A smaller sensor sees a narrower slice of the scene through the same lens. The crop factor tells you how much narrower.
Optional. You can skip this lesson and still do everything in Start.
| Sensor | Approx. size | Crop factor |
|---|---|---|
| Medium format | 44 × 33mm | 0.8× |
| Full frame | 36 × 24mm | 1× |
| APS-C | 23.5 × 15.6mm | 1.5× (Canon 1.6×) |
| Micro Four Thirds | 17.3 × 13mm | 2× |
| 1-inch | 13.2 × 8.8mm | 2.7× |
| Phone main camera | about 10 × 7mm | about 3.5× |
Multiply the lens's focal length by the crop factor to find what it frames like on full frame.
The lens itself doesn't change. The smaller sensor just records the middle of the picture the lens makes.
For background blur, multiply the f-number by the crop factor too. An f/2 lens on Micro Four Thirds blurs the background about as much as f/4 on full frame. Brightness doesn't change: f/2 is still f/2 for exposure.
| If you shoot… | A smaller sensor (crop) helps or hurts? |
|---|---|
| Birds, wildlife, sport | Helps. Every lens frames tighter, so you get more reach for less money and weight. |
| Wide landscapes, interiors | Hurts a little. You need a shorter focal length to go as wide, for example 10mm on APS-C to match 15mm on full frame. |
| Portraits with soft backgrounds | Hurts a little. You need a wider aperture to get the same blur. |
| Low light | Hurts a little. A smaller sensor collects less total light, so noise appears at lower ISOs. |
| Travel, hiking, everyday | Often helps. Smaller bodies and lenses mean you actually carry the camera. |
24mm. 12 × 2 = 24. That's about the same view as the main 1x camera on many phones.
Full frame is the size of a frame of 35mm film, the standard for most of the 20th century. Photographers learned focal lengths on it: 24mm meant wide, 50mm meant normal, 85mm meant portrait. Crop factors let everyone keep using that shared language, whatever sensor they own. When a phone maker says "24mm main camera" or a compact says "24–600mm zoom", they're translating to full frame for you.
