Last updated: 13 February 2003
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Subject: SAC7 Piggyback setup with ETX70-AT Sent: Saturday, January 25, 2003 13:22:27 From: firstname.lastname@example.org (Ed Carlos) I finally got around to taking pictures of my setup. Unlike regular digital camera, the SAC7 does not have any adapter for any type of mounting. I had to build my own from a few things from Home Depot. The main ring is from a 4inch PVC. I had cut it in half to reduce the width of the ring. The internal diameter of the ring is over 3.5inch. This was good because I had to put in a double tape and a tennis grip material so that it stays put and not slide around. I drilled a hole on the top and used a 1/4inch flat head bolt and nut to attach the 2inch electrical conduit hanger. The conduit hanger is what holds the camera. I had to change the nut of the conduit hanger to a wing nut to make tightening easier. Inside of the conduit hanger is a double tape with a 1/2inch rubber ring. It's a from a vaccum cleaner. To mount the whole adapter onto the scope, I cut the PVC accross and attached it again using small brass hinge and embroidery loop lock. The camera lens attaches to the extension tube. The extension tube goes through the conduit hanger. The SAC7 attaches to the other end of the extension tube. Attached are pictures that would probably help show how to put the whole thing together. It works really well but I'm having problems with the weight. I'm planning on creating a counter weight but I don't know how to balance things out. As you can see in the picture I tried to put the adapter and camera towards the forks. However, I'm still getting slewing problems. I can't tell whether I need to put the coounter weight at the back or the front. Do you know how to calculate the weight balance and where and how to position them? Clear Skies Ed
Mike here: For a counterweight, since the telescope is "somewhat balanced" around the fork attachment points, I'd suggest some weight on the rear of the OTA. I say "somewhat balanced" because, as you know, if you unlock the altitude axis, the aperture end of the tube drops down. So when you add the extra weight forward of the forks you make it worse.
Subject: Re: SAC7 Piggyback setup with ETX70-AT Sent: Tuesday, February 11, 2003 18:00:18 From: email@example.com (Ed Carlos) I tried adding counterweight on my ETX70AT scope to offset the piggyback SAC7 and 55mm lens (polar aligned), but it did not seem to help my slewing problem. The scope still continue to stall when slewing on the RA. I did suspect the recent cold spell here in the Northeast. As an experiment I tried the scope with the piggyback indoors. It seems to work fine. I know it's been cold lately but I'm not sure if it would actually affect the performance of the scope. Do you know if there are any operational limits for these scope? I know I was out when it was around 20deg(my wife thinks I'm insane), but I thought I've also tried it when it was around 32-35deg. In either case the problem occured. If it's not the weather then this is the second ETX70AT that I have had the same problem. I'll need to contact Meade again to get it fixed. Any ideas or clues would be appreciated. Clear Skies EdMike here: The ETX telescopes are not designed to slew with a lot of weight hanging off them. I wouldn't have thought the SAC imager would be too much though. Low temperatures will cause the lubrication to become thick and could cause stalling. Occasionally doing a lot of slewing around may keep the lubrication looser.
I think it is the extreme cold temp. I spoke to Meade and they confirmed that ETX scopes should be brought in every to warm up. They suggested about 45minutes. I tried it again last night at about 20deg. The scope was fine at the beginning even with the SAC7 and camera lens with mount. After a couple of hours it did start to stall again. I'll monitor it more and if it keeps happening I may elect to return the scope to have it looked at by Meade. In any case here's an attached pix of M42 at prime focus with ETX70AT. I took three separate images at 60 seconds each under a bright moon. As always some CCD image processing and here you go most of the moonlight is gone and more structure of the nebula is present.
Mike here: On the Beehive photo I think the trailing might be just that; trailing due to "field rotation". This will occur if the telecope is mounted in Alt/Az as opposed to Polar mode.
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