What Is Lens Flare? Ghosting, Veiling and the Sunstar

Point any lens at the sun and it shows you the same thing: coloured rings appear somewhere in the frame, the blacks turn grey, the picture goes flat. This is lens flare, and most photographers’ relationship with it is split down the middle — half avoid it at any cost, half chase it for the cinematic look. Both do it without knowing the one thing that matters: where flare actually comes from.

Two clarifications before we start, because both cause real confusion.

Flare is not made by the scene, it is made inside your lens. That matters practically: a polarising filter cuts specular reflections — the glare on wet leaves, glass, skin — and has no effect at all on lens flare. Screwing one on usually makes flare worse, because it is one more piece of glass. The ND and polarising filter guide covers what a polariser genuinely does.

And “flare” names two different behaviours with two different cures, which is where most of the confusion lives. We will separate them below.

Let’s set the axis too: backlit portraits covers how to manage flare in the field while shooting into the sun, and the sharpest aperture covers what f-number does to sharpness. The question here is different — how does flare actually form, why do some lenses produce so much more of it, and which part of it is genuinely in your hands?

The physics: every glass surface sends some light back

When light passes from glass to air — or air to glass — not all of it gets through. At every boundary where the refractive index changes, a small share is reflected back. On an uncoated glass surface that share is roughly 4%.

Four percent on one surface sounds trivial. But a lens is not one piece of glass. An ordinary zoom holds 15 to 20 optical elements, which means more than 20 glass-air surfaces. Lose 4% at each:

• Uncoated, 20 surfaces: transmitted light is 0.96²⁰ ≈ 44%. More than half the light stays inside the lens.
• Multi-coated, 20 surfaces (about 0.3% per surface): 0.997²⁰ ≈ 94%.

This is where flare begins. That reflected light does not vanish inside the barrel; it strikes another surface, turns forward again, and lands on the sensor somewhere it does not belong. Every flare blob in your picture is light that was torn off some part of the scene and delivered to the wrong address.

Two phenomena, one name

Ghosting

Countable blobs produced by a bright light source reflecting twice. Three features make it easy to identify:

• They take the shape of the aperture. Stop down and the blobs become hexagons, heptagons — whatever your blade count is. Wide open they stay round, because the opening itself is round.
• They line up. Because a double reflection inverts the light through the optical axis, ghosts string out from the light source along a line through the centre of the frame, heading for the opposite side. Sun in the top right, ghosts marching to the bottom left.
• They all move together. Rotate the camera a few degrees and the whole chain shifts as one.

Veiling glare

This is scattered light spreading across the whole frame like a thin fog. There are no blobs; instead:

• Blacks stop being black and sit on a grey floor.
• Colours wash out, saturation drops.
• The picture looks hazy even though focus is perfect — because the problem isn’t sharpness, it’s contrast.

Veiling glare is the sneakier of the two precisely because it doesn’t announce itself. Most people look at a frame like that and conclude the lens is soft. The lens is sharp; its contrast has been stolen. On the histogram the sign is unmistakable: the distribution never reaches the left edge, it stops against a wall well short of zero.

Why do some lenses flare so much more?

Put two lenses on the same scene and they behave completely differently. The reasons aren’t mysterious — all of them are measurable:

• Element count. Zooms carry far more glass than primes. A 24-70mm zoom will almost always flare more than a 35mm prime. That is why your first prime looks unexpectedly clean into the light.
• Coating quality. Modern multi-coatings drop per-surface reflection from 4% to a fraction of a percent. Older lenses — especially pre-1970 — have single coatings or none at all. The “cinematic flare” reputation of vintage glass isn’t romance, it’s a technical shortfall.
• How matte the barrel is. The more matte and ridged the inside of the tube, the more stray light gets absorbed. On cheap lenses this internal finish is the first thing cut.
• How bulbous the front element is. Very wide lenses gather light across an enormous angle with a domed front element, and a hood can only shield so much of it.

The filter problem: the number one cause of flare

This gets its own section because it is the most common mistake.

