20D - improved Katz Eye focsuing screen - Part 1/1

Started Aug 13, 2005 | Discussions thread
OP Doug Kerr Forum Pro • Posts: 20,898
Re: How was the metering testing done?

Hi, Nadine,

The testin was done with teh camera aimes at a cloth target with a unoiform patternm on it, fairly-evenly illuminated.

The camera was set to Av mode and f/8. The shutter speed indicated was the recorded as an indicator of the relative indicated Ev.

The results, for different lenses and differentn focal lengths, and differentt metering apertures (a result of the selection of different focal lengths on the zoom lens) were recorde in one session with the OEM screen and then in a differen session with the Katz Eye Plus HiLux screen in place.

For each setup, the test was done:
With Evaluative metering, each of the 9 AF points preselected
With Partial metering
With CWA metering

With the 50 mm f/1.4 lens in place, thesre was little difference in metering result between the two screen types for any of the 11 metering setups.

However, with a meteirng aperture or f/3.5, f/5.0, and f/5.6, there were differences (with teh 50mm f/1.4, and thus with the "OEM screen" situation) for:

Evaluative metering with the center AF point preselected
Partial metering
CWA metering

With a metering aprture of f/3.5, the greatest difference with the reference readings was for Parial metering: about 2/3 stop overexposure.

With a metering aperture of f/5.0 or f/5.6, both Evaluative metering with the center AF point preselected and Partial meteirng showed a difference of about 1 stop in the direction of overexposure.

It does not appear that different lens types nor different focal lengths (on their own) much change theh pattern of differences.

Nadine Ohara wrote:

I tested with both my 50mm f1.4 and my 16-35mm zoom at the widest
and found no difference between the two, but of course, my testing
was very rough. I understand your comments about smaller apertures
possibly making a difference, but how do lighting situations make a
difference . . .

It is important to note that these tests were all with a relatively-uniform luminance scene. Presumably, with a secne with varied luminance, the results might be different (owing to the specific way the new screen influenced the overall weighting pattern for the metering type involved, something that of course was not measured).

. . . and why do different lenses make a difference?

My assumption is only by virtue of their different maximum (metering) apertures. This affects the "cone angle" of the light exiting the lens toward the screen, and the angular distibution of the light leaving the screen (toward the viewer and, at a differnt angle, toward the exposure metering sensors) depends on that.

Best regards,

Doug

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