Fomapan filter factors ?

[Mark J]

Hi All
I'm just wondering is anyone has worked out any filter factors for the Foma emulsions.
I'm well into a pack of 5x7" already, mainly test shots of one sort of another, but hoping to keep my future hit rate high.
According to the datasheets ( ... ) they all look the same and are rather red-biased.
To be honest I'm not sure if the 'Y' axis begins at zero on those plots, but anyway..

My first impressions with a yellow filter (Hoya Y / K2 ) is that it might only need 2/3rds stop, rather than my normal 1 stop for Ilford film.
I suspect the Orange might not be 2 stops, either.

I could get a roll of 35mm to work it all out ( might still ) but interested to hear what anyone else has found.

[Drew Wiley]

Do bracket testing with the 35mm equivalent for each filter you have in mind. Use a neutral gray target and compare it to an unfiltered reference shot, ideally using a densitometer. A little work up front will save you some potential errors later. You also need to be more specific about exactly which Fomapan product you have in mind,
as well as what you specifically mean by an "orange" filter, number and brand wise (Hoya too?, meaning light orange).
As I recall, the factors weren't too far off from most "typical" panchromatic films, but certainly differed from the more specialized films like TMax.

[Mark J]

I could have predicted that this is the way it would go.

Yes, I know how to do the work, it's just that the idea of a forum is that we can share information and that someone might already have some numbers.
The film is Fomapan 200, for me. I will get some 35mm on my next order, however I am taking actual photos at the moment, when i have time, so it may not get done as quickly as I'd like.

[BrianShaw]

How exact do you want to get? I find being with 1/3 stop to be quite acceptable.

[Mark J]

Exactly - a third of a stop.

[Drew Wiley]

In terms of red or medium green filters, there can be as much as half a stop difference in green sensitivity among current pan films, or up to a full stop with red or deep blue. The biggest problem with any strong filter when using Foma 200 in particular is that you don't want to get into long exposure reciprocity failure territory whatsoever.

As far as common Hoya filters go, I used the same filter factors as for Delta 100, for example, with consistent success. Y light yellow : 1 stop. O light orange : 1-1/2 stops. XO light yellow green : 1-1/2 stops. X1 medium green : 2-1/2 stops. R equivalent to med 25 red : 3 stops. Avoid a deep 29 red. I never tested a 22 deep orange with it. (Hoya doesn't offer a 22 or 29, but they are filters I carry in my kit.)

All bets are off at long exposures. The filter factors themselves will tend to diverge, not just increase.

[Mark J]

Thanks, those are useful starting points. Maybe suggests that the published curve is not as odd as shown, if you can use Delta 100 numbers ?
I can believe the G(XO) is only 1 1/2 because I accidentally shot it instead of the Y with a 1 stop factor, and it's wasn't too far off.
My Orange is a nice Rodenstock No.22 , I will get a factor for it when i can get round to exposing the 35mm.

If I want long exposures, I'll use something else ! ( although I have seen elsewhere in tests that their predictions are pessimistic )

[Drew Wiley]

For deep orange 22 (made by B&W or Heliopan) try a 2-stop factor. But watch out - what B&W labels as a 22, and possibly Rodenstock too, is actually mild orange rather than equivalent to the Wratten no. 22 deep orange effect. - sometimes they're dual labeled; and the true deep orange B&W one is labeled 041. It can get confusing if you don't see the filters in person first.

[Eugen Mezei]

Do bracket testing with the 35mm equivalent for each filter you have in mind. Use a neutral gray target and compare it to an unfiltered reference shot, ideally using a densitometer.

How would a grey target help him? He needs the antagonist color of the filter to see (and measure) the effect of it.

[Tobias Key]

I don't have any practical experience of Fomapan 200 but judging by the data sheet it is less sensitive to blue light than to red light. In practical terms that seems to mean it behaves as if it has a yellow filter on it even when shot without one. I guess that would mean that a yellow filter might have less exposure compensation needed as the filter matches the spectral sensitivity of the film. The downside might be that contrast gets excessive with darker orange/red filters and you might lose shadow detail. Compare the spectral sensitivity on the data sheets .

Fomapan 200 https://www.foma.cz/en/fomapan-200

HP5+ https://www.ilfordphoto.com/amfile/file/download/file/1903/product/691/

There is certainly a difference to HP5+ and I think that is what you are observing.

