William Optics has rolled out the UltraCat 108, a 108mm apochromatic refractor aimed at serious astrophotographers. With a 5-element Petzval design and support for large-format sensors, it’s clearly built for wide-field, high-res imaging. Its reasonably fast too at f/4.8. But while it brings a lot to the table, it’s not without a few quirks that are worth knowing about.
Imaging-Only, No Eyepieces
Let’s start with the basics: this scope isn’t for visual astronomy. The backfocus is just 65.7mm, which means you can’t use standard 1.25″ or 2″ diagonals. That might be a dealbreaker for some, but it’s a conscious trade-off. William Optics has clearly prioritized imaging performance over versatility here.
Strong Optics
The UltraCat 108 uses a 5-element Petzval layout with Super ED, ED, Lanthanum, and something they call X-Element glass. On paper, that’s a solid combo—meant to reduce chromatic aberration and keep the field flat across a 60mm image circle. That’s great for full-frame and even medium-format sensors.
That said, real-world results can vary. Some users have pointed out that while the design is solid, performance can depend on the specific unit you get. Manufacturing tolerances are a thing, even at this level. So, it’s worth checking out sample images or reviews before pulling the trigger.
Built-In Features: Handy, Mostly
There’s a lot packed into this scope:
WIFD (William’s Internal Focuser Design): Keeps the focuser internal, which helps with balance and stability. It’s clever, though maybe not as intuitive to tweak manually.
STX Sensor Tilt Corrector: Lets you adjust tilt without removing your camera. That’s a time-saver, especially with big sensors.
Built-in Bahtinov Mask: It’s in the lens cap. Super handy for focusing, though some might prefer a removable version.
Anti-Shrink Lens Cell: Helps keep things aligned when temps change. Nice touch, but long-term durability is still TBD.
These features are clearly aimed at making imaging smoother. For many users, they’ll be a big plus. For others—especially those who like to customize every part of their setup—they might feel a bit locked in.
Compatibility
The UltraCat 108 comes with M68, M54, and M48 adapters and works with most major camera mounts—Canon, Nikon, Sony, Fuji, etc.
One thing to flag: there’s no built-in filter drawer or wheel. That’s not unusual—most refractors don’t have one—but it’s something to plan for. If you’re doing narrowband or multi-filter imaging, you’ll need to add your own filter system. Not a huge deal, just another piece to budget for.
Also, it’s not exactly lightweight. At nearly 8 kg and up to 588.5mm long, you’ll want a solid mount—especially if you’re adding a heavy camera and filter wheel.
Price
At around $3,798 USD, the UltraCat 108 is in premium territory. It’s up against scopes like the ASKAR SQA106 and the Takahashi FSQ-106. It holds its own spec-wise and offers more built-in features than some competitors. Whether that’s a plus or not depends on how much you value integration vs. flexibility.
Final Thoughts
The UltraCat 108 is a well-thought-out imaging scope. It’s fast, flat, and built for big sensors. The integrated features are genuinely useful, and the optical design is solid—though, as always, it’s smart to check real-world results before buying.
It’s not for everyone. If you’re looking for a dual-purpose scope or want to build a fully modular setup, this might not be the best fit. But if you’re after a streamlined, imaging-focused tool that’s ready to go with minimal fuss, it’s definitely worth a look.
