streetshooter wrote:Your 40 is a 40 but sees like a 60. So let's think it's a 60 and... your 1.4 fstop stays that always.
Nice wording and spot on Don! I will add:
Your 40 sees like a 60 but almost feels like a 40 (interpreting feels as DOF).
DOF will remain almost that of a 40mm in FF (this means bigger than a 60 in FF)
Bigger than a 60 in FF but slightly smaller than a 40 in FF...
How much means "almost" and "slightly"...
As I pointed previously, taking your lens DOF marks for FF, you should use +1stop marks for the GXR A12M (roughly, just a little less even). This means stopping down to 8, use DOF marks of 5.6 to evaluate your DOF.
Using one of the DOF calculators pointed by Don:
40 FF 2.8 @1m 0.106mDOF
40 FF 2.0 @1m 0.075mDOF
40 FF 1.4 @1m 0.053mDOF
40 APS-C 2.8 @1m 0.071mDOF (almost as FF @ 2.0, just a little less as said >> +1stop marks)
40 4/3... 2.8 @1m 0.053mDOF (as FF @ 1.4 >> +2stop marks)
Obviously your lens DOF marks are and act as one of those "old" slide rule or "slipstick" (mechanical analog computer) . Will always work, even without batteries, and it is soldered to the lens!