Quote:
Originally Posted by astronobob
Awesome Test images Ted, , wow 150 mins - to infinity and beyoooond  |
Thank you Bob
Quote:
Originally Posted by Octane
That's pretty damn amazing to get such good stars after 150 minutes at that focal length!
What did you do to the mount to get it performing that way? I only just pulled mine apart last month for the first time in over 10 years of owning it. I cleaned all the bearings and shafts, regreased it all with lithium grease and put it back together again. I didn't touch the worms or their housing (not confident enough). I'm stoked to get 30 minutes out of my G-11 with round stars; admittedly, I've never tried pushing it any further than that as I try to make use of every clear night I possibly can, either doing narrowband or full colour when the Moon isn't around.
Really interested to know what magic you've wielded to get it to work that well!
H
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Thanks H. No magic here but perhaps a bit of luck. I pretty much did what you did. All the needle bearings had stopped rolling with hardened grease. So they got cleaned up and re-lubed.
I also removed both the RA and Dec worms and worm blocks. Thoroughly cleaned the worm. Plenty of crap in amongst the grease. That grease is really tough to clean but mineral turps did the best job. Then re-lubed both worms.
I then checked the endplay between the bearing blocks. The RA worm assembly is the Losmandy's one piece unit. It had no play what so ever, so I slightly relieved the pressure by introducing just a very tiny hint of play. I then reassembled into position.
The next effort was to ensure optimal meshing with main gear i.e. tangential and loaded with right pressure. Gee it would have been great to have this assembly was spring loaded! Several ways to do this including being able to turn the worm by fingers as a good indicator. I took the lazy suck it and see way. Not sure it has sound logic though
I unclutched the shaft in down position and held the worm block against the main gear with gentle pressure. I then gently rocked the shaft and felt the force on the work block from side to side. I tried to find a center point of that rock i.e. no force felt on the opposite side after shaft is let go from being forced on the other side. I then tried to keep the block in this position whilst I did it up. The DEC assembly has less opportunity for imprecise positioning of the worm, other than you can slightly change meshing pressure and angle.
I then did some unloaded slewing tests. If these sounded OK and no binding occurred, I then loaded up the mount and did slew tests. If all OK I then mounted a camera. I started with taking a couple of unguided exposures around the 4 minute mark. Of course the assumption is that I have close to perfect polar alignment (I'm close).
I checked the consistency of the PE across those exposures. If the PE streaks look fairly continuous i.e. no jumps and of similar length, then good. If not then you can use the adjustment on the Losmandy one piece block to slightly alter meshing characteristic.
Next is to check how well the mount responds to guiding corrections during one period of the worm. This is where things like bias balance in RA has to be investigated to see what inconsistencies can be moderated. We need to see the rate of error and where they occur in the cycle. Various pieces of software can give you this feedback This is also where you detect whether the DEC correction have problems. If inertia is significant you may get motor lags errors. You may have to play with pressures of the DEC worm block against the main gear. Then depending on the results and how fussy you are, you may go back and repeat earlier steps.
Anyhow I have no idea if any of this made a difference or I was just chasing shadows and jagged a good part of the main gear.
I am sure others have a more sane way or achieving the same deal
Ted
LOok forward to seeing your future images 
