Tominon 105 mm. on copal 0.0

[domenico Foschi]

I just received a tominon 105 mm. for some possible macro work . I just realized that it mounts on my copal 0.0 that houses my SA 90 f. 8 . When i position the iris at f. 8 it is almost halfway of it's range with the Tominon. Before f.8 the iris can be opened considerably more, at the point that with the Tominon i cannot see the blades anymore , giving me a full range of f.stops for this lens . Am i correct to think that i don't need to make any correction in the f. stop scale ? Thank you.

[Edward (Halifax,NS)]

At the f/8 setting the actual aperture of the 105mm lens wil be f/9.33 and f/22 will be f/25.66. At the wider f/stops you will be losing about a half a stop. At the smaller ones the difference is much smaller.

[Edward (Halifax,NS)]

Correction: It seems that you lose a half a stop across the board.

[Jim Galli]

Domenico, for macro work you will have plenty of bellows extension factor to deal with anyway. My guess is that the 1/3 stop won't matter much compared to all the fudge factor for bellows draw and reciprocity failure.