Does anybody know where I can get hold of these, or alternatives that can be adapted? I have searched high and low, but no luck!

Which filter do you need?

I am after either a yellow or preferably an orange filter.....

Yeah, this is kind of a pain in the neck to source these things. So far, I have been able to locate two of these, (a skylight, and a UV-both off of e-Bay).

Here is what I have been able to find out:

1) The 250mm f2 EDIF lens has 12 elements in 9 groups and the 350mm f 2.8 EDIF lens has 9 elements in 7 groups. Both lenses were originally supplied with a "Neutral" filter installed. The 46mm rear filter counts as one of the lens' elements and Olympus cautioned that the filter is an integral part of the lenses internal optics and that the lens cannot be used without a filter installed.

2) The filter holder has standard 46mm threads and a 46mm filter of any type can be screwed into the filter holder. The original Olympus filters are extremely slim and have no front threads (nor are any required). The filter holder with a standard third party filter installed will not fit into the lens (because the filter is too deep-front to back).

I have a 46 mm orange (G) filter, and I have thought that I could grind off the front threads of this to see if it would then fit into the lens body. I haven't gotten around to doing this yet since I haven't had time.

Dave

Have you seen this:

http://olympus.dementix.org/eSIF/om-sif/lensgroup/filters.htm

Interesting link. So, theoretically an orange filter is out there somewhere! I have the neutral filter that came with the 350....

From the original instruction sheet from Olympus supplied with a 46mm Rear Filter-the available options were:

1) Skylight (1A)
2) L39 (UV)
3) Y48(Y2, yellow)
4) O56(O2, orange)
5) R60(R1, red)
6) A4(81C, amber)
7) B4(82C, blue)
8) Neutral (Not Neutral Density, filter factor of 1.0)

I have a full set of these filters. Are you still interested in them?