Mount Payload Ratings Are Visual-Only: The Derating Table for Anyone Attaching a Camera
A published payload figure is a visual-observing number. For guided imaging, work to about 50% of it; for visual, about 80%. An 80mm refractor imaging rig totals around 7.5 kg once flattener, camera, filter wheel, guide scope and focuser are counted, which needs a mount rated at 15 kg — not the 11 kg mount the tube weight suggests.
Halve it. That is the short version: whatever payload a mount manufacturer publishes, plan a guided imaging rig against roughly 50% of it, and a visual setup against roughly 80%.
This is not pessimism and it is not a safety margin in the engineering sense. The published figure describes the mass the mount can hold up and slew without stalling. Imaging asks a completely different question — whether the mount can track that mass smoothly enough that a star stays inside a few microns on a sensor for five minutes, repeatedly, in a breeze. Those are different problems and they have different answers.
The derater above takes a stated payload and returns both working figures. Below it, a component list so you can total what you are actually going to bolt on, because the tube is usually under half of it.
The two derates and why they exist
The visual derate, around 80%, exists because a mount at its rated limit is slow to settle. Nudge a fully loaded mount at 250x and the image will oscillate for four or five seconds before it steadies. Drop to 80% and that falls to a second or two. Nothing has broken; the experience is simply worse at the limit, and a mount you have to wait on is a mount you use less.
The imaging derate, around 50%, exists because guiding corrections have to actually move the load. A worm and gear carrying its maximum mass has more flexure, more stiction and a larger periodic error amplitude than the same drivetrain carrying half. The guide software commands a 0.3 arcsecond correction; the drivetrain absorbs part of it in backlash and the rest arrives late. The visible symptom is elongated stars in one axis that no amount of guide-parameter tuning fixes.
There is a third reason nobody puts on a spec sheet. Wind. A 200mm Newtonian is a sail with roughly 0.16 square metres of side profile. A light gust puts a torque on the mount that a static payload rating says nothing about, and it is why long refractors and open-tube Newtonians behave worse at a given mass than a compact Schmidt-Cassegrain of the same weight.
Mount Manufacturer-stated payload Working visual (~80%) Working imaging (~50%) Counterweights count? Notes Sky-Watcher AZ-GTi (alt-az) 5.0 kg 4.0 kg 2.5 kg None fitted Alt-az; suitable for short-exposure and EAA work, not long guided subs without an equatorial wedge Sky-Watcher Star Adventurer GTi 5.0 kg 4.0 kg 2.5 kg No Star tracker class; a 72mm refractor plus camera is the honest ceiling Sky-Watcher EQ3-2 5.0 kg 4.0 kg 2.5 kg No Visual mount. Imaging at anything above a small refractor will disappoint Sky-Watcher HEQ5 Pro 11.0 kg 8.8 kg 5.5 kg No The classic entry imaging mount. Comfortable with an 80mm apo rig, stretched by a 6-inch Newtonian Celestron Advanced VX 13.6 kg 10.9 kg 6.8 kg No Fine visually with a C8. Marginal for a C8 imaging rig once a camera and OAG are on iOptron CEM26 12.7 kg 10.2 kg 6.4 kg No Centre-balanced design; lighter head than the rating suggests ZWO AM5 (strain wave) 13 kg without counterweight, 20 kg with 16.0 kg 10.0 kg Optional Strain wave drives change the tradeoffs — no periodic error in the classic sense, but guiding wants short exposures Sky-Watcher EQ6-R Pro 20.0 kg 16.0 kg 10.0 kg No The workhorse. Handles an 8-inch imaging Newtonian or a C9.25 rig properly iOptron GEM45 20.5 kg 16.4 kg 10.3 kg No Similar capability to an EQ6-R at noticeably lower head mass Celestron CGEM II 18.0 kg 14.4 kg 9.0 kg No Capable, heavy head; check the tripod is the version you think it is Celestron CGX 25.0 kg 20.0 kg 12.5 kg No Comfortable with a C11 imaging rig Losmandy G11 27.0 kg 21.6 kg 13.5 kg No Long-standing premium option; the payload figure here is more conservative than most Published payloads change between production runs, so confirm against the current spec sheet — but apply the same two derates whatever the number says, and buy against the imaging column if a camera is anywhere in your plans. Counterweights never count toward payload on any mount. They sit on the opposite side of the RA axis and their entire job is to cancel the load, not add to it. They do add to what the tripod carries and to what you carry to the garden, which is a separate and increasingly relevant problem past about 15 kg of counterweight.
