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Siebert 1.25" OCA Type 1A for Reflector OR Refractor Sold!

Price - $85.00

Ad Number: 191304

Posted: 02 Dec 2019

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For sale is the 1.25" Siebert Type 1A OCA with two detachable lens elements that will work on both reflectors AND refractors, providing 1.25X magnification factor to retain low power wide views when binoviewing.

You will be able to reach focus using this with just about any newtonian/dob or refractor.

Reflectors / Newts / Dobs:
Recommended for use in f/5.9 reflectors and slower to minimize light cut off. Will reach focus and work in faster focal ratio reflectors, but there will be some light cut off in f/5 and faster.

Will work for virtually all refractors. You simply unscrew the lens elements from the OCA tube and then screw them onto the corresponding binoviewer and diagonal nosepieces. (Your diagonal replaces the silver tube)
This OCA is a good, affordable fit for most entry level binoviewers with clear aperture under 24mm, such as Williams Optics (20.4mm), Arcturus (21mm), Celestron, Stellarvue, etc. This can help get binoviewers to reach focus without having to resort to high mag barlows or more expensive OCAs.

(Thanks to CN user Mike Lynch for letting me this OCA is also 100% compatible with refractors, by attaching lens elements to diagonal and binoviewer nosepieces!)

Front aperture: 22mm
Recommended scope f/ratio: f/5.9+
For Refractors & Reflectors
OCA length/light path length: 65mm
Accepts female threaded 1.25 filters on the telescope end
Installs onto 1.25" nosepiece threads
Machined aluminum construction
weight 2.2 oz
Optics in great shape and are fully multicoated.
Harry Siebert's hand crafted eyepieces have a very raw, industrial look and finish to them, but are optically excellent and well regarded. MSRP $159 + shipping to buy new from Siebert; this is priced nearly 50% off.

$85 + $5 Shipping CONUS, Paypal Accepted.


  • Condition Very Good
  • Location Long Beach

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