Polarizing filters for plane spotting: when filters really help your aircraft photos

Ask landscape photographers which filter you absolutely need, and you almost always hear: the polarizer. At the airport fence, things look different. Your subjects move fast, you work with long focal lengths and need every stop for short shutter speeds. Even so, there are moments when a polarizing filter in plane spotting saves exactly the picture: deep blue sky with the sun to the side, a cockpit without reflection, a wet runway without glaring spots. This guide shows you what polarizing, neutral density and protective filters do physically, when they help with fuselage, sky and propeller – and when you are better off leaving them in the bag.

The short answer

A polarizer helps you when spotting if the sun is to the side, there is enough light and reflections or a pale sky spoil your picture. It hurts if you need every stop for shutter speed, have the sun directly behind you or shoot into the sun. Neutral density (ND) filters, by contrast, are a tool for deliberately long exposure times, especially with propeller aircraft and helicopters. UV and clear-glass filters are primarily front-element protection on digital cameras.

How a polarizing filter works

Light normally oscillates in all directions perpendicular to its direction of travel. When it is reflected from non-metallic surfaces or scattered in the atmosphere, part of it oscillates preferentially in one direction – it is polarized. A polarizer lets through only light of a certain oscillation direction. If you rotate it to the right position, it blocks a large part of the polarized light.

For you as a spotter, that has three visible consequences:

• The sky becomes darker and richer. Scattered skylight is most strongly polarized at roughly a right angle to the sun. There the filter can deepen the blue considerably and make white clouds stand out more.
• Reflections become weaker. Glare on water, glass, wet asphalt and paint is partly polarized and can be dampened. This is most effective when viewing the surface at an angle, for glass at roughly 56 degrees from the perpendicular (Brewster’s angle).
• Colors look stronger. Because the filter reduces diffuse reflections on surfaces, the inherent color of paint, grass or concrete comes through more.

An important limitation that really matters at the airport: glare on bare metal is largely unpolarized. With unpainted or polished fuselages, engine inlets and chrome-plated parts, the filter does little. On painted surfaces, cockpit windows and cabin windows, by contrast, it has a noticeable effect.

Circular or linear?

In stores you come across two designs. Optically, both produce the same effect. DSLRs, however, direct part of the light via semi-transparent mirrors to the autofocus and exposure metering system. Linearly polarized light can lead to measurement errors there. The circular polarizer (usually labeled CPL or “circular”) has an additional retardation layer behind the polarizing layer that avoids this problem. Mirrorless cameras do not have the limitation – you will almost always buy a circular filter anyway because it is the standard.

When the polarizer helps at the fence

Most spotter photos are taken with the sun behind you: side view, light on the flank, a cleanly lit livery. In exactly this constellation, the polarizer effect on the sky is weak because you are then not shooting at a right angle to the sun. It shows its strengths in other situations.

Side sun and a pale sky

If the sun is to your left or right, you are looking roughly into the part of the sky with the strongest polarization. A hazy-looking, light blue sky then becomes richer, and contrails and clouds stand out more. Especially with photos of aircraft in the climb that you show with plenty of sky around the subject, that can make the difference between a flat and a three-dimensional image. How the sun relates to your viewing direction is best planned beforehand – the logic behind it is explained in the guide Planning with sun position.

Reflections on cockpit windows and fuselage

For close-ups at the parking position, on the observation deck or on an apron tour, cockpit windows often reflect sky and surroundings. With the polarizer, you can weaken such reflections so that more of the cockpit interior becomes visible. Glossy paint surfaces that flash brightly in raking light can also be calmed. At decks such as the observation deck at Hamburg Airport, you are close enough to the aircraft that such details are worth it in the first place.

Wet runway and water surfaces

After a rain shower, the asphalt often reflects glaringly. Sometimes you want this reflection – a jet doubling in the wet runway is a strong subject. Sometimes it is a nuisance because bright spots make the picture busy. With the polarizer, you can decide steplessly how much reflection stays in the picture. You will find more ideas for such days in the article Plane spotting in bad weather.

When you have too much light anyway

On a blazing summer day with bright concrete and white fuselages, the light loss can even be welcome, for example if you deliberately want a longer shutter speed or a wider aperture. Then the polarizer incidentally takes on the job of a weak neutral density filter.

When the polarizer hurts

As appealing as the effect is, the filter brings several drawbacks for the typical spotter picture.

Light loss costs shutter speed

The biggest drawback is the light loss. Depending on the filter and rotation position, you lose roughly one to two stops, under unfavorable circumstances more. For landscape photographers with a tripod, that does not matter. For you, every stop means either a halved shutter speed, a wider aperture or a doubled ISO. With landing jets at a long focal length, under overcast skies or in the evening hours, exactly this reserve can be missing. Which shutter speeds make sense for which subjects is in the guide Camera settings for plane spotting.

Backlight and night

In backlight, every additional glass surface in front of the lens is a risk: bright light sources can reflect back and forth between filter and front element and create ghost images or veiling flare. With night shots with bright position lights, landing lights or apron lighting, this applies even more. On top of that, at night you need every photon anyway. In both situations, you are better off taking off filters of any kind. You will find more in the guides on backlight photography and photographing at night.

Wide angle and uneven sky

With wide-angle shots, for example from the deck across the whole apron, your image captures a large section of sky with differing strengths of polarization. The result can be a sky that is dark blue on one side and pale on the other. With telephoto focal lengths, the problem hardly occurs because the angle of view is small.

