Bill Prewitt's Imaging Page

Yet another curious guy with a Camera



20 inch F5 Dobsonian Telescope with BVC mirror

RIMS system

30 inch project

Fun with EL wire - NEW

Astronomical Images

Digital altazimuth drive

Latest project, a 12.5 BVC scope

Gorilla-proof mirror shipping crate

Amateur Telescope Making

CCD Astronomy

Cleaning a mirror with blue spray

JAVA Fractal Graphics Programming

Cave Images

The Making of a Nerd

Caving in Kuala Lumpur

Contact me


Amateur Telescope Making

For the last six years, I've been working on telescope, mount, and imaging projects almost every free night when it's cloudy. Since I live in Northeast Ohio, that's almost every night, so I've done a lot of building.

Here is my 12 1/2 inch, f5 Dobsonian telescope. It has a rotatable tube so you can reach the eyepiece.

It sits on this Shaw equatorial platform that I built from scrap aluminum, plywood, and an old Xerox machine (Xerox machines are actually telescope drives, put together funny).

The drive mechanism uses a 200 step stepping motor from an old disk drive, driven from a half-stepping controller circuit with a remote speed control for manual guiding. There was some vibration visible at the eyepiece when over about 200X magnification, so I have replaced the stepper with one of the geared DC motors in the Xerox machine (it operated the paper size changer). For speed control, I built a little PWM "lamp dimmer" circuit. This has completely eliminated any vibration visible at the eyepiece.

The original platform design is by Chuck Shaw, and you can find his plans for it on the ATM Page.. Thanks, Chuck.

Link to The ATM page

I made a few modifications. This Gymbal and shaft came from a Xerox machine I took apart with the help of my son, Thomas.

The bearings also came from the Xerox machine. They are mounted on aluminum angle, cut to a compound angle to match the platform tracking duration and our latitude, 40 degrees.

Here you can see both sets of bearings, and one of the 3/8 " aluminum chords, which are secured by triangular 1/2" aluminum braces.

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CCD Astronomy

Since I'm an electrical engineer, I thought it would be a reasonable project to build a CCD camera to interface to my computer.

The CCD Camera Cookbook by Berry, Kanto, and Munger, is a wonderful book. It takes you through building and testing your camera step by step. It includes software to direct your step-by-step checkout of the circuit boards.

Here is my CCD camera and power supply with all of the cables and tubing, but no water pump or computer.

The power supply provides +/- 15 volts DC for the camera, and 0 to 7 volts DC at 6 amps to the water-cooled thermoelectric cooler in the camera head. The stock design had a 5 volt supply for the water pump, but I use a 115 VAC garden fountain pump, so I included a 12 volt DC supply for my equatorial platform instead.

The camera head has a Texas Instruments TC245 CCD chip in it. This chip is designed for color TV, but they make the part available without the red, green, and cyan filter layers, so you can use the extra resolution. When cooled to -30 degrees Centigrade, thermal noise is very low, so you can make up to 1 hour exposures. I added a National LM34CH monolithic temperature sensor and LCD temperature display (battery powered). This close-up shows the head (I like brass), and the temperature readout. A circuit for the LM34CH mod is on The ATM page, but I built mine with isolated battery supplies. The Cookbook Camera Home Page has a wealth of information for builders and users.

Link to Cookbook Camera home page

I've taken some images, and they look pretty good when processed by Berry's Multi245 and Aip245 software.

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Fractal Graphics Programming - including JAVA source code

Back in 1990, I was fascinated by fractal mathematics and chaos. I wrote C routines to try the algorithms that intrigued me. Once I got some of these things to work, I wrote graphics and 24pin printer binary driver routines to make high-resolution plots of the functions. I've been porting some of them to JAVA Applets

You'll need to have a current Java plugin in your browser - available free from Sun at: Sun Microsystems Java download

Fractype applet This applet plots an iterated function set (IFS) fractal of the word you type in the box. It's a generalization of an exercise in Barnsley's book.
Source code for is available under the GNU public license

Mandelbrot Set applet with source code This applet plots the Mandelbrot Set of the complex region you select. Source code for is available under the GNU public license

Julia Set applet with source code This applet plots the Julia Set of the complex number you enter. Source code for is available under the GNU public license

(Not fractal), but I wrote some web calculators that you may find useful

Subdiameter lap simulator applet This applet plots the effect of a given subdiameter lap stroke if executed over all 360 degrees Source code for is available under the GNU public license

Here's a web calculator for the sagitta (center depth) of a spherical mirror.

ATM Sagitta calculator

Here's a web calculator for everything you'd want to know about your eyepieces when used in your telescope.

ATM magnification and field of view calculator

Here's a web calculator for estimating the original gravity of batches of beer when separating first middle and last runnings.

Parti-Gyle estimator

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To Contact me

If you have any questions, flames, or advice, blaze away.... I'm listening. Send email (but not spam) to:

bill dot prewitt {whereupon}

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Last Revised: 3 Jan 2008