Every filter you screw onto the front adds two more glass-air surfaces. On a good multi-coated filter the cost is negligible. On the cheap “protective” or UV filter that came bundled with the lens, two problems arrive at once:

1. The coating is weak or absent. Reflection goes back to 4% per surface.
2. A filter is a flat plate. Light reflecting off the sensor hits that flat surface and comes straight back, producing a sharp-edged ghost, symmetric about the centre of the frame. Those ghost lights sitting exactly opposite street lamps and headlights in night shots are almost always the filter’s doing.

The rule is simple: shooting into the light, or at night against bright point sources, take the protective filter off. A filter earns its keep against sand, spray and real physical risk; on an ordinary night walk you pay more than you get. This matters especially in night street photography, where the frame is full of bright point sources by definition.

The five things actually in your hands

Tool	What it does	Its limit
Lens hood	Blocks light from outside the frame	Useless if the sun is INSIDE the frame
Shading by hand	Works at angles the hood can’t reach	Your hand must stay out of frame — check it
Partly hiding the sun	Restores contrast instantly	Dictates your composition
Removing the filter	Closes the ghost path	Leaves the front element unprotected
Cleaning the front element	Reduces veiling glare	Modest effect, but free

The most misunderstood item here is the hood. A hood is not a shield, it is a visor: it only stops light arriving from outside the frame and striking the front element. If the sun is inside the frame, having it fitted changes nothing. At that moment your only real tool is angle — stepping sideways so a branch, a pole or your subject’s head partly hides the sun does more than any accessory.

Dust and fingerprints on the front element, meanwhile, are direct fuel for veiling glare: every speck scatters light. A pass with a microfibre cloth before you turn into the light is the cheapest win in the camera bag.

Aperture, sunstars and the trade

The most sought-after form of flare — the sunstar — is actually a product of diffraction: stop down and a point light source splits into rays as light bends around the blade edges.

• Around f/11-f/16 brings the rays out. Wide open, no star forms.
• Blade count sets ray count: an even number of blades gives the same number of rays (8 blades → 8 rays), an odd number gives double (7 blades → 14 rays).
• Lenses with rounded blades give lovely bokeh but mediocre sunstars. You rarely get both.

The trade deserves to be stated honestly: at f/16 diffraction costs you sharpness. We put numbers on that in the sharpest aperture. If you want the star, you’re paying that price knowingly — usually worth it in a landscape, rarely worth it where fine detail is the point.

When to let flare stay

Flare isn’t always a mistake. It earns its place in three situations:

• Adding warmth. A soft orange veil leaking in from a corner warms up a frame shot in the golden hour — its natural partner.
• Suggesting depth. Showing that something sits between the light source and the lens adds a layer to a flat frame.
• Marking the moment. In a backlit portrait, flare testifies that the moment really did happen facing the sun.

The boundary is this: flare is a gain as long as it doesn’t eat the subject. A ghost blob parked on a face is not atmosphere, it’s an error. In a silhouette flare is a straight enemy — the moment it lowers contrast the subject loses its blackness, and you’re left with neither a silhouette nor a portrait.

What editing can rescue, and what it can’t

The two phenomena part ways here as well:

• Veiling glare is largely recoverable. Pulling the black point down and adding contrast (or “dehaze”) hands back the contrast that was stolen. In the RAW workflow it’s a few seconds’ work. The cost is that noise becomes a little more visible.
• Ghosts are not recoverable. They are real pixel data with no scene underneath them. The only route is cloning or healing by hand, and outside plain sky it usually leaves a trace. This is why the fight against ghosting is won at the moment of capture, not in editing.

Common mistakes

• Treating the hood as a shield. With the sun in the frame it does nothing; the answer is angle.
• Forgetting the cheap filter is still on. It is the number one source of ghosts when shooting into bright lights at night.
• Reading veiling glare as a sharpness problem. The lens is sharp, its contrast was stolen; stopping down won’t help.
• Planning to fix ghosts in editing. There is no scene data underneath them.
• Trusting a polariser. It cuts specular reflection, not lens flare — and adds another layer of glass.
• Turning into the light with a dirty front element. Every speck of dust feeds veiling glare.