Re: ATM 4" ronchi, day 4

["Peter John Smith" <pjifl@bigpond.com>]

Rod Forrester wrote with respect to Ronchi testing :-

> It's too bad I can't get the camera to take pictures outside of ROC,
> as they really seem to confirm I got rid of the TDE and that I am near
> if not on the parabola.

I believe this phenomenum simply reflects the fact that the rays now cross
in front of the camera iris position.  Hence they will not all fit
simultaneously into the iris of this camera.  This is made more obvious with
faster mirrors (lower F:NO with steeper ray angles) and modern CCD cameras
with short efl lenses and tinyl iris sizes.

When inside ROC the rays (by definition) simply cross behind the grating in
more accessible space.

I find myself using the inner position far more than the outer one simply
because spectacles make the inner position more amenable to all rays passing
into the iris of my eye.

Once used to interpreting Ronchi images inside of ROC,  I believe there is
little to choose.  To me interpretation seems more instinctive inside ROC.

Peter Smith.