Total your real load before choosing a mount
The tube is the number people quote and it is rarely more than half the rig. Everything above the saddle counts: rings, dovetail, finder, focuser motor, diagonal, camera, filter wheel, guide scope, dew heater, cables, and the mini computer velcroed to the tube ring.
Add them up honestly, then compare against the working column that matches your use.
Component Typical mass Counts toward payload? Note 72mm ED refractor OTA 1.9 kg Yes The lightest genuinely capable imaging tube 80mm ED refractor OTA 3.2 kg Yes Varies 2.8-3.6 kg by model and focuser 100mm ED refractor OTA 4.7 kg Yes Long moment arm — behaves heavier than the figure 6-inch SCT OTA 4.5 kg Yes Compact profile, low wind loading 8-inch SCT OTA 5.7 kg Yes The most common imaging tube that overloads its mount 9.25-inch SCT OTA 9.5 kg Yes Needs an EQ6-R class mount minimum for imaging 11-inch SCT OTA 12.7 kg Yes CGX class or above 150mm f/5 imaging Newtonian OTA 5.5 kg Yes Significant side profile; treat wind as an extra kilo 200mm f/5 imaging Newtonian OTA 8.8 kg Yes Large sail area, long moment arm, needs 20 kg-class mounting Tube rings plus Vixen-style dovetail 0.8-1.2 kg Yes Almost always forgotten in the total Losmandy-style dovetail plate 1.0-1.5 kg Yes Heavier than Vixen but far stiffer; worth the mass 9x50 finder plus bracket 0.35 kg Yes Also shifts balance sideways 50mm guide scope plus rings 0.55 kg Yes The lightest guiding option 60mm guide scope plus rings 0.9 kg Yes Better guide star availability, real mass penalty Off-axis guider plus guide camera 0.35 kg Yes Lighter than a guide scope and immune to differential flexure Cooled CMOS camera, APS-C class 0.7 kg Yes Plus the power brick weight on the cable DSLR or mirrorless body plus adapter 0.7-0.9 kg Yes Hangs at maximum leverage behind the focuser Five-position 2-inch filter wheel 0.6 kg Yes Adds both mass and back-focus complications Field flattener or reducer 0.35 kg Yes Small, but it is at the far end of the lever Electronic focuser motor 0.3 kg Yes Usually mounted asymmetrically — rebalance after fitting Dew heater strap plus controller 0.25 kg Yes Controller can be moved to the tripod to save the mass Control computer plus cabling 0.35 kg Yes Cable drag matters more than cable mass 2-inch dielectric diagonal 0.5 kg Yes Visual only 2-inch wide-field eyepiece, 30mm class 0.9 kg Yes Swapping this mid-session unbalances the mount noticeably Counterweights 2-10 kg each No Cancel the load; they burden the tripod, not the payload rating Tick off every item that will be on the telescope at once, total it, then require a mount whose stated payload is twice that figure for imaging or 1.25 times it for visual. Two worked examples make the point better than argument.
An 80mm ED imaging rig: tube 3.2, rings and dovetail 1.1, flattener 0.35, camera 0.7, filter wheel 0.6, guide scope and camera 0.67, focuser motor 0.3, dew heater 0.25, computer and cables 0.35. Total 7.5 kg. Double it and you need a mount rated 15 kg. An HEQ5 at 11 kg is over its imaging working figure. An EQ6-R at 20 kg is comfortable. That surprises people — an 80mm refractor asking for an EQ6-class mount — but the arithmetic is not negotiable.
A C8 visual setup: tube 5.7, dovetail 1.0, finder 0.35, diagonal 0.5, eyepiece 0.9. Total 8.45 kg against an Advanced VX working visual figure of 10.9 kg. Fine. Now image with the same tube: 5.7 tube, 1.0 dovetail, 0.5 reducer, 0.7 camera, 0.35 OAG, 0.3 focuser, 0.25 dew heater, 0.35 cabling. Total 9.15 kg against a working imaging figure of 6.8 kg. Over by a third, and this is exactly the combination that fills forums with questions about elongated stars.
