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Moonlight Instruments CS Crayford Focuser

Posted by Steve Hollenbach   05/08/2009 03:13PM

Moonlight Instruments CS Crayford Focuser
The model I ordered was Moonlight’s CS dual rate focuser with a 1.15 inch travel on a rotating base. It threads directly onto popular SCTs of 8 inches or larger. It happens to fit the 7 inch Maksutov.

The price was a little steep ($345), but comparable to other Crayford focusers, and less than others I found with the same capabilities.

Sales and service were excellent at Moonlight. They had experience with my application, the part was in stock and they must have shipped it a few minutes after the call.

The package arrived in three days. Moonlight didn’t waste time on a fancy inner box. It was packed very well and arrived quite clean and without a scratch. There was no special trick to get it to work. Just install it and start observing. It was even in collimation.

The blue anodized finish and highly polished machine-work are really something to see, just exemplary. It adds a few pounds to the scope back, but I didn’t weigh it. The Vitual-View it replaced is a little over one pound.

The fit on the Meade 7" MAK is direct, as that OTA is nearly identical to its 8 inch counterpart. Threading it on was not difficult and it “snugged down” without much effort. Holding is done with three thumb screws pressing in on a brass compression ring. The diagonal fit was concentric and tight. Everything fit and functioned perfectly; the first time, right out of the box.

My primary goal for this focuser was to eliminate image shift on a Meade 7 inch Maksutov. Mine is an OTA off a GPS model with the mirror lock. With the mirror locked up, there is no image shift detectable, and I tried to shake it loose. It was rock solid.

My secondary goal was to replace a Virtual View rotating visual back. That’s not easy, as that rotator is exceptionally smooth and strong. The Moonlight CS’s rotation was very smooth, and the thumb screw set it easily without any sign of slippage. This is not a clutch like the Virtual-View and so requires the rotational axis to be set rather than left with some friction to hold it still or let drift. In use; there is absolutely no backlash, vibration, looseness or run-out play.

Focusing was excellent as anticipated. You just set the mirror close to the focal length needed, the lock is engaged and the Crayford does the rest. An unexpected plus was that the Feather-touch focuser I installed in the body of the scope two years ago became obsolete. It will certainly improve my LX50 OTA once installed.

However, when I rotate it, the rather long dual-speed knob hit the Feather-touch focuser. This is not a fault, simply something to be aware of on the smaller OTAs. I kept the original focusing assembly with the triangular knob, and measured it. There could also be an interference fit with that knob in some positions. It’s close. The thumbscrew also has a slight interference fit with the Feather-touch, but is easy to adjust. On the early LX50 rotation should work without any interference.

For those of you who followed my articles on the Meade 7 inch Maksutov, this completely solved the last of the minor problems on that OTA; image shift. I also added a Meade dew shield, and am no longer considering flocking the inside of the OTA. The next big step will be a home built observatory.

Overall impression: The Moonlight CS is outstanding.