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Post Info TOPIC: Focal Reducer


L

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Focal Reducer
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Test for a DIY focal reducer from a repurposed second-hand telescopic 4 x 28 gun sight. 

A 80mm F6 refractor + Vesta pro webcam and IR-cut filter were used for the test.

Most of the commercial focal reducers use standard 25mm f4 achromatic lenses as used in common compact binoculars.



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L

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DIY Focal Reducer
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Test for a DIY focal reducer from a repurposed second-hand telescopic 4 x 28 gun sight.  The achromatic lens was removed and simply glued to the front of a filter cell.

A 80mm F6 refractor + Vesta pro webcam and Solar and IR-cut filters were used for the test.



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L

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RE: Focal Reducer
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Antares 0.5 x focal reducer test.



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L

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The Moon through a 60mm refractor and Vesta Pro webcam.
Baader contrast filter + UV_IR cut filter.
Test for DIY Focal reducer

Focal reducer made from the front lens elements of a broken 1960 vintage camera.
(An added bonus was that the focusing wheel travel was increased allowing for easier focusing).



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L

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Antares 1.25" 0.5x focal reducer screws on to any accessory such as eyepieces, camera adapters, etc. that accepts standard 1.25" threaded filters and provides a nominal reduction of 0.5x. Use of this focal reducer effectively halves the focal ratio of your telescope, resulting in a wider field of view and significantly shortened exposure times for astrophotography.
The actual reduction will vary a little over or under 0.5x depending on exactly where the focal reducer is placed in the optical path.


$35.00

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Ed ~ The focal reducer is basically the opposite of a Barlows lens; consisting normally of an achromatic doublet (as found in binocular objectives), or a Plossl design, etc. So it quite easy to source (for a DIY money saving solution) such a suitable sized lens, and place it into a barlow lens (remembering to remove the front barlow lenses). The focal reducer lens can be held in place by an eyepiece or camera/webcam adaptor.  Effectively this is like placing a camera/webcam behind a (preferably) long focus eyepiece (resulting in a wider field of view).
Two points to note are that using a very short focal length achromatic doublet will introduce spherical aberrations, and that a simple lens will introduce noticeable chromatic aberration.

The bottom line is that with the proper material a DIY Focal Reducer will be as equally effective as a shop bought solution.



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