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http://forums.dpreview.com/forums/post/24921571
MORE ON FOCUSING
One of the interesting things that the camera can do is to "assist" your manual focusing. This is enabled in the
custom setup menu ("FI with S lens used"). If enabled, then while the meter is on the autofocus sensor monitors
your focusing (using the centre focus point only). When you hit the right focus point the green hexagon below the
viewfinder will light up and stay on. I've found that in dim lighting conditions and with fast lenses (ie, 50mm f/1.4),
the focus detection is very touchy and seems more distracting than helpful. But if you find it too annoying you can
just go back into the menu and disable it again.
If you do enable the focus assist, you can also use what's known as "focus trap" mode. This is enabled by turning
the autofocus switch to the "AF" position. Of course the camera can't actually autofocus a manual lens, but in this
position it will disable the shutter button unless you've got good focus and the green hexagon is lit in the
viewfinder.
You should be able to use this for difficult focusing situations - macros spring to mind. Set the autofocus switch to
"AF", frame the subject in the viewfinder, focus as best you can and then hold down the shutter button while
slowing moving to and from the subject. With the shutter button held down, the camera will fire as soon as you hit
the correct focus point.
It sounds good in theory, although I admit I haven't actually tried this particular technique yet.
SUMMARY
There are a few things that need to be set up, but once that's done it's actually very easy to use manual lenses.
Pressing the AE- L button to set the shutter speed is simple to do and faster than mucking about with the shutter
speed on my old K1000 and ME Super cameras.
The only caveat is that the smaller APS- C sensor used in Pentax's digital cameras means that lenses have a
reduced field of view compared to when they're used on a full- frame 35mm camera. The effect is like multiplying
their focal length by 1.5, so that a 50mm lens on a K100 digital camera gives you the same picture you'd get with
a 75mm on a film camera. This is a disadvantage if you want to take wide shots, but an advantage for telephoto.
If you've got some old Pentax lenses lying around, the K100 will put them to good use!
