It’s not the focal length that is changing, it’s the amount of the image that is being discarded by the sensor (see the second diagram earlier). Yes, the reach is similar to that of 1.53x whatever focal length the lens is, but there aren’t all the other benefits that longer lenses have in play (compression, bokeh rendition etc). Your focal length isn’t changing – it is not changing. ![]() Using the screengrabs from the video at the top, this crop in is about this much: Full frame left, cropped sensor right. So we’ve established that the sensor is smaller but the image gets thrown at it exactly the same – this means that if you (with a crop sensor) want to get the entire dog in the frame with the same set-up and composition as me (on a full-frame camera), you need to be further away. This is a consideration, and one you should have in your mind, but for me and the questions I get asked, which are almost all exclusively to do with bokeh and backgrounds, it has another implications. This means that your images will probably be darker on a cropped camera than on a full-frame camera at the same exposure values in the same scene. One is that with lots of the image spilling outside of the sensor, you’re actually wasting some light. There are a number of impacts that this ^ has on you and your photography. In fact, all you end up with is a smaller rectangle picking the middle section and it discards all the extra bits, they’re never read. However, when you pop that lens onto a cropped sensor, the image reaching the sensor is exactly the same size – that doesn’t change. With a full frame lens on a full frame sensor, the image that comes in ends up just about perfectly sized to have as little “chopped” off as possible. The extra curvy bits are discarded, never read. The image does come into the camera as a circle, and the sensor only sees the parts that fall within its 4 straight sides. Lenses have circular openings but sensors are rectangular. Stick with me here, there are exceptions and inventions to help us out but I’ll get to that in a second. Now, where this becomes relevant is when you use full frame lenses on crop sensor cameras, or really just any lens on a cropped sensor camera in the past. Knowing this number is sometimes useful, but usually it’s just a number that exists and there it is. ![]() So this camera has 1.5x as a crop factor. Here’s a rough explanation of this in practice (apologies for my not straight arrows):Īs you can see, 36 divided by 23.6 is 1.53. The difference between the dimensions of each sensor, with full frame being industry standard (the same dimensions as 35mm film, coincidentally), is the “crop factor” – a term you may know well. When we talk about full frame or cropped cameras, we’re actually talking about the sensor. The sensor is the light-sensitive area of the inside of your camera which reads the image coming through from the lens and captures the pixel data there as an image.
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