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Mount load capacity?

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#1 james d colby

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Posted 23 August 2019 - 02:14 PM

I have an EQ3-2 mount and would like to use an 8 inch newtonian on it.  Is there a way to strengthen the mount to enable it to carry say 23 pounds?   Jim in Picton, Ontario



#2 Astrojensen

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Posted 23 August 2019 - 02:28 PM

I'd say 23lbs on an EQ 3-2 is pushing it beyond the comfort limit. An 8" honestly needs something like an EQ-5/Vixen GP at the least.

 

I tried a 6" f/8 newtonian on my own EQ 3-2 and it was very wobbly. Not recommended. A strong tripod could possibly help somewhat, but the main issue is that the mount really is too small and the DEC axis in particular is too weak. 

 

 

Clear skies!
Thomas, Denmark


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#3 OldManSky

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Posted 23 August 2019 - 02:30 PM

Carry?  Sure.  

Use without frustration?  Probably not.

 

The bearings, castings, etc. on that mount aren't beefy enough (and can't be reasonably changed due to size restrictions) to carry that big of a scope and that much of a load without significant wobbling/vibration.  

 

Sorry.  But to carry an 8" Newt, you need a beefier mount.


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#4 fcathell

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Posted 23 August 2019 - 02:35 PM

It usually is not a matter of the mount being unable to handle the weight itself, but the flexure that occurs with the extra weight and the resultant vibration and damping issues.  This will be very much exaggerated with a Newtonian due to the moment arm of the tube, particularly if it is a medium to long F-ratio.  The same consideration holds for long refractors.  I've put a 7 lb refractor on a mount rated for 20+ lbs and it was a total bust due to the length of the tube and any trace of breeze which would cause unacceptable vibration. As stated in one of my posts in another forum, this is main reason I abandoned refractors for planetary viewing and compromised with Maks.

 

Frank

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#5 vtornado

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Posted 23 August 2019 - 02:36 PM

Hello James, and welcome to cloudy nights

 

Usually I am a yes man, glass half full man, but in this case no way.

 

Yesterday I just sold a 200mm f/5 newt.  The reason why I sold it, it was too much telescope to mount.

My OTA weighed 18 lbs with rings and dove tail.  Add a finder and eyepiece and now we are at 19.

It did mount on an Orinon skyview pro mount, and a celestron heavy duty tripod (2 inch legs).

You will also need about 15 - 20 lbs of counterweights.  As you see I know have 60 lbs of telescope to move.

This mount was also the bare minium.  There were shakes in focusing, I'm sure if it was breezy it would not

settle.   The SVP is quite a bit beefier than the EQ3.

 

You will also have to invest in a pair of Wilcox rings, On an EQ mount if you move the scope to  a different

part of the sky the eyepiece will be pointing at a weird angle, so you will have to rotate the tube.  Which means

loosening the rings, and the telescope can slip down and then your balance is all off, and you have to do a rebalance.

That being said there is a way to make a pair of Wilcox rings either from a spare ring, or a 5 gal paint bucket.

 

A 8 inch SCT will probably work on your mount, if you need 8 inches of aperture.  It will be narrow field however.


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#6 F.Meiresonne

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Posted 23 August 2019 - 02:40 PM

I used for years a 6 inch F/5 on that  mount, a good match but at the max. An 8 inch newt even a short F/4 F/4.5 is just too much to view with comfort


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#7 fcathell

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Posted 23 August 2019 - 03:13 PM

By the way, I have an old Orion Astroview mount and I think it is equivalent to an EQ3. I had a C-8 on it for years and it was totally adequate for visual use. If I were going to do imaging I would have probably moved up to a larger mount.

 

Frank


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#8 db2005

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Posted 23 August 2019 - 03:30 PM

I wouldn't put anything much larger than a 130mm f/5 newtonian on an EQ3-2.  Maybe a 6" SCT, but definitely not an 8" SCT.

 

As a useful rule of thumb I prefer to avoid loading mounts to more than 50-70 percent of their rated capacity, as fairly vibration-free views are important to me (and maybe more important to me than to many others, so your mileage may vary). The EQ3-2 is rated at just 5 kg capacity, so putting a 22 lbs scope on it does not seem feasible at all. I would say even the EQ5 would be challenged by a 22 lbs scope, especially a long one. I personally use a C8 and EQ5 together and while stability is acceptable I wouldn't put much more weight on the EQ5. A few times I tried the EQ5 with a 6" f/8 Newtonian, and I found that combination to be (barely) acceptable, challenged primarily due to the scope's length. Personally I find newtonians somewhat awkward to use on a GEM, but that's another thing and of course your mileage may vary.


Edited by db2005, 23 August 2019 - 03:31 PM.

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#9 Riccardo_italy

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Posted 23 August 2019 - 04:45 PM

No you can't.

 

I had an EQ3.2, I made for it a wood tripod, robust, light years better than the standard alluminium tripod.. At most, and with a pier or a wood tripod, the EQ3.2 can reasonably carry a TAL100 (tested) or, probably, a 120/1000 (as the TAL is very heavy for a 4" refractor).

 

Now I have a 8" f6, and a very light one (Orion UK, less than 8kg). The thing is big and heavier than the refractors said before. No way with an EQ3.2 but also no way with an EQ5. The guy who sold me the 8" f6 used an EQ5, and he told me he was selling the scope as it was too big for the mount.

 

With a good tripod, you might marginally carry a MAK150 (and with a lot of frustation, I'm not suggesting it!) or, easier, a C6. The EQ3.2 is ideal with a C5 (I tried it) or a Mak 127. In term of newton, probably - again, with a good tripod - you could marginally arrive at a 6" f4. No more than that.


Edited by Riccardo_italy, 23 August 2019 - 04:48 PM.

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#10 james d colby

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Posted 23 August 2019 - 09:31 PM

I'd like to thank all of you for your wise advice which I shall follow.  What a wonderful community!  Jim



#11 EFT

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Posted 24 August 2019 - 01:00 AM

You can't really change a mount's rated capacity.  You can exceed it and often not do any damage, but the performance will be poor.  In the worst case, overloading a mount can cause damage or even failure.




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