Correcting the Too-short Celestron Hand Control Cable

One of the perennial, if minor, "what were they thinking" topics in astronomy hardware is the short coiled cable used to connect Celestron hand controls to their mounts. The cable, stiffly coiled like an old phone handset line, is simply too short.

This wasn't so bad on my old CG5 ASGT where the mount head isn't all that large, but on my CGEM it couldn't be ignored. It was possible to have the handset pulled right out of its tripod leg cradle as the scope turned in RA. That's not something you want to see when you're imaging, since it means the coiled cord was torquing the mount and then letting the handset become a free-swinging weight in whatever breeze there might be.

One solution I tried for a while was a coiled extension cable. The added cable was so heavy and droopy that it was awkward to handle and tended to get snagged on the mount. Then I came across a video that shows how to replace the stock cable with one that's more user-friendly.

All you need is

• A piece of flat 6-conductor telephone cable, preferably one with at least one end having an RJ12 connector attached--if not, you'll have to do that yourself. These can be found many places; on Amazon they're typically around $5 to $6.
• A soldering gun and solder (A good, fast-heating gun is much preferable to the old pencil type)
• A wire cutter
• A craft knife for stripping very thin wires
• Heat-shrink wire tubing (I found this on eBay)

Extremely helpful to have is a soldering jig to hold the ends of the wires together as you solder them.

The most important consideration is getting the wire connections correct. In my case the wire colors and order in the cable exactly matched that used by Celestron, so it was easy to get things right. If you get the connections wrong its quite possible you'll ruin your handset.

The filter from the old cable will be reused on your new cable. Aside from that, you can discard the old cable. Or toss it into your pile of stuff you probably should trash but are keeping "just in case" it might be useful someday.

The job takes an hour or so, when you're done you'll have the kind of cable Celestron should have provided in the first place!

A DIY Binocular Mount

Thanks to a change in plans--a wedding I want to attend is on the same Saturday as the Wisconsin Observers Weekend--I am going to go to this year's Nebraska Star Party. No offense intended to WOW, but NSP is a bit of a bigger show with more people and darker skies. NSP begins as the annual Jeffers Petroglyphs party ends, so I'll be able to save a couple of hours of drive time by going straight from Jeffers to NSP.

But what to do at NSP? I'll have my imaging gear from Jeffers with me, but maybe I should just make my first NSP a strictly visual affair. All that really dark sky, you know!

I've come into possession of an old pair of Celestron binoculars, their 11x80 Giant model from the 1990s:

This is not the model that was labeled "Comet Hunter" or "Comet King" apparently to cash in on Halley's Comet in 1986. What reviews I can find for this later model are mixed.

Good features from my standpoint:

• It was free
• It has a wide FOV (4.5 degrees)
• It comes with a mounting bracket. 

Cons:

• Probably not the greatest optical quality
• Heavy (6.7 pounds) 
• Exit pupil (~7mm) that is too large for my old eyes. I'm 60, and although I haven't measured, I would guess my pupils don't open past 5mm. This means that some of the objective size is being wasted, but some people suggest this has a small silver lining in that one's eyes can move a little laterally and stay in the light.

My past experience with large binoculars suggests that a mount is a very good thing to use for steadiness and comfort. A little googling turned up this plan, which I am adapting to the top of my CGEM tripod. The CGEM tripod has two threaded holes for mounting the azimuth post. These are perfect for attaching a base plate. In my case I'm changing the plan to substitute a 3/4" piece of hardwood for the 3/8" aluminum plate. The rest will be pretty much as the design suggests.

I was unable to find the nice round counterweights seen in the explanatory pictures, so I'm using lead scuba weights from the appropriately named Lead-co USA. Construction begins next week.

An update on May 20: Lead-co uses fixed-cost USPS mailing boxes, and I had paid for a medium sized-one. It turns out that the weights I bought fit in the small box, so Lead-co refunded the difference. Nice!

Clouds, WOW, Focal Reducer

The abysmal spring of 2013 continues with clouds, clouds and more clouds. My plan to attend the Wisconsin Observers Weekend this weekend has fallen through because of weather. The first night is being clouded out as I type this, Tomorrow night is forecast to be partly cloudy (at best) and Saturday night is forecast to be rainy (50% chance) and cloudy.

Worst. Spring. Ever.

