What is the crop factor
Now there are many SLR cameras. The most popular of them are amateur and semi-professional cameras with a “crop matrix”. But what is a “crop”? What does “cropping factor” mean?
In this article I will try to lift the veil of mystery.
Historically, the film frame has a size of 24 × 36 mm. In digital photography, such a matrix is called “full-size” or FF (Full Frame). But in the production of plates of this size there are various problems, a lot of defects, for example, which leads to the high cost of such a matrix.
Marketers came up with the following move: cut the blank for the matrix into smaller sizes. This leads to a significant reduction in the price of the final matrix: the workpiece of the same dimensions can be cut into more photo matrices, and the effect of marriage is less significant.
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Different companies have different matrixes differently. Canon began to do less than the matrix by 1.6 times, and Nikon by 1.5 times, Sony, also reduced the "crop matrix" by 1.5 times.
Since the cropping matrix is smaller, only part of the light passing through the lens hits it. This is due to the emergence of the term - the crop factor.
When shooting, it creates the feeling that a camera with a crop matrix brings closer than a full-frame one. In fact, the camera itself cuts a rectangle 1.6 times smaller from a full-size frame and saves it.
Having photographed on the FF machine and cutting a rectangle 1.6 times smaller on a computer from a photo in the center, you will get exactly the same frame as you would get on the crop matrix.
It is also erroneously considered that the cropping matrix increases because in order for the FF device to get into the frame as much space, you need a lens with a focal length 1.6 times larger than on a crop. For example, about the same space would fit in a 50mm lens on a crope that would fit in a lens with a focal length of 80mm on FF. But this is due to the “cutting out” of a smaller area of the image circle than that of the full-frame matrix, and not the magnification of the picture, since the focal length is a physical characteristic of the lens (objective), and the size of the matrix does not affect it.
It is this imaginary increase in focal length when shooting to crop and is the "effective focal length". And to get it you need to multiply the focal length of the lens on the crop factor, which is equal to the ratio of the crop matrix and full-length.
DOF - Depth of Sharply Pictured Space - this is what is sharply depicted in the photo.
Again, DOF - does not depend on the matrix. It directly depends on the distance to the object, and back to the open aperture and focal length of the lens. That is, the closer the object is to be photographed, the greater the focal length, and the larger the aperture is, the less will be the area of sharpness in your image.
And it only depends on the size of the matrix how much this area will hit you in the frame.
As you can see, from the same distance, at the same focal length, with the same aperture, I got the same field of sharpness as on the crop matrix, as on the full-frame one. The only difference is how much of the unsharp line gets into the frame.
But again, due to the fact that a much smaller area of the image circle fits into the crop matrix (see Fig. 1), then in order to photograph the face portrait of a person, you will have to move further than with a full-frame camera. And the farther the object, the greater the field of sharpness, the greater the depth of field, and therefore it seems that the crop matrix blurs the background worse.
In this regard, there is the term "effective aperture" in relation to crop cameras. The essence of this term is that if you shoot with the FF camera, then you will have the following parameters: focal length 85mm, aperture 2.8, distance to the object 1m.
You already have to take a 50mm lens on a cropping camera in order to fit as much space into a frame from 1 meter, and since the focal length is 1.6 times smaller, in order for the DOF to remain the same, you will have to open the aperture 1.6 times as much, t. e. up to 1.8.
Crop largely justify its translation from English - cut off. Due to the smaller matrix, the camera captures only less space on the image, and the optical characteristics are not affected by the size of the sensor in any way. Its size affects only the human feeling, because will have to further move away and lose in the degree of blur.
In this article I will try to lift the veil of mystery.
Historically, the film frame has a size of 24 × 36 mm. In digital photography, such a matrix is called “full-size” or FF (Full Frame). But in the production of plates of this size there are various problems, a lot of defects, for example, which leads to the high cost of such a matrix.
Marketers came up with the following move: cut the blank for the matrix into smaller sizes. This leads to a significant reduction in the price of the final matrix: the workpiece of the same dimensions can be cut into more photo matrices, and the effect of marriage is less significant.
')
Different companies have different matrixes differently. Canon began to do less than the matrix by 1.6 times, and Nikon by 1.5 times, Sony, also reduced the "crop matrix" by 1.5 times.
Effect on shooting
Since the cropping matrix is smaller, only part of the light passing through the lens hits it. This is due to the emergence of the term - the crop factor.
When shooting, it creates the feeling that a camera with a crop matrix brings closer than a full-frame one. In fact, the camera itself cuts a rectangle 1.6 times smaller from a full-size frame and saves it.
Having photographed on the FF machine and cutting a rectangle 1.6 times smaller on a computer from a photo in the center, you will get exactly the same frame as you would get on the crop matrix.
It is also erroneously considered that the cropping matrix increases because in order for the FF device to get into the frame as much space, you need a lens with a focal length 1.6 times larger than on a crop. For example, about the same space would fit in a 50mm lens on a crope that would fit in a lens with a focal length of 80mm on FF. But this is due to the “cutting out” of a smaller area of the image circle than that of the full-frame matrix, and not the magnification of the picture, since the focal length is a physical characteristic of the lens (objective), and the size of the matrix does not affect it.
It is this imaginary increase in focal length when shooting to crop and is the "effective focal length". And to get it you need to multiply the focal length of the lens on the crop factor, which is equal to the ratio of the crop matrix and full-length.
Influence on the DOF
DOF - Depth of Sharply Pictured Space - this is what is sharply depicted in the photo.
Again, DOF - does not depend on the matrix. It directly depends on the distance to the object, and back to the open aperture and focal length of the lens. That is, the closer the object is to be photographed, the greater the focal length, and the larger the aperture is, the less will be the area of sharpness in your image.
And it only depends on the size of the matrix how much this area will hit you in the frame.
As you can see, from the same distance, at the same focal length, with the same aperture, I got the same field of sharpness as on the crop matrix, as on the full-frame one. The only difference is how much of the unsharp line gets into the frame.
But again, due to the fact that a much smaller area of the image circle fits into the crop matrix (see Fig. 1), then in order to photograph the face portrait of a person, you will have to move further than with a full-frame camera. And the farther the object, the greater the field of sharpness, the greater the depth of field, and therefore it seems that the crop matrix blurs the background worse.
In this regard, there is the term "effective aperture" in relation to crop cameras. The essence of this term is that if you shoot with the FF camera, then you will have the following parameters: focal length 85mm, aperture 2.8, distance to the object 1m.
You already have to take a 50mm lens on a cropping camera in order to fit as much space into a frame from 1 meter, and since the focal length is 1.6 times smaller, in order for the DOF to remain the same, you will have to open the aperture 1.6 times as much, t. e. up to 1.8.
Summary
Crop largely justify its translation from English - cut off. Due to the smaller matrix, the camera captures only less space on the image, and the optical characteristics are not affected by the size of the sensor in any way. Its size affects only the human feeling, because will have to further move away and lose in the degree of blur.
Source: https://habr.com/ru/post/111304/
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