Quote:
Originally Posted by gregbradley
There is a thread that shows a ray diagram where the filters cause the light to bend less in extending the focus point of the light a bit further out.
Greg.
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Here is a link to the focus shift diagram on my website:
http://www.faintgalaxy.com/focusshift.htm
I think the confusion of the +1/-1 thing is because from QSI's point of view the filters are internal to the camera, hence making the 'camera unit' use less back focus out of the total available than what the mechanics would measure.
I always see the filters as 'helping' in the usually limited backfocus situation by lengthening the path available.
So be my calc:
79 - 50.4 + 1 = 29.6mm
or alternatively by QSI interpretation:
79 - (50.4 - 1) = 29.6
So Paul has it correct.
EB