Will the William Optics 90mm rings fit my telescope tube that measures 91mm?
No. The William Optics 90mm rings are machined for a precise fit and have no tolerance for oversized tubes. If your telescope's outer diameter exceeds 90mm, even by 1-2mm, these rings will not fit.
How should I measure my telescope for the William Optics 90mm rings?
For the most accurate measurement, use a set of digital or dial calipers. Measure the outer diameter of the main optical tube in several places to ensure it is consistently 90mm. Do not rely on specifications found online or in manuals, as these can vary from the actual product.
Can I use these 90mm rings to mount a William Optics Guide Star 61 guide scope?
You must measure the physical outer diameter of your specific Guide Star 61. While the model name suggests a certain aperture, the tube's outer diameter can be different. We do not maintain compatibility lists; a direct measurement of your equipment is the only way to confirm the 90mm requirement.
I plan to mount a 90mm finder scope on my main telescope. What else do I need besides these William Optics rings?
These 90mm rings will hold the finder scope tube itself. To attach them to your main telescope, you will need a dovetail bar (sold separately) that is compatible with both the rings and your main telescope's mounting points or saddle. Mounting hardware to attach the rings to the bar is also typically sold separately.
Why is such a tight tolerance important for the William Optics 90mm rings?
A precise, non-slip fit is critical for astrophotography. Any play or movement between the rings and the optical tube can cause image shift, trailing stars, and loss of guiding accuracy. The rigid 90mm design ensures the optical tube and any attached guide scope remain perfectly aligned with the mount throughout the night.
Are the screws for attaching the William Optics 90mm rings to a dovetail bar included?
No. Mounting hardware is generally not included. The type and length of screws required depend on the specific dovetail bar you are using, so you will need to source the appropriate screws for your setup separately.
