How to photograph a star ceiling on a phone

A phone camera decides exposure by averaging the scene. Point it at a dark ceiling with small bright points and the average is nearly black, so the camera pushes the exposure up hard, amplifies the sensor noise along with the image, and guesses badly at the white balance because there is no neutral reference anywhere in frame.

The result is a washed-out, grainy, colour-shifted picture. Everything below is about taking those three decisions away from the camera.

A long exposure is unavoidable in a dark room, and hand-holding a long exposure is what produces most of the blur people blame on the projector. Brace the phone against something solid — a shelf, a door frame, a stack of books — or use a small tripod if you have one.

Then use the timer rather than tapping the shutter. Pressing the screen moves the phone at exactly the moment it matters, and a three-second timer removes that entirely.

Most phone cameras let you tap a point and then drag a slider to adjust brightness. Tap on a bright part of the projection and pull the exposure down until the dark parts of the ceiling look dark on screen. Trust the screen, not your instinct — a photo of a dark room should look like a dark room.

If your phone has a professional or manual mode, set the ISO as low as it will go and let the shutter stay open longer instead. Low ISO and a long exposure on a braced phone is dramatically cleaner than high ISO handheld.

Automatic white balance has nothing neutral to work from in a coloured projection, so it wanders — which is why one photo comes out orange and the next comes out blue. If your camera has a manual white balance, set it and leave it.

If it does not, take the photo and correct it afterwards. Every phone photo editor has a temperature slider, and pulling the warmth down until the whites in the scene look white gets you most of the way back.

A photograph of a ceiling and nothing else has no scale, and it reads as a flat pattern. Include an edge of the room — the top of a wardrobe, a curtain rail, a corner — and the picture suddenly reads as a space.

A person in the frame does it even better, but they have to be genuinely still for the length of the exposure. Somebody lying down looking up works; somebody standing does not.

Your eyes adapt to darkness over about twenty minutes and a camera sensor does not, so a projection always looks better in the room than in any photo of it. That gap never fully closes and it is worth knowing before you spend an evening chasing it.

The realistic goal is a picture that looks like the room felt, not a measurement of it. Getting the exposure down, the ISO low and the white balance fixed will get you there in about five minutes.