Originally posted by FHPhotographer I've started using an Pentax A50 for trap focus on my K20, does the following apply to an manual lens set to "A" and am I damaging the K20 using it that way?
I pulled this quote from a response by PDL to an earlier Forum thread: Never have the front switch set to AF.s or AF.c and twist the focus ring - on a FA (or AF) lens de-coupled or not. By twisting the focus ring you can/will damage the gears/motor of the AF mechanism.
Brian
Yup, I said that.
On a non-Pentax and Pentax Auto Focus lenses without Quick shift (not the DA series of lenses), if you use the focus ring to finess focus, you can end up damaging the gears in either the lens or the body. The focus motor is not designed to be rotated by the gear linkage in the lens. All you have to do is chip one tooth off of the series of gears to cause issues.
However, If you are using a manual lens - focusing the lens does not effect the AF motor. The prefered setup is to set the camera body to MF on the front switch. By my experience on the *istDs, K10D and K20D, when the switch is set to MF the AF screw on the lens mount is retracted. Therefore with a AF lens (using only screw based AF) the AF motor function is disabled. The AF circuits are still usable.
In my case - when I use my FA 50mm, my Tokina AF 28-70mm macro or my Vivitar 300mm manual lens (the only pure manual lens I have) and I want to manually focus with these three lenses. I set the switch to MF (retracting the AF screw) - when I want to use the AF circuits to check focus I press the OK/AF button and use the green hexagon to see if I am in the ball park. (Note: I have de-coupled AF from the shutter button so I can not speak to whether this works with shutter button activated AF or not)
With manual lenses - there is no connection between the camera and the lens used in focusing. Therefore there will not be any damage to the gearing/motor in the camera. Although I would still suggest that when using manual focus lenses that you set the focus switch on the front of the camera to MF, if for nothing else but to retract the screw on the lans mount.
The Elitist - formerly known as PDL