Originally posted by DSims So why are these DOF calculators wrong?
Can someone help here?
Again I ask - how are DOF calculators
wrong, precisely?
.
---------- Post added 05-06-14 at 08:54 AM ----------
Originally posted by clackers Not this again!
You've cheated by moving the camera, John - you're really talking about FoV, not DoF, and changing two variables, not one.
No, he kept distance to subject the same, F-stop the same. What changed was FL - to maintain the same FOV.
Quote: The DoF isn't the relative percentage of the frame that's in/out of focus, it's the absolute amount of the subject.
The relative % of the frame in focus does come into play when you crop. The absolute measured distance between the 'acceptable focus' borders in front and behind the subject and the distance from the sensor and the front acceptable focus area does not change, it can't change by cropping, but the % of the frame in focus changes radically by cropping.
Here's Joseph James' example demonstrating this:
People can get caught up in the tape measurements only, and miss the fact that the % of the frame (image) in 'acceptable focus' has changed quite a bit as a result of the crop, and thus falsly state that 'cropping does not change inage DOF'. It does.
This is why, while using the same lens on FF and apsc from the same distance gives aps-c less DOF, cropping the FF image to the same FOV as aps-c (1.5x) causes the DOF of the resulting image to be identical to the aps-c image.
.
Last edited by jsherman999; 05-06-2014 at 08:00 AM.