Load capacity - CG5 GT

[Uranium235]

Hiya,

For a while now ive been tempted to go over to the dark side in terms of owning an APO. But, one thing needs to be cleared up before I can say "go for it" in terms of actually buying it.The plan is to replace the ST80 with an Equinox 80 or ED80, which will probably add another 1.5kg to the load.The CG5 GT is max rated at 35lb (15.8kg) and the overall setup should be about:

150P = 4.9kg

Equinox = 3kg

1000d = 0.45kg

Misc (tube rings, bars + guide cam) = 1kg

Total = 10.57kg (67% of max load)

Thats about bang-on 2/3 of the load capacity. Now ive read some posts that the max for any mount (for good guiding) is 1/2 of total - some others say 2/3. Im not really up for buying a new mount, and Id like the chance to use the newt and equinox together (newt guides, equinox images). I know i could just have the ST80 and the Equinox on the mount no problem, but that seems like a bit of a waste of a perfectly good newt to me.

Is 10.5kg too much for good guiding?

Thanks muchly in advance for any advice.

[GuillermoBarrancos]

I have the exact same mount. It's very heavy and stable.

I don't think it should be a problem. Just make sure you use 2 counter weights (mine came with an extra, second, counterweight) to balance it off.

Also. In utmost case you can put on a crossbar on the mount and have your newt on one side of the crossbar and the Equinox on the other side.

I have seen people using that kind of setup as well, to balance the mount off even more. Like on the picture below.

[Uranium235]

Ahhh thanks! That pic shows me it can be done then.

Im already using the second counterweight since using the piggybacked guidescope, but theyre both right at the top of the bar at the moment, so theres room to move. Im just hoping that at 10.5kg, the guiding will be ok - at least I should get tons of good guide stars from the newt

Ive thought about a side by side setup, maybe thats one for the future though becuase it would add another £130 to the bill (unless i can get one 2nd hand).

[philming]

Another option I've seen used with a C8 on a CG5-GT is the "optical divider". Sorry I'm not native English, so I'm not sure it's the proper term.

And as a matter of fact he has done brilliant pictures with this (did M51 the other night and the result was impressing).

[Uranium235]

I think i know what you mean, that sounds like an off-axis guider. Its a good idea but finding a cheap one would not be easy because I would need either the Orion (which would only work on the refractor) or the TS OAG which would work on both scopes - but that ones a lot more... twice the price in fact

It might be cheaper to just get another dovetail bar so i can mix & match between scopes according to whatever the target is for that session.

[ollypenrice]

I think you should be fine. The mount is within its payload. We often talk of overlaoding the mount in terms of weight but you must also avoid overloading its accuracy by asking it to handle too much focal length. Here short apos are a joy and very 'guidable.' On the other hand the bulky Newt may catch a bit of wind?

You will probably want a reducer/flattener for the 80.

As for OAGs, they are harder work than separate scopes because they won't fill your guide chip with hundreds of candidates! On the other hand there will be no flexure. OAGs come into their own on big, long focal instruments.

Olly

[Uranium235]

Thanks Olly, thats cleared that one up then

I see, so imaging at prime focus with the 80 isnt so affeted by the mount load... cool. So is the skywatcher FF any good? And if i did get one, would it have a filter thread? Ive never used one, so ive no idea how it fits in the optical train (yet).

As far a wind goes, Im pretty fortunate that where i put the scope is sheltered on the E,W and North sides - with a clear view to the south nearly all the way down to the horizon (terraced garden, sloping down).I have it halfway down on the patio, as any closer to the house then I wouldnt be able to see polaris.

On a side note, Im going to buy a masonary drill bit tomorrow to drill 3 shallow holes in the slabs to mark where the mount legs should go - that will save me loads of time with moving the mount around while polar aligning - and will avoid the situation of me accidentally kicking the mount leg and knocking out the alignment...lol... done that a few times!

[ollypenrice]

I'd post a separate question regarding flatteners on the ED80 because there is a shedload of experience out there. Me, I know nothing Mr Fawlty!

Olly

[Uranium235]

okey doke

Will wait until I actually get the scope first tho before looking into field flatteners. Awww... im so looking forward to getting my now sweaty hands on that thing. Hooray! no more collimation!