* Astronomy

Antares 0.5 x focal reducer test.

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.