But anyway, I did manage last week to shoot some test images with my .63 Celestron Focal Reducer.  I fiddle with my adapters until I got a spacing of about 104mm (I think), and here's what I got:

Flat Field test

This is taken using a Celestron 925 XLT and Celestron 0.63 Focal Reducer/Flattener. The camera is an SBIG-ST8300M with filter wheel (total back focus 38mm). Spacing was provided by a Celestron SCT-to-T adapter #93633-A (about 58mm).

The above full-field image is six 10 second exposures (2x2 binned) aligned and stacked, then given a stretch by Images Plus. The scope was not even roughly polar aligned and was unguided. I was also shooting through overhead power lines. Yechh.

I think it's fairly flat, at least flat enough to make me happy. Some vignetting is present, but it's about the same as found when imaging without the FR. I will probably tinker with the spacing in the future.

What's nice is that this setup gives a much more solid connection between the scope and camera. I look forward to using it SHOULD THE FREAKING SKY EVER CLEAR. Really, no, I'm okay, but thanks for asking.

Celestron Alignment Stars Diagram

Celestron uses the 80 brightest stars for the stars that can be used duing alignment. This is a subset of the named stars list. While I may know many of the stars, I certainly don't know them all, so I've prepared a GIF image file marking the constellations and the locations of the 80 stars. If you find it useful, here it is:

The alignment stars are in bold letters. Here are links to the full-sized variations of the chart:

Black stars on white background
White stars on black background
Red stars on black background

Credit: The background constellaton chart (a PDF file) comes from this U.S. Naval Observatory page.

Yet Another Accessory; Prelude to PEC

Like most go-to mounts, my CGEM can have its software upgraded. The CGEM also has the ability to compensate for periodic error in its tracking motion. Both of these require that the mount's hand control be connected to a computer. And there's the catch.

For some reason, Celestron refuses to create a cable that goes from hand control to a USB port on a computer. It continues to use a cable that requires the computer to have a serial port. Almost no laptops manufactured now have serial ports. Serial ports disappeared years ago, not long after parallel ports passed into oblivion. So why does Celestron continue to require them? Apparently so that they can overcharge for their branded serial to USB cable, which runs from $39 to $45, depending on the vendor. It's vaguely like what how many big-box stores charge for $60 HDMI cables that can easily be found elsewhere for $3.

In fairness, Celestron does include the hand control to serial port cable with the mount. So there's no need to purchase that half of the link.

Getting serial to USB is up to you. So far as I know any serial to USB cable will work; there's nothing magical about Celestron's model. So it's off to Amazon.com for a  cable that costs only about $11.

One More Reason to Like the Internet

During the Summer of '10 I managed to break my CGEM mount when a Celestron power supply went wacko and fed it a voltage that was too high. While trying to pin down the problem I also hooked my CG5-GT to the bad supply. That mount also died. The little red LED didn't light, the hand control stayed dark.

Ouch.

The CGEM was new and still in warrantee, so Celestron fixed it. It has worked beautifully since returned, and I highly recommend the mount to anyone seeking something that can gracefully carry up to 30 pounds of gear. The CG5 languished, however, since it was not needed. Frankly, I admit I was not in a hurry to get it open and find that it was dead; which would mean that its resale value had probably fallen from $400 to $100. Not to mention that it was relatively useless.

I wanted this mount back in working order either to sell it or to use it at star parties as a platform for wide-field DSLR imaging of constellations.

Today I decided to open up the seemingly deceased patient, hoping that inside lurked a fuse or some component that could be replaced easily. No such luck; I found that the CG5's brains are on two small circuit boards devoid of fuses. Nothing seemed to be out of normal in appearance, so it looked like a case of blown electronics.

A google search ("repair CG5") turned up a 3rd party repair service that had gone out of business last December. There were also threads that reported dead mounts because of loss of contact in the center pin of the power socket. I dutifully widened the split center prong but nothing changed.

Another commonly reported problem was the failure of the on/off switch, which was said to go bad often in CG5s. Cleaning or bypassing the switch was said to sometimes restore function. I took out a jumper cable and easily bypassed the switch, hooked up the power supply, and the mount lived! The handset fired up, ready to do an alignment.

I popped the top off the switch and inspected it.  The contacts were a little dirty; there was the slightest hint of arcing damage by on the business end of the tiny, see-saw like strip of metal in the switch. I scraped it all clean, put it back together and the switch now works.

All thanks go to the Internet, and the people who shared their solution for a specific problem. They saved my mount!