EP weight limit

[nicnac]

After reading thru the threads today i noticed a comment on EPs stating that a particular brand of EP was too heavy to be used on a dob, now i was contemplating matching the skywatcher Nirvana range with the 250PX truss but now im considering the afore mentioned issue. The Nirvs come in at 1000g top end, is that going to be too much?

What do you guys think on this??

[brianb]

You should be able to balance the tube somehow, or fit an effective friction brake.

But 2lbs for an eyepiece is ridiculous .... does it come with its own wheeled trunk for transportation?

[Macavity]

I think the key is indeed BALANCE. You can buy nifty little weights (tho' usually rather expensive!). My experience, but obvious really: If the Eyepiece is on the top of the tube, add weights at the opposite end, preferably *under* the tube. Overall, think "see-saw" (with fat and thin persons?) and you can usually achieve near perfect balance.

The main hassle arises if your eyepices are of different weight...

[John]

I've been using the Nirvana 28mm and Nagler 31mm (both 1kg eyepieces) in my 12" Meade Lightbridge and I have needed to add weight to the bottom of the tube to keep things in balance - the altitude brake fitted to the scope is pretty puny !. I think the 250PX Flextube is natually better balanced than the Meade is but, as Brian says, you will need some counterweighting to avoid "nose droop".

I tried a Skywatcher Aero ED 30mm a while back and, while it's not as well corrected as the Nirvana / Naglers it's a nice 70 degree FoV eyepiece for it's cost and much much lighter.

John

[dark knight]

The dob can have counter weights added to the bottom of the tube, Steve (Albedo0.39) replaced one of the feet at the bottom of my wifes dob tube (Liightbridge) with a counter weight and held it in place with a correctly threaded bolt. It still leaves enough clearance for the tube to swing in alt without fouling the dob mount. To say it is brilliant would be an understatement, she no longer uses the supplied friction brake when using heavy eye pieces. When reverting back to lighter eyepieces she can either use the friction brake or remove the counter weight, easy peasy and a very simple solution.

[John]

This is my counterweight system:

[Astro_Baby]

Thats really neat - what weight are the indivual weights on that ?

Someone on here did their Dob balancing with a lenhth of chain. A lot of these super wide EPs are pretty heavy cos they have so much glass in them.

[John]

It's an old Meade system that was intended for SCT's. The weights are 1, 2 and 3lbs respectively (only 2 shown in the pic) so that plus the adjustable positioning makes it a versatile solution. I'm not sure now that I've got it in the optimum position though ATM - more research leads me to think the weighting ideally should be positioned on the part of the tube opposite the focusser. I've got to see if the system will fit there without hitting the rocker box.

John

[dark knight]

John, to be honest due to the nature in which the rocker box works, it is not necessary (well I can't see an advantage) to put the weights on the eye piece side of the tube, your system works and looks good to boot.

[Rusty Strings]

I use a large permanent magnet from a large loud speaker as a moveable counterweight, only works on steel tubes though

John

[acey]

When I needed to counterweight an 80mm finder on my dob I used flexible exercise weights from a sports shop, which I wrapped round the bottom end of the tube.

[John]

....But 2lbs for an eyepiece is ridiculous .... does it come with its own wheeled trunk for transportation?

I agree that it does seem extreme but it seems to be the going rate for well corrected 30mm-ish 80+ degree AFoV eyepieces. The Meade 5000 UWA 30mm weighs even more than these - almost another 1lb more

I think it's not just the number of lens elements in them, but the size of those chunks of glass - the Nagler 31 has at least two elements around 75mm in diameter - which explains it's girth as well as it's weight.

John

[Chris H]

Have a look how this guy has balanced his Orion XT10i, it is a bit DIY but it looks good and I think it would work well even with very heavy eyepieces like the Nagler 31 or UWAN 28.

Counter Balance Weights for Orion XT10 Telescope