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William Optics 3.5"-2" RotoLock Visual Back Adapter
The William Optics 3.5"-2" RotoLock Visual Back Adapter converts the M92 x 1 male thread of a 3.5" William Optics focuser into a secure, self-centering 2" female receiver. This precision-machined adapter adds just 25 mm of optical length, creating a mar-free grip on your most valuable eyepieces and accessories without the hassle of traditional thumbscrews.
The 2" RotoLock System: A Secure, Self-Centering Grip
The RotoLock system replaces conventional thumbscrews with a simple, intuitive rotating collar. A gentle twist of the knurled ring engages an internal compression band, applying uniform pressure around the barrel of your 2" diagonal, eyepiece, or camera nosepiece. This design ensures your accessories are perfectly centered on the optical axis, preventing tilt and maintaining sharp focus from edge to edge.
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No More Scratches: The compression band provides a firm hold without gouging or marring the finish on your accessory barrels.
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Perfect Axial Alignment: By applying even pressure, the RotoLock automatically centers the accessory in the drawtube, which is critical for imaging and high-power visual observation.
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One-Handed Operation: The large, knurled ring is easy to operate even with gloves on, and there are no small thumbscrews to drop or lose in the dark.
M92 Threads for 3.5" William Optics FLT Focusers
This adapter is engineered specifically as an upgrade for William Optics refractors equipped with their robust 3.5" rack-and-pinion focuser. The male M92 x 1 threads ensure a rigid, direct connection to the focuser drawtube, eliminating any potential for flexure. Consuming only 25 mm of optical length, the RotoLock is an efficient solution for visual observers and imagers who require a solid 2" connection without sacrificing significant back focus. Available in multiple anodized colors, it allows you to match the aesthetic trim of your William Optics telescope for a seamless, integrated look.
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Will this William Optics RotoLock adapter fit a non-William Optics telescope?
No, this adapter is designed specifically for the M92 x 1 male thread found on William Optics 3.5" focusers, typically included with their FLT series refractors. It is not compatible with standard SCT threads or other focuser brands.
How does the RotoLock system on this 3.5"-2" adapter work?
The RotoLock adapter uses a rotating collar that tightens an internal, split compression ring. As you twist the collar, the ring gently and evenly squeezes the barrel of your 2" accessory. This provides a secure, self-centering grip that is superior to the single-point pressure of a thumbscrew.
What is the advantage of the RotoLock adapter over a standard 2" visual back?
The primary advantages are:
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Self-Centering: Ensures perfect alignment of your diagonal or camera with the telescope's optical axis.
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No Marring: It will not leave scratches or gouges on your eyepiece and accessory barrels.
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Secure Grip: Provides a stronger, more reliable hold on heavy accessories, preventing sag or wobble.
I use a William Optics FLT132 for imaging. How does this RotoLock adapter affect my 25 mm optical path?
The adapter's 25 mm optical length must be factored into your total back focus calculation. You must subtract this 25 mm from the available back focus of your telescope and flattener combination to determine the remaining distance for your camera and other accessories.
Can I use the RotoLock adapter with a heavy 2" diagonal on my William Optics FLT refractor?
Absolutely. The RotoLock mechanism is ideal for heavy accessories like 2" dielectric diagonals loaded with large eyepieces. The uniform grip provides a much more secure and stable connection than a single thumbscrew, significantly reducing the risk of wobble or accidental slippage.
How do I install the William Optics M92 RotoLock adapter?
Installation is straightforward. Simply unthread the existing visual back or adapter from the end of your 3.5" focuser's drawtube and carefully thread the M92 RotoLock adapter on in its place until it is snug.
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| Focuser-Side Connection |
M92 x 1 Male Thread |
| Accessory-Side Connection |
2" RotoLock Receiver (Female) |
| Optical Path Length |
25 mm |
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William Optics 3.5"-2" RotoLock Visual Back Adapter
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William Optics 2-Year Warranty
