Factor differences: Kodak filter # vs. Lee filter #

There's a significant discrepancy in the filter factors of Kodak vs. Lee filters of the same filter number. Mathematically, isn't a factor applied the same regardless of the company or the filter (i.e., a factor of 4x is +2 stops regardless of manufacturer). When there is no apparent difference to the naked eye between a Kodak #11 (I have one of these for comparison) and a Lee #11, what's the reason for the discrepancy, apart, of course, one is made by Kodak and one by Lee?

Kodak #8: 2x or 1 stop
Kodak #11: 4x or 2 stops
Kodak #21: 4x " "
Kodak #23A: 6x or 2 2/3 stops

Lee #8: ?x or 1/3 stop
Lee #11: 2.5x or 1 1/3 stop
Lee #21: 2x or 1 stop
Lee #23A: 4x or 2 stops


Thanks for the info.
Chuck

Dear Chuck,

I assume these are Wratten numbers?

The thing about a filter factor is that it isn't fixed. It's a matter of subject and film, so a yellow filter will have much more effect on a blue sky than a grey wall, and more effect on an ortho film than on a pan film (and still less on an extended red film).

With this in mind, filter factors are as much a matter of opinion as of eternal verity. If you have the chance, why not compare two, on the same film with the same subject? I'd certainly be interested in what you found, though I have to say, only idly.

Cheers,

Roger

Roger Hicks said:

Dear Chuck,

I assume these are Wratten numbers?

Click to expand...

Roger,

The Kodak #11 is certainly a Wratten number. The Lee #11, I guess, is the Lee #11, at least that's the number given on the filter, IDK. I only know that with those factors being so different and, visually, the appearance so not different, then the factors will seem to produce different results for a given film.

BTW, when I am able to determine, through empirical means , the difference produced by these different factors, I will, only idly, pass on the results.

Thanks
Chuck

Roger Hicks said:

Dear Chuck,


With this in mind, filter factors are as much a matter of opinion as of eternal verity.

Cheers,

Roger

Click to expand...

Hi Roger,
I'm not so sure about that. The filter factor is supposed to provide compensation for the additional density caused by the filter - i.e. it is the additional exposure necessary to get the same exposure for a neutral tone such as a gray card. The varying effect on colors is kind of the point of using a filter and serves to affect the contrast range of a scene.

Chuck1 said:

... then the factors will seem to produce different results for a given film...

Click to expand...

That's the point: Which film are these filter factors appropriate for?

Ideally the filter factor should be that which gives the same density on film with the same exposure of a gray card. But the spectral sensitivity of different films are a lot more different than most people realise - and I don't mean only the "extremes" like Kodak tech. Pan and Efke 25, but otherwise similar films like Plus-X, FP4+ and APX100.

Before you can state a filter factor, you really need to state which film that factor is for.