This post is more a stream of consienceness than a tutorial.SO please keep this in mind..
A cold and wet day in Picton, a rare to myself and I was chatting to Tim and Kevin in a yak conference whilst I took some BW400CN and reversed it. Before you all scream REDSCALE I would like to remind you all that BW400CN Is black and white. Kodak is the only maker of chromographic film with an orange backing (mind you, all Of kodak's c-41 film has a deep orange backing) and yes, I know there is ilford and Fuji, but their backs are clear (shows up grey) so no good for this experiment.
This is so I can have a built in filter for my black and white film. All the time I was doing this still chatting. All finished and I proudly show off my new pink film.. And suddenly Kevin asks innocently enough.. What will you shoot it at? Aargghh I had forgotten to work out a filter factor. And of course a camera can't work this out being on the wrong side of the lens. Lol. I took a guess at 2 or 3 stops and it was then that Kevin and I dug out our lightmeters. I couldn't find the one David lent me, think its in my camera bag.. Anyway.. He showed me how to measure the light drop off of a film. He didn't have the same film but it works and my brain had a click moment. OF COURSE!!
He measured the light. I used an app called Light Meter not my usual one, but does this job.
So you set an arbitrary asa, and select an arbitrary shutter speed measure the resulting f stop.
Hold the film over the the light Meter and measure again. The first reading with no film was f/4.5. Holding the BC400CN in front of the light meter I measured again and got f/2.2 that's close enough to two stops.
So I have to adjust the exposing times by two stops. That's rating it at 100asa.
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| Kevin's example, before putting the film across (Kevin's photo) |
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| Kevin's example 2 with asa 100 film (Kevin's photo |
In Kevin's Example, he selected 1/30th of a sec and asa 400 (The figures don't matter) and he got f/11 when he put his asa 100 film across he got f/1. He is meauring the whole thickness of the fim but if we redscale we are only looking to get the light through the anti-halation layer and not all the way through that would be 2.5 stops.
My meauring was 7.5stops. and using a 100 speed film gave me 6 stops. all this runs around 2-3 stops we have to allow for the anti-halation layer. Now of course this is all witch doctory and at the end of the day, red-scale is always 2 stops at least depending on your wanted result. Slightly underexposing will ove a deeper red. This only means in my case that the red/orange filter strength for my B&W film is 2-3 stops strength.
remember this is only to get you a ball park place to start. by all means just shoot at 2 stops and if you are wanting a different result move over or under.I feel 4 stops would be too much and you would lose too much detail. Then again if you are using colour film and want yellow then 3 stops would be a setting to use.
My town was hit with another heavy storm and I had to toss stuff into David's car and go to a safe place for the car.
Sitting in a cafe watching the storm, I went to load the newly re-spooled film into my F-1. Um. D'oh! In the rush I had forgotten to cut a new leader. Sigh. Going to Coles, I found the cheapest scissors i could find and a laundry marker. Problem fixed. But my photo op had passed. Oh well.
