Mystery: What is this box of filters for?

[pdh]

Here we have something that I turned up from a long-dead photographer's darkroom last year, and I'm just getting round to try and found out what they are for.

It is a set of four threaded filters in a fitted velvet-lined box, and very solidly made to boot.

They are all glass, and quite thick glass by the look of it - perhaps gelatine sandwich?

The case is clearly constructed to take the filters.

The four filters are marked, respectively, "Alpha", "Beta", "Gamma" and "K2" (in the 2nd photograph, they are in that order L to R)

As best as my cheapo Screwfix caliper can tell, the threads seem to be a touch over 46mm O/D (46.3?) - they won't screw onto any of my 46mm stuff. No idea what the tpi is as I don't have a gauge nor any intention to buy one.

There isn't a single mark on any of them or on the box to indicate a manufacturer, but my guess (given the other stuff I got as part of the same lot) is that they will be early-mid 20th Century and made in the UK

"K2" is rather obvious, but why "Alpha", "Beta", "Gamma" ?

Are these part of an LF set of gear or darkroom gear?

I posted the same information at APUG and there were some suggestions that these were for astrophotography, but no-one has been able to offer a definitive answer.

[Steven Tribe]

Alpha, Beta and Gamma could just be identification marks, rather than having a deeper meaning. They are a, b and c in "real" Greek. My School was devided into 4 houses (like Hogwarts?) called alpha, beta, gamma and delta. This was a temporary identification when the School was founded in 1926. They never found a permanent replacement!

Perhaps a set for Autochrome adjustment?

[Jac@stafford.net]

Ilford nomenclature
alpha beta gamma k.2

But in numerical order they are:
104, 105, 401, 402 (light-yellow, yellow, light-green, yellow-green)

[Bill Burk]

Now you're getting somewhere...


http://www.ebay.co.uk/itm/ORIGINAL-ILFORD-402-GAMMA-GREEN-FILTER-FREE-SHIPPING-/251076355042?nma=true&si=wVza8NnSZQ9jdOUt4545Q8WN0SE%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

http://collectionsonline.nmsi.ac.uk/detail.php?type=related&kv=8203134&t=objects

139334

[pdh]

aha!
that's excellent :)

The eBay item has a clip rather than a thread, and I also have a yellow filter of exactly that design kicking about from the same source.

Generally my google-fu is up to the mark for this sort of thing but I had got nowhere. Sometimes there's no substitute for what's racked away in the recesses of memory. Thanks Jac for that, and thanks Bill for the links.

[IanG]

I've an Ilford filter pamphlet somewhere that came in an Ilford Formulae book, when I find it I'll put it online.

This is a set of "Correction filters" for Panchromatic film according to a 1960's Ilford Manual of Photography.

Ian

[pdh]

That sent me scuttling off to dig out my (1971) Ilford Manual and there on pp.294-295 are indeed references to Alpha Beta and Gamma filters. Not to K2 though, curiously.

[IanG]

There were more in the Series, a Delta (Deep Yellow) for instance is listed pre-WWII, but I can't find the details of them all at the moment. I think I scanned them a few years ago.

K2 is Ilford's code for a light Yellow filter so borderline between "Correction" and the "Contrast filters - deep yellow (Delta), Orange and Red.

Ian

[pdh]

So was "K2" originated by Ilford but then became a generic descriptor used by the rest of the industry?
(I have plenty of modern yellow filters marked K2)

[IanG]

I think K2 was originally a Wratter designation for the Pale Yellow filter (before Kodak bought the company) but Ilford used it as well. At one time Ilford called their Yellow filter an ISO filter.

Alpha was Pale yellow, IS)/K2 Yellow and Delta Deep Yellow..

Ian

[Doremus Scudder]

... As best as my cheapo Screwfix caliper can tell, the threads seem to be a touch over 46mm O/D (46.3?) - they won't screw onto any of my 46mm stuff. No idea what the tpi is as I don't have a gauge nor any intention to buy one. ...

Well the mystery of the designation seems to be solved, but what about the strange size. It doesn't seem to line up with series filters either... (series VI 41.3mm is and series VII is 50.8mm) (see https://en.wikipedia.org/wiki/Photographic_filter#Series_filters )

Maybe Ian has some knowledge of this?

Doremus

[IanG]

I think for motion picture/cine use where there's less correction etc at the positive stage. We don't use correction filters in normal B&W photography, we use filters for effects, contrast etc.

Ian