Dave, Firstly, if you're metering TTL, and/or using OTF flash automation with the Super Program you won't need to compensate for anything, the internal meter will be affected by the extensions exactly the same as the film will be.
If you're transferring exposure values from an external meter, or using a non-TTL/OTF auto flash, then you will need exposure compensation. I'll write the formula longhand because I'm sure that the autowrap of one of our email clients would mangle any multiline formula I try to write. It is: The corrected aperture (the one you actually set the lens to) is equal to the indicated aperture (what the external meter indicates) times the lens's focal length divided by the extended focal length (FL plus extension). Don't forget to include the extension of the focusing helical, either. A rough guide could be that a tube of 1/4 the objective's focal length adds about 1/2 stop. A tube of half the objective's focal length adds about a stop. A tube equal to the focal length adds 2 stops. These are when the lens itself is at infinity focus, any helical extension adds a little more. However, non-macro lenses rarely extend more than about 1/3 stop's worth on their own helical. Happy (flower) hunting. regards, Anthony Farr ----- Original Message ----- From: <[EMAIL PROTECTED]> > > Hi all. > First off,got an email from Aaron.Hes on holidays for the next two weeks. That will buy me > some time > to take some more photos.lol > > Second,i ts a lovely day today,i have it off and plan to shoot some closeup flowers.I want > to use the SP > with the K adaptor and screw in some M42 tubes.I realize some exposure factors will be > needed.Is > there a rule of thumb.Probably only the first and or second tube.Is 0ne stop per tube a > good starting > place?? > > I'll check back this afternoon. > > Dave > > >
