Steve Jolly [EMAIL PROTECTED] wrote: >Indeedy. Metering with the mirror locked up is nice, but surely the >nicest feature of OTF metering is that it can respond to changes of light >mid-exposure, for which purpose a pattern printed on the shutter is not >required. As far as I can tell, the necessary sensors and electronics to >perform this kind of OTF metering are built-in to *all* modern Pentax >cameras, not just the LX. Despite this, the LX is the only Pentax camera >that can do it, and I'd be interested to know why.
One thing that occurs to me is that the LX uses a relatively complex half silvered mirror, and a secondary mirror behind the main mirror, in order to get light onto the metering cell while the mirror is down. OTF metering while the mirror is up seems easy in comparison. Isn't the pattern on the shutter still required for the type of metering that you describe? At speeds higher than the sync speed the meter needs to decide to release the second curtain while the first is still moving. At a very high speed, where the slit is narrow, most of the patterned shutter will still be visible to the meter cell at that moment. I wonder if the different natures of flash and ambient light also makes a difference? Flash is always fairly bright, while the LX can also handle extremely low light levels with the same meter. I suspect that the LX meter requires a greater degree of dynamic range and linearity than most TTL flash meters were designed for, even if the basic integrating principle is the same. Steve.
