Counterweight system for Alt Az when changing eyepieces

[Commanderfish]

I'm about to receive an Alt Az mount (specifically an Ercole Giro mount).  

My eyepieces range from 1050 grams down to 431 grams (they have green letters on the side ;)) - and I have a little 3.5mm for occasional lunar use which is probably about 250g.

I know that changing from the heavy ones to the light ones is going to change the balance on the setup, especially on my 127mm Apo which is 952mm long (FL).  This requires re-balancing by loosening the tube rings or the dovetail and sliding the scope. Doable but annoying, and not without risk for the scope.   I saw Stu's fantastic sliding counterweight system which he built for his big Vixen Apo.  I was thinking about replicating it, but then wondered if there was a simpler way of doing it which could easily be applied to different scopes.

So I thought:  what about small counterweights, either magnetic or velcro?  I could attach a few to the focusser when changing from a big heavy 2 " to a lighter one.  A handful of 100g and 200g weights would solve the problem.  I realise however that my OTA is aluminium - I guess most are these days.  Are there any steel parts a magnet can attach to?  

Assuming not, self adhesive velcro is easily available from DIY stores.  Velcro could be added to the focuser or diagonal, and to each counterweight.

Has anyone tried a system like this, or can anyone forsee problems?

[Moonshane]

Televue sell a brass equaliser which works very well. 

 

Note that the usual problem is when looking at the zenith as the scope (diagonal end) tends to swing forward and the objective swings backward if there's too much weight at the top end. I used to use such measures but now just use eyepieces of a more equal weight. 

[YKSE]

Isn't it so that the moment a heavy granade leaves the focuser, OTA goes head dive? supposing it is well balanced with an heavy eyepiece.

[Commanderfish]

Well there is a top lock on the mount which enables you to lock any movement whilst changing the eyepiece, so that won't be the issue as such.  The issue is me wanting a lazier way of balancing the scope after an eyepiece change.  I'm not likely to change my eyepieces from 100 degree ones with green lettering

Yes you are right that I would be balanced up with the heaviest eyepiece in the scope at the beginning, since that is the lowest mag/widest field.  Hence my thought that adding weights when I change to a lighter eyepiece would be an easy solution to balancing. The weights (magnetic or velcro) could be stored on the mount while using the heavier eyepieces.

[YKSE]

OK, then it'll be a good way to try reducing the weight difference between the heaviest and lightest EPs, a heavier 2" to 1.25" reducer is a good approach, since the lightest ones are likely the 1.25" ones. If you can get the weight difference down to around 500 grams, you should be able to aim at best balance for about mean weight of the extremes, add a small balance weight (100g to 200g?), with small move of the balance weight, it should compensate the heviest and lightest ones.

[Commanderfish]

Yes I think you are spot on in principle.  I only have one eyepiece which I use in 1.25" mode (Nagler type 6 3.5mm); I do have a heavier steel 2"-1.25" adapter to use with it.  The rest are Ethos ranging from 431 grams up to 1050 grams.  Actually they all weigh between 431 grams and 568 grams, apart from that one big one that weighs 1050g. 

My question is this:  how best to attach the weights?  Aluminium is not magnetic.  The OTA and diagonal are alu (and carbon in the diagonal).  Seems unlikely that the focuser is steel.

So that leaves us with velcro weights I guess.  Not as elegant, and means sticking a velcro strip on to the set up... maybe on the underside of the diagonal? Pulling velcro weights off would also exert enough force to mess with the position of the scope, even with the mount locked, I suspect...

[YKSE]

Maybe something like an iron dovetail on the scope for balance weight?

[Commanderfish]

Good idea YKSE - the dovetail probably is iron - trouble is that the dovetail is not a useful place to add weights, as the dovetail is pretty much on the mounting axis; the weights need to be close to the eyepiece end.

[Commanderfish]

Anyone else got any clever ideas? Searching ebay for weights seems to come up with endless weight loss products...

[Stu]

Is this any good Dinesh? If you have a long enough dovetail it may help?

http://www.teleskop-express.de/shop/product_info.php/info/p752_Baader-Balance-Weight-1kg-with-Vixen-Level-Clamb.html

[Paul73]

The Tevue solid brass 2" to 1 1/4" adapter is the one that you want. Seems a bit pricy, but seems to do the job.

or, you could just buy matched weight eyepieces like me. Wish that I had gone for the above adaptor now!

Paul

[John]

I have a similar set up to yours and very similar eyepieces (Ethos, Naglers, Pentax XW's, Nagler zoom). I have a long dovetail bar on my refractors and can slide the scope forward or back a bit quite quickly depending on which eyepieces I'm using.

I did have the Tele Vue Equaliser but found that I didn't use it.

 

[Commanderfish]

16 hours ago, Stu said:

Is this any good Dinesh? If you have a long enough dovetail it may help?

http://www.teleskop-express.de/shop/product_info.php/info/p752_Baader-Balance-Weight-1kg-with-Vixen-Level-Clamb.html

That's genius Stu!  Exactly the sort of thing I need.  I have a long dovetail on the SCT but a short one (21cm) on the ED127.  I was avoiding changing the dovetail on the ED127 since if I go over 26.5cm, it won't fit in the custom aluminium flight case which it came in.  That said, I am getting a scope bag to hold it, so I could fit a longer dovetail.  I was trying to understand the google translation of the above page, I think they are basically saying it will fit on any Vixen dovetail plate without any modifications - is that what you think it says?

Cheers  

[Commanderfish]

I was looking through the dovetails for a longer Vixen plate that would fit my longest scope, which is an Explore Scientific ED127, which is currently on the little 21cm Vixen dovetail that it came with.  It looks like this 32cm Vixen Dovetail would be suitable, not too chunky so the original screws should fit (I hope) and with enough length to slide a weight around probably.  I've never actually bought an after market dovetail, does this look about right?

http://www.teleskop-express.de/shop/product_info.php?products_id=232#ebericht

[Commanderfish]

Hmm if I use this smaller 24.5cm plate I will still be able to fit my ED127 in it's flight case without hacking the perfectly cut foam to pieces.  But it only has holes for the middle screws for the the scope rings, not the additional two pairs of side holes.  It's also 7.4cm shorter so i don't know if the weight will slide enough to compensate for up to a maximum 700g change in eyepieces (though if I don't use my 3.5mm x 272 mag eyepiece, no more than 600g of weight change).  

http://www.teleskop-express.de/shop/product_info.php/info/p4884_Skywatcher-dovetail-rail---Vixen-Style---PS25--24-6-cm-.html

Best go with the 32 cm?

[Stu]

11 hours ago, Commanderfish said:

That's genius Stu!  Exactly the sort of thing I need.  I have a long dovetail on the SCT but a short one (21cm) on the ED127.  I was avoiding changing the dovetail on the ED127 since if I go over 26.5cm, it won't fit in the custom aluminium flight case which it came in.  That said, I am getting a scope bag to hold it, so I could fit a longer dovetail.  I was trying to understand the google translation of the above page, I think they are basically saying it will fit on any Vixen dovetail plate without any modifications - is that what you think it says?

Cheers  

Dinesh, if you click on the Union Jack flag towards the top right you should get an English translation, does that help?

[Commanderfish]

Yes thanks, found that late yesterday!  

I'm fairly confident I've understood it correctly, so I've ordered the sliding 1KG counterweight with Vixen fitting, and a 32cm Vixen dovetail to replace the 21cm one on my ED127!  If the dovetail is still not long enough to create a large enough moment to counterbalance a large eyepiece change, I'll have to order a second weight which will thread on top of the first one.  The highest difference in my eyepieces is 600g, so this should be enough.