Very interesting thread this.
What if you are using a 35mm camera with a zoom lens for metering. Is it not so that the bellows factor is "factored" in when using an SLR reading? A zoom lense has variable max f-stop from min to max. So if I use a zoom lens to get about the same size as on the ground glass, will the metered value be usable on the folding camera?
Or am I as per usual completely off?