Quote Originally Posted by Nicholas Lindan View Post
If you can mount the lens in your enlarger then the Darkroom Automation enlarging meter can read out the f-stops to 0.01 stop.
This is EXACTLY the way to go. For exposure you want T-stops and the advice given here is useful for ANY lens. I would suggest that one performs this with all objectives for exposure consistency. F-Stops is a geometric measurement useful for depth-of-field but not for exposure (other than as a rough guide).

Two objectives of the same true focal length (we need to keep in mind that the focal lengths reported on the barrels of most objectives is not their real but only their nominal lengths) and set to the same f-Stop won't probably have identical transmission of light. The number of lens elements, coating etc. all have a significant impact on transmission. F-Stops can even be quite misleading. A typical f/0.95 superspeed, for instance, might have a geometric aperature greater than the focal length and whence an F-Stop less than 1 but can't, as we all know, violate the basic laws of physics and pass more light out then going in.. In still photography given the relatively low dynamic range of photographic papers we safely ignore this but the effect is not insignificant w.r.t. the dynamic range of film so in cinema and diapositive processes we tend to talk about T-Stops (Transmission Stops) for lighting and F-Stops for Depth-of-Field. Good cinema objectives are for this reason calibrated to T-Stops.

One does not, of course, need the meter above but nearly any baseboard enlarging meter is sufficient.

With the enlarger you can cheaply (as one would say "Good enough for government work") calibrate both the F-stops and T-stops!