could shoot an exposure series, then look for visual density matches. Or make some reference prints. A pretty effective way to visually compare densities is to cut samples in half, then butt the two samples together.

Ps, in case this is not as clear as I hope it is: if an unknown filter is shot at, say, +1, +1.5, and +2 stops exposure, then each exposure can be visually compared vs a no-filter reference. If you say, oh, it's a match somewhere between +1.5 and +2, then the "factor" is between +1.5 and +2 stops. (You would have to convert from f-stops to an actual factor.)

Yellow, 1 stop
Orange 2 stops
Darker green, 2 stops
Red, 3 stops

You knew all that...

I’m with Mr Bill. Given that the filters don’t appear to match standard B&W filter densities a test shoot is probably your best bet.

btaylor said:

I’m with Mr Bill. Given that the filters don’t appear to match standard B&W filter densities a test shoot is probably your best bet.

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Sure, testing is the best bet.

But above pure density, the color Itself is what’s most important. Yellow filtering by itself kills enough blue light to match one stop. Once yellow reaches orange, it’s eats 2 stops. Add more red to it, and it becomes “red-orange”, it eats 2.5 stops. Add more red and it becomes “red”. Red eats 3 stops.

It’s the color, not the density. That’s how film sees, not how our eyes see.

wiltw said:

Except for the FLD, these filters lighten/darken certain colors when captured on Black & White film.

Click to expand...

Of course the FLD filter has its effect on b&w too. It means minus-green.
But it should be not pronounced. The OP though stated that the filter has higher density than he expected for an FLD.

I myself only buy used and local and thus typically for less than the OP. But more important: by this the majority of filters have some wellknown brand and I thus can look them up in old catalogs, even up to a spectral curve.

Sigh. Okay, looks like "test roll" is on the table for the near future (when I finish the roll of Superia Xtra 400 that't in the Kiev now).

I'm not technical enough to spend lots and lots of my time and many rolls of film trying to extract the complete spectral curve from my meter, film, or filters -- obviously, anything that looks orange to my eye will darken skies and leaves, and do so more strongly than "yellow" will. Green will darken skies and lighten leaves, assuming I expose with the "correct" filter factor.

So, for initial testing, it looks like I'll use 2x for yellow, 3x for orange, 8x for red, 4x for green, bracket for the blue (still not sure what I'd use that one for, but it was offered for the same $3), and bracket the FLD -- may also check the FLD on color film as its labeled effect (if it's a narrow cut, it might be as little as 2x and still look pretty dark, or the photos I found from online vendors might have been generic).

blue can be used for an ortho effect with B&W.

Donald the green is probably a 58 or 61 so you could start with that filter factor. The blue is probably a 47 or something like it.

You could probably use the blue and green for split printing in the darkroom too if they fit your lens.

Thanks, @Patrick Robert James I don't need them in the darkroom; I've got two 24x24" gels, one a pretty deep blue and one a strong yellow, with a couple 4x4" chunks clipped off one corner (already used for under-lens filtration). I bought them specifically for split filter printing. I'd have gotten magenta instead of blue, but I couldn't find local stock at the time on a magenta with enough green cutoff to suit me. I believe I have 0 or 00, and at least 5, as equivalent filtration. Not to mention that I don't believe I have a single enlarging lens that will take a 40.5 mm filter thread. Too big for the 80mm Anastar or 50 mm El Nikkor, too small for the Industar 61 105mm and the 135 mm (Tessar?).

