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Balance and changing eyepieces


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What is the best way to compensate for the change in balance when changing eyepieces? On a 102mm/F7 weighing 4kg the difference in balance point between a 109g 1.25" eyepice and a 925g 2" eyepiece is quite significant.  To add more complexity I have just aquired a AZ-EQ5 GT and want to dual mount so this also affects the azimuth balance, though this likely has more leeway?

Using a diagonal and heavy 2" eyepiece already creates a torque on the altitude axis as the altitude changes as the cog is off the axis of the ota even if there is a static horizontal balance. 

Should I be trying to balance with the heaviest setup then add weights to compensate when using lighter eyepieces? As this mount has encoders it should be possible to release the clutch to check the balance without losing alignment. 

Am I just overthinking this?

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43 minutes ago, John said:

You could try using one of these with the lighter 1.25 inch eyepieces:

https://www.widescreen-centre.co.uk/tele-vue-bec-0005-2-125-equalizer-hihat-adapter.html

 

 

Only about 340g so that is no where near enough I'm afraid. Just looking at the ADM counterweight kits, maybe if I put an extra rail on the tube rings I could add a weight to that as needed.

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8 hours ago, Toltec said:

I think I've worked it out. Get a long Vixen type dovetail, a dovetail clamp and make up an arm and weight to connect to the clamp. I can then move that to rebalance as needed.

If you make or buy such a device, you can also correct for any radial lack of balance:

 

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On 24/01/2022 at 07:47, Zermelo said:

If you make or buy such a device, you can also correct for any radial lack of balance:

 

I found that thread and video, I had noticed that having a heavy 2" eyepiece on a diagonal meant the cog was no longer co-axial with the OTA and therefore the stable balance becomes with the eyepiece facing down. It means there is a small torque on the alt axis at any other position really. I don't have enough experience to know how important that is though, I'm only visual for now so it is less to do with tracking smoothness and more about what it means for the mount mechanics.

I've ordered a long vixen rail and a clamp from FLO and a set of slotted 100g disc weights from an educational supplier, I can make up an arm and drill/tap as needed.

I may be overthinking this of course!

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On 24/01/2022 at 10:59, M40 said:

FLO do some counterweight kits, maybe one of those may work? https://www.firstlightoptics.com/adm-counterweight-kits.html

 

I found those after asking my original noob question thanks :)
 

I'd like a bit more flexibility in what mass I use and didn't like the idea of a threaded rod stuck out from the telecope ready to catch an unwary knuckle. I have ordered one of these-

https://www.philipharris.co.uk/product/lab-equipment/balances/weights-and-accessories/hanging-slotted-masses-steel-1kg-9-x-100g-masses-and-hanger/b8a73088

plus a vixen rail and clamp. I will hopefully be able to cut down the hanger, put a thread on to the shaft and file two flats about 3mm up from the base to allow weights to be added and removed by simply unscrewing it a few turns. I'll make up something to cover the thread that projects through a suspension arm when there are only a few weights attached or put an internally threaded bar on the inside of the arm to screw the hanger into.

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How about the non-Astro specific solution? I’m using ankle exercise weights for fine balance (about £10 for 2 from Argos or similar). Takes about 10 sec to put on the tube with non scratching Velcro strap, can be slid up and down the tube to suit.

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I use a 6" long bolt of the same thread as a threaded hole on my DSV-2B mount with about a pound of washers I had laying around hanging off the end of it.  It swings up to horizontal when the mount is at zenith to partially counteract the effect of the eyepiece in the diagonal.

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  • 2 weeks later...
 
This is what I eneded up making last Sunday, I can move the balance point by trimming both the position and weight on the balance arm. Note the flats on the thread of the weight holder, this allows the100g discs to be added and removed without having to completely unscrew it. I am using an az-eq5gt in dual mount and while that makes it possible to release the clutch without losing alignment I intend to work out the position and weight needed to balance various combinations of eyepieces.
 
The extra vixen rail is handy for holding the tube while mounting up as well.
 
What do you think?

IMG_20220210_215115_HDR.jpg

IMG_20220210_215154_HDR.jpg

IMG_20220210_215313_HDR.jpg

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I have my counterbalance weight protruding out away from the tube to offset the weight of heavy 2" eyepieces at higher altitudes on my alt-az mount when using my refractors.  It's also mounted about the same distance forward as the eyepiece is backward relative to the altitude axis.

Let us know how your arrangement works out for you.

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