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Optec-DSI 3.5-inch Telescope Adapters

 

High Performance 3.5" Threaded Extension Rings

Telescope Adapters and Extensions for the Optec-DSI 3.5-inch thread

Extensions, Adapters and Retaining Rings

Rich Simons of Deep Sky Instruments and Optec have jointly developed a new, larger diameter standard spacer for large aperture telescopes.  Like the Astro-Physics 2.7-inch spacer set, the Optec-DSI 3.5-inch spacers are available in a five different lengths.  

The AP 2.7-inch thread has become an astronomy industry standard thanks to the tireless efforts of Roland and his team at Astro-Physics.  Optec has produced a complementary extension set and a few new adapters in an effort to extend this industry standard. However, there are times when the 2.5" clear aperture of the AP2.7 spacers will not allow enough light through clipping the edge rays. 

Optec-DSI 3.5-inch extension tubes feature female threads on one end with male threads on the opposite endDSI 3.5 Extension Tubes with knurled bases to help attach and detach these tubes.  The extensions can be combined and stacked. We believe our four and five piece sets will provide all the needed extension for fixed focal length telescopes with 1/4" (6.35mm) increments using a minimum number of pieces.  Click here for a table of the optimized spacer combinations. 

All extensions and mounts are made from high strength 6061 aluminum alloy and black anodized.  Anti-reflection threading and internal baffles on the largest extension tube help minimize internal reflections.  All internal surfaces are painted and baked with a non-reflecting ultra-flat black paint. 

Extension Tube Sets

Stock #19889
DSI 3.5 Extension Tube Set, 4-piece set
  • Includes: 1/2", 3/4", 1", and 1-1/2"
  • Possible spacer combinations:
    0.5" through 3.25" with 1/4-inch increments plus 3.75" with all spacers combined.  (See Table for combinations.)

DSI 3.5-inch Extension Ring 

Stock #19890
DSI 3.5 Extension Tube Set, 5-piece set
  • Includes:  1/2", 3/4", 1", 1-1/2", and 3"
  • Possible spacer combinations: 
    0.5" through 6.25" with 1/4-inch increments plus 6.75" with all spacers combined.  (See Table for combinations.)

DSI 3.5-inch Extension Ring

 
 Individual Extension Tubes and Retainers
Stock #19891
DSI 3.5 Extension - 1/2" Length
  • Overall Height: 0.88"  (22.4mm)
  • Clear Aperture: 3.25" (82.5mm)
  • Weight: 1.0 oz. (30 g)
  • Back-focus Usage: 0.50" (12.7mm)

DSI 3.5-inch Extension Ring 

Stock #19892
DSI 3.5 Extension - 3/4" Length
  • Overall Height: 1.13" (28.7mm)
  • Clear Aperture: 3.25" (82.5mm)
  • Weight: 1.4 oz. (40 g)
  • Back-focus Usage: 0.75" (19.1mm)

DSI 3.5-inch Extension Ring

 
Stock #19893
DSI 3.5 Extension - 1" Length
  • Overall Height: 1.38" (35.0mm)
  • Clear Aperture: 3.25" (82.5mm)
  • Weight: 1.8 oz. (55 g)
  • Back-focus Usage: 1.00" (25.4mm)

DSI 3.5-inch Extension Ring

 
Stock #19894
DSI 3.5 Extension - 1-1/2" Length
  • Overall Height: 1.87"  (47.5mm)
  • Clear Aperture: 3.25" (82.5mm)
  • Weight: 2.4 oz. (70 g)
  • Back-focus Usage: 1.50" (38.1mm)

DSI 3.5-inch Extension Ring

 
Stock #19895
DSI 3.5 Extension - 3" Length
  • Overall Height: 3.38" (85.8mm)
  • Clear Aperture: 3.25" (82.5mm)
  • Weight: 8.2 oz. (230 g)
  • Back-focus Usage: 3.00" (76.2mm)

DSI 3.5-inch Extension Ring

 
Stock #19897
DSI 3.5 Retaining Ring
  • Overall Height: 0.14" (3.5mm)
  • Clear Aperture: 3.45" (87mm)
  • Weight: 0.4 oz. (15 g)
  • Back-focus Usage: 0.10" (2.5mm)
  • Anodize:  Gold

DSI 3.5 Retaining Ring