Antares

Used Antares 1.25'' Focal Reducer


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  • $15.00
  • Regular price $30.00

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This is a used Antares focal reducer for 1.25'' accessories and eyepieces.  However, it is otherwise unmarked, and we are not sure if it is a 0.5x or a 0.63x reducer.  It is in good, clean condition, with a tiny speck on it that we are unable to clean.

 

 

Antares' 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.

Specifications:

  • Focal length = 95mm
  • Total item length (including external thread) = 15mm (0.59")
  • Total item length (excluding external thread) = 12mm (0.47")
  • Clear aperture = 23mm (0.91")
  • Weight = 0.6 oz.
  • Made in Canada

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 focal length specification of this reducer is 95mm. Hence, the "working distance" of this specific reducer is 47.5mm, i.e., this reducer will provide a reduction of 0.5x when the center of its lens assembly is placed 47.5mm 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 (not included), 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
0.43x
0.5" / 12.7mm
0.37x
0.75" / 19.1mm
0.30x
1" / 25.4mm
0.23x

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.

    SKU: U2204-JSH-FR1
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