B + W Red filter type 40E ?

[Cor]

Hi,

I have this very old, but in good shape, dark red B + W glass filter, type 40 E. I cannot find any information about it. I want to use it for IR photography.

By looking through it it is definitely darker than a red (wratten 25 filter) and looks quite similar to my Wratten 70 filter, my standard IR filter. It's not as dark/opaque as a 89b (B + W 77E).

I would really like to know at what wavelength it's transmission is 50 %, but any other info is most welcome too.

Long version:

I have this ultra low weight 4*5 kit consisting of a Gowland Pocket, 90mm Angulon (f6.8), 150 G-Claron and 210 G-Claron for travelling. When shooting Maco IR film I use a Cokin type 70 filter (square, P) in front of the lens, which is a nuisance (I hold it infornt of the lens during an exposure), and it gives rise to unwanted reflections as well.

This small 40E filter might fit the bill: it almost fits the Angulon (1mm too small), it's a little bit too big for the 150 Angulon, so I have to find a step up ring. The 40E lens came with a funny brass ring, in which the 40E (about 39mm ) screws, extending its diameter to about 49 mm, which fits into the 210 G-Claron.

I assume that the ring will not cut off too much of the projected image of the 210 G-Claron lens, since this lens is said to almost fill a 8*10 negative.

Or do I make a mistake here ?

best,

Cor

[Bob Salomon]

40E is the size, not the type. E is the thread pitch. B+W uses E and ES to designate the thread pitch on their filters. 40 is not a common size but 40.5 is. E is a metric pitch of 0.75 and ES is 0.5 pitch.

Have you compared it to a red 29 filter?

[Cor]

Thanks Bob,

I already had the idea that it could mean the diameter, and it explains why it just does not fit the 90mm Angulon, which is 40,5 mm. I do not have a 29 red, I used to have access to a spectrophotometer, so I could ran a transmission spectrum of my filters. Now I have access to a much smaller one, and I think that even this small filter won't fit in.

In the end I guess I just have to make a test shot with this filter, it ain't rocket science and my hunch is that it will work.

Best,

Cor

40E is the size, not the type. E is the thread pitch. B+W uses E and ES to designate the thread pitch on their filters. 40 is not a common size but 40.5 is. E is a metric pitch of 0.75 and ES is 0.5 pitch.

Have you compared it to a red 29 filter?