Ah!  Everybody uses Wratten numbers (except for Nikon, which uses Hoya
numbers; on the other hand Hoya usually uses Wratten numbers)... So a No. 12
yellow filter, of any brand, will be a very close substitute for what you
originally specified.

Funny, works here, Calumet has a ton (well, a few ounces) of them.  
Maybe it is one of those UK things.  Are they still on ration?

Using google and entering:

     wratten 12 uk

One finds:

http://www.silverprint.co.uk/acc6.html

I am not sure this has not all been a troll...

 How are you going to use it? Hold it in your hand? Mount it? You can get
glass #12. That should last almost forever if you don't step on it. Or you
could get a sheet of filter material from Lee. Tell them the wavelengths you
need to absorb. That's assuming you can live with the quality of lighting
filters. The stuff is fairly cheap. Letting you treat it like a throw away.

Lee doesn't have much info on it's website but you could look at the Rosco
one.

http://www.rosco.com/us/filters/roscolux.asp#SPECIFICATIONS

Pick the filter that provides what you need. Stuff can be cut to size.

Nick

You should be able to obtain glass filters with approximately the same
specifications. The Wrattan filters spectrophotometric curves are in
Kodak's publication B-3. The other manufacturers should also be able to
give you the curves for their filters.

A 12 is a blue cut filter, normal use was in IR false colour work.
Good luck getting one out of the yellow bird... Can't remember the
cutoff wavelength. Any of the good filter supliers should be able to
supply a glass one that will do the job. If all else fails, try Zeis.

 But those are lighting filters. Are they good enough for use in front of
th lens? I've used them for spilt printing but that's between the light
source and the negative.

      Nick

Ah!  You're in luck.  Almost any photographic filter described as "medium
yellow" (comparable to Wratten 12 or 15) will work just fine.  It sounds as
if an exact equivalent is not needed.

Since the size of the filter is not critical, as long as you can hold it up
to your eye and look through it, I'd suggest checking secondhand filters at
a store that sells used cameras.

Yeah, that's what we have been trying to tell you!

Wratten #12, 3x3", B&H New York, ~$27, they ship internationally

or

Deep Yellow filter, 49/52/55 mm, ~$10-20, _any_ competent camera store.
Filter is glass and comes in a metal ring.  This is
probably your best choice.

or

Roscolux #12, 20x24", B&H or any theatrical supply, ~$6

How is this confusing?

yellow filters cuts off all blue radiation from your cobalt glass
filtered light source, but transmitt green radiation of excited dye.
it imroves contrast of an image, making it easier to detect fine
hairlines of a damage.

Wratten 12 is quite popular, was used as standard filter in color
infrared photography. many other filters from various suppliers will
work as well. Lee filters are of very good quality, I used them in IR
photography with great success.

*I'm even more confused than ever now with all this technical talk.
*
*I used to work with a Professor of Ophthalmology who used to use a
*piece of Kodak Wratten gel filter no.12 - it looked like a very flimsy
*square (i'd guess approximately 3 x 3 inches in size) of yellow
*plastic material which he held in front of the patient's fluorescein
*stained eyes whilst viewing them through a slit-lamp biomicroscope
*using a cobalt blue illumination source.
*
*Recently I came across a medical review article by my now-retired Prof
*whcih states:
*"Fluorescein staining is the standard method used to demonstrate
*ocular surface damage. This orange dye, which fluoresces green when
*excited by blue light, is applied to the eyes. Optimal results are
*obtained by viewing through a yellow barrier filter, such as a Kodak
*Wratten 12 absorption filter, used in combination with the standard
*blue exciter filter of the slit lamp. This technique reveals surface
*damage on both the cornea and conjunctiva. Usually, staining has a
*characteristic distribution and is confined to the exposed
*interpalpebral area of the ocular surface. In the absence of a yellow
*filter, staining is poorly seen on the bulbar conjunctiva. With
*regular use of a yellow filter and routine examination of the upper
*bulbar conjunctiva, the clinician is unlikely to miss the diagnosis of
*SLK in a symptomatic patient."
*
*I guess I'll have to email him to see where he gets them from.
*
*Thanks
*
*Simon
*
*
*
*rwatson767@aol.com (RWatson767) wrote in message news:<20041202145618.21692.00001185@mb-m14.aol.com>...
*> Simon3000
*> >Kodak Wratten Gelatin filter no.12 ??????
*>
*> I am a medical doctor looking to purchase a Kodak Wratten Gelatin filter Number
*> 12 for use in assessment of patients with dry eye using fluorescein tear
*> staining.
*>
*> What size? There are or were several sizes. Some round ones also.
*>
*> Bob  AZ

Get some filter frames or make a frame to sandwich the
gel between and handle carefully. It should last quite
a while.

Yes, #8 Yellow, #12 Yellow, #15 Yellow are the correct names.

If the suggestion is to carefully choose the transmittance
probably best to stick with #12, the minus blue. Both the 15
and 12 block all transmission in the 400 nanometer range, but
the 12 allows more of the yellow green at 520-530 (which is I
gather what you want and is why 12 is commonly used.) A #8
likely passes too much cyan/blue for the purpose.