Originally posted by UncleVanya Sorry - I'm not joining a facebook group for more info on this. I am unlikely to be that helpful in this case. I am not certain that the f/stop data is even transmitted in a way that isn't an offset against a known minimum. I was under the impression that the lens id was transmitted and the focal length and so forth and from this the camera determined the f/stop but I'm likely confused. I know that with manual focus A series lenses the entire thing is done via the contacts not the data pin - but since you have a data pin then that may be ignored?
ok, I will copy / paste
"The manual focus lens and Face Detection feature in the Pentax body are already a reality
Who do portrait photography with non-traditional manual focus lenses (let say, projection lenses), probably knows that Face Detection does not work as one of the autofocus modes in Live View. Normally we use center focus point to acquire focus, we enlarge the image, then do focusing more precisely, then diminish the image, recompose and press shutter button. This is NOT CONVENIENT. Try the autofocus lens and see how comfortable it is to shoot people when their faces are recognized by the camera, you are able to compose the image ant shoot.
It's even harder to use any kind of lens with Petzval optical schema. Those lenses have curved area of focus. If you do focusing in the center, then reframe the picture and shoot, the face will be out of focus.
Well, that's it. I decided to cheat the camera. I made the m65 adapter with a chip and now my manual focus projection lenses are able to work with face detection feature. No need to recompose the image after focusing with central point, because focusing is done where you choose the face to be.
I made adapter for my Visionar 168 mm and Kipronar 165 mm lenses. The EXIF shows 170 mm focal distance. But it is possible to make 70, 80, 90, 100, 110, 120, 135, 150, 170 and so on until 300 mm focal lenght. Aperture is f4,5 (should be f1,9), but exposure is right. Maybe I will try to reprogramm the chip if I find the way to access ROM data.
This adapter is for m65 focusing helicoid.