Filter factor guidance : yellow-green or mid green

[Mark J]

I have been searching a little and have not found much info relating to filter factors for the yellow-green or green filters.
I was commenting elsewhere that I haven't used these enough, so I'm going to get one or two filters soon, so I'm wondering if we could gather a few numbers from people on this subject.

It seems that even with the mainstream films from Kodak and Ilford, the green sensitivity is one of the more variable quantities you could pick.
Also, there are a few types of yellow-green and green out there - brands could be mentioned.

I note that these days you don't get any info from the film manufacturers.
I haven't bought a new filter for years ;o) so I don't know how much info they provide.

If possible ( Ha ! ) I'd like to avoid digressions into meter variables and what the scene contains.
Let's say we're just looking at a grey card or a mixed scene.

What can people offer me ? ( Filter type + film )
Thanks in advance ...

[BrianShaw]

This is the first place I go for such information:

https://images-eu.ssl-images-amazon....1x9LZAkTES.pdf

Regarding variations for film and meters... don't overthink it; Assume all is the same for those factors unless and untill you have a real need to split hairs. Pay more atttention to the potential contrast variations imposed by your scene's lighting conditions and subject colors.

Regarding film manufacturer reccomendations, there are filter recommendaitons for FP4+, HP5+, and Tri-X. Google the data sheets!

[Mark J]

Thanks, I'm not overthinking it !
I have quite a big stash of film datasheets and had looked at several yesterday.
Of the ones you list, only Tri-X ( which I didn't have stored ) shows filter factors. This is useful, thanks. Tri-X doesn't show much of a dip in the green of course.
...but I realise now that all the Kodak ones do at least have factors for the Wratten filters .
All of the Ilford films say "Follow the instructions provided by the filter manufacturer" .
I should have started by looking at Kodak, not Ilford Adox and Fomapan !

The B&W green one looks less dense than a Wratten 58, from the filter factor. I need to double-check but is the (13) the Wratten equivalent ?


I have one data point myself that i exposed Delta 400 with a Cokin green gel at the weekend and it came about how I expected with 2.3 stops extra.
Not very scientific, but useful. However I need some glass filters.

[Drew Wiley]

Specific filter factors can make a real difference. For example, the filter factor for Hoya X1 medium green is 2-1/2 stops for Delta 100, but only two stops for TMax 100, and even less for ACROS 100. So you could hypotehtically end up with an entire stop of error unless you tested in advance. This discrepancy would be even more for deep green like 58 or 61. Similarly at the red end. With TMax you need a 3 EV correction for a deep 29 red, whereas across won't accommodate itself to anything that deep a red, even with a 4 stop filter correction. You can't go any deeper than 25 red with ACROS because it's orthopanchromatic, not panchromatic per se. And remember, filter characteristics vary somewhat brand to brand, and even the same number attached to a color of filter might mean a completely different thing.

The major manufacturers like Kodak and Ilford do provide filter factors on their respective technical data sheet, but only for the most common filters. But that should just be a starting followed by more specific testing relative to your own anticipated purposes. Expending a roll of 120 doing such testing is a wise way to preclude more serious losses when it comes to large format time and budget expenditure.

Mark - the B&W 13 is a medium green more akin to the Hoya X1. A Wratten 58 is classified as a deep color separation filter, though not in as stringent a sense as the even deeper 61 green. I don't know of anyone making a 61 glass filters anymore, although my old one is Tiffen (they still make 58). I've never found the need for a true deep green filter in the field, unless it's hypothetically for in-camera RGB color separation purposes. I do use them in the lab. The ordinary medium-dark Hoya X1 works fine for me to sufficiently darken reddish hues in landscapes, along with the light yellow-green X0.

[Mark J]

Yes, I'm thinking I might make a small crib-sheet and laminate it, for some of the combinations I might be using. It would be good to get fairly close, if I'm shooting more 5 x 7. Testing is the ultimate answer and it's a good point re. using 120. I have just bought a roll of 120 Foma 200 for evaluation, even though it has a bad rep in 120, for possible 5 x 7 purchase.

[Drew Wiley]

Test for the films you specifically plan to use. Not all pan films are identical with respect to realistic filter factors. Beware with Foma 200 of the very short developing times, utterly miserable reciprocity failure with long exposures, and unrealistic box speed. I recommend 100 as your starting point film speed, and around six minutes time to try with most developers. It's needed filter factors seem similar to FP4 or HP5.