IR Filters

I have recently accquired a Lee 87 IR filter and also some Ilford SFX200 film. My aim is to use the two together this weekend on a camping trip to Suffolk. So I decided to try out the filter on my digital kit to get a feel for the exposure compensation I would need.

I fitted the filter to my 17-40 F4L attached to the 5DII, set up a shot of some flowers in the garden, bright sun little wind so ideal conditions. Took shot without filter to get standard exposure, switched everything to manual, dialled in -5 stops (as recommended by variou sources) and nothing. Tried various other settings all to no avail.

Then got out my 10D which has been IR converted. Same procedure as above, attached the filter set exposure compensation and got a hugely over-exposed shot. In fact after some experimentation I realised that the filter only affects the conventional light meter in the 10D and if I expose at the same settings as without the filter I get a reasonable result.

So my 5DII is not IR sensitive and I dont need exposure compensation for the 10D IR. From all this I still think I need -5 stops for thr SFX film. Any Ideas?

Without filter
https://www.cambridgeincolour.com/fo...achmentid=4727

With filter
https://www.cambridgeincolour.com/fo...achmentid=4726