Posts Made By: John MacDonough

Could the Stellafane folks be asking for an eye piece like that so that all entrants have an eye piece that gives a 1mm exit pupil so there is some common ground during judging?

A 5mm or 6mm ortho...
A 5mm or 6mm Plossl...
An old Orion Epic ED-2 5.1mm (blacks out easily, but only $35 if you find one used)
Meade 5.5mm UWA
I'm pretty sure Explore Scientific makes a 5.5mm eye piece, too
Tele Vue 5mm Radian
Tele Vue 5mm Nagler

If you go to Orion's website and look up the Starblast 6i you can read the manual (go to the bottom of the StarBlast page and follow the link to tech support). Near the end of the manual you'll find four finder charts for alignment stars. A few are visible from the southern hemisphere, so you should be able to align the scope. It looks like the database is pretty limited in southern hemisphere objects, but I think you can tell the IntelliScope computer to display current coordinates, so if you have an old-fashioned list with object coordinates you would be all set.

If all you changed on your scope was Bob's Knobs, you're likely not collimated yet. You can't really use a planet to collimate, you must use a point source like a star. To check to see if you're collimated, point your scope at a fairly bright star, use a 15mm-20mm eye piece and defocus the image of the star until it looks like a bull's eye. If the center dot of the bull's eye isn't centered in the rings, you need more work on collimation. If the defocused star shows as a tear-drop shape, or a figure eight, then you need a lot of work on collimation.

You can get pretty good collimation on any clear night by getting the center dot of a defocused star image centered in the bull's eye pattern. However, to get collimation really dialed in, you need a night of very steady air so you can use really high magnification and only a small bit of defocusing to make sure the image is truly concentric.

After you've had a chance to evaluate your scope's collimation, let us know what you see. We might be able to help a bit more.

OK, here's an update photo a few years after my last post:

And of the inside with my new mount:

And after dark...

Thank you, Greg.  I really enjoyed your 8" f/16 build thread on the other site.  I continue to be envious of the machining capabilities you have access to.  I can design most any mechanical part I want, but getting it realized is where I have trouble.

Whew! I spent four years and nine months "getting ready", but I finally upgraded.  I saw an MI-250 for sale and jumped.  I bought it in September 2019, and installed it about a month later in October.  It took me a while to figure out how to adapt my concrete pier to MI-250, figure out contingency plans in case Plan A failed, and get mounting plates cut and drilled.

The MI-250 is a pretty big step up from the G-11 I was using.  I took the mount almost completely apart for cleaning and regreasing.  I did not disturb the mount for the worms: they looked like they were set carefully and precisely to ensure the worms are tangent to the worm wheels and I don't have the instruments necessary to repeat that.  Everything else went well, though.

The MI-250 moves with silky smoothness.  I had to spend much more time precisely balancing everything to get it stable when the clutches are disengaged.  It has much less static friction than my G-11 does.  I even had a ask a friend to make me a counter weight to balance my finder scope.

For visual observing, Gemini II is a pain in the butt.  I took the Gemini I included with the MI-250 and put it on the G-11 I am keeping as my travel mount.  The Gemini II I had on that G-11 is now on my MI-250, permanently mounted in my observatory.  At least I won't have to build pointing models with Gemini II often.

As Greg Schaffer recommended in a previous post, I've got far less than 100 pounds on my mount.  The sixty or so pounds I have (plus equal counter weights) was a strain for my G-11, but my MI-250 doesn't seem to mind at all.  Slew speeds are 65% faster.  Tracking is plenty good enough for visual, of course.  The scope I have in my observatory is no beginner's astrophotography scope (5250mm focal length), so it will be a while before I know if it's a good mount for imaging.  

My only gripe about the MI-250 is the adjustments for altitude and azimuth are poor, making polar alignment frustrating.  Oh, and the bubble level is off...

For visual or photography?

Installation day (odd, the photo is right-way-'round on my computer...):