Barry_Green
Moderator
Pursuant to a discussion in another thread, I decided to test the DVX lens for diffraction (diffraction being the propensity of light to become un-focused as it flows through a tiny aperture). The XL1 had some serious soft-focus issues at f/32, and an article on bealecorner.com recommends going no lower than f/11 (meaning, in practical terms, he's recommending to avoid f/14 and f/16, and he hints that diffraction can start to become troublesome as early as f/11).
To test, I just set up a resolution chart, and shot at wide-open (f/1.6), f/5.6, f/16, and a fourth shot at the darkest I could get it right before the iris closes (which is probably close to f/22 or maybe even smaller).
For the results, f/5.6 is definitely the best, delivering clear lines up to the 540 mark, which is the theoretical limit of DV.
f/16 is just a tiny bit lower resolution, resolving cleanly up to about 520 lines. Not enough to even notice a difference, really. No diffraction worries.
Wide open is another story. At a full wide-open aperture, the resolution takes a hit, going only to about 470 lines.
And at the limits, just a minor hair above "closed"? Horrible. Resolution drops off to about 270 lines. I would certainly attribute that to diffraction.
So for the utmost highest resolution, stick to apertures between f/2.8 and f/14. Much wider than 2.8 and you'll lose a little resolution, maybe 10%. But avoid really closing the lens down -- pure f/16 is okay, but you can get some much smaller apertures that still say f/16 on them, and those are *not* okay.
Stay between f/2.8 and f/14 and diffraction will not be an issue.
Common wisdom says that lenses perform their best at about 2 stops down from wide-open, and 2 stops above minimum. That seems to hold for the DVX as well, although wide-open still gives you 90% of the resolution possible under the very best of circumstances, so it's really no big deal. Avoid the tiniest aperture of f/16 or below and you should always be getting great resolution from the DVX lens!
To test, I just set up a resolution chart, and shot at wide-open (f/1.6), f/5.6, f/16, and a fourth shot at the darkest I could get it right before the iris closes (which is probably close to f/22 or maybe even smaller).
For the results, f/5.6 is definitely the best, delivering clear lines up to the 540 mark, which is the theoretical limit of DV.
f/16 is just a tiny bit lower resolution, resolving cleanly up to about 520 lines. Not enough to even notice a difference, really. No diffraction worries.
Wide open is another story. At a full wide-open aperture, the resolution takes a hit, going only to about 470 lines.
And at the limits, just a minor hair above "closed"? Horrible. Resolution drops off to about 270 lines. I would certainly attribute that to diffraction.
So for the utmost highest resolution, stick to apertures between f/2.8 and f/14. Much wider than 2.8 and you'll lose a little resolution, maybe 10%. But avoid really closing the lens down -- pure f/16 is okay, but you can get some much smaller apertures that still say f/16 on them, and those are *not* okay.
Stay between f/2.8 and f/14 and diffraction will not be an issue.
Common wisdom says that lenses perform their best at about 2 stops down from wide-open, and 2 stops above minimum. That seems to hold for the DVX as well, although wide-open still gives you 90% of the resolution possible under the very best of circumstances, so it's really no big deal. Avoid the tiniest aperture of f/16 or below and you should always be getting great resolution from the DVX lens!