Stress patterns in plastic and glass

Through a polarizer, stresses in tempered glass and in some plastic panes become visible as blotchy or rainbow-like patterns. This affects, for example, photos through windows, protective panes on decks or transparent canopies. If you have to shoot through a pane, check beforehand in the viewfinder whether the filter creates patterns. General tips for such situations are in the article Photographing through fences and glass and – for pictures from the cabin – in the guide Photographing from the airplane window.

Neutral density filters: the tool for propellers

A neutral density filter or ND filter reduces the amount of light evenly, without deliberately changing colors or reflections. In spotting it is a niche tool – but in that niche, quite indispensable.

The designations differ by manufacturer. Two notations are common:

Designation	Optical density	Light transmission	Stops
ND2	0.3	50%	1
ND4	0.6	25%	2
ND8	0.9	12.5%	3
ND64	1.8	about 1.6%	6

Why propellers need a neutral density filter

A propeller aircraft with frozen blades looks as if the engine were stopped. For visibly turning propellers, you therefore need comparatively long shutter speeds. The problem: in the sun there is so much light that you would have to stop down very far even at the lowest ISO. By the classic “Sunny 16” rule of thumb, in sunshine at ISO 100 and f/16 you get a shutter speed of about 1/100 second – for even longer times you would have to go to f/22 or beyond.

Stopping down far has two drawbacks: diffraction makes the image softer, and dust on the sensor becomes visible as dark spots in the sky – how to remove it is explained in the guide Cleaning the camera and sensor. An ND filter of one to three stops allows you the same long shutter speed at a medium aperture, where your lens works sharpest. Which times work for which propeller type is explained in the guide Photographing propellers. You only get the motion itself sharp with clean panning technique.

The same applies to helicopters, whose rotor blades also look frozen at too short a shutter speed, and to video: if you shoot spotting videos with your camera, you usually want a shutter speed that matches the frame rate and need a neutral density filter for that in the sun as well.

Variable ND filters

Variable neutral density filters consist of two polarizing filters one behind the other, one of which is rotated. That is practical because one filter covers a whole range. The price is possible image quality: two glass elements and the combination of two polarizers can lead to loss of sharpness, color casts and, at very strong settings, uneven darkening. Cheap neutral density filters in particular also tend toward color shifts – these can be corrected via white balance, but cost you time in post-processing.

UV and protective filters: glass as insurance

Originally, UV filters were meant to reduce the blue cast and haze on film. Digital sensors are far less sensitive to UV light, so this effect hardly matters in practice. What remains is the function as protective glass for the front element.

At the fence, this argument is not entirely without merit: wind, dust, sand, splashes from a rain shower or careless contact with the chain-link fence can hurt the front element. A good clear-glass filter is easier to clean and cheaper to replace than a front element. Against that stands that every additional pane can create reflections in backlight and at night – much stronger with cheap, uncoated filters than with high-quality ones. A lens hood, by the way, often protects the front element mechanically just as well and improves contrast at the same time.

Buying and using filters: what to watch for

• Check the thread diameter. Telephoto zooms often have large front diameters. If the value is not on the lens, you will find it in the data sheet. With step-down rings, you can use a large filter on smaller lenses; the reverse usually does not work because of vignetting.
• Coating matters. Multi-coated filters reflect significantly less light than simple glass. Especially with polarizing and protective filters, that is the most important quality difference.
• Slim frame for wide angle. On short focal lengths, a thick filter frame can shade the image corners. For telephoto focal lengths, that is not critical.
• Drop-in filters for super telephotos. Some fast super-telephoto lenses have a filter drawer in the rear section because a front filter would be huge. For these there are special, smaller polarizer inserts from the lens manufacturer.
• Buying used is worthwhile. Filters hardly wear out as long as the glass is scratch-free. What to look for when buying used is in the article Buying a used camera and lenses.

And in use:

• Check the effect in the viewfinder. A mirrorless viewfinder shows you the effect including exposure directly; with an optical viewfinder you also see it well.
• Do not overdo it. A sky that looks almost blue-black quickly looks artificial. Often a partial effect is enough.
• Editing can do a lot, but not everything. Darkening the sky and raising saturation is no problem in photo editing. A reflection that covers the cockpit, by contrast, you cannot remove afterward – only the filter can do that.

The filter in everyday spotting

In practice, many spotters carry a polarizer for their most-used telephoto zoom in the bag and screw it on only selectively. An ND filter is added when propeller aircraft, helicopters or airshows are on the plan – at airshows with many propeller aircraft it is especially useful. For the standard picture – side view of a landing jet with the sun behind you – the lens usually stays filterless so that shutter speed and contrast stay at their maximum.

Which focal length you need at all and how big your filter ends up as a result is in the guide Lens and focal length for plane spotting. And when the air shimmers over the asphalt on bright summer days, no filter in the world helps: against heat shimmer, only a different time of day or a shorter distance helps. For soft, warm light without filter tricks, take a look at the golden hour.

Conclusion

Filters are not mandatory accessories at the airport but specialty tools. The polarizer pays off with the sun to the side, good light and distracting reflections. But it costs you shutter speed and has hardly any effect on the sky with the sun behind you. The neutral density filter is the tool for turning propellers and rotors in sunshine. Protective filters are a trade-off between front-element protection and possible reflections. If you use your filters selectively and take them off when in doubt, you get more out of them than someone who leaves them on the lens permanently.