If demand higher performance from the larger formats, we have to stop down a bit further. With this standard reasoning - where the acceptable level of blurring (circle of confusion) varies with the film format - the difference in sharpness between the focal plane and the outer edges of the circle of confusion becomes greater when using a larger format. The depth of field you get at 50 mm stopped down to aperture 8 is the same as when using a large format normal focal length 150 mm when it has been stopped down to f22 (150/50 = 3, 3 x f8 = 24 = f22). The 150 mm used for large format is three times longer than the 50 mm used on 35 mm cameras. If you do the calculation, you will find that in principle you retain a given depth of field if you increase the aperture by the same factor as you increase the focal length. Therefore the longer focal length has to be stopped down further to keep a satisfactory depth of field. A longer focal length with a given aperture will give a shorter depth of field. We have assumed that the result will be pictures of the same size regardless of what negative format we used.Ī larger negative demands a longer focal length to reproduce a scene with the same perspective. The negative -and hence any blur - is not enlarged as much with large format film. How blurred can the image be away from the plane of focus before it becomes unacceptable? With larger formats we can tolerate a reduced sharpness without getting an blurred final image. Depth of field was discussed in detail in an earlier article, in which it was argued that depth of field is a question of definition. We first determine what depth of field we desire and thus the working aperture. The MTF was measured in the centre of the picture, and the objects photographed are placed in the middle of the negative. The tests we ran to make these comparisons were all done with the object placed in the centre of the picture.
The normal focal length for 35 mm film is 50 mm, for medium format 80 mm, and for 9x12 cm approximately 150 mm. The relationship in size between close and distant objects is the same in reality as it is in the picture. The perspective we acquire when using a normal lens is the same perspective that we see when we look at the object with the naked eye.
The normal focal length corresponds to the diagonal of the negative size. We are going to photograph it using three different formats (24x36 mm, 6圆 cm, and 9x12 cm). Imagine an object that is going to be reproduced with a certain perspective. Let us begin by looking at the optical image projected onto the film in the camera an image whose quality is limited by the lens' quality and optical construction, and by the laws of diffraction. The same perspective regardless of format
However, our test shows that 35 mm can be almost as sharp as large format, if you take the photographs correctly and choose the right film.īy Lars Kjellberg We will analyse what happens to the focus both in a negative and the final print when using 35 mm, medium format, and large format. However, our test shows that 35 mm can be almost as sharp as large format, if you take the photographs correctly and choose the right film.ģ5 mm, medium format, or large format? A large format negative does not have to be enlarged as much as a 35 mm negative, and the results are therefore much sharper. A large format negative does not have to be enlarged as much as a 35 mm negative, and the results are therefore much sharper.
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