FWIW I have found the filtration factors printed on B&W filters do NOT correspond to the factors which give me the best results.
I did exhaustive tests using several different films (D400, TriX, D100) in 120 (Mamiya 7) and 35mm (Leica MP) and found the filter factors provided resulted in over exposure with yellow and orange filters. Normalising neutral coloured shadows, I found I only needed to add 1/3 stop for a yellow and 1 & 1/3 for an orange, rather than 1 and 2 stops respecitvely. Up to this point I was gettting irked by exposure jumping up and down on each roll when using my Mamiya 7 (which does not have TTL metering).
On the leica MP/6 I use TTL metering and forget about it with orange and yellow filters. For red and deep red TTL is unreliable and will underexpose.
I would bet a regular yellow will require no more than 1/2 stop more light on a Leica MM. I have one, but have not tested yet due to house move.
I did exhaustive tests using several different films (D400, TriX, D100) in 120 (Mamiya 7) and 35mm (Leica MP) and found the filter factors provided resulted in over exposure with yellow and orange filters. Normalising neutral coloured shadows, I found I only needed to add 1/3 stop for a yellow and 1 & 1/3 for an orange, rather than 1 and 2 stops respecitvely. Up to this point I was gettting irked by exposure jumping up and down on each roll when using my Mamiya 7 (which does not have TTL metering).
On the leica MP/6 I use TTL metering and forget about it with orange and yellow filters. For red and deep red TTL is unreliable and will underexpose.
I would bet a regular yellow will require no more than 1/2 stop more light on a Leica MM. I have one, but have not tested yet due to house move.