My Telescope Page

As a kid, I had a cheap refractor that I spent more time disassembling and tinkering with than looking through. Consequently the image quality was not the best. In 2003 my wife bought me a Celestron Nextrar 114GT for Christmas which opened the door for me to get back into astronomy after a 30 year hiatus. There was a lot to learn as I scoured the web for all I could find about beginning astronomy. I found lots of useful information including what I could do to improve upon the scope that I had.

The first thing I realized was that the 8 AA batteries would never last very long, especially in cold weather. I paid a visit to the local battery outlet and picked up a 5 Amp Hr gel cell like is used in home security systems. All that was needed was a small camera bag and a bolt hook from the local hardware store and I had a long-duration power supply that doubled as a weight for my tripod.

The second thing I realized was that LCD displays don't like cold weather. The display kept going out or otherwise becoming unreadable. After some reading on the web I discovered that installing a simple heater should do the trick since Celestron has not taken care of the problem.

I disassembled the controller and tapped into the 12V supply from inside. Many others have done the very same thing except that I decided to run resistors on both the top and bottom of the display for more even heating. I used four 33 ohm resistors which use a total of 125mW. This has proven to be sufficient down to about freezing, the point at which I find something else to occupy my time.

I used a conductive epoxy to pot the lead wire and resitors to the display thus ensuring the best heat transfer.

I can turn the heater on and off via this slide switch. If I were to do it all over again, I think I'd choose a different switch and/or location since I tend to knock it to the off position as I pull the controller out of its holder during use.

I was not impressed with the supplied acessory tray so I built my own. I used 1/2" Bakelite and attached with 1/4"-20 thumb screws from beneath threaded through the existing holes in the tripod spreader. With the new tray in place the tripod is a lot more stable and does not fold up when I pick it up.

For $11 I picked up this compass for the nights when I cannot see the north star. It has a built-in LED illuminator and can be adjusted for the difference between geographic and magnetic north depending on your longitude.

To get proper alignment with this scope it is best to set the tripod level in addition to setting the scope level. For this purpose I use a $4 level that I cut short for convenient use.

To illuminate the tray without destroying my dark adaptation I installed some LED's into the cone that houses the coupling screw. In this picture you can see that I used an RCA jack to supply power from my battery.

There was plenty of room inside to install the wiring and resistors for 12V operation.

But after using this a few times I realized that I could use some more light, especially if there was nearby light which caused glare. A visit to the local auto parts store yeilded a ready-made 12V ring light of three LED's.

Of course this was too bright in some cases so I built a control panel for my power input and outputs. I added a potentiostat so I could vary the brightness of the LED's from off to full on. From left to right I have a 2 amp fuse, power in, power to my controller/drive motors, power to my LED's , woops!, and potentiostat for varying the brightness of the LED's.

I wanted a locking connector for all my power needs so I ended up using BNC connectors which are normally used for video cables and other low voltage signals. They are actually quite easy to use for power and work like a charm.

In operation, I was not very impressed with the image quality that I was getting out of this scope. What I later found out was that I was seeing coma, blur that leads from points of light, caused by improper alignment of the mirrors. After quite an education from multiple sources and several attempts at allignment (collimation) I decided to build a laser collimator.

I built it using some aluminum stock and a cheap laser pointer. The laser is held in place and adjusted by three socket head cap screws. The forth screw turns the laser on.

The collimator is held in position by the two eyepiece screws

Inside the sight window you can see that the laser passes through hole in the target as it should. Here's a good source for instructions on laser collimation and one for the 114GT in particular. I found it best to remove the built-in barlow before trying the laser method as it spreads out the beam too much. You just have to remove the eyepiece holder then unscrew the retaining ring underneath.

After a little while in front of a milling machine, I had myself a camera bracket. It has a series of 1/4" clearance holes in the top for various cameras and/or lenses, and mounts to the tube clamshell via the single bolt. I drilled and counterbored the bracket to accept the factory-supplied bolt. I simply had to cut the shank back to allow for the extra thickness of the bracket.

This mount holds the camera off center to allow for unobstructed use of the red dot finder. The picture above shows the mounting of a Nikkor 500mm f8 mirror lens with a Nikon F3 and MD-4 motor drive combination. This particular lens comes with a tripod mount so I can attach it via the lens rather than the camera body. I also have a Nikon D1 digital camera which is about the same size and weight as the F3. The next project is a counterweight to offset the camera/lens as the drive clutch begins to slip at about 60 degrees inclination.

Hopefully, pictures will be coming real soon.

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