Ha Longish Exposures NG3576 & NGC3372

[Star Catcher]

Hi All

I've been having some tracking issues with my G11 mount and following some maintenance with the help of a friend I decided to test it with some longish exposures.

The first image is the nebulae complex including NGC 3576, 3579, 3581, 3582, 3584, 3603, 3856. The image was taken through an RC10 using an STL6303E camera. The image consist of 6 X 60 minute subs through 7nm Ha Filter. On the right you can see why some people call it the statue of liberty nebula.

The second image using the same equipment, is a segment of the Carina nebula. Eta Carinae is just outside of the field on the right hand side of the image. This is a fairly deep image because it consists of a 1 X 150 minute exposure.

Whilst the high cloud and seeing conditions reduced the depth of this exposure, it did not interrupt the guiding and I am now much happier with the tracking performance.

Thanks for looking.

Ted

[alpal]

Nice work Ted,
You've a great polar alignment not to get frame rotation with that length of sub frame.
I hope you'll take some RGB too?

cheers
Allan

[glend]

Impressive Subs Ted. You have to be happy with that tracking. But i have to ask why? The risk you take in putting that much time into a single Sub would not warrant a single Sub of that duration, imho. As a demonstration its a great result.a tribute to your setup for sure.

[Star Catcher]

Thanks Glen. Well because I can :). Sort of like.... why climb a taller mountain? No but seriously I was curious to see what exposure limit is possible from my Sydney suburban observatory location and to test the mount. I do understand the limitations from things like seeing conditions on the resolution and risks from wind & clouds during long exposures. There are I believe however some advantages doing longer subs.
Ted



Thanks Alan. Unfortunately being in the suburbs of Sydney, RGB filters are a problem. Si and O3 are an option in the near future.
Ted

[Placidus]

Bravo and well done.

[strongmanmike]

Sliiiiightly over processed perhaps :question: :) but, still, looks like the mount adjustments/repairs worked a treat Ted, you must be relieved?...150min single exposure??? wow! :thumbsup: LOok forward to seeing your future images :thumbsup:

Mike

[Atmos]

That single 150min exposure looks brilliant! The best I'd ever managed with my EQ6 was 60min and even that was a little bit eggy. Your G11 must be humming along something nicely :thumbsup:

[cometcatcher]

Exquisite detail you have in this object. Which reminds me that I have to revisit it soon.

[Star Catcher]

Thank you Kevin. I have only imaged it once before and this is a much better effort. I have to admit it is one object I keep forgetting about.



Thanks Colin. It is the longest I have ever done. Happy with the mount, now if only it just stays that way :) The G11 can be testy sometimes.





Thank you Mike.

[astronobob]

Awesome Test images Ted, , wow 150 mins - to infinity and beyoooond :D

[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

[Star Catcher]

Thank you Bob



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