Originally posted by Digitalis In fact, if the subject image size remains the same, then at any given aperture all lenses will give the same depth of field.
if you don't believe me, check this out...
DOF2
the only thing the aperture changes really is the quality/character of the OOF areas, a f/1.2 will diffuse things more than an f/2 aperture would
also your subject to background ratio affects the amount of blurring too. a 35mm lens includes too much background for things to get really oof at hyperfocal distances so to achieve isolation you need to get closer.
The focal length used (or equivalently distance to the subject at constant mag) also changes perspective, hence the apparent SIZE of things in the background. This can have a huge effect on perceived isolation. Here's a further interpretation of what the link you referenced has to say:
Here's the same image comparison without the distracting inset:
Notice the isolation impact caused by the bunny in the foreground. The shorter lens makes the bunny appear larger, hence more out of focus & (in my mind) less distracting. If there were no discernible background in the photos, I think the shorter focal length would better isolate the subject, while if the bunny were not in the photos, the longer lens might better isolate the subject.
Here's another example from the web - note the top & bottom images on the left are the same f-number hence same DOF, but the change in focal length makes a big difference in perceived isolation:
The apparent SIZE of things in the background/foreground as well as the sharpness of their edges makes a big difference in what attention we give them when viewing a photo.
Quote: ...lens includes too much background for things to get really oof at hyperfocal distances so to achieve isolation you need to get closer.
This is not always true because of the psychological effect of the size of oof items in the background/foreground; In the examples I showed, getting farther from the subject increased the isolation by simplifying the background and making it appear fuzzier (at least in my view.)
The above discussion involves MY personal interpretation of images. I have no idea how you might perceive the relative isolation of the subjects in the photos shown above & would like to hear what you think.
Dave
Last edited by newarts; 03-22-2009 at 07:43 AM.