Purpose

Planetary imaging

Planetary imaging is the one branch of astrophotography where a modest mount is enough and a bright sky barely matters. Everything depends instead on aperture, focal length, optical quality and the atmosphere — and on the technique of recording thousands of frames and keeping only the sharpest.

What you are trying to do: Capture high-resolution video of the Moon and planets and stack the sharpest frames.

What matters, and why

Aperture: Sets the resolution ceiling. The Dawes limit is roughly 116 divided by the aperture in millimetres — about 0.91 arcseconds for 127 mm, 0.57 for 203 mm, 0.42 for 279 mm. On the rare nights when the atmosphere cooperates, this is what separates a good image from a spectacular one.
Long native focal length: Planetary imaging wants an effective focal ratio around f/5 times the camera's pixel size in microns. Starting from 2 000 mm rather than 800 mm means far less amplification, which means fewer optical surfaces and an easier time finding focus.
Optical quality and contrast: Planetary detail lives in mid-frequency contrast, which is exactly what a large central obstruction reduces. This is why a good Maksutov can look better on Jupiter than a larger telescope with a 45 percent obstruction.
Collimation: Nothing degrades high-magnification planetary detail faster than slightly misaligned optics. On any reflector or Cassegrain this needs checking regularly, and the tolerance is tighter than for visual observing.
Thermal management: A tube warmer than the air produces convection currents inside it that destroy fine detail. Large closed tubes can take an hour or more. This is the most commonly ignored variable in planetary imaging.
Tracking: The mount does not need to guide to sub-arcsecond accuracy — it needs to keep the planet on a small sensor for a two-minute capture. Almost any tracking mount manages this; an undriven Dobsonian base does not.

The technique shapes the hardware requirements

Planetary imaging is not long-exposure photography. You record a video of a few thousand frames, software grades every frame for sharpness, and the best few percent are aligned and stacked. The atmosphere is turbulent but not uniformly so — over two minutes, some frames catch moments of steadiness, and those are the ones you keep.

Three consequences follow, and they are why planetary imaging feels so different from deep-sky work:

The mount barely matters. It must hold the planet on the sensor. Periodic error gets removed by frame-by-frame alignment.
Light pollution barely matters. These targets are orders of magnitude brighter than the sky.
Seeing matters enormously. It is the variable you cannot buy your way past.

Sampling: how much amplification you need

Planetary cameras have small pixels, and you need an effective focal ratio high enough that the optical resolution is spread across enough of them. The usual working rule:

target f/ratio ≈ 5 × pixel size in µm

A camera with 2.9 µm pixels wants roughly f/15. From an f/10 Schmidt-Cassegrain that is a 1.5× Barlow. From an f/4 Newtonian it is nearly 4×, which is why fast Newtonians are awkward planetary instruments despite having plenty of aperture.

Over-sampling is the more common error. It produces a dimmer image, a lower frame rate, more noise, and no additional detail — the resolution was never there to record.

Thermal management, which nobody enjoys

Air inside a tube that is warmer than the outside air rises in visible plumes. Through the eyepiece this looks like the planet is boiling. On a capture it destroys everything below a few arcseconds.

The remedy is time. A 127 mm Maksutov wants 45 to 90 minutes; a 200 mm Schmidt-Cassegrain about an hour; a large Newtonian benefits from a fan behind the primary. Take the telescope outside when you get home, not when you start.

Collimation at planetary tolerances

Visual collimation that looks fine at 100× can be visibly off at the 300× to 500× effective magnifications that planetary capture reaches. The reliable test is a defocused star at high power: the rings should be perfectly concentric, and you adjust until they are.

On a Schmidt-Cassegrain this means the three secondary screws and a fair amount of patience. On a Newtonian it means secondary alignment first, then primary. Neither is difficult; both are the difference between a soft image and a sharp one.

What a good night actually looks like

Most nights, seeing limits you to around 1.5 to 3 arcseconds, and a 130 mm telescope extracts most of what is available. A handful of nights a year the atmosphere settles to under an arcsecond, and on those nights a 200 mm or 280 mm telescope produces images that were research-grade a generation ago.

Buying a large telescope for planets is a bet on those nights. It is a reasonable bet — but it is worth knowing that is what you are buying.

