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Old 17-01-2021, 05:15 PM
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mura_gadi (Steve)
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Balancing a Sw 8" dob with goto

Hello All,

In a classic case of doing before thinking, I have been using a set of magnets in an old shirt pocket to balance my Dob. While I have used this method for many hours in the past 18months, I find myself wanting to use the actual goto function and regret magnetizing my scope tube. The compass ideally would go straight on the tube at TDC, which I can't do till I have demagnetized the tube. That should be easy enough...

Before I leap off on a tangent again to find I have missed the obvious, I thought I would ask the community with years and years of experience.
With the goto the tension nut is covered, I'm reluctant to use the scope outside for extended periods due to dew etc with the cover removed for adjustments.

Some of my thoughts (as stolen from websites and books) are:
a) Velcro Strip and heavy/variable weights in the pocket(with velcro) as before as I like the idea of being able to move the weight further from center for adjustments. But even with a 1"+ strip I'm not sure how much weight I can hold with velcro alone at near vertical.

b) There are 3x3mm(i think about 3mm) un-used threaded holes in the base of the scope. Attach a bracket using the used 3mm threads and have a wooden base with a few hooks on it that I can add extra weight to if needed. Not sure how much weight I could addon as the thread depth is about 7mm

c) same as B but use a length of chain and rest it on the ground, adding more loops to the hooks if I need more weight at the back. Again not sure how much weight I can place on three 3mm threads/bolts though...


So, any thoughts and suggestions of those who have been there and done that would be awesome.

Thanks
Steve
Ps. I may add as much as 3kilo's at the focuser, so, I may need to add a lot more at the mirror cell base for balance.

Last edited by mura_gadi; 17-01-2021 at 05:27 PM. Reason: added Ps.
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Old 18-01-2021, 07:24 AM
Startrek (Martin)
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You don’t have to balance a Skywatcher goto dob
Just set the tube roughly level or to “0” marker on inclinometer scale on the inside support
Make sure the scope is horizontal and pointing roughly to North or South ( I use north and doesn’t have to be really accurate )
Make sure all the “settings” in the Synscan are correct ( including choosing AZ Alt mode , not EQ mode )
And start a 2 star alignment , 1st Star you will have to use handcontroller to centre Star in eye piece ( I use an Orion 20mm 70deg illuminated reticle eye piece , nice wide field and plenty of eye relief ) Second alignment Star should end up very close or spot on centre. Once done your aligned and ready to navigate across the night sky
It’s that easy !
Good luck !
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Old 18-01-2021, 07:25 AM
Startrek (Martin)
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Sorry missed one important item
Base of dob should be nice and level on all sides NSEW !!!
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Old 18-01-2021, 08:02 AM
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gaseous (Patrick)
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Without wanting to contradict Martin in any way, I've found the SW 8" goto model can require some balancing when using heavier eyepieces/barlows, whereas the larger models with the significantly heavier mirrors are probably less prone to requiring balancing. My old 16" certainly never needed any balancing, but my 8" will become very "top heavy" with a largish eyepiece. I use the velcro strip method running down the back of the tube, with a 1.5kg gym weight also with a velcro strip wrapped around it attached wherever required. It's certainly enough to balance a scope, and there have never been any issues with the weight falling off when the scope gets near vertical - if your velcro is decent you'll need to give it a decent tug to remove the weight. Just remember to remove the weight before dropping the tube struts when you're packing up!
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Old 18-01-2021, 08:18 AM
Startrek (Martin)
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Quote:
Originally Posted by gaseous View Post
Without wanting to contradict Martin in any way, I've found the SW 8" goto model can require some balancing when using heavier eyepieces/barlows, whereas the larger models with the significantly heavier mirrors are probably less prone to requiring balancing. My old 16" certainly never needed any balancing, but my 8" will become very "top heavy" with a largish eyepiece. I use the velcro strip method running down the back of the tube, with a 1.5kg gym weight also with a velcro strip wrapped around it attached wherever required. It's certainly enough to balance a scope, and there have never been any issues with the weight falling off when the scope gets near vertical - if your velcro is decent you'll need to give it a decent tug to remove the weight. Just remember to remove the weight before dropping the tube struts when you're packing up!
No problem Patrick , I have a 12” so this issue doesn’t happen when slewing to targets ( even with my Paracorr type 2 and Ethos 21mm combo )

Sounds like the 8” was never originally designed for heavy eye pieces and Barlow configurations ??

Cheers
Martin
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