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03-04-2009, 09:56 PM   #1
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Polarizer

Hi. I am looking to buy a circular, or linear polarizer for the LX?

Thanks.

03-04-2009, 10:51 PM   #2
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circular, as it won't interfere with the pre-exposure metering. I'm not sure what I'd use a linear for anyway, what with all the TTL metering and AF tech not working with it.
03-04-2009, 11:54 PM   #3
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For the LX it does not matter.

But I'd buy a circular because is compatible with more modern cameras (just in case)

QuoteOriginally posted by boobai Quote
Hi. I am looking to buy a circular, or linear polarizer for the LX?

Thanks.
03-05-2009, 03:59 PM   #4
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QuoteOriginally posted by titrisol Quote
For the LX it does not matter.
Not quite. The LX meters uses a sub mirror to reflect light to the meter for manual exposure, and this can be thrown off by use of a linear polarizer.
I believe, but may be wrong (I don't have my technical manual handy) that even in auto exposure, the OTF metering which isn't affected by a linear polarizer doesn't come into play until the indicated shutter speed is below the X-Sync speed.
If this is correct, then a linear polarizer can affect auto exposures as well.

03-05-2009, 06:17 PM   #5
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QuoteOriginally posted by Wheatfield Quote
Not quite. The LX meters uses a sub mirror to reflect light to the meter for manual exposure, and this can be thrown off by use of a linear polarizer.
I believe, but may be wrong (I don't have my technical manual handy) that even in auto exposure, the OTF metering which isn't affected by a linear polarizer doesn't come into play until the indicated shutter speed is below the X-Sync speed.
If this is correct, then a linear polarizer can affect auto exposures as well.

Thanks for backing me up
03-05-2009, 06:26 PM   #6
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How can a linear polarizer affect LX AE at speeds faster than X?

Chris
03-05-2009, 06:39 PM   #7
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"When using a polarizing filter on a lens fitted to the LX the photographer should note that a linear polarizing filter can lead to erroneous pre-exposure meter results, this inconsistency is caused by the summation of the polarizing effect of the secondary reflex mirror and the linearly polarized light passed by the filter. Auto exposure will not be affected by the use of a linear polarizer however if the camera is to metering is to be relied upon for manual exposures a circular polarizing filter should be used."

from Digital Image Studio, The Pentax LX
03-05-2009, 06:54 PM   #8
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As I understand it using a linear polarizer affects manual meter readings in certain cases,
but will not cause incorrect exposure during AE photography at any shutter speed.

Chris

03-06-2009, 03:27 AM   #9
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I stand corrected.
I never heard of circular polas until the advent of AF (Nikon N4000 - late 80s) and since the LX is older didn't even think of it.

HOWEVER.... The LX has a secondary metering system that operates after the mirror flips us, and that is affected by linear polarizers.
BUT that is for Manual exposures, not for Auto.

Gee this camera was advanced for its time!


QuoteOriginally posted by Wheatfield Quote
Not quite. The LX meters uses a sub mirror to reflect light to the meter for manual exposure, and this can be thrown off by use of a linear polarizer.
I believe, but may be wrong (I don't have my technical manual handy) that even in auto exposure, the OTF metering which isn't affected by a linear polarizer doesn't come into play until the indicated shutter speed is below the X-Sync speed.
If this is correct, then a linear polarizer can affect auto exposures as well.
03-06-2009, 05:54 PM   #10
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QuoteOriginally posted by titrisol Quote
HOWEVER.... The LX has a secondary metering system that operates after the mirror flips us, and that is affected by linear polarizers.
BUT that is for Manual exposures, not for Auto.
???????

Chris
03-07-2009, 11:50 AM   #11
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From MIR website Pentax LX - How does its metering works
QuoteQuote:
The Pentax LX metering can has a exposure range down to - 6.5 EV (125 sec at f1.2) to EV 20 (1/2000 sec) while the F3 can only perform from EV 1 to 18 (i.e. . f/1.4 at 1 sec to f/11 at 1/2000 sec with 50 mm f/1.4 lens and ISO 100 film). But both cameras also uses the same cell to measure light reflects off the film plane during a flash exposure (TTL OTF flash). How could that be done ? In fact, physically, the SPC in the LX is only slightly more than half the size of the Nikon F3 in comparison. The trick is Pentax's "refined" automatic exposure system with IDM (Integrated Direct Metering). Why I said it as "refined" instead of developed ? Because, it is a refined metering system from the Olympus pioneered OTF metering system, first seen in 1975 with the Olympus OM2.

The IDM system measures the actual amount of light reaching the film plane during exposure, regardless of aperture setting or which focusing screen or viewfinder is being used. Even if light conditions change during the brief moment of exposure, shutter speed is adjusted instantaneously to compensate. When the camera is operated in the automatic exposure mode, the IDM system switches on the instant the mirror flips up and the front shutter curtain begins to move (see illustrations). It calculates the amount of light hitting the film plane and instantaneously controls rear shutter curtain motion for correct exposure. Light values, metered through the actual aperture, are monitored for the duration of the exposure - not the instant before the shutter is released. Thus, shutter speed is correct, even in changing light.

Flash output is also directly measured as it reaches the film plane. Bounce flash, diffused flash, and filtered flash photography are all possible without exposure compensation (with Pentax dedicated TTL Auto Flash units).
03-07-2009, 12:59 PM   #12
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AFAIK that is correct. Thanks for the clarification, titrisol.
As I read it your previous post states something different.

Chris
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