Ad Astra Observatory

Hi Ron,

Now that I’m all comfy with how the Moonlite focuser works in my

photography setup, I’m ready to start tuning the drawtube length /
extension so that I can stay low profile and still be able to use
eyepieces, etc.

I have questions.

1) Do you ever make drawtubes with less than 1.5” of travel? My camera
comes to focus with about 1/4” of spare backfocus (”inward” travel), and

if I can figure out how much travel there is between my various
eyepieces, I can probably live with something “really short” in the
drawtube, and just using an extension tube to bring the eyepieces into
focus. I can’t imagine there’s more than 1/2” of focus travel between my
various eyepieces; I’ll have to measure this.

2) can you construct a 2” extension tube of a different length than 1.5”
if I can figure out exactly what length I need?

Here’s my current setup:

I have an Orion 8” f/5 Newt, with a Moonlite CR-1 with hi-res stepper
motor and a “fairly long” (2”? longer?) compression-ring drawtube. Since

it’s an Orion, I have some amount of spacer blocks in the setup, but I
can’t remember exactly how much height that adds. I could easily
re-collimate the scope so that the camera comes to focus at the
racked-in position of the focuser.

Everything works fine, but the long drawtube (racked in for camera, but
long enough to rack all the way out for eyepieces) protrudes into the
light path. Ideally, I’d love a drawtube that was short enough not to

protrude past the tube wall, but I’m writing to see if that’s realistic.
Do you think that 1.5” is the shortest realistic draw tube length, or do
you think that, if the setup was tuned properly, a shorter (<1” travel?)
one is possible?

I have a set of calipers that I can use to measure everything; I’m just

trying to see what my options are. I enjoy the non-marring and solid
grip of the compression ring, but I noticed the setscrew-style drawtubes
on your site and I could easily be convinced to use that drawtube
instead. I might even see if I can run the focuser without the spacer
block; I’m fighting a vignetting problem and want to be able to blame
the MPCC or T-Ring instead of my yards-long drawtube. (:

Please advise.

Best,

Jimbo S. Harris
Newark, CA