Film-Tech Forum ARCHIVE: SMPTE Contrast Evaluation Test Film

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Posted by Frank Angel (Member # 248) on 01-09-2010, 11:07 AM:

Does anyone know if the Contrast Evaluation Test film was ever made available? It was designed and a mock-up presented at one of the Projection Committee meetings (John Pytlak moderated) but I don't know if it has been made available or has been put into general use.

It was a nifty tool -- just run it thru the projector a series of graded black and white blocks are shown in the frame, and if memory serves me, you evauated where the blocks were matched where you could no longer distinguish between them, the number there was you contrast ratio.

So far this test film doesn't show up on the SMPTE test film list.

Posted by Steve Guttag (Member # 268) on 01-09-2010, 01:51 PM:

Frank,

No...it never went anywhere beyond testing. The testing showed that the targets did not give meaningful information about contrast and was way too subjective. I tried it in many different theatres, including the Uptown, in DC...which should have had miserable contrast on their Cinerama Screen. While the Uptown did to poorer than others...everything was decidedly skewed towards the "good" side.

It was also discovered that the projection light needed to be at 16fL for more consistent results. The other thing that was discovered was that as ones eyes adapted to the dark, again, the subjective level changed.

Finally, once one had this "information"...what would be done? Since it was a subjective test film...odds are one would already, subjectively, know if they had an issue.

Glenn Berggeren worked on the other Contrast Test film which was for meter measurements. For the most part, that one moved forward with the only real objection being one does not know where the contrast is being lost...in the lens, on the port, ambient lighting in the theatre...etc. Unfortunately, the cost of making the test films for trial became a bit expensive for the various parties (even John P. changed within Kodak and didn't have the same access to getting test films made). That pretty much stalled the whole Contrast thing.

I wish the Glenn B film would move forward but Glenn, is not as mobile as he once was and is tending to family matters. It was a target that could be ported to DCinema so measurements could be made between the two and one could draw some meaningful conclusions for either.

Note, there is another faction that also feels the way we measure light in theatres is all wrong and does not tell, reliably the actual light. It seems that many/all of the meters are subject to not only the 1-degree area of interest but also if other light enters the lens, it can affect the meter's reading, even if it is outside of the spot. As such, one method is to mount a tube to the spot meter to effectively put a blinder on it except for the 1-degree area.

With contrast, you have two limiting factors in measuring it. The first is the upper number...for film it is 16fL and for digital it is 14fL. Then there is the lower number...which for most meters is .01 (+/- the accuracy of the meter) and for some special meters .001 (again, plus the accuracy). If you wanted to measure the contrast of your DCinema projector (claimed to be 2000:1...you'd need a PERFECTLY DARK ROOM and a meter that accurately could read .007 fL. With film that would be .008 fL. In truth, there are no rooms that will let you get above 1000:1 and most are in the few hundreds to one. The 2000:1 bogus number is based on projecting black and then white, not at the same time.

Steve