A lot of good photographs sit behind glass. Fish in an aquarium tank, a helmet in a museum case, a street seen from a café window, a city from an observation deck. Most of them come back from the camera with a ghost of the photographer’s own jacket across the frame, a green cast, and the autofocus locked on a smudge. None of that is the glass’s fault. It’s how we stand in front of it.
The first thing to understand is where the reflection comes from. Glass reflects whatever is brighter on your side of it. In a dark aquarium hall that’s the screen of the phone next to you, an exit sign, or your own lit face. In a museum it’s the ceiling spots and the window behind you. On an observation deck at night it’s the room lights. The subject behind the glass has to be brighter than the reflection, or the reflection wins.
Get close and get square
The single most useful habit is putting the front of the lens almost against the glass. When the lens is close, there’s no room for light from the side to bounce into it. Keep a few millimetres of gap if the glass vibrates or the museum has rules about touching cases, and never press a lens hood into a display.
Shoot as square to the glass as you can. At an angle, the glass acts more like a mirror and also adds distortion and softness, especially thick aquarium panels, which bend light like a weak lens. Straight on keeps reflections down and the image sharper.
A soft rubber lens hood helps a lot. It folds against the glass and blocks side light completely. If you don’t have one, a hand cupped around the lens, a dark scarf or the sleeve of a dark jacket does the same job. Dark clothing matters more than you’d think. A white shirt is a reflector.
Settings that work behind glass
Turn the flash off. Pointed at glass, it bounces straight back into the lens and flattens everything. Many aquariums ban it anyway because it stresses the animals.
Aquariums and museums are dim, so expect to push ISO higher than you’d like. A modern sensor handles it. A sharp, slightly noisy frame beats a clean blurred one. Open the aperture, but not all the way if you’re shooting through thick glass. A stop down from wide open usually sharpens up an image that the glass has softened. For moving fish, keep the shutter around 1/250 second or faster and use continuous autofocus.
If the autofocus keeps catching scratches or water marks on the glass, switch to a single small focus point placed on the subject, or focus manually. Focusing through a smudge is a losing game, so pick a clean patch of glass to shoot through. Many photographers carry a microfibre cloth for exactly this.
White balance in aquariums drifts toward green or blue from the water and the tank lighting. Shoot raw if you can and correct it later. In a museum, the case lighting is often warm and mixed with cooler room light. Setting white balance from a neutral grey area inside the case gets you close.
When a polariser helps, and when it doesn’t
A circular polarising filter can cut reflections on glass, but it works best at an angle of about 30 degrees to the surface, not straight on. That’s the opposite of the get-close advice. Use it when you can’t get close, for shop windows from the street or a car window, and rotate it while you watch the reflection fade. It costs you a stop or more of light, which hurts in a dark aquarium. In most indoor situations, getting close and blocking light works better than a filter.
Last, be patient with people. The family pressed against the same tank is part of the reflection problem and part of the place. Wait for a gap, shoot a few frames, and let the next person in. The best aquarium pictures usually come in the quiet half hour before closing.