Last updated: 21 October 2005

Paul Rini focal reducer

Sent:	Tuesday, October 18, 2005 09:02:50
From:	Giuseppe Pellizzer (
I wanted to report my preliminary experience with the Rini focal reducer
( and my ETX-90.
The focal reducer is a black aluminium piece. I find that the piece is
well made and the optical quality looks good. It fits in the telescope
like an eyepiece and then the webcam adaptor is inserted into it. That
is, it is used pretty much like a Barlow, except that it reduces the
focal rather than increasing it. It is not for visual use because of too
much vignetting, but it works well with webcams. The reducer is labeled
0.5X and I wanted to check what reduction I was getting with it. The two
Moon pictures that I sent you were taken with and without the reducer.
Then, I have measured the distance between Moon features that I could
find in the two pictures. The ratio of the distance (the units are not
relevant here) measured in the picture with reducer and that in the
picture without reducer gives the measured reduction. I found that the
actual reduction was 0.34X. I could take the whole quarter Moon in two
shots with my ETX-90 and the focal reducer, rather than having to take
so many shots that I always miss a piece somewhere. So, all in all I
think that this is a good focal reducer although it will reduce the
focal more than what it is indicated on the barrel.

Thanks again for your website,
Giuseppe Pellizzer

Without Focal Reducer
With Focal Reducer

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