Quote Originally Posted by falke View Post
..... That is about 4.29 million km. (but maybe that is just a random value for infinity put there by Canon). I checked EXIF of another shot by James and it gives the same value for infinity.

.....

Frank, that subject distance is most likely a problem with Lightroom rather than a technical analysis of how DOF works in unison with focal length.(or any randomness on the part of Canon)

I've never seen any comments or issues raised on the topic, but it seems that any image edited in LR3(at least for me), gets this 4million klm figure as subject distance... even macros!

Then again, the fact that they(Adobe) can't keep their grubby hands of your metadata and replace it with their own garbage is probably some master plan of theirs to rule the world!(and now I'm off into wild blue OT territory too! )

Ms Monny;

your comment
To me larger f/stops are for a shorter dof and smaller f/stops are for longer dof (f22 = infinity)
indicates that you may have a basic grasp of aperture and DOF.

larger apertures(small f/numbers) give you a shallower DOF for sure, but this is important to note that only for when there is a larger distance between near and far subject matter in the scene.

That is, you can still shoot a landscape at f/1.4 if you like, but you need to focus very far out into the deeper part of the scene, not close up. If you focus on something close up then the background is more blurry.
If you focus on something out in the far distance, then everything close in will be blurry.

eg. if everything in the scene is at a distance of 5 meters, and you shoot at f/0.75(yep 0.75, not 7.5!!) and you've focused at that 5meter distance, then everything is in focus, there is no sense of a shallow DOF.

Apart from your comment that a smaller aperture gives you a deeper DOF, other reasons for using a smaller aperture other than those given already, may be for a longer shutter speed, or better image quality all across the frame.

many lenses my give their best ultimate sharpness result at say f/5.6 or f/8, but the sharpness of the details at the corner of the frame may still be low. So, even tho we may know that the lenss is best at f/8, we may set it to f/11 because at f/11 the corners may produce better image quality than at f/8.

shooting at f/22 doesn't instantly mean that you get a DOF that extends to infinity either! it may give you an impression that it does when using a short (say 10mm) lens, but using a longer focal length doesn't necessarily give you this result if you've focused in very close. Also think of macro, and how magnification works there. Even a short focal length lens can give you very little DOF at f/22, because you may need to focus in very close.
So again, the near distance is more important for determining DOF, than just about any other variable.

Also, someone made the comment that sensor size has an impact on DOF.(this is not true). It only has a bearing, because for some reason, we humans need to alter another variable called Field of View(which is similar to changing sensor size, but not the same thing).
So when going from a smaller sensor to a larger one, there seems to be this need to maintain a particular FOV. This is a human failing that often gets confused as a variable in the determination of DOF.
There's absolutely no reason for the need to move closer in, or further out from a scene to match a focal length to a sensor size.