Ummm...this is silly.
- Av metering is less reliable than green button. They use different algorithms. So, if you want the meter linearity of the K10D, go ahead and use Av
- The automatic aperture* (what you have with the lever intact) is a good thing because it allows you to focus and frame wide open with stop-down for exposure only. Back in the old days, it was a heavily promoted feature and is still a huge usability consideration when buying M42 vs. K-mount lenses. For perspective, I suggest shooting an M42 body with the lens in both the M and A positions. Ten minutes will make a believer out of you. Translation? Usability with a fully manual aperture sucks. Just 45+ years of experience speaking here.
- Ruins the resale unless your intended market is the MILC crowd and even then they more experienced users are springing for a coupled adapter. I know this is out of scope, but should still be a consideration. Really folk, they are not making this stuff anymore.
Part of the confusion comes from the notion that there is sometime special or desirable about "continuous" metering. To be honest, it is often enough not your friend, though is usually pretty benign due to the nature of a center-weighted averaging meter. Below is a short primer on stop-down metering, yes the kind you are using with a non-A contact lens.
- Meter the subject. This may be done a number of different ways depending on what your aim is. If is a face meter for the face.** Sometimes this means taking your reading up close and backing away. Sometimes it is enough to simply measure the incident light (gray card or equivalent).*** Use the camera's meter or a hand-held unit. Both work equally well. If none of this makes sense there are books on exposure. All metering failing, you can simply shoot/chimp/adjust and go from there.
- Once you determine your exposure, shoot at will until either the light or your subject changes. Surprise! You don't have to re-meter in between exposures.
Steve
* Not the same as automated aperture control where aperture is controlled by the body and not the ring on the lens.
** For Caucasians this means taking the meter's numbers and adding two stops more light. For darker skin, let experience be your guide.
*** Incident measurements work incredibly well. Unless you are wanting to place the exposure to a particular value in the subject (spot metering), measuring reflected light (what your camera normally does) is sort of a mess.
Last edited by stevebrot; 04-20-2015 at 05:28 PM.