J,
I'd like to see if my understanding here of the little paragraph joseph wrote is correct. In Summary,
1. One can theoretically
calculate the equivalent focal length required for say, a Pentax K5 lens to achieve the same shallow DOF as a 5D MK2. This is the reason for the argument that the DOF of FF isnt superior than a Crop sensor.
2. However, the actual lens required to have the same shallow dof and fov may not exist on the crop sensor format, if one hunts for shallow DOF only.
3. The opposite is true if one is hunting for a narrow DOF.
For example, if our 50-135 2.8 is roughly the fov for an FF 70-200 2.8, the same can not be said if I were to look for the equivalent DOF, because at 150mm i would need it to be a f2 to give me the same DOF. And since there isnt any zoom lens f2, for all intend and purposes, if shallow DOF is what I am looking for, a FF format is what I need.
Did I get that about roughly right?
Second part of the question : (derived from the first)
If say, the sweet spot for every lens is around F8 (F8 and be there), whether you own a crop or a FF, then basically, for the same given FOV, if I have a 50mm on an FF at F8, to achieve the same kind of sharpness on a Crop I would need to be at 75mm F12 or something..which means that if I had dialed F8 on the crop sensor for reasons of exposure, then I will always get a less sharper result.
Is this also correct?
In summary - an FF, given the lens that is right now out for sale, can always reach a shallower DOF, and will always be sharper at the same FOV given the same f stop.
?
Originally posted by jsherman999 How would you explain it to someone who asked, who maybe didn't have your hands-on experience? I'd assume you'd use casual terms as folks in this thread have done, 50mm f/2.8 = 35mm f/1.8, etc. In doing that, you're actually talking about
equivalence, even though the term wasn't used back then.
The differences you were seeing first-hand in FOV and DOF mounting those same lenses on different formats are actually explained by the concept of equivalence, and described well by folks like Joseph James and simplified by folks like Bob Atkins.
You think this discussion is 'vicious'?
(Also, I'd refer you to the title of the thread. Is there a more appropriate place this should be discussed?)
.