So we each got some new gear for astrophotography in the mail today. Bob got the Celestron Micro Guide Illuminated Reticle Eyepiece and I got a 38mm ballhead and a T-ring for my DSLR.
The T-ring was more complicated that I was expecting. The T-threads are located on a removable ring that is held to the bayonette mount by three set screws. This worries me as I'm not sure that the T-threads are necessarily perpendicular to the plane of the CMOS sensor. We'll have to do some testing to find out. Also, there are additional threads on the inside edge of the bayonette and a small set screw there, I guess for holding internal filters or something. Not sure what its threaded for; the box had no instructions or information of any kind.
Next was the ballhead, and this has some serious issues. It is a FLM Centerball 38 F with the power release head. First off, let me say that this device is really well machined; it looks great and the action is incredibly smooth. It has independant lock knobs for panning and for the ball, as well as a friction controller on the ball and a release knob for the head. The controls are all easy to use and conveniently placed. The tripod mount hole is a 3/8" Euro standard but includes a threaded insert for use with American 1/4"-20 tripod threads (like the one on our camera mount). The camera mount plate is threaded for 1/4"-20 and the head has a great cork base.
Now, there are two issues with the ballhead and they are basically two instantiations of the same thing. First, the small metal lug that attaches to the tripod mount on the camera is screwed in with a flathead screw and is prone to loosening. I had to get a really big screwdriver and crank down on that screw before I couldn't pan the camera on that joint while attached to the ballhead. Not a show-stopper, but irritating. The other problem is more serious and I think represents a fundamental design flaw in the device. once you slide the camera into place on the head, you tighten it down with a large knob under the cork plate. This knob must also be tightened thoroughly in order to prevent the previous problem. However, once it gets more than hand-tight, the action of tightening it loosens the threaded attachment of the head to the ball!!They are threaded in the same direction and there are no set screws on either. Basically, in order to get the head tight up against the camera, you have to detach the ball from the head, and vice-versa. There was no way to get both joints suitably tight using just my hands.
The threaded rod that attaches the ball to the head is loose at both ends and can be totally removed. It has a 3/8" thread but inside the ball it is turned down to a 1/4"-20 thread so it is reverible and presumably acts as an adapter for something but I'm not sure how this is meant to be used. Anyway, the solution I found was to thread the rod into the ball as per usual and then the head onto the rod, then remove the camera attachment lug and use a large flathead screwdriver sideways as a big lever arm to really tighten the head down onto the ball. With a 12" screwdriver I was able to put an enormous amount of force on the joint and it locked up pretty well. I can unlock it with the same technique, but not by hand. Then I was able to hand-tighten the head to the camera without loosening the ball attachment. But what a pain. I specifically bought this ballhead to be over-beefy to prevent flexure; having it freely rotate due to loose and un-lockable joints is inexcusable.
Anyway, once I got this worked out I went over to Bob's place to test it out on the telescope. We discovered immediately that you could not attach the ballhead to the camera mount because of two problems: the attachment bolt on the camera mount only stuck up about two threads worth, and the threads in the base of the ballhead are recessed about two threads worth!
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Left: The bottom of the camera mount after countersinking the hole
about 1/8". Top Right: The original position of the attachment bolt.
Bottom Right: The new position of the attachment bolt.
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The knob on the attachment bolt has an irritating bevel on the bottom that runs into the bottom of the camera mount and prevents the bolt from going farther up into its attachment. We decided to just counter sink that area with a 1/2" drill bit to allow for more bolt travel. We sunk the hole down about 1/8" into the forged aluminum and it worked like a charm. The bolt now sticks up about 4 threads worth and attaches securely to the ballhead.
The only issue with the camera mount now is that the knob on the attachment bolt is difficult to grip and basically hand-tightening is not enough. We will have to bring pliers with us to get this connection secure. We have come to the conclusion that this camera mount blows and that no one should ever buy it. When we have spare money floating around, one of us will spring for some Losmandy dovetail rails and a corresponding camera mount.
Last is the Celestron illuminated reticle eyepiece, which is basically the Cadillac of illuminated reticles. We can't really mess with it until we're actually out there in the field, but it looks great. The reticle isn't just two crosshairs like usual; there is a linear scale across the middle, a semicircular position angle scale, concentric guiding circles, and a large circular scale around the circumference. The manual for the eyepiece is surprisingly detailed and contains a lot of interesting math for using the various scales. This device will require some study and futzing to get the hang of it, but so far it looks awesome.