Hi All I posted this on the large format forum but thought there may be some great advice here as well. A few months ago I purchased a pinkhham and smith 18" 6 Semi Achromatic. I have been trying to gain some sort of knowledge base for accurately or semi accurately focusing this beast. My theory has been to focus as good as possible and then do a series of shots in +/- 2mm increments to find where the chemical focus is on the lens. I believe that I have found this to after blowing through some instant film. It appears that in increase in in bellows extension of 2mm at approx 12ft works best. I have read somewhere that approx .25% adjustment for the focal length is the amount to use for this adjustment. For this lens that would equal approx 1.5mm so this seems OK. I shot using my 4x5 back vs the 8x10 since I have some instant fuji available. This lens is soooo hard to focus with all that spherical aberration. Trying to find the models eyes is similar to looking through murky water. Are there any techniques to assist with initial focus on this thing? My intent is to shoot the figure and portraits so any advice would be greatly appreciated.