----- Original Message ----- From: <Bob G> Subject: Pentax & Polarizers:Circular or Linear
> Hi Guys.. > Article in this month's PopPhoto implies that SLR metering and/or > autofocus > systems may be inaccurate with LINEAR polarizers in place..I dont use > autofocus enuf to care, but does anyone know if an SF-10 or ZX-7 exposure > meter will get compromised by the (far less expensive and already in my bag) > linears. ????????? > What can happen with a linear polarizer and a camera that uses a beam splitter to direct light to a sensor is that cross polarization can over reduce the amount of light reaching the sensor. In the case of autofocus (all AF SLR cameras use a beam splitter to direct light to the AF sensor) the sensor can (but not necessarily will) go blind due to extreme light reduction. In this case, the AF will hunt around and generally not work. However, not all AF cameras use a beam splitter for directing light to the metering cell. I suspect that the Pentax AF SLR cameras are using a metering cell looking at the focussing screen, in which case metering will not be affected by the use of a linear polarizer. As far as I know, the only Pentax SLR using a beam splitter for metering is the LX. It is normal to get some light meter deflection when using a polarizer, as they do reduce the light transmission, and the reduction is variable depending on the amount of polarized light that is being absorbed by the filter, so it is hard to say for sure from a blind test if the meter is being goofed by the filter. Perhaps someone on the list can tell you if the cameras in question use a beam splitter to direct light to the metering cell. If not, I am sure a quick email to Pentax themselves could answer your question. William Robb - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
