Tune Up Your 100ED Focuser

Or
(Make It Stop! Make It Stop!!)

It just dawned on me that good astronomy stories never begin with: "It was a dark and stormy night". That's ok, though, because the night I will refer to was very clear and calm. I had set my steel pier mount in my favorite spot in the back yard and was ready to test my then new 100ED SVP as an instrument of astrophotography. I was thrilled with the prospect of getting a few good shots that night. Everything was set. My 80ED rode piggyback as a guidescope with a ccd camera attached to it, while the 100ED held my Canon Digital Rebel (300d). I don't know what your practice is, but after setting up, I like to take a few steps back and call it good by declaring: "Lookin' good, lookin' good!".

The human eye is much more sensitive to objects that are in motion than objects that are stationary. They teach you that concept in the army to prevent being detected at night, and new amatuer astronomers learn the concept when the notion of "tapping the scope" is the topic of conversation. Those thoughts passed through my head as my eye caught something moving at the back end of the 100ED. It was the draw-tube on my focuser! It's not supposed to move on its own.

OR IS IT?

naaaaaa.

Not being much of a believer in ghosts, I immediately knew that the weight of the camera was slowly pulling the draw-tube down. There really should be more friction on the drawtube than that, but apparently there wasnt on mine. I remembered seeing an online article by a guy who had the same problem and fixed it with a knife sharpening stone. I decided I'd give it a try. It worked.

Why didn't I simply put a link to his website from mine? I mean, I freely admit it wasn't exactly an orginal idea of mine. Well.... you know me, I'm such a ham. I have to record the results myself.

Oh, but yeah, all glory to the other guy's original idea!

Hip hip!! Hoorah!! Hoorah for the other guy!! (anybody have one of those party-favor blower thingies?)

Ok...Now that we've got that out of our system.....let's move on.

If you pull your draw tube out as far as it will go you'll see the cause of the tension (or lack thereof) problem in the focuser. Notice on the flat part of the drawtube that only the outer edges of the flat are shiny? That is because the steel roller that moves the drawtube in and out are only riding on those areas.

Your mission, should you choose to accept it, is to take a knife-sharpening stone and run it back and forth over the flat edge until the whole surface is flat.

How to get the drawtube out of the focuser.

All you need is a small phillips screwdriver to loosen the four screws on the bottom of the focuser. The tube will come right out.

Assemble in reverse order.

Below: Click "Play Movie" to see a few handy tips for honing the drawtube.

 

Warning: Attempt this modification at your own risk. Performing this modification may invalidate your warranty. Andy accepts no responsibility for any damage you may incur during this procedure.

Man, I hate having to give that warning every time I start talking about modifications, but it's only fair to remind you that sometimes things don't work out to satisfaction.

I am reminded of the story of the guy with a severly cut toe who ended up suing his doctor. Doc told him, "Soak your foot in salt water". The dummy proceeds to go play at the beach. After all, the ocean is salt water. His toe got infected, he sued the doctor. Nuff' said.