tested focusing with diopters

Did an experiment with the focusing mask and the camera (and the 70-210 lens).

This exercise forced me to clean the back element of the view finder. Crikey! It was filthy. Put better batteries in the single white LED light for the false star.

I focused on an object without my glasses while looking through the optical view finder. Then I set the diopter so I had a good corrected view for my eye. With a Y-mask installed, aimed at the false star, I then focused using the diffraction pattern. I centred the moving line in the other two, as per usual, making a symmetrical pattern.

Out of curiousity, I checked what the camera chip was receiving by using the on-board Live View. Zoomed 2 times then 10 times. It showed a centred, symmetrical pattern.

Then I put my eyeglasses on. The view in the camera view finder was fuzzy, of course. I adjusted the camera view finder diopter for a crisp image. The diffraction pattern was centred, symmetrical pattern. I did not need to touch it. The camera was focused.

I don't know why or how exactly but it seems, after this brief test, that focus with the mask is an absolute. What I see in the view finder is unaffected by my vision correction requirement. And it seems that the data sent to the sensor is also in good focus. Or to put it another was, I did not change the focus for my vision. I set the focus for the camera, not me.

I could see with a flip mirror this might be an issue. And you'd want, which is often the case, a parfocal solution.

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I don't recall the exact number but, having mild myopia, I believe my prescription is around -1.5.