ETX TECHNICAL TIPS Last updated: 12 March 2003

DS-70EC Focus Modification

Sent:	Sunday, March 9, 2003 21:25:49
From:	bcdlr@insightbb.com (Dan Reynolds)
Here's my solution for the focuser slop that I experienced on my DS70EC.
I'm sure this would help with the other DS scopes that use the all
plastic focuser. There are three JPGs that go with this mod, focus1-3,
but they are all basically the same photo just different angles. In the
photos the red arrows point to the pieces of milk jug, the green arrow
points out the "groove" that the rack travels in.







This mod replaces the "Velcro-type" shimming material used by the
factory with pieces of milk jug cut to fit (aka polyethylene). You
probably should remove the focuser from the scope tube and remove the
knob assembly, and focuser tube.  In the focuser itself you will see six
small "ribs" or ridges that the focus tube (the part with the rack on
it) rides on. Cut five pieces of milk jug to fit into the spaces between
these ridges (see photos). I attached the polyethylene with thin double
stick tape. Check your fit by inserting the focus tube. You may have to
remove one or more pieces of the poly if it is too tight but try to keep
the pieces equally centered otherwise whenever you change directions
focusing the tube will "wiggle" in that direction. You could also narrow
the width of the milk jug pieces. Keep in mind though, that the next
step will help make things work better. Put everything back together.
Use spray silicone and treat the focuser tube several times with the
silicone working it back and forth in the focuser. I sprayed it on,
wiped it off lightly and then repeated the process until the focus
operation was smooth as silk.

There is still some hesitation in the movement when you first use the
scope but if frees up pretty quickly and on my scope the FOV wobble is
completely gone. Now, to get my machinist friend to make two large brass
knobs...

Dan Reynolds

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