Which optical designs suit this

Suitable

Schmidt-CassegrainsA long focal length folded into a short tube. The most common serious all-rounder, and the default choice for planetary imaging at scale.
Maksutov-CassegrainsSmall, sealed, high-contrast compound telescopes built around a thick meniscus corrector. Superb on the Moon, planets and double stars; slow and narrow-field for everything else.
Newtonian reflectorsThe cheapest way to buy aperture, in exchange for bulk and routine collimation.
Apochromatic refractorsThree or more elements bringing red, green and blue to a common focus. Sharp, contrasty, and equally at home visually or on a camera.
Ritchey-ChretiensTwo hyperbolic mirrors, no coma, long focal length. The classic small-galaxy instrument — and the least forgiving of a mediocre mount.

Poorly suited

RASA astrographsAn extremely fast Schmidt camera with the sensor at prime focus. There is no eyepiece and there never will be.
Petzval refractorsRefractors with the field flattener built into the optical design: focus, attach a camera, and the stars are round to the corners.
Achromatic refractorsClassic two-element lens telescopes: cheap, sealed, maintenance-free, and visibly false-colour on bright targets.

Telescopes we recommend for this

Schmidt-Cassegrain

Celestron NexStar 8SE

Aperture: 203.2 mm (8")
Focal length: 2032 mm (80")
Focal ratio: f/10

The most capable complete package here for planets and small deep-sky objects, on a mount that is at its honest limit carrying it.

7.5 / 10 for this purpose

Why: 203 mm and 2 032 mm native focal length on a mount that tracks well enough for video capture, in one box.

Schmidt-CassegrainOTA only

Celestron EdgeHD 11 (OTA)

Aperture: 279.4 mm (11")
Focal length: 2800 mm (110.2")
Focal ratio: f/10

A superb long-focal-length instrument that will expose every weakness in your mount, your seeing and your guiding before it shows you what it can do.

7.7 / 10 for this purpose

Why: More aperture and more native focal length than anything else here, for anyone with a mount to carry it.

Maksutov-CassegrainOTA only

Sky-Watcher Skymax 127 (OTA)

Aperture: 127 mm (5")
Focal length: 1500 mm (59.1")
Focal ratio: f/11.8

The best lunar and planetary view available from a telescope this small, bought at the cost of a very narrow field and a long cooldown.

6.7 / 10 for this purpose

Why: The best planetary contrast per kilogram — small, sealed, high-contrast and easy to set out early to cool.

Dobsonian

Sky-Watcher Classic 200P Dobsonian

Aperture: 203 mm (8")
Focal length: 1200 mm (47.2")
Focal ratio: f/5.9

More light grasp per unit of money than anything else on this site, on the simplest mount ever devised, with no imaging future whatsoever.

5.9 / 10 for this purpose

Why: Excellent aperture and low obstruction, but only with an equatorial platform underneath it.

What else you will need

A high-frame-rate planetary camera: The core technique is recording thousands of frames in a short window and stacking the sharpest few percent. A small fast camera is far more important here than a large cooled one.
A Barlow or telecentric amplifier: To reach an effective focal ratio around five times the pixel size in microns. A 2.9 µm pixel camera wants roughly f/15.
An atmospheric dispersion corrector: Genuinely important for targets low in the sky, where the atmosphere spreads the image into a small spectrum.
A collimation tool: A Cheshire, a laser, or a defocused star and patience. Non-negotiable on any reflector.
Dew heaters and a cooling fan: The corrector plate of a Cassegrain dews early, and a fan shortens cooldown considerably.

Common misconceptions

Planetary imaging needs a very expensive mount.

It needs a mount that tracks well enough to hold the planet on a small sensor for a couple of minutes. Periodic error that would ruin a deep-sky exposure is invisible in a video capture that gets aligned frame by frame.

A larger telescope always gives better planetary images.

Only when seeing allows. A 280 mm telescope in 3-arcsecond seeing resolves no more than a 130 mm one, and its longer cooldown and greater sensitivity to tube currents can make it perform worse on a given night.

Light pollution ruins planetary imaging.

The Moon and planets are bright enough that sky brightness is essentially irrelevant. This is the one purpose that works well from a city centre balcony.

Mistakes we see most often

Setting up ten minutes before capturing and imaging through a tube full of convection currents.
Over-sampling with too much Barlow amplification, producing a dim, soft, noisy result.
Ignoring collimation and concluding the telescope is soft.
Imaging a planet at low altitude without an atmospheric dispersion corrector.
Capturing for too long on Jupiter, where rotation blurs detail beyond a few minutes.

Every telescope, scored for planetary imaging

Ranked by the same scoring engine used across the site. This is a listing, not a recommendation — the hand-picked choices are above.