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Hardware Issues

 

SBIG FW8G-STT (focusing)

SBIG FW8G-STT (filter adapters)

Meade RA clutch lever

Meade vibration supression pads

Homemade electric focuser for the Meade LX600

SBIG FW8G-STT - Issue # 1

Out of the box there was an issue, focus stars looked like donuts cut in half. No amount of turning the focus knob of the device would bring any improvement. In the autoguider image below, you can see a way out of focus star to the right.

I didn't think this would be a difficult problem to fix, but had a fear of voiding the warranty if I tried. Tim Puckett of SBIG was kind enough to call me and said crack it open, warranty will still be good. After opening it up, I found there was very little range of motion for the focus block.

The image below is of the focuser block all the way out.

Below is with the block all the way in. Like I said, not much range of movement.

Undoing the jam nut (not visible in the photo) and flipping the block over revealed the problem. A long screw is used as the "pivot point" for the autoguider shutter. This screw was nearly all the way out.


 

The fix was simple, turn the screw back in until snug, then back it out a bit so it doesn't bind the shutter.

The focusing block now has full range of motion, in the photo below it's all the way in.

 

After reassembly and testing, problem is solved.

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SBIG FW8G-STT - Issue # 2

Another out-of-the-box problem, just took a while to discover it. I finally got around to purchasing photometric filters, and per the SBIG web site, their filter adaptor should allow the use of 1-1/4" filters in the filter wheel (it natively takes 36mm filters). After installing the adapter its obvious there is a serious problem. The filter/adapter combination won't stay put. If you can see the movie (depends on your browser and version, it's viewable in IE and Chrome), the problem is obvious. The filter adaptor is too small in all dimensions to be held frimly in the fiter wheel.

Talked to SBIG about this Friday and was told this may be a bad batch of filter adapters.. Was told I'd get a call back on Monday, but nothing yet.

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A week after our initial contact, an SBIG representatived send me an email asking if I had installed the "O" rings that are supposed to secure the filter adapters. What "O" rings? Turns out there were in the shipping case, but being black against a black background were not immediately noticable. Live and learn.

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MEADE INSTRUMENTS RA CLUTCH LEVER (LX 200 AND 600)

Anyone who has ever actually used the stock clutch lever in the dark and/or in the cold knows that whoever designed this part never used it. It's very difficult to use with bare hands, and forget about it with golves on. To force it into actual usefulness, only a few modifications are necessary.

1. Remove it from the telescope.

2. Drill and tap a hole into it to fit whatever suitable screw you have handy.

3. Find a piece of aluminum to serve as an extension, and drill a hole in that.

4. Assemble and enjoy.

See photos below.

 

 

If you don't have a tap, you can do something simiilar by just finding a self-tapping metal screw and drilling the correct sized hole.

 

 

I had a piece of aluminum u-channel lying around, so I used that as the lever. About anything would work, but aluminum won't rust and you don't have to paint it.

 

 

To keep the bolt from working loose, I drilled a smaller hold and tapped a short piece of music wire into it.

 

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I I put a spacer in to elevate the assembly slightly. This one isn't stainless steel, but I'll swap it out for one soon.

 

 

The finished product. No more broken thumbnails or having to use a screwdrive to loosen the RA clutch.

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MEADE INSTRUMENTS ANIT-VIBRATION PADS.

They came with the telescope, so I foolishly assumed they should be able to support its weight.

After a couple of frustrating and wasted nights wondering why my tracking and pointing had gone south, I found these. They had been in place for less than six months. Why two of them broke is a mystery, my setup actually weighs less than the stock 12" LX600 with wedge, since I don't have the StarLock mounted.

 

 

 

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The Meade 12-inch LX600 - focusing issue and fix

I wouldn't want to leave anyone with the impression that I am not happy with Meade products. I could be happier with them, but for their flaws (which all have work-arounds), for the money, in my opinion, they can't be beat.

One of the issues that has come up with the f/8 LX600 is that with my imaging train (SBIG AO-8T, self guiding filter wheel and STT 1603 camera) things will not come to focus if I'm also using a crayford-style focuser. Not sure who to blame for this, as I've not heard that it's a widespread problem. In any case, the blame isn't as important as the fix. In that regard I can only thank Meade for finally fixing the mirror-flop problem in their later model SCT's.

In the past I've used the Optec crayford-style focusers, and have been very happy with them. But with the new f/8 version LX600, neither that focuser, nor the Meade crayford focuser, will come to focus with my imaging train. Time for another home-made solution, which, in short, is making an electric focuser that eliminates the need for an on-axis craford focuser, but still provides the convenience of electrical remote focusing.

Mechincally, the solution isn't hard to implement, but it does require a bit of electrical work. The focusing port on the telescope provides about 12 volts DC to the focuser, and when focusing is changed from "in" to "out", the telescope simply reverses the polarity. This is great if you have a 12 volt DC motor and gearbox you can couple to the focusing knob, but the motor/gearbox I had on-hand has a 3 volt motor. So I had to step down 12 VDC to about 3 VDC, and also provide not only positive but negative voltage to the motor.

Turns out the solution isn't difficult. A common voltage regulator is the NEC 956, which is an adjustable positive voltage regulator. Wiring up a simple circuit I was able to bring the native 12 VDC from the 'scope down to about 3 VDC, which made the gearbox motor much happier (since it's a 3 volt motor). The negative voltage issue was dealt with as simply, using an NEC 957 negative voltage regulator. This circuit now allows the focus to be adjusted either "in" or "out" by implementing the controls native to the LX600, and by using the focusing features in TheSkyX as well.

Some would argue that this isn't as good as a crayford focuser, and I would completly agree with them. But stuck with "not as good" is much better than being stuck with "nothing at all", and since mirror flop is greatly reduced in the LX600 (compared to the LX200), and things come to focus regardless of the temperature or filter, I'm quite satisfied with the solution.

Beta testing. The breadboard is tie-wrapped to the arm holding the focusing motor. No need to drill any mounting holes in the 'scope, is has unused tapped holes and screws that serve nicely.

The two trim potentiometers allow the voltage that controls the in and out speed to be independently adjusted.

The size of the pullys really isn't important, since the trim pots allow a wide range of voltage (speed) adjustments.

If you feel the need to go back to manual focusing, just slip the belt off one of the pullys, not much tension is requied to keep it on, so it slides off easily.

Just don't loose it in the dark. :-)

After testing is complete, all components will be soldered to a circuit board and housed in a weather-resistant enclosure.

Advantages of this system over a Crayford focuser is cost (my total investment in parts can't be over $30), and not being limited to a Crayford's narrow range of focus travel.

Disadvantages are that the mirror can't be locked down so mirror flop and focus shift is a possibility (but much less of one than in the XL200's). "Pretty picture" folks may find this objectional, but for variable star and asteroid work focus going slightly out of adjustment isn't a show stopper since the photometry software will easily compensate for slight focus shifts.

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