Astro-Physics 2.7-inch Threaded Extension Rings, Adapters and Retaining Rings

Astro-Physics 2.7-inch Threaded Extension Rings, Adapters and Retaining Rings - View 3

Astro-Physics 2.7-inch Threaded Extension Rings, Adapters and Retaining Rings - View 4

Astro-Physics 2.7-inch Threaded Extension Rings, Adapters and Retaining Rings - View 5

Astro-Physics 2.7-inch Threaded Extension Rings, Adapters and Retaining Rings - View 6

$122.1 ~~$165~~ In stock

Category: Astrophotography Accessories

Description

Telescope Adapters and Extensions for the AstroPhysics 2.7 thread

Extensions, Adapters and Retaining Rings

The ubiquitous AP2.7 inch thread has become an astronomy industry standard thanks to the tireless efforts of Roland and his team at Astro-Physics. Optec has produced an extension set and a few new adapters in an effort to extend this industry standard.

Optec's AP 2.7-inch extension tubes feature female threads on one end with male threads on the opposite end 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.

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.

Specifications

Spacer Lengths Available: 1/2", 3/4", 1", 1-1/2", and 3"
Clear Aperture: 2.52" (64mm)

Extension Tube Sets

Stock #19880 AP2.7 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 below for combinations.)
Stock #19881 AP2.7 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 below for combinations.)

Individual Extension Tubes and Retainers

Stock #19882 AP2.7 Extension - 1/2" Length Overall Height: 0.88" (22.4mm) Clear Aperture: 2.52" (64mm) Weight: 1.0 oz (30 g) Back-focus Usage: 0.50" (12.7mm)
Stock #19883 AP2.7 Extension - 3/4" Length Overall Height: 1.13" (28.7mm) Clear Aperture: 2.52" (64mm) Weight: 1.4 oz (40 g) Back-focus Usage: 0.75" (19.1mm)
Stock #19884 AP2.7 Extension - 1" Length Overall Height: 1.38" (35.0mm) Clear Aperture: 2.52" (64mm) Weight: 1.8 oz (55 g) Back-focus Usage: 1.00" (25.4mm)
Stock #19885 AP2.7 Extension - 1-1/2" Length Overall Height: 1.87" (47.5mm) Clear Aperture: 2.52" (64mm) Weight: 2.4 oz (70 g) Back-focus Usage: 1.50" (38.1mm)
Stock #19886 AP2.7 Extension - 3" Length Overall Height: 3.38" (85.8mm) Clear Aperture: 2.52" (64mm) Weight: 8.2 oz (230 g) Back-focus Usage: 3.00" (76.2mm)
Stock #19887 AP2.7 Male-to-Male Adapter Includes #19888
Stock #19888 AP2.7 Retaining Ring Overall Height: 0.10" (2.5mm) Outside Diameter: 3.5" (88.9mm) Clear Aperture: 2.69" (68 mm) Weight: 0.6 oz (15 g) Anodize: Gold

Target Extension	Spacers Required	AP2.7 Spacer Stock Numbers	DSI 3.5x24 Stock Numbers
0.50”	½”	19882	19891
0.75”	¾”	19883	19892
1.00”	1”	19884	19893
1.25”	½” + ¾”	19882, 19883	19891, 19892
1.50”	1-½”	19885	19894
1.75”	1” + ¾”	19884, 19883	19893, 19892
2.00”	1-½” + ½”	19885, 19882	19894, 19891
2.25”	1-½” + ¾”	19885, 19883	19894, 19892
2.50”	1-½” + 1”	19885, 19884	19894, 19893
2.75”	1-½” + ¾” + ½”	19885, 19883, 19882	19894, 19892, 19891
3.00”	3”	19886	19895
3.25”	1-½” + 1” + ¾”	19885, 19884, 19883	19894, 19893, 19892
3.50”	3” + ½”	19886, 19882	19895, 19891
3.75”	3” + ¾”	19886, 19883	19895, 19892
4.00”	3” + 1”	19886, 19884	19895, 19893
4.25”	3” + ¾” + ½”	19886, 19883, 19882	19895, 19892, 19891
4.50”	3” + 1-½”	19886, 19885	19895, 19894
4.75”	3” + 1” + ¾”	19886, 19884, 19883	19895, 19893, 19892
5.00”	3” + 1-½” + ½”	19886, 19885, 19882	19895, 19894, 19891
5.25”	3” + 1” + ¾” + ½”	19886, 19885, 19883, 19882	19895, 19893, 19892, 19891
5.50”	3” + 1-½” + 1”	19886, 19885, 19884	19895, 19894, 19893

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Customer Reviews (4.8 / 5 · 5 reviews)

Madison ★★★★★ Oct 21, 2026

Finally got the right spacing for my imaging train with these threaded rings — the fit is perfectly snug with no play. The retaining rings hold everything secure even when I swap filters.

Joseph L. ★★★★★ Oct 20, 2026

I was worried about getting the right back focus for my setup, but these extension rings clicked together perfectly and held everything solid. The threads are clean and consistent, which made swapping between adapters a breeze.

Madison G. ★★★★★ Oct 18, 2026

Finally, extension rings that actually thread smoothly without catching or cross-threading — the threads on these are buttery clean. I needed exactly 10mm to dial in my back focus for the reducer, and this set covered it perfectly.