Rebecca wrote:
[Some comments from the camera store salesman about her ZX-50
and lenses -- snipped for brevity....]
> Anyhow, I ended up leaving the store feeling pretty bad. Because
> now I have these lenses that I dont know if they will hurt my camera.
> Also, why would you have to buy a auto focus filter when you use
> the camera in manual most of the time? I hope ya'll can shed some
> light on this for me.
Hi Rebecca,
Sounds to me like the salesman either doesn't know what he's talking about,
or doesn't know how to explain things simply. Don't worry about doing
physical harm to your camera. Your lenses are fine with your camera. I've
got an MZ-50 (international version of ZX-50), and I use the entire range of
Pentax bayonet lenses, from the original K (manual focus) versions to the
current F (autofocus) versions. The ZX-50 body lacks a particular
mechanical linkage in the lens mount that almost all other K bodies have.
Because of this quirk, the ZX-50 body does not "know" where you have set the
aperture ring of your lens, so it can't meter correctly unless you set it on
A. As long as you set the aperture ring on the A setting, the ZX-50
metering will work just fine. If you use a lens with no A setting, the body
will only meter properly if you've set the aperture ring to wide open.
That's about all there is to it. (You can always take pictures with non-A
lenses with the aperture ring stopped down somewhat, but you'll have to
manually compensate for the smaller aperture setting by increasing the
shutter speed.)
As far as filters go, one generally uses a circular polarizer for AF bodies
and a linear polarizer for MF bodies. (For all other filters, you use the
same one on an AF or MF body.) Wish I could remember how the autofocus
system works -- I saw it once, and it's not really that complicated, but I
just can't recall the details. Anyway, I do remember that one of the
optical elements is a beamsplitter -- an element that reflects part of the
light and transmits part of the light. If you put a linear polarizer in
front of your lens, the light that hits your beamsplitter will be linearly
polarized. It turns out that the intensity of light reflected by the
beamsplitter will depend on the orientation of your linear polarizer. If
you have the polarizer oriented a particular way, the beamsplitter won't
reflect any light, and your autofocus system isn't going to work. On the
other hand, if you use a circular polarizer, the light hitting this
beamsplitter will be circularly polarized ("scrambled", effectively), and
the reflected light intensity will not change as you rotate your polarizer.
But you're manually focusing, so why should you care? The reason you should
care is that even though you're manually focusing, you may still want the
reassuring "beep, beep" indication from the ZX-50 that confirms your subject
is in perfect focus! So you may want to spend the extra $13 on a circular
polarizer. And don't worry too much about what the camera salesman says --
he may or may not know what he's talking about, whereas you can always go
back, do research, etc., and find out the facts for sure.
Hope this clarifies things a little. Good luck with your photography!
Bill Peifer
Rochester, NY
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