Please explain filter identification

[lrochfort]

Hello,

I'm looking to buy a yellow filter for my FSU lenses. I've found a selection for 40.5mm filters with what I think is the right thread pitch.

However, they're described as Y-n, such as Y-12, Y-17, with the exception of some that are advertised as "2x".

I understand the 2x designation, but not the Y-n. What does that mean and how do I adjust my exposure?

My Googling skills don't seem up the job!

Thanks all.

 

[ferider]

n is usually the Wratten number, see here, for instance: http://en.wikipedia.org/wiki/Wratten_number.

Don't know about 17 though.

 

[Rob-F]

wratten #8 is also known as a K2 cloud filter; Wratten #9 is the K3 cloud filter. But #17 I have never heard of.

If you are familiar with the picture of the Golden Gate by Adams, he wrote that he took it with a #9.

 

[sevo]

But #17 I have never heard of.

I have another light yellow #17 (perhaps pre-war Agfa by the looks of it), and have sometimes come across others, by a variety of German makers - presumably that number is not Wratten, where a #17 is not even in older Kodak gel filter lists, and would be between some orange filters. It might be some old German nomenclature that made its way into the USSR with the spoils of war...

 

[02Pilot]

Funny that someone else brought this up just now. I just picked up an incomplete set of 34mm filters made by Bel-view, originally for Minolta, to use on my Elmar 90 f/4. The yellow is marked Y2, which seems a common designation, but the green is marked G0, and the orange is simply marked O. Any idea what the filter factor for the latter two might be?