Cropped Sensor to Full-Frame


Today’s Question: I’ve been shooting with a Canon cropped frame sensor and decided to move to a Canon mirrorless full-frame sensor. If I shoot an image at 200mm on a full-frame camera and then crop it in Lightroom so it looks the same as if I shot it at 200mm on a cropped frame camera, will I be losing quality? Will it be lesser quality than what I get from the cropped frame camera? I’m trying to decide if I can do that to get the same quality results I’m currently getting or if I need to invest in a lens for the full-frame camera that will give me 320mm.

Tim’s Quick Answer: The key issue to consider here is the resolution of the final image. If the two image sensors are of the same resolution, there will be more pixels available with the cropped sensor since the full-frame image would need to be cropped to achieve the same field of view. That doesn’t automatically translate to image quality, but it could depending on how large the image was going to be printed or otherwise shared.

More Detail: Comparing different sensor sizes in the context of focal length and effective resolution can be a bit of a challenge when the sensors are of a different size. The issue is simpler to understand when we assume the two sensors have the same resolution.

We commonly use the 35mm format as the basis of comparing different sensor sizes. As a result, a full-frame sensor is one that matches the dimensions of a single frame of 35mm film. A sensor smaller than this size is referred to as a “cropped sensor”, with a cropping factor that represents the relationship in size to a full-frame sensor.

A smaller sensor is cropping the image circle relative to a lens that could otherwise be used on a full-frame sensor. For example, if you have a 1.6X cropping factor, a 100mm lens from a full-frame camera will provide the same field of view as a 160mm lens (100mm X 1.6) when used on the cropped sensor.

In both cases the full image sensor is being used to capture the image, but a different portion of the scene is being captured. You would therefore need to crop the image from the full-frame camera to match the field of view from the cropped sensor. If the sensors had the same resolution, that would mean the image from the full-frame camera when cropped to the same field of view as the cropped sensor would have fewer pixels.

Of course, then you have to consider how many pixels are needed. If both images even after cropping provide enough pixels for the intended output, then they will effectively have the same image quality all other things being equal. If the images need to be enlarged to produce a print, the cropped sensor image will provide better output quality because it is closer to the final resolution. The more an image needs to be enlarged, the more the quality will be degraded.

Put simply, if you need to crop after the capture because you didn’t have a long enough lens focal length for the intended framing, it would be advantageous to buy a lens with a longer focal length in order to achieve better image quality. But this depends on both how large you need to print or otherwise share the image, along with how willing you are to spend more money to achieve improved image quality.