Moment arm: the variable no payload figure contains
Two 8 kg loads are not equivalent. An 8 kg Schmidt-Cassegrain puts its mass close to the saddle. An 8 kg refractor with a 1,000mm tube and a camera train hanging off the back puts a substantial fraction of that mass half a metre from the axis.
Torque is force times distance, so the long tube loads the drivetrain far harder for the same reading on the scales. It also flexes more, and flexure between the imaging train and the guide scope is the classic cause of stars that are round in the guide log and elongated in the sub.
Practical adjustments: treat a long refractor as if it were 20-25% heavier than it is; use a Losmandy-style plate rather than a Vixen one past about 8 kg, because the wider plate resists twist far better; and move to an off-axis guider rather than a guide scope once the tube is long enough for flexure to matter, which for most people is around the 1,000mm mark.
What overloading looks like at the eyepiece and in the data
It rarely announces itself as a failure. It announces itself as a mount that never quite works.
Visually, the tell is settling time. Focus, take your hand off, and count. Anything past three or four seconds at high magnification means you are near or over the limit — or the tripod legs are not fully extended and locked, which produces the same symptom for free.
In imaging, the tells are more specific and easy to misdiagnose.
- Guide RMS that is acceptable at 2-second exposures and falls apart at 4-second ones — the drivetrain is not responding cleanly to corrections
- One axis consistently worse than the other, usually RA, with a periodic component matching the worm cycle
- Stars elongated in the same direction across the frame, worsening on windy nights
- Guiding that degrades as the target crosses the meridian, where the balance geometry changes
- Corrections that overshoot then correct back — the classic signature of backlash under load
- A mount that guides beautifully with the guide scope removed and badly with it fitted, which is differential flexure rather than payload as such
Before assuming payload, check three cheaper things. Balance in both axes, slightly east-heavy in RA. Tripod legs fully extended, spreader tight, feet on solid ground rather than decking. And polar alignment good enough that declination is not fighting a drift it can never win. Those three fix more guiding complaints than a mount upgrade does.
The tripod usually gives up before the head
Mount heads are advertised; tripods are supplied. A 20 kg-rated head on 1.75-inch steel legs is a genuinely capable setup. The same head on 1.5-inch legs, or on the aluminium tripod that came with a lighter model, is not — and no amount of derating the head fixes a tripod that resonates.
Test it directly. Load the mount, extend the legs to observing height, rap a leg with a knuckle and watch a star at 200x. A well-supported setup rings for under two seconds. A poor one rings for six and will do the same every time a breeze arrives.
Two cheap improvements before spending on legs. Keep the legs as short as the observing position allows, because extension is where almost all the flex lives — a tripod at minimum extension is dramatically stiffer than the same tripod fully out. And put the feet on something solid; vibration suppression pads help on a hard surface, but nothing helps on a wooden deck, which acts as a drumhead and will ruin high-magnification work regardless of what is standing on it.
If you are building toward a permanent setup, a pier is the single largest improvement available for the money. It removes the resonance problem entirely and cuts setup time to nearly nothing, which is the variable that decides how many nights the equipment actually gets used.
Reading a payload spec without being misled
Three questions to ask of any published figure.
Does it include the counterweights? A handful of manufacturers quote a total system mass rather than an instrument payload, which makes the mount look dramatically more capable than it is. If the figure seems generous against the mount's physical size, this is usually why.
Is it a visual or an imaging figure? Most makers state visual and do not say so. A small number publish both, and those figures are worth trusting because the company has already done the derate for you. Where an imaging figure is published and sits near 50% of the visual one, the manufacturer is being straight with you.
What tube was it measured with? A rating established with a compact catadioptric does not transfer to a long refractor of the same mass. Where a maker names the reference instrument, that tells you more than the kilogram figure does.
The general habit this site keeps returning to applies here as much as it does to a laser's wattage or a telescope's magnification. The headline number is measured somewhere convenient to the manufacturer. Restate it at the point where you will actually experience it — in this case, at the sensor, over a five-minute exposure, with the wind up.