Quote:
Originally Posted by Mr Tonka
Just to clear up the bolded section. If you stand the same distance from the subject with a 24mm lens as you would with a 100mm lens, the DOF is going to be only applicable at the near point on the 24mm lens because the far point will be infinity. But who is going to take a photo of a car with a 24mm lens from a distance of 50'? For a 24mm focal length, you'll likely be within 5' of a car to capture an image like you posted above. That makes your DOF at F4, a very shallow 2.1' leaving much of the car OOF.
DOF is just a math equation and if you mount a 24mm lens on the OP's camera choose F4 and stand at 5' (likely distance for that focal length) the DOF is going to be shallow at just over 2' leaving much of the car OOF.
Same camera, same F4, with a 100mm lens at 50' equals a deeper DOF of just over 12' likely getting the entire car in focus. Even if you double your distance from the subject with the 24mm lens, the DOF is still about 20% shallower than that of the 100mm lens.
Distance from the subject is a HUGE factor when calculating DOF. Stand just 40% closer to the subject with the 100mm lens and your DOF will decrease by 60%!
Stand 40% closer with the 24 and the DOF drops from 2.1' to 9".
Decrease the F value to accommodate lower light and the DOF shrinks again. The difference between the two focal lengths is even when you decrease your distance from the subject by 40% the DOF at 100mm is still about 6x larger than at 24mm.
Add a tripod to the 100mm lens, bump to F11 and you're back to a 13' DOF. While the 24mm lens being bumped to F11 will only garner about 3' DOF.
So in some instances your bolded statement is true, but when you factor in distance from the subject, a crucial factor, all the numbers change drastically.
http://www.dofmaster.com/dofjs.html |
Agree with all of that. My real point was the opposite end of your point above. While DOF shrinks with both smaller aperture and increased focal length, as focal length shrinks, (i.e., ultra wide angle lens ~14-18mm 35mm equiv./ 10-12mm DX) DOF increases to the point that you can practically set your focus to infinity with a 16mm lens and from almost any distance to subject you are going to have everything in focus.
I guess the exception to this rule with an ultra wide angle might be if you wanted to take a detail shot of say a side view mirror where part of the fender is in the foreground. In that case the near fender will be out of focus but everything beyond the mirror should be in focus.