White filter (2 images)

[Tickhiller]

I have been sorting out some old photographic kit belonging to my late father in law. Amongst the lenses was this filter. It appears like a normal 55mm thread filter but is slightly translucent white. The old boy used a Chinon CS and died before digital SLRs were accessible to normal folk.
Any suggestions as to what it is.

[huwevans]

I think it's probably for using the camera's TTL meter to get an incident light measurement, rather than the usual reflective one.

[swanseadave]

^^WHS^^
I can think of no other possible use.

[Malcolm_Stewart]

You could probably use it on a modern DSLR for setting a Custom White Balance - like an Expodisc, except that my Expodisc is honeycombed on one side, but otherwise like what you've shown. (Does it say EXPO/DISC on the other side?)

[Tickhiller]

I think it's probably for using the camera's TTL meter to get an incident light measurement, rather than the usual reflective one.

Interesting thought Huw but it does not let much light through, would it not block most of the incident light?

[Tickhiller]

(Does it say EXPO/DISC on the other side?)

There are no markings on it at all

[huwevans]

Interesting thought Huw but it does not let much light through, would it not block most of the incident light?

It's meant to - light loses several stops when it reflects off a typical subject. So for a meter that's set up for reflected light readings to indicate a correct exposure when pointed directly at the source (instead of the subject) there has to be an adjustment equivalent to that loss. The incident 'filter' - usually a dome in the case of hand-held meters (or 'Invercone' in the case of the classic Westons) - absorbs an appropriate number of stops, and diffuses the light to reduce directionality. The end result is a reading which depends on the strength of the light source, and is independent of the reflectivity of the subject, or an 'incident reading'.

[Benchista]

It's entirely possible that it's what Huw suggested - certainly such "filters" were around - but in the absence of any marking, I think it's something slightly different. I have something pretty much identical, and it's a light source diffuser from a zoom slide copier - removable so you can add an appropriate colour balancing filter.