With a growing selection of affordable monochrome cameras, more imagers are now using mono cameras that require multiple filters and filter wheels.
QHYCCD offers six filter wheels for filters ranging in size from 1.25-inch to a 50 x 50mm. Prices are quite reasonable, starting at $279, for good build quality and included accessories.
The build and designs are similar, so the popular 36mm (CFW3-M) and 2-inch / 50mm (CFW3-L) 7-position models I’ve tested are representative of the line.
Filter and Filter Wheel Size Selection
Make sure you do your homework when it comes to selecting the filter size you’ll use. Filters that are too small results in completely blocked light around the outer edges of the sensor and image.
I found the 36mm unmounted filters worked well with the APS-C sized sensor of my QHY268M, even with a reducer at f/5.2.
The larger 2-inch / 50mm filter wheel is needed for APS-H cameras with full frame sensors, such as the QHY600.
A word of caution; 2-inch mounted filters are not the same as 50mm unmounted filters. The thread of 2-inch filters restricts the clear aperture to 43mm. That’s large enough for APS-H but not for full frame sensors with a 43.8mm diagonal.
I’m using the CFW3-L filter wheel for 50mm unmounted filters (clear aperture of 48mm) with my QHY600 with good results. A fast optical setup (below f/4.0) or large filter-to-sensor distances, however, will require the larger CFW3-XL filter wheel with 50x50mm unmounted filters.
Parts and Accessories Included
The QHYCCD filter wheels include several accessories.
I really like the included spacers. They are very well designed, bolting on and adjustable in 0.5mm increments. This avoids the change in orientation that can occur with threaded extensions. I also like the tiny lip they have that blocks light leaks from between the spacers.
The spacer output threads can be M42, M48, or M54. A 2-inch nosepiece is also included, along with a lot of different length screws.
Adapters and Connectors
The QHYCCD filter wheels are quite versatile. They come with a QHYCCD camera dovetail adapter for QHYCCD cameras, but you can remove it and use the filter wheel’s female M54 with any camera.
The same is true for the telescope side; should you choose not to use the QHYCCD bolt-on spacers, simply remove them and use the built-in M54 female thread of the filter wheel itself.
The filter wheels come with two connector options. QHYCCD users can use the proprietary cable that plugs directly into QHYCCD cameras. Others can use the USB connection and the included USB 2.0 cable.
The QHYCCD filter wheels are made entirely of CNC machined aluminum (including even the blue electronics cover).
Fit and finish is very clean with machined ribs to both strengthen and lighten the housing. The design is remarkably efficient with no gears or chains (more on the mechanism later).
The wheels themselves are nice and slim; the 36mm version is 17mm thick, and the 2-inch / 50mm version is 21mm thick.
The 36mm weighs 691 grams (1.5-lbs), while the 2-inch / 50mm weighs 911 grams (2 lbs.).
Loading the Filters
Removing the filter wheel’s telescope-side cover, which is held in place by seven screws, reveals the machined aluminum wheel that holds the filters. The wheel can be removed as needed, for example to bolt the filter wheel directly to a QHYCCD camera.
2-inch filters can be threaded into their slots. Unmounted filters, like the 36mm and 50mm ones I use, are held in place with a less elegant system of tiny screws and felt-type washers. I’m not a big fan of this system these as it’s a bit finicky and there is no edge mask to minimize light leaks. I opted for plastic 3D-printed masks that are available from third-party vendors like Buckeye Stargazer.
The internal mechanism is quite interesting. QHYCCD has eliminated the usual mechanical parts like gears and chains. Instead, the beveled outer rim of the wheel presses against a rubber friction drive spur. The friction drive eliminates potential gear backlash. The gearless stepper motor is spring-loaded, keeping constant pressure on the friction drive.
Precision and Repeatability
Repeatability is essential with filter wheels. Even the smallest error can mean offset flat calibration frames, leading to uncorrected dust motes in the final image.
I had some issues with the filter wheel not repeating perfectly at first, and noticed online forum members complain about this issue with some models. I contacted QHYCCD, who replied the next day saying a new firmware upgrade would force the wheel to spin in only one direction. The minute-long update process fixed the issue.
The homing sensor and backlash-free friction drive ensure that the filters return to the exact same position every time. I tested each position and the wheel repeated and indexed PERFECTLY, as seen in the video below:
Filter wheel rotation and repetition test. Credit: Rouzbeh Bidshahri.
My current setup is a notoriously demanding full-frame system with an extreme 0.66x reducer. Corner vignetting is about 50%, meaning very accurate flat calibration is required to perfectly correct images.
In the example below, an uncorrected raw is compared to a corrected stack that shows no dust motes or residual vignetting, indicating the filter wheel is doing its job properly.
Overall, I’m very happy with the QHYCCDCCD CFW3 filter wheels. They are light, well-built, and priced reasonably. There are many different sizes to choose from to fit most needs.
I really like the supplied spacer kit and the friction drive mechanism that requires zero maintenance and provides very precise indexing and repetition. But I would like to see filter masks included, as they can improve image quality and are easier to install than the provided screws and washers.
With the new firmware update, the filter wheel has been working flawlessly, and I’ve been getting excellent results!
MSRP: From $279 to $1199