Posts Made By: Keith Lawson

I'm a research & development machinist for the Air Force. We make rocket motors, hardware, and support components for scientific research.

I got into telescope making out of necessity. Since I couldn't buy (1976) I figured I could build.

Keith

David,

Nice job! Looks real good I can't wait to hear your report when you take it to a nice dark sky location. I bet it will be flat out awesome 8) You're going to blow some people away with that scope. There is nothing like a wide field view with high contrast and pinpoint stars!

Keith

Verdict. Well... You already know the answer but the differences were not as great as one might think. The cassini division in Saturn's ring was easier to see in the refractor. Both scopes revealed 6 moons. The double stars were just a tad tighter in the refractor but lunar detail was just about the same in both scopes. The C-9 held it's own surprisingly well. It was more sensitive to the seeing conditions but that was to be expected. The seeing was about 5/10. Not a great night but I had fun anyway.

Believe it or not, the SCT will get a more use than the refractor. Ease of use is the main reason. Even though the refractor is easy to setup (for an 8 inch refractor) the SCT is easier (no step ladder needed). Plus the fact that if the night turns out to be crap the time spent setting up won't feel as much a waste of time.

The SCT works well enough to keep me happy on the average nights I get here. The "big gun" refractor will come out on those superb (predicted) nights. I have yet to have one of those nights since I have completed the refractor. When it does I know the refractor will blow me away 8O

Knowing me though, I will get probably get another itch and both will be sold for another project.

If anyone is interested in the details on the observing session let me know.

Keith

Jeff,
Here is my solution to the "CAT" cooling problem. It's a closed loop cooling system. There is a cooling fan in each "nacelle". There is no need for filters beacuse the inside air is re-circulated to keep it at a consistent temperature which eliminates any and all temperature currents. It makes a huge difference in high performance observing.

The scope in the photo is a C-11. I have performed this mod on a C-9.25 and a C-8. In all, I have never had a problem with temperature currents either from the tube, primary or secondary. Other than collimation and a good set of optics, IMO this is the biggest killer of "CAT" performance. I'm about to perform this surgery on a another C-9 that has a great set of optics. If anyone is interested I can post the progress of this "operation" when I start.

Keith

Nice work Steve 8) Can we see a pic of the scope without the shrouds. You know I like to see the details of your work. That mount is something else. Almost too pretty to use

Keith

All,

Uh oh, he went and done it Decided to go with a "air stirring" mod. Much easier to install. How well will it work :S Only time will tell

The fans are installed and the picture also shows the thick paper baffles designed to spin the air within the tube just behind the mirror. The only thing that remains is the electrical port and to finalize the wiring. So far so good. Hope to have the OTA up and running by sundown tomorrow.

My fingers are crossed If all goes as planned the fans should spin the air within the tube just enough to break up the currents from the secondary, the sheath of the primary and equalize the temperature of the air within the tube. If the mod works I will take pictures at the focus to show the difference.

Keith

Motors and mount.

Minimal Invasive. After the scope is put back together these six screws and the small electrical port will be the only give away of the mod. The performance should be "off the hook" for the moon and the planets I hope, I hope, I hope

Keith

All,

Just mounted up the scope. The usual temperature plume was seen in the out of focus star pattern. Turned on the fans and instantly saw the plume start to spin and dissipate. Scope currently cooling from a temperature difference of 15 degrees. Garage 62 degrees/Current nighttime temp 47 degrees. The wind is blowing and the seeing sucks but I don't care. It works

I guess as with all designs we find better and easier ways to get the desired result we want. This was so simple I had it completed in two days. My other designs were not so easy.

Keith

Update to the update:
** Scope is ready for lunar/planetary use after 5 minutes. After 20min the swirling temperature pattern is barely discernible. Not bad for a temperature difference of 15 degrees. No filters needed. No outside air introduced into the OTA (no dust). Whoopee! Now if I could just get my hands on a C-14 (for me) Anyone need a 8.5" refractor?**

Ahhhhh....... there is nothing quite like ATM fever. I've been dealing with that disease for 30 years. It never goes away. The project scope looks real nice. Good luck on the endeavor 8)

Keith