Makers quote payload for observing, and photography asks for a considerably wider margin. A tracking error invisible at the eyepiece is a smeared star on a sensor, and the published figure usually excludes the counterweights.
This is where a specification that reads like a hard limit turns out to have been measured against a softer requirement.
What the number is measured against
A mount holding a tube steadily enough for someone to look through it. The eye tolerates a surprising amount of slow movement and averages out small tremors, so a mount loaded to its rating is perfectly usable visually.
Why a sensor is less forgiving
A sensor integrates. Movement that the eye smooths over accumulates into an elongated star, and the longer the exposure the more of it accumulates. A mount at the edge of its capacity flexes, and flex appears as tracking error that guiding corrects in the wrong direction.
What the figure usually excludes
The counterweights, which are part of the load on the bearings, and often the camera and accessories. Read what the maker says is included before doing any arithmetic with it.
What to do instead
Add up everything that will sit on the mount — tube, rings, bar, finder, guide scope, camera, focuser motor — and compare that against roughly half the visual rating. If the answer is close, the money is better spent on the mount than on the tube.
If this page and the manufacturer’s own documentation disagree, follow the documentation. Every aperture, focal length, payload rating, field, eye relief, transmission figure and thread size on this page comes from the maker’s own published figures, with the unit as printed and the source named. None of it is measured here, and no figure is converted into another convention, because a converted number is a different number. And for any payload figure: makers quote it for observing, and photography asks for a considerably wider margin. A tracking error invisible at the eyepiece is a smeared star on a sensor, and the rating usually excludes the counterweights. This page reports the maker’s figure with the use it was quoted for, and derives no photographic capacity from it.
The questions that keep arriving
Is there a rule for how much margin?
The habit among imagers is to use roughly half the visual rating, and it is a habit rather than a published figure. This site reports the maker’s number with the use it was quoted for and derives nothing from it.
Does the camera weigh much compared with the tube?
Often less than expected, and it matters more than its weight suggests, because it hangs at the back and changes the balance. Rebalancing after adding a camera is part of fitting one.
Last reviewed 17 September 2026