lamiaceae wrote:
I was just going to say that. Canon makes it's own sensors that are slightly different from the Sony or other brand sensors, Nikon, Pentax, and Sony use. As corrected above
Canon DSLR crop factor 1.6
Nikon, Pentax, Sony DSLR crop factor 1.5
It would be so nice to not have to think about the crop factor business. What is the crop factor for a 4x5" view camera?
I was just going to say that. Canon makes it's ow... (
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4x5 film view camera crop factor is about .29, if my rough math is accurate. Divide the diagonal dimension of a full frame sensor into the diagonal of the larger format... That gives you the crop factor.
A NORMAL lens is based on the diagonal dimension of the film frame, and provides ROUGHLY a 45° angle of view. On a 4x5 it's about 150mm. On Full Frame, it is about 50mm. Those are rounded dimensions... On DX Nikon, and Sony, Pentax, and Fujifilm APS-C, it is about 35mm. On APS-C Canons, it is 28 to 35mm (take your pick, or set a zoom to something in the middle). On Micro 4/3, a normal lens is 25mm.
Lens makers have traditionally rounded their focal lengths to even numbers for clarity. Common full frame prime lenses are 20, 24, 28, 35, 50, 85, 100, 135, 180, 200, 300, 400, 500, 600... in mm.
For MOST sensor or film formats, there are lenses specifically designed to work with that size image. HOWEVER, because there were tens of millions of full frame 35mm film lenses around when digital cameras were developed, and the first sensors were smaller, those "full frame" lenses' MOUNTS were used on cameras with smaller DX and APS-C and APS-H sensors. The image circle projected is larger than the sensor. The smaller sensor "crops" the center out of the projected image.
Lenses designed specifically for a particular format are refracted to project an image circle just wider than the film or sensor. A lens of equivalent coverage for a larger format will be larger and heavier*, and when used on a smaller sensor, won't perform quite as well as a lens of equivalent quality that is designed specifically for the smaller format. (That statement may shock a few people, but if you look at lens test charts on dpreview.com, you can compare MTF performance of the same lens on full frame and APS-C cameras, and see the difference.)
This isn't usually much of an issue when full frame lenses are used on APS-C sensors, but it starts to become an issue when full frame lenses are used on Micro 4/3 sensors. That's one reason MetaBones developed the SpeedBooster... It reduces the size of the projected image circle to fit the smaller sensor better. This improves performance over what it would have been without the SpeedBooster, and concentrates the light over a smaller area, providing an extra stop or more of intensity.
*An 85mm f/1.2 Canon EF L ii weighs 2.2 pounds, but a 42.5mm f/1.2 DG Nocticron weighs 15 ounces. Both produce roughly the same angle of view, which is very useful for portraits. The full frame lenses have to gather 4X the light, to project a 4X larger area image circle for full frame than for the 4/3 sensor. You get more depth of field with the shorter lens — f/1.2 on the shorter one is equivalent to f/2.4 on the longer one.
It is important to note that there are FOUR *common* sensor sizes for interchangeable lens cameras: Full Frame (1x), APS-C Canon (1.6x), APS-C Nikon, Sony, Fujifilm, Pentax... (1.5x), and Micro 4/3 (2x for stills; video varies by camera). There are TWO types of digital cameras with interchangeable lenses — dSLR and mirrorless. The difference is that dSLRs have reflex viewing mirrors and optical viewfinders. Mirrorless cameras use electronic viewfinders and/or LCD or OLED screens to preview the image. dSLRs are available in full frame and APS-C formats. Mirrorless cameras are available in full frame, APS-C (1.5x), Micro 4/3 formats and Nikon's 1 system which uses a smaller CX sensor with a 2.7x crop factor.