Mirrorless with Conventional PD AF...

Started Jul 22, 2012 | Discussions thread
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WilbaW Forum Pro • Posts: 11,549
Mirrorless with Conventional PD AF...

The imminent announcement of the Canon mirrorless system seems to have stimulated some discussion about the merits of mirrorless versus DSLR. That got me thinking about how else we could eliminate the reflex mirror and have the best of both worlds.

I assume you understand how the reflex mirror sends the image to the viewfinder while a secondary mirror directs some of the light to the phase-detect AF sensor, as in -

Reflex mirror = "Main mirror"
PD AF mirror = "Sub mirror"

(Anyone got a better diagram?)

Surely we could delete the reflex mirror and pivot the PD AF mirror directly in the mirror box? That would give us -

  • a much smaller mirror box with correspondingly shorter mount flange to image sensor distance,

  • greatly reduced mirror slap,

  • more freedom to increase the frame rate with continuous PD AF,

  • state-of-the-art full-time CD AF on the image sensor with state-of-the-art PD AF on a separate dedicated sensor.

The PD AF mirror could be semi-transparent so that we don't notice it's there (just like we don't notice the loss of light to the PD AF sensor with a current DSLR). We could send more light to the PD AF sensor than we do now to improve performance, in which case the mirror would be somewhat visible in the viewfinder, or it's ghost could be masked in processing the viewfinder image. The mirror could be pivoted from the top or the bottom of the mirror box, or from the side, or it could slide sideways or be swung through an arc... whatever way gives the least disturbance to the stability of the image.

Has this idea been discussed before? Implemented?? It seems so simple and obvious...

Note: I'm not advocating EVFs, just exploring this alternative, so no need to jump in with all the "EVFs are horrible!!" stuff.

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