Snafoo wrote in post #15183478
This doesn't make sense to me. DOF increases with distance, but it's absolute, not relative, isn't it? If DOF at 10 feet is, say, 1 inch, and at 80 feet it's 8 inches (for the same aperture and lens FL), then an object at the focus plane will be a full 7 inches more in focus than at 10 feet, regardless of the amount of cropping. Where is my logic failing here?
This doesn't make sense to me. DOF increases with distance, but it's absolute, not relative, isn't it? If DOF at 10 feet is, say, 1 inch, and at 80 feet it's 8 inches (for the same aperture and lens FL), then an object at the focus plane will be a full 7 inches more in focus than at 10 feet, regardless of the amount of cropping. Where is my logic failing here?
Imagine we have an object 1' tall with an APS-C camera...
- At 3.5' with 50mm f/16 we see an area 1'x1.5', the object fills the frame height; DOF is 0.72' (on an 8x12" print)
- At 7' with 100mm f/16 we see an area 1'x1.5', the object fills the frame height; DOF is 0.71' (on an 8x12" print)
- At 35' with 500mm lens f/16 we see an area 1'x1.5', the object fills the frame height; DOF is 0.71' (on an 8x12" print)
At 70' with 500mm lens f/16 we can see an area of 2'x3', the object is 1/2 of the frame height; DOF is 2.9' (on an 8x12" print). But if we print a 16x24 print, the object on the print is once again 8" tall (same as when photographed at 35', situation #3 above), the DOF on the print is again reduced to less than 0.8'
