Quote Originally Posted by Frank F
Exposure compensation is not tube length dependent, it is the TOTAL distance form focal plane to nodal point and dependent on focal length of the lens. In more clear terms, use a TTL meter, the problem goes away.

I can look up the compensation and the image area size for given Proxars or extension rings if someone will post what they want.
Yes. But the change in that distance with the addition of a tube is a given. In my case, I have added 16mm. Actually, that just answered my own question... just as with the bellows extension. So, with the 150mm at infinity - exposure factor is (150+16)^2/150^2 or 1.224 or about half a stop. Correct?

So it follows that on a shorter lens, the exposure factor increases. Thx Frank for getting the neurons firing again, rather than asking more silly questions in forums! :rolleyes: