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GSO's popular 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. For example, use of this reducer will convert an f/10
telescope into an f/5 scope.
The 2-element reducer features
fully multi-coated optics in a black-anodized aluminum filter cell. It
also has additional 1.25" female threads so you can screw/stack
additional 1.25" filters on to this reducer. This focal reducer will
work well for
visual use too when coupled with the right kind of eyepieces and
telescopes; it is not recommended for very fast scopes or very wide
angle eyepieces for visual applications.
Note that the use of any optical element like barlows and focal
reducers changes the focus point of your telescope, requiring
additional in-focus or out-focus travel. The exact amount of focus
travel required will depend on the optics and mechanics of your
specific set-up (telescope, diagonal (if used), barlow/reducer, and
eyepiece). Hence, be aware that you may not be able to reach focus with
all eyepieces or in all configurations with a given barlow/reducer. In
our tests, when screwed into an eyepiece, this focal reducer required
approximately 8mm of additional in-focus travel so please make sure that
your focuser can
accommodate this travel requirement.
Focal length (estimated) = 101 - 103mm (3.98 - 4.06")
Total
item length (including external thread) = 13mm (0.51")
Total item length
(excluding external thread) = 10mm (0.39")
Clear aperture = 22mm (0.87")
Weight = 0.5 oz.
Made in
Taiwan
Varying the Reduction Factor of a Focal Reducer
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. The exact focal length specification of this reducer has not been provided by the manufacturer, but we estimate it to be approximately 101-103mm. Hence, the "working distance" of this specific reducer is estimated to be 51mm, i.e., this reducer will provide a reduction of 0.5x when the center of its lens assembly is placed 51mm from the focal plane of the eyepiece or imaging device. Move the focal reducer closer to the eyepiece/camera and its reduction factor will increase. Move it away and the reduction provided will decrease.
By using additional spacers or extension tubes (sold separately), you can vary the amount of reduction you obtain with this reducer as follows:
Extra Spacer Length |
Nominal Reduction Provided |
0" / 0mm |
0.50x |
0.25" / 6.4mm |
0.44x |
0.5" / 12.7mm |
0.38x |
0.75" / 19.1mm |
0.31x |
1" / 25.4mm |
0.25x |
However, do not be tempted to buy only the longest spacer tube to get the most reduction. A focal reducer will provide good results as long as it is placed "close" to its working distance. For example, it is possible that a 0.5" spacer will provide good results, a 0.75" spacer will provide acceptable results, and a 1" spacer might be unacceptable for your telescope/eyepiece combination. You will usually have to determine this by trial and error for your
set-up, so you might want to consider buying more than one spacer.
Copyright Notice: This description was developed by Agena
AstroProducts. It was NOT provided by the supplier/manufacturer of this product. Please do not copy for personal or commercial use.
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