[mental4astro (Alexander)]

Hi all,

With my passion for lunar sketching, and so being at the mercy of the prevailing atmospheric conditions as to what magnification I can push things to, focusing can become a very tedious affair. The small knob on the back of an SCT is difficult to get really fine control over. Yes, there are focusing motor drives available, but these will just over complicate the simplicity I am looking for with my time at the scope.

Then while playing with my son's Lego one day, a memory of a long ago read article was sparked on how to achieve a fine motion control on the focuser knob of an SCT - make the knob bigger in diameter.

An off-cut from a hole-saw cut gave me the largest diameter dial I could use with the space afforded to me by the knob and the 2" visual back. It was then just a matter of widening the center bore to allow the plywood dial to fit over the knob. The knob is a shade under 20mm in diameter, the 20mm forstner bit made an oversized bore, so a snug and positive fit was achieved with just a little piece of fine sandpaper between the knob and dial - this also allows me to easily remove the dial should I want to and no damage or residue is done to or left on the original focus knob.

PRESTO! A new fine focus control knob!

The amount of force needed to wind the focuser is now just a baby's breath. It is much easier to turn the knob just because of the effect of the larger diameter dial. I can much more carefully adjust the focus, hasn't altered the way I store my old C8, and I've kept the situation for me really, really simple. All that's left to do is give the new focuser dial a lick of varnish. Couldn't get any easier.

This simple mod does not eliminate mirror shift, nor would it, and that is controlled in another way.

Mental.