Photographing the Moon and Planets: Why Video Beats a Photograph

Point a 150mm telescope at Jupiter, take a photograph, and you get a small cream-coloured disc with maybe a hint of a belt. Then you see what someone else got with the same telescope and it has the Great Red Spot, four distinct bands, and structure at the poles.

The difference is not the telescope, the camera, or twenty years of experience. It is that they took a video and you took a photograph.

The atmosphere is the whole problem

At high magnification you are not photographing a planet. You are photographing a planet through roughly a hundred kilometres of moving air.

That air is not uniform. It has cells of slightly different temperature and therefore slightly different refractive index, and they drift and churn on a timescale of tens of milliseconds. Each cell bends light passing through it by a small angle. The image of Jupiter arriving at your sensor is being continuously smeared, wobbled and re-shaped by all of them at once.

Take a one-second exposure and you have averaged over maybe fifty different states of the atmosphere. The result is the blur of all of them — soft, and reliably so, no matter how good the optics.

But the atmosphere is not equally bad at every instant. Every so often, for a fraction of a second, the air along your line of sight settles and the image snaps into focus. Anyone who has spent an evening at the eyepiece has seen it: mush, mush, mush, and then for half a second the planet is there, sharp and detailed, and then it is gone.

Those moments are what you want. You cannot predict them, so you record continuously and find them afterwards.

Lucky imaging

Record a video — several thousand frames at a few milliseconds each. Grade every frame for sharpness. Keep the best few per cent. Align and stack those.

That is the entire technique, and it is why planetary imaging looks nothing like deep-sky imaging despite both involving stacking.

The proportions are unfamiliar if you have come from deep sky. There, you might reject 10% of 300 frames. Here you routinely keep 5% of 4,000 and throw away the rest without a moment’s thought. Those 200 frames were taken during genuinely still air; the other 3,800 were taken through soup. Averaging them in would drag the result back toward the mush.

The counter-intuitive part: keeping fewer, better frames beats keeping more, worse ones — up to a point. Too few and noise takes over, because you have not averaged enough. The usual sweet spot for a decent night is somewhere between 5% and 25%, and the right figure depends on how variable the seeing was. On a night of steady air, keep more. On a turbulent night, be ruthless.

What you need

Less than you would think.

A telescope, ideally with some focal length. Planets are small. 1000mm is workable, 2000mm is comfortable. A Barlow lens multiplies what you have, and for planetary work this is one of the few places where cheap magnification genuinely helps.

A camera that shoots fast video. A dedicated planetary camera is ideal — small sensor, high frame rate, uncompressed output. But a phone held to the eyepiece has produced perfectly good lunar work, and any mirrorless camera shooting 4K video will do for the Moon.

No tracking, strictly speaking. For the Moon at short focal length you can let it drift through the frame. For Jupiter at 2500mm you want a tracking mount, or you will spend the session re-centring. It does not need to be a good tracking mount — errors that would ruin a 300-second deep-sky sub are irrelevant across 5 milliseconds.

No cooling, no darks, no flats. The target is bright. Thermal noise never gets a chance to matter.

This is the cheapest serious astrophotography there is. It is also the only kind that works from a city centre, because a planet is bright enough that light pollution is simply not a factor.

Recording, practically

Format. SER if your capture software offers it, uncompressed AVI otherwise. Not MP4 — the compression is designed to throw away exactly the fine detail you came for, and it does so before you get a chance to grade anything.

Exposure. Short. Milliseconds. Watch the histogram and keep the brightest part of the planet around 70–80% of full scale. Clipping the bright limb loses detail you cannot get back.

Frame rate. As high as the camera and your storage allow. More frames means more chances at a still moment.

Duration. For the Moon, as long as you like. For Jupiter, keep it under about 90 seconds — it rotates fast enough that a longer capture smears surface detail by rotating it during the recording. Saturn tolerates two or three minutes. Mars, about the same as Jupiter.

Focus obsessively. At high magnification, focus is unforgiving and it drifts as the tube cools. Refocus between captures. It is the single biggest determinant of the result and it is free.

Then: grading, stacking, sharpening

Three steps, and all three are where the software earns its place.

Grading means measuring sharpness on every one of those thousands of frames and ranking them. Akastroid does this and shows you the ranking, with a thumbnail of each graded frame — you can see the difference between the best frame and the median one, which is usually startling and is the best available argument for why the technique works.

Stacking aligns the kept frames — planets drift and wobble between frames, so alignment is per-frame — and averages them. Averaging 200 frames cuts noise by roughly a factor of fourteen, which is what makes the next step survivable.

Sharpening is where planetary images are actually made. Wavelet sharpening amplifies detail at chosen spatial scales, and on a stack of 200 good frames you can push it far harder than any single frame would tolerate. This step is genuinely interactive and worth learning by feel: too little and you have wasted the stack, too much and you get bright rings around every edge.

Start with the Moon

If this is new, do not start with Jupiter. (The other daytime option is the Sun, which uses the same technique and has safety rules you cannot skip.)

The Moon is bright, large, forgiving, and spectacular at any focal length. A 60-second video of the terminator — the line between lit and unlit, where the shadows are longest — will give you a result on your first attempt that looks like the pictures that got you interested in the first place.

Jupiter is small, dim by comparison, demands accurate focus and rewards good seeing specifically. It is the natural second target, not the first.

What this does not do

Multi-video derotation — recording several videos over an hour and de-rotating them onto a common surface to beat the 90-second limit — is a real technique and Akastroid does not do it. If you get deep enough into planetary work to need it, WinJUPOS is the tool and it is free.

Nor will any of this rescue a video shot out of focus. Grading finds the best frames you took. It cannot find frames you did not take.

The short version

• Seeing, not optics, limits planetary detail. Video beats a photograph because it samples the atmosphere thousands of times.
• Keep the best 5–25% of frames. Throwing away 95% is normal and correct.
• SER or uncompressed AVI. Never MP4.
• Under 90 seconds for Jupiter; it rotates.
• Focus, refocus, and refocus again.
• Start with the Moon. It works the first time.