A late follow up to this query regarding the 11si infinity focus. I've shot several rolls through an 11si in the past week (and have loved the experience). But I can offer an observation based on my use of the model. The mirror lock up switch on the side of the lens mount is not an ergonomic master stroke. For starters it is well placed to be difficult to use with certain lenses (particularly auto aperture types) fitted to the camera. But it's also somewhat imprecise in its action. I think the design and particularly the placement of the sliding button that actuates the lock up leaves a bit to be desired.
You can see what I mean by checking the image below. It's not ideal as the 11si (one of three I've handled recently) is black painted and the black lock up switch does not stand out. But the serrations of the button slider are just visible directly underneath the shutter release button on the lens (and adjacent to the self timer lever, the presence of which does not improve access to the lock up switch).
If you have average size fingers, it's best actuated by sliding an index finger up between the lens and the body, which is about the only way you can get a good grip on the serrations of the switch. Of course, you're most likely to want to use the lock up when the camera is fitted to a tripod, in which case, doing the above, is...easier said than done.
What is germane to the topic of infinity focus accuracy, however, is that it's possible to bump the switch when fitting or removing lenses. Yes, of course if the mirror is completely retracted, it will be very obvious. But, it's also possible for the switch to rest in a position that leaves the mirror
mostly lowered, but not quite resting on its stop. If this happens, when you're focusing a lens, the viewfinder image...won't
quite reach infinity!
So, before assuming your late type Alpa (9, 10, 11 series) needs its focus calibrated: if the camera in question is fitted with a mirror lock up switch, then, slide the switch up and down a couple of times to verify proper operation, and ensure that it is positively moved fully to the "down" position. It may well save you the expense of getting the focus calibrated by one of the few technicians who will work on these rare Swiss wonders, as there might not be any need for corrective adjustments after all.
Cheers
Brett