[Drew Wiley]

A gray target is what you want to determine filter factors. Or course you can use something like a MacBeth Color Checker chart, which has an excellent gray scale on it as well as the color patches.

Here's part of the problem : different films see color values differently than we do; and colors in nature often reflect wavelength combinations we don't intuitively recognize; and colors in artificial charts don't behave like those in nature.

Then there's the problem of meter spectral sensitivity itself. So unless one wants to make a very complicated exercise out of all this, it is best to rely on a single common denominator neutral standard when doing filter factor tests.

And you can't assume the only use for a contrast filter involves only attenuating something on the opposite side of the color wheel - the antagonistic color. These filters are applicable for lightening similar colors too, or more mildly moderating in between hues.

And like I just implied, in nature what appears to be an opposite to our eyes might be something quite different to film. Use a red filter to darken green leaves and the result will be much lighter than you think, because leaves contain not only green chlorophyll, but red and yellow pigments too, just as nature itself reveals them in the Fall when the chlorophyll has faded out. So yes, after determining basic filter factors using a gray card, it is also important to do real-world testing in the field with appropriate subjects.

[Drew Wiley]

Foma 200 has a much steeper toe, or longer straight line, than HP5, and can therefore resolve deep shadow values significantly better than HP5 in high contrast scenes. Not just theory - I've done it. But you still need to apply the correct filter factor in each case, and also be quite aware that Foma 200 is not in fact a true 200 speed film. I shot it at 100. I've even shot 12-stop extremes in the mountains using a deep red 29 filter with no loss of deep shadow gradation at one extreme, or excellent highlight separation in bright clouds and gleaming ice, at the other extreme. But if you're going to skate on the very edge of the ice rink like that, it takes some practice.

And once again, as I have stated before, I don't rely on compression or compensating or minus development to do that - just an appropriate film. No, Foma 200 is not a replacement for Super-X 200 or Bergger 200; but it is the last "straight line" film available. But if you afford it, TMY400 is close enough, true 400 speed, and way more versatile.

[Eugen Mezei]

And you can't assume the only use for a contrast filter involves only attenuating something on the opposite side of the color wheel - the antagonistic color. These filters are applicable for lightening similar colors too, or more mildly moderating in between hues.

Sure, I mentioned the antagonist color to simplify the problem.
Ofcourse the filters own color will be rendered lighter, as will all other colors be affected (to a different degree).

But if you shot only a greycard, how will you know how the colors are rendered by the filter? A MacBeth shows this.
Also how will you measure the factor by which you should prolong your exposure? Sure you get a factor for neutral, but you are mostly interested to a correct exposure of your scenery. Let us say you photograph red roses. (Without a filter both the flowers as their leaves will give more or less a neutral grey.) You are interested to know which filter factor you have to apply (either to your green or red filter, depending if you want the leaves or the flowers to be lighter/darker) so that in combination with the specific film you know how much to expose in order to have the separation you intend. I do not see (but I can definitively wrong) how a greycard will help here.

[Mark J]

I know what you mean, but I don't know how easily I could use all of that extra data in the time it takes to take a photo. For me it seems enough to get a good fix on the change of the average exposure. I know what the filter will do (in my head) to the colours, and can deal with that. But your method could easily get bogged down in how intense each colour is, it seems like a step too far.
I guess if I was exposing 20x24" , I might go to these lengths !

[Drew Wiley]

Eugen - Let me repeat - yes, it can be helpful to do initial tests including the color patches on the MacBeth Chart as well as the gray scale, but those patches are not always equivalent to similar looking colors in nature. So there is absolutely no substitute for actual experience outdoors with specific filters and films, and then printing sample results. But you have to start somewhere.

I have decades of experience both shooting and printing, and to this day, simply apply grayscale-based filter factors when shooting black and white film. It's not like working in a studio. Light changes, shadow patterns change, weather can be dicey - you need to decide things quickly and spontaneously, without complication.

Yes, I have all kinds of negs of MacBeth charts with the density of every color patch recorded. But that's all in relation to much more complex color printing protocol using hard color separation filters, and what those are used for; but it's wholly unnecessary for general black and white shooting. Trying to juggle too many variables at once in the field is a recipe for frustration, not success.