Quote:Originally Posted by Buckaroo Banzai
When i go to a typical theatre watching 35mm I notice that the picture is often out of focus, or soft focus. This probably happens as much as one third to half of the time. I know it's not a problem with the print because often I'll see the sides are in perfect focus but the center is not, or vice versa, or the very top and bottom is in focus but the center is not, or vice versa. When the image is in focus though I would say the resolution of a 35mm print in even a typical theatre is probably about (in only my humble estimation) 1.7k to 2k. I've never seen a digital presentation out of focus/soft focus.
Can someone here answer me this then. Are 35mm projectors so much harder to focus than digital projectors or what? What gives?
Consultant Matt Cowan's
defines film resolution terms and outlines a 2001 ITU test
taking place in various international movie theaters. Test patterns were produced like entertainment films and measured with both instruments (static) and rated in the theaters by about 6 expert observers. Figure 1 in the ITU paper shows the projected resolution bursts, and Figure 4 the subjectively viewed and averaged values for each theater. The varying values on each screen reveals focus variations. I assume the per-picture-height numbers mean the highest resolvable multiburst blocks seen by experts (before, say, vertical lines--for horizontal resolution--merge into gray). Also, multiply horizontal resolutions by 1.85 for resolution per picture width
Cowan writes (below his ITU results table about 1/2 down):
Note that the observed numbers are lower than the measured numbers in the vertical due to the influence of the projection lens and the motion instability created by the projector. Horizontal numbers are substantially lower, induced by the projector motion as well.
Looks like ITU-like tests are needed to accurately compare film-vs.-digital projection. If you average values in Cowan's theater-results table and convert to lines/PW, the comparison suggests resolutions typical of 720p HD. These sub-links
outline measured HD resolutions from video experts just before HDTV's U.S. introduction. -- John