I have purchased a couple of those new white lens cap thingys. They are a screw-on cap which is a white diffuser for getting the white balance on a digital camera. So they sort of act like a giant lumisphere on an incident lightmeter.
OK so I want to use it to do pre-exposures on my LF setup. I hope to put an ND filter underneath it and then pre-expose the film.
How on earth do I take measurements ?? I have fitted the 77mm one to my Nikon film camera a F100 with an 85mm lens and it says f8 - 1000th - 100 ASA. I then retract the lumisphere into the head of the lightmeter (Sekonic L358) and take another measurement. It says f8 - 1/250 - 100 ASA which is 2 stops more exposure. The reflective head on the lightmeter reads f8 - 1/6400th - 100 ASA which is nearly 3 stops less exposure than the Nikon ...
Is it possible to take a reading from the ground glass or something ? Perhaps I should setup the LF with a known good lens and take an incident reading with a retracted lumisphere on the ground glass ??
I must admit to being a bit of a goose with exposures sometimes.
This is particularly tricky for me.
Edit: I think I do want to refer to a reading from the ground glass if possible as this would be a 'constant' if I use the same lens and shutter. I absolutely do not know what I'm doing here ...