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/f...3/product/691/

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