APS-C, MFT or full frame: crop factor and reach in plane spotting

At the fence you hear the sentence all the time: “With APS-C you get the crop factor, so your 400 turns into a 600.” Half right. The focal length doesn’t change, and yet a smaller camera can give you far more detail on a distant ATR at the runway end than an expensive full-frame body. How that fits together, when APS-C, Micro Four Thirds or full frame in plane spotting come out ahead and how to compare reach properly is what this guide clarifies – with a calculator, tables and clear decision aids.

The short answer

If you often stand far from the runway and like photographing smaller aircraft, a smaller sensor with high pixel density gives you the most reach for the money – APS-C or Micro Four Thirds. If you’re mostly up close, shoot a lot at dusk or want maximum image quality in low light, full frame has the advantage. And whatever the format: a spot a hundred meters closer gets you more than any sensor change.

What crop factor actually is

Every lens throws a round image circle toward the back. A full-frame sensor of 36 × 24 millimeters uses a large rectangle of it. A smaller sensor sits at the same place but captures only the central part. The image you get is therefore a crop – just as if you had cut a full-frame photo down to the middle.

The crop factor describes how much smaller the sensor’s diagonal is than that of full frame. Typical values:

Format	Sensor size (approx.)	Crop factor	Area compared to full frame	Aspect ratio
Full frame (35 mm)	36 × 24 mm	1.0	100%	3:2
APS-C (Nikon, Sony, Fujifilm)	23.5–23.7 × 15.6 mm	approx. 1.5	approx. 43%	3:2
APS-C (Canon)	22.3 × 14.9 mm	approx. 1.6	approx. 38%	3:2
Micro Four Thirds	17.3 × 13 mm	2.0	approx. 26%	4:3
1-inch (bridge and compact cameras)	13.2 × 8.8 mm	approx. 2.7	approx. 13%	3:2

The dimensions are nominal values; individual cameras differ by tenths of a millimeter. What matters is the principle: with the crop factor you work out the full-frame equivalent focal length. A 100–400 mm shows the angle of view of a 150–600 mm on APS-C and of a 200–800 mm on Micro Four Thirds.

The aspect ratio is easily overlooked with aircraft. At 4:3, Micro Four Thirds is slightly “taller” than the 3:2 of the other formats. With an elongated side profile, more sky is left above and below, which you crop off for a classic landscape format anyway. For photos of aircraft taking off in the climb or with scenery around them, 4:3 fits well, though.

Why cropping still brings reach

If a small sensor only crops, you could also just crop on the computer on full frame. True – as long as you have enough pixels. This is exactly the heart of the matter: at the airport you are often “reach-limited.” That means that even at the long end of your lens, the aircraft is smaller than the frame, and you crop afterward anyway.

In this situation only one thing counts: how many pixels land on the aircraft? And that depends not on the megapixel count of the whole camera but on the pixel density – how many pixels sit on one millimeter of sensor. An example with real cameras:

• The Canon EOS R5 has a full-frame sensor with 8192 pixels across 36 mm. That is about 228 pixels per millimeter.
• The Canon EOS R7 has an APS-C sensor with 6960 pixels across 22.3 mm. That is about 312 pixels per millimeter.

If you put the same lens on both cameras, the image of the aircraft on the sensor is exactly the same size – in millimeters. But the R7 puts about 37 percent more pixels across the width on it. The R5 has more megapixels overall, but if you crop it to the R7’s framing, it is left with only about 17 megapixels. The R7 uses its full 32.5 megapixels for the same framing.

It looks quite different if you compare the full-frame camera with a lower-resolution APS-C camera or with very high-resolution full frame. The Sony α7R V, for example, puts 9504 pixels across just under 36 mm, so about 266 pixels per millimeter, and in the APS-C crop it still keeps about 26 megapixels. The lesson: never compare formats across the board, always compare specific sensors.

Calculator: how many pixels land on the aircraft?

Worked example: an ATR 72 at the runway end

An ATR 72-600 taxis 800 meters from the runway, and you have a 400 mm lens. On the sensor it is imaged about 13.6 mm long – the same on every format. How much that is in the photo is shown by the table:

Camera / sensor	Share of image width	Pixels on the aircraft (approx.)
24 MP full frame	38%	2,270
45 MP full frame (EOS R5)	38%	3,100
61 MP full frame (α7R V)	38%	3,620
24 MP APS-C	58%	3,470
32.5 MP APS-C (EOS R7)	61%	4,240
20 MP Micro Four Thirds (OM-1)	79%	4,080

The two smaller sensors with high density come out ahead even though the OM-1 has only about 20 megapixels. An older 24 MP full-frame camera lands far behind. That is exactly why APS-C and Micro Four Thirds are so popular among spotters who shoot a lot of regional traffic or at distant runways.

Where full frame has the advantage

The calculation above holds only as long as you have to crop. As soon as the aircraft fills the frame even on full frame – at an observation deck with a nearby taxiway, under the approach path, with widebody jets – the picture turns around. Then the full-frame camera uses its entire area for the subject, and a larger sensor gathers more light overall at the same exposure.