But I just found the full list of Wratten filters, and, linked from that page, the SMPTE color bar chart. The red I have appears to be a true tricolor -- green, blue, and cyan are completely blocked, yellow, red, and magenta look the same as white (cyan, magenta, and yellow in this case are additive mixes). The green isn't a true tricolor; blue and red are still distinguishable from black and each other, but cyan, yellow, and green look (virtually) the same as white. The blue is less perfect than the green; blue and magenta look almost the same, but red is still reddish, rather than black, cyan looks the same as white but blue is "bluer" while green and yellow are almost the same. So, I'm going to go with the red being a 25, 3 stops correction, orange and yellow being the usual contrast filters, 21 at 2 stops and 8 or 12 at 1 or 1.3. Green, as you suggest, is probably 58, 60, or 61 -- and the chart doesn't give a filter factor for any of those. The blue looks likely to be more of a 47 than 47B (the latter appears to be used for calibrating monitors, and this isn't quite that pure on mine) -- but again, no filter factors given.

Based on appearances, it looks like I'll have to go with 3 stops for the green and the blue, same as the red, but I don't expect to use them much anyway. @John Koehrer that was more or less what I'd been thinking -- this blocks almost all green and red, so should actually simulate pre-ortho emulsions like collodion and ca. 1880 dry plates.

The FLD doesn't block any of the colors on the SMPTE color bar chart, and against my monitor doesn't seem as dark as it looks in its box; I'm going to test it a couple times with the assumption it needs 1 stop of filter factor. Not really sure where I'll do that, fluorescent lights are much less common than they used to be, and the Superia Xtra 400 I've currently got loaded in the Kiev these fit has the fourth color layer, introduced specifically to allow correcting out fluorescent color cast with filtration during printing. My shop at work has old style long tube fluorescent lighting, I may try a couple shots in there with that filter.

As I recall from my apprenticeship in a printing shop (more than 40 years ago), tri colour filters are process filters used, at the time, for analogue colour separations when reproducing coloured originals for quadrichromie.
This might be an interesting exercise in B&W photography, trial and error...

The FLD filter is mainly for colour photography (transparencies) in fluorescent tube lit situations, but now there is so many LED light...
And, as you are at colour photography, you might also look on the WWW for a Mired colour Fahrenheit degrees table.

You're correct -- for photographers, you'd use tricolors to make the separation internegatives for things like tricolor gum or tricolor carbon. And these should work well enough for that, (though I'd probably need a different thread size for anything that would make big enough negatives for that).

The difference between a red tri-color and a common red contrast filter is quite small, though, and for B&W film it won't matter. The green might be too strong; most green contrast filters (to darken skies and lighten foliage) are lighter than this one, as far as I know. But I'll try it at +3 stops on a test roll and see what I get.

Just be aware, there is no standard for FL filters. Each filter manufacturer makes theirs for what they believe is the average fluorescents. But there are so many different daylight flourescents you may get excellent balance from one makers FLD and terrible results from another’s.

Bob S said:

Just be aware, there is no standard for FL filters. Each filter manufacturer makes theirs for what they believe is the average fluorescents. But there are so many different daylight flourescents you may get excellent balance from one makers FLD and terrible results from another’s.

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Terrific.

Fortunately, when I shoot color, it's generally color negative, which allows for some additional correction during printing or after scanning.

More important is that a filter is a lens, and it’s focal length is in meters rather then mm. In order to not optically effect your lens resolution it must be optically flat and in perfect parallism to the lens and the film or sensor. Best filters are dyed in the mass glass. They are one piece. Cheap filters are usually two pieces of glass with a colored substance between them. Good filter are just one piece of glass optically ground front and back to have minimal effect on resolution. Cheap filter sandwich have multiple surfaces that are rarely, if ever, optically flat. In other words, you get what you pay for.
Really good filters have brass mounts. Cheaper ones are plastic or aluminum. So test before you shoot anything important.
One exception to solid glass are polarizers which are always a sandwich.

The Pentax Digital Spot meter accepts 40.5 mm filters, and if you have one, or can borrow one, you could use it for evaluating the filters.

Sounds like color filters to add tints to color shots just for the heck of it. I once got a gift of whole bunch of filters just for that purpose that I never really used. It has nothing to do with contrast filters for BW or color correction filters used for different lighting conditions.

If it were me I would likely get a colour checker and grey scale chart and shoot this with each filter checking both exposure value and effect on colour tones.