I have debated the merits of upgrading to FF for a while now. I think the pros outweigh the cons (other than cost) for the most part except possibly in one very important area for me, and that's macro shots. Could someone help me to determine if my logic/research is correct?
I currently shoot with a 60D and the very good EF-S 60mm macro. Generally for macro, you're not shooting wide open, or even close to it. In general, I'm at f8 (range varies from f5.6-f11 most of the time) so that I get a somewhat decent depth of field.
If I were to switch to FF (either 6D or 5D3), I'd be using the 100mm macro instead (similar FOV to the 60mm macro on the 60D ~ 96mm). To obtain a similar depth of field, would I not need a much smaller aperture?
For instance, I just used http://www.dofmaster.com/dofjs.html
to come up with the following scenario:
If I were using my current setup (60D + 60mm macro), the following parameters:
f8, 6.3' distance to subject
Would yield the following depth of field:
***I realize this is not a macro shot but I used it because "1 ft" is a nice round number with some "play" to it - an actual macro calculation would have resulted in a very small fraction of a foot making a comparison much harder.
Now, if I were to pick up say, a 5D3 and the 100mm macro, in order to achieve 1 ft of depth of field at a distance of 6.3', I'd need to shoot at roughly f14.3 (the online calculator says this would be .99 ft).
Here's the problem... Diffraction/lens sharpness. I'm fairly sure that even as good as the 100mm macro is (even the L), it can't possibly be as sharp at f14 as the 60mm macro is at f8, can it?
What about when I'm in a pinch and need to go to f11 with my 60mm macro on APS-C? I'd need to go to over f20 to achieve a similar DOF with the 100mm on FF.
So, is my thinking/calculations correct in this case? Or am I overlooking something? Could the 100mm macro (L or not) be as good or better than the 60mm macro when obtaining a similar depth of field? Is the smaller APS-C sensor the key here? And finally, would I be even BETTER served (for macro) by going down to m4/3?
Thanks for any insight!