Help with understanding mount payload capacity

[Gmx76]

hi, so I have an entry level scope, Starquest 130p on an EQ2,  but want to start an upgrade path in the next couple of months.  I am primarily interested in EEVA (aka EEA) so don't need super long exposure capacity, but do want goto 

For budget reasons I'm looking at either EQ3-2 Pro or Explore Scientific iExos-100. I think the Eq3 imaging payload is around 5kg from what I can read on SGL and the ES mount is 6.8kg. Seemingly more bang for buck.

What I don't get is if/how counterweight are factored into these capacities, so eg on the ES, 2kg counterweight means you only have 4.8kg left.  Is that how it works? Thanks

Edited July 4, 2020 by Gmx76

[Cornelius Varley]

9 minutes ago, Gmx76 said:

What I don't get is if/how counterweight are factored into these capacities, so eg on the ES, 2kg counterweight means you only have 4.8kg left.  Is that how it works? Thanks

The counterweight is considered as part of the mount so is not part of the overall payload. 

[Gmx76]

That's what I read elsewhere but on HarrisonTelescope's site it states for the ES iExos-100:

Mount weight capacity: 6.8kg/15 lbs Photographic; 8.6kg/19 lbs Visual (Equip & Weights)

Suggesting it includes the weights.

[pete_l]

Quote

the Eq3 imaging payload is around 5kg from what I can read on SGL and the ES mount is 6.8kg.

The payload capacity is not a hard and fast quantity: 4.9kg does not equal "perfect" and 5.1kg does not equal "unusable". They are largely estimates made for sales & marketing purposes that represent the absolute maximum weight of your equipment (excluding the counterweights needed to balance it all) that will gave any sort of usable control of movement.

How that relates to a particular mount's ability to keep tracking to the 1 part in a million (roughly: 1 arc-second) needed for imaging, depends on the quality (i.e. cost) of the parts, the goodness of the design and the integrity of the manufacturer.

 

But it gets more complicated! It is harder for a motor to control the movement of a 1kg payload if that is positioned at the end of a pole 1 metre away, than if the same 1kg payload is right up, close, to the motor. The same principle applies to counterweights: if they are close to the mount they aren't as "whippy" as if right at the end of the counterweight bar. One might even discover that the ability of a motor varies whether it is "pushing" a payload upwards, or "pulling" it downwards - on the east or west side of the meridian.

 

While some people will say there are "rules" about de-speccing an advertised load capacity by X percent, that is not a complete guide either. Telescopes come in all sizes: long ones, short ones, thin ones, fat ones. Ones with things sticking out at all angles (which makes balancing them in all 3 axes virtually impossible) and ones that vary considerably with / without dew shields, finders, heavy cameras, filter wheels, extension tubes, dangling cables and all the rest. The weight of the payload is only part of the story. How it is distributed (and how close it all is to the motor) is an important factor too.

Edited July 4, 2020 by pete_l

[Nigeyboy]

I have the EQ3-2, with a SW 150-PL. Its at its limit, and I only plan to use it for planetary AP once I sort out the motors for it. For more 'Deep Sky' AP I intend only to use my DSLR and assorted lenses.

[Gmx76]

OK thanks all