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What mount is this? (and can I tune it?)

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#1 Falcon-

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Posted 11 September 2009 - 02:02 PM

Greetings all! - I am new to the forum, and new enough to all this that perhaps this could go into the beginner's area so I hope I do not step on any forum etiquette first time out with a long post!

I have been doing working at getting into Astrophotography and have started out using what equipment I had available. For me that meant a borrowed Canon Rebel XT with a truly terrible 28-90 F/4-5.6 lens and an equatorial mount that came with our third-hand beat up newtonian. The mount has a clock drive that has allowed me to do some wide-field shots, but even at that I end up tossing about 2/3 of my shots.

Now I *know* a better mount is going to be the #1 thing to improve my shooting but I am hopping that slight improvements can be made to my existing mount as budget is alas lacking at the moment.

I am not sure how to attached more then one image, so I have uploaded images of my mount here:

Posted Image
Posted Image

Can anyone help me identify what it is? Is there any hope I can improve it's tracking?

I already intend to move the camera mount position to be closer to inline with the weight arm as in it's current configuration the mount starts out balanced when flat as pictured, and then progressively gets unbalanced due to the off-axis position of the camera. I have not actually had any successful shooting with the scope shown, I have been using the standard 28mm-90mm camera lens instead. I also had the RA apart and wiped off some of the old glue... er.. grease and applied some marine lube I had on hand, but I did not use a de-greaser or attempt to mess with the gears at all at that time.

With his rig I have managed to take shots like these (large images):
- Orion - First ever successfull stack
- Andromeda
- Milky-way including the North American Nebula and others
- Labeled view of the south sky including Omega and Lagoon nebulas
- Milky-way with city light intrusion

FWIW the first image was stacked with Deep Sky Stacker (can not seem to keep colour in that app...) and the rest are shot and stacked with Nebulosity.

I have made a quick video of a small cropped area of the last sequence I shot to demonstrate the way the tracking seems to slip into and out of accuracy. The sequence was 20 images at 90-seconds per image, the video is a 320x240 crop of the center of each image.

- tracking error demo - 800k .mp4 file

I had some focus issues so the stars are not specs (blame the lens, working on that!) but it is a good example of the tracking issues I have seen. Notice how I will get one or two frames of clarity, then several frames of slip. I assume that the steady slow drift seen throughout is simply a polar alignment issue.

So, any advice on even slight improvements to my existing mount's tracking? If you need more info (other pictures, whatever) just let me know!

- Sean

-- Edited to include a better tracking error demonstration --

#2 TxStars

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Posted 12 September 2009 - 07:43 AM

Looks to be about the same as the Orion EQ-1.
http://www.telescope...roduct_id=09011

A drill and some lapping compound is about all that can help tracking.
http://www.newmantools.com/clover.htm

#3 Falcon-

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Posted 12 September 2009 - 11:14 AM

perhaps I need better images - it may be functionally similar to the EQ-1 but it is physically a bit different - biggest obvious dif being the fact that the RA shaft comes directly out of the latitude pivot rather then being offset like very other EQ i have seen on the 'net. This mount is something like 30 years old...

Lapping compound 'eh? Had not thought of that (or used it before) - would hate to make the existing slop larger, but smoothing out all the internal surfaces would be good if I can do it without removing too much material

#4 TxStars

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Posted 12 September 2009 - 10:59 PM

A lot of the older mounts like the one you have had an eccentric on the worm to allow for some adjustment.

#5 Falcon-

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Posted 12 September 2009 - 11:25 PM

TxStars

thanks for the info - would I be looking for a set screw on the worm gear then? (or set screws perhaps)

I will not be back home till tomorrow so I can not just glance at it right now, but I will look tomorrow night and perhaps snap some closeups of it

#6 TxStars

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Posted 13 September 2009 - 12:13 AM

There would be an eccentric on one or both ends of the worm gear, this has a small set screw holding it.
When you loosen the set screw you can turn the eccentric and change the spacing of the gears.

#7 Falcon-

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Posted 15 September 2009 - 12:29 AM

Looks like no such luck in this case, or at least if there is an adjustment for the worm I am missing it! I took three shots of the RA worm & drive:

- here
- and here
- and also here

I have always found it odd that the drive to scope gear mesh had such tiny teeth... more like groves then gear teeth. That meshing causes the drive to slip if there is any resistance or if the spring has gotten too lose.

#8 jason_milani

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Posted 15 September 2009 - 05:55 AM

Who's that sleeping on the couch?

#9 TxStars

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Posted 15 September 2009 - 10:04 AM

Glad you posted a photo.
Yours is a little different but it looks like you should be able to adjust it some.
Losten the lock nut then turn the adjustment to losten up the rotation of the worm gear.
This can be taken apart for cleaning and re greasing.

Attached Files



#10 TxStars

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Posted 15 September 2009 - 10:15 AM

Losten adjustment 1 and 2 to adjust the distance the worm is from the main gear.
You will have to press on the worm with your hand when you tighten it back up to maintain good contact.
It's a trial and error thing till you get it all working smooth.
Cleaning it out and re-lubing it would be a good starting place.

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#11 Falcon-

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Posted 15 September 2009 - 04:29 PM

Thanks - I guess what I need to do now is first rebuild the camera mount on the end to be more balanced, and then see if I can not do some measuring of the error and start adjusting! If only I had clear skies tonight.....

#12 Falcon-

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Posted 15 September 2009 - 09:51 PM

I have not made any adjustments to the worm gear yet, but I have build a new mount method for the camera. This method puts the weight as close as possible to the center, and puts the center of the lens at the center of the dec shaft axis. Already the balance is WAY better and hand-working the RA controls does seem smoother with this change.

In this image I have a second bracket set up that has another 1/4-20 bolt on it, in this case with a scope mounted. That second bracket can be removed entirely of course and just have the camera mounted. Interestingly when using both brackets the ring clamp for the original 4.5" newtonian will fit between them! So once I get some longer bolts I could mount the camera on the outside, where the galileoscope is currently mounted, and have the original newt in use. Not expecting great things out of such an arrangement mind you, but kinda a fun setup.

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#13 TxStars

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Posted 16 September 2009 - 08:08 AM

When you get it ready make sure your Dec slo-motion is 180deg from where it is now. (would be hard to use where it is and it might be in the camera's field of view)

#14 Falcon-

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Posted 16 September 2009 - 02:38 PM

I tend to just take the slow motion controls off during imaging anyway as they have a bit of permanent flop in one direction and so cause extra error on the ra axis. I had it upside down like that because I found with the old way I mounted things the mount bracket would crash into the the mount if I had it the other way - just forgot to put it back when I put on this iteration.






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