Sent: Monday, December 14, 2009 03:04:41
From: Joep (email@example.com)
I have been a long time ETX-70/80/90 user and lurker of your website. I
have never been someone very keen on opening my ETX scopes to do all
kinds of mods and improvements, but now I have done it. So let me please
share this, as so many others have done on your excellent website. It
has always been my opinion, that what partly makes the ETX scopes,
excellent scopes is the fact that they are backed up by top sites such
In the past I have done astro photography attempts with my ETX scopes.
IMO, their fork mounts are not very well suited for this. Until today
the best attempts werer with my ETX-90 OTA on an LDX75 mount, coupled to
a Meade .63 reducer and a Canon 1000d camera.
This all changed this weekend:
As my ETX-70 was kind of redundant with the ETX-80 A while ago I decided
to take it off of it's fork mount and see if I could come with something
to make it work on the LDX75 mount. It lay around for a while in that
state, but this weekend as I was glancing over some other redundant and
semi-broken stuff a picture formed in my mind that included a GSO
crayford focusser, a William Optics 66 ED Petzval mounting bracket and
the WO Petzval read lens doublet. The WO is a Petzval, configured with 2
doublets of which the rear one contains an ED lens.
I took off the back of the ETX and stripped the GSO focusser from all
it's attachment rings. I discover it slides in the back of the ETX as if
it was made for it! It's this one:
As with the WO 66ED Petzval I assembled the petzval rear lens doublet
inside the focuser.
I also tried without the petzval lens though. In any case I needed to
cut off some of the ETX metal tube to reach focus. It was a matter of
trial and error. I have optimized for use with my DSLR camera, to reach
focus with an eye piece I need to use a small extension tube.
Still, this can be a great mod for others even without the petzval
element, with the modofication you end up with a great grab-n-go scope
for a photo tripod or equatioral mount, or for use as a guide scope. All
you need to buy is the $100 GSO crayford focuser. All tools I needed
were a screw driver and something to cut the tube with. Yes, and some
care to remove ETX parts without damaging the scope.
I attached some pics of the modified scope and some short 30 sec
exposures I took last night. The tape is now removed, I put that on to
make it easier to put cutting marks on the ETX metal tube. And I also
cleaned optics after I had final assembly.
PS. Did you notice all magazine adds (in Sky@Night to name one) for the
ETX-70 again, presumably for x-mas?