More light means less noise, more dynamic range, more reserves when lifting the shadows under the wings. With the same framing and the same exposure, an APS-C sensor gets a good one stop less light, a Micro Four Thirds sensor about two. In clear midday light at ISO 200 you hardly see it. In the golden hour and blue hour, in gray rainy weather or on night shots, on the other hand, you do.

Another point: with short focal lengths, a small sensor becomes a disadvantage. A 16 mm wide-angle shows only the angle of view of a 32 mm on Micro Four Thirds. For scenes with terminal, apron and sky you need correspondingly shorter lenses on small sensors – more in the guide to wide-angle and standard lenses.

Aperture, depth of field and exposure

This is where most misunderstandings arise. So, cleanly separated:

• Exposure: An aperture of f/5.6 lets the same amount of light per area onto the sensor, no matter how big it is. Your camera settings – shutter speed, aperture, ISO – therefore stay identical in the same light.
• Depth of field and total light: If you compare equal framings, f/5.6 on a smaller sensor behaves like an f-number larger by the crop factor on full frame. A 100–400 mm at f/5.6 on Micro Four Thirds corresponds in angle of view, depth of field and noise behavior roughly to a 200–800 mm at f/11 on full frame.

Format	400 mm shows the angle of view of	f/5.6 behaves like this for depth of field and noise	Exposure at f/5.6
Full frame	400 mm	f/5.6	same
APS-C (1.5)	600 mm	approx. f/8	same
APS-C Canon (1.6)	640 mm	approx. f/9	same
Micro Four Thirds (2)	800 mm	approx. f/11	same

For spotters, the greater depth of field of small sensors is usually more an advantage than a disadvantage: with aircraft at long distance you want the whole aircraft sharp anyway, and bokeh hardly matters. Only with detail shots or portraits of crews at the fence do you notice the difference.

Lenses: size, weight and compatibility

Because a small sensor needs a smaller image circle, lenses for APS-C and especially for Micro Four Thirds can be built more compactly. With telephoto lenses, though, this advantage is smaller than often assumed: the length of a tele depends heavily on the focal length itself, and the front element diameter on focal length and speed. A Micro Four Thirds zoom up to 400 mm with the angle of view of an 800 mm is still much handier than a true 800 mm on full frame – and that is exactly the appeal.

A few compatibility rules you should know:

• Full-frame lenses on APS-C work without problems within a system. You use the best, central part of the image circle – edge shading and soft corners matter far less.
• APS-C lenses on full frame don’t cover the large sensor. Many mirrorless full-frame cameras then automatically switch to an APS-C crop mode, and the resolution drops accordingly.
• Crop mode on full frame you can also activate manually. It brings no additional detail, but shows you the later framing in the viewfinder and saves storage space on bursts.
• Teleconverters work the same on every format: they extend the focal length by their factor and cost light. How much is covered in the guide to teleconverters.

Which systems offer which telephoto lenses is compared in the article on camera systems from Canon, Nikon, Sony, Fujifilm and OM System. For an overview of the popular superzooms, see the comparison of 150–600 mm lenses.

What a smaller sensor doesn’t solve

More reach through high pixel density sounds like a miracle cure. Three limits remain:

• Heat haze and atmospheric haze. Both arise in the air between you and the aircraft. A small sensor magnifies the frame and with it every bit of air turbulence. What helps is in the guide Avoiding heat haze.
• The resolution of the lens. Densely packed pixels show every weakness of the glass. A cheap telephoto zoom that looks crisp on a 24 MP full-frame camera can look soft at the long end on a 32 MP APS-C camera. Stopping down by one stop often helps.
• Camera shake. Because the framing is tighter, every tremor becomes more visible. You therefore work out the usual rule of thumb for minimum shutter speed with the full-frame equivalent focal length. With jets you are on the safe side with short speeds anyway; with propeller aircraft needing longer speeds it gets tight faster on small sensors.

Which format suits you?

A few examples from practice: at the Munich Airport visitors’ hill (Besucherhügel) or the Zeppelinheim viewing platform in Frankfurt, the runways are far enough away that almost every spotter has to crop – here pixel density pays off. At Maho Beach on Sint Maarten, by contrast, the widebody jet barely fits in the frame; a short zoom is what’s needed there, and the small sensor brings no advantage.

If you’re still right at the beginning, read the beginner gear under €1,000 and the buying guide for the best camera for plane spotting first. If you want to stay compact, bridge cameras and superzooms offer an alternative with an even smaller sensor and an extreme zoom range.

The test with your own photos

Before you change format, look at your images. How heavily do you typically crop? If you often end up keeping only a third of the image width, you are reach-limited – then more pixel density or more focal length brings a real gain. If you keep almost the whole image, a denser sensor is wasted, and full frame pays off more in light and noise. How to crop and straighten cleanly is shown in the guide to cropping aircraft photos. You can work out the right focal length for each distance in the article Which lens for plane spotting?

Conclusion

Crop factor is no magic trick but a crop. Still, it gives spotters real reach, because at the airport you almost always crop – and then pixel density counts, not sensor size. APS-C and Micro Four Thirds thus deliver a lot of detail on distant aircraft with more compact gear. Full frame scores in low light and everywhere the aircraft fills the frame anyway.