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11-04-2007, 10:47 PM   #1
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k100d stop-down metering problem

K100D with SMC-M 50mm/1.7.
I know how to work the manual lens, but noticed a weird problem with stop-down metering in low-light conditions.

in "M" mode, I first tried the DA 18-55 lens metering in a room lit by a 100W bulb. I tested f5.6-22 aperture range and the exposure metering came up with speeds from 0.3sec-6.0secs (f22/6.0 secs)

Now, with the M 50/1.7 lens with stop-down metering, I got the following results:
f5.6 - 0.3 secs
f8.0 - 0.7 secs.
f11 to f22 - all get 0.7 secs when stop-down metered.

So, above f8.0, the metering is wrong.

Have you experienced the same problem?

Regards,
Stan

11-05-2007, 12:34 AM   #2
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It is normal. It is actually a problem with stopped down metering. When the user stops down the aperture of the lens, the TTL metering light sensor receives less light than when it is wide opened.

In your case, you shot in an already low light situation. After stopping down further, at some point, the light metering cell simply cannot "see" anymore which is called to be "out of the metering range" (for this case, it is out of the lower limit). In case of wide opened metering mode, there is a warning to tell the user that the lowest metering range has been reached and the sensor is unable to measure further, but in stopped down metering, there is no aids and indication to tell the user that, for the current Pentax's design.

Do note the primitive problem of stopped down metering is still the light loss caused by teh aperture cut which cause even more troubles to take the metering readings in low light conditions.

QuoteOriginally posted by stanjo Quote
K100D with SMC-M 50mm/1.7.
I know how to work the manual lens, but noticed a weird problem with stop-down metering in low-light conditions.

in "M" mode, I first tried the DA 18-55 lens metering in a room lit by a 100W bulb. I tested f5.6-22 aperture range and the exposure metering came up with speeds from 0.3sec-6.0secs (f22/6.0 secs)

Now, with the M 50/1.7 lens with stop-down metering, I got the following results:
f5.6 - 0.3 secs
f8.0 - 0.7 secs.
f11 to f22 - all get 0.7 secs when stop-down metered.

So, above f8.0, the metering is wrong.

Have you experienced the same problem?

Regards,
Stan
11-05-2007, 07:47 AM   #3
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From f11 to f22, was the ".7" indicator in the viewfinder blinking? It should if it's outside metering range and that's what I've found with my manual lenses.
11-05-2007, 11:44 AM   #4
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Original Poster
RiceHigh, what you describe was exactly what I though too.
What confused me, though, was the lack of warning - no blinking indicator in the viewfinder when the stop-down metering failed.

If Pentax fixed the stop-down metering warning indicator, I wouldn't have a problem with this.
But its very misleading to have an indication of successful metering with bogus values.

Thank you all.
regards,
Stan

11-05-2007, 12:37 PM   #5
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Oh, I doubt it's all that conspiratorial. Besides, why would anyone shoot at f/22 in a darkened room anyway?
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