Greg, ZX-L (MZ-6) is also my first modern camera, Zenit ET being its predecessor <grin>. So I think I can be of some help for you.
So, I'm considering switching to a flash with infrared AF illumination.
I'm clear on how that helps with an AF lens. My question is -- does it
also help with the camera's focus-assist feature?
I am totally unaware of infrared AF illumination flashes that are made/compatible by/with Pentax. What ZX-L *can* do *instead*, is use the flash (normal) light to lighten the subject for a short time and try to focus while subject is lit. For instance, built-in flash can do it. By the way, not all Pentax flashes have AF assist light capability. You can check it in your ZX-L manual.
From my little experience with that: in some cases built-in flash in AF assist mode worked wonders with my FA 50/1.7 lens. In some other cases, I would still miss the shot. I am afraid that if it is too dark for AF to come to focus, it is basically a missed shot. Imagine you're trying to do some candids... Now, if subject it is stationary, then perhaps you could take your time and focus manually even with ZX-L's focusing screen...
BTW, has anyone found a way to swap out the ZX-L's focusing screen with one that has a split-image?
I think that potentially you could fit ZX-L with other focusing screens, such as that of MZ-M, which is known to have split image, etc. However, I am afraid that in such a case you would totally lose spot metering. Notice, that if you take off the lens and point the camera on the well lit window and look in the viewfinder you'd see a small circle just in the middle of the screen. AFAIK, this is the spot of spot metering. If you remove default focusing screen and replace it with split screen, you're going to lose spot metering.
Whether or not it would be acceptable - it is your call.
Personally, my choice was to buy old and used ME Super to be able to use proper manual focus when it was necessary...
HTH.
Boris
