There is one not so obvious difference between Nikon cameras, and that is the sensor size. The sensor is the part of the camera that senses incoming light. Some high end cameras have big sensors and low end cameras tend to have small sensors.
There are three main sizes with Nikon cameras with exchangeable lense: FX, DX and CX. The big FX sensors are used in cameras like D3, D4, D700, D800. DX is used in cameras like D3200, D5100, D90, D300. The smallest CX sensors are used in J1 and V1 cameras.
A Nikon lens made for a big sensor works with any smaller Nikon sensor. This means that any Nikon lens fits a CX camera - in theory. (You need an FT-1 adaptor, and autofocus may not work and there may be some other limitations.) A DX camera can take both FX and DX lenses. An FX camera only works well with FX lenses.
The focal length of a lens does not change with the camera. This means that magnification, zoom and angle of view are the same for all lenses with the same focal length on that camera. If you take a 200mm CX lens and a 200mm DX lens and a 200mm FX lens and put them on the same CX camera one after the other, the magnification is identical for all of them.
However, the same 50mm lens magnifies more on a small sensor than on a big one. In the picture below there are three shots of the same object with the same lens and focal length, but three different cameras.
The FX camera (a D800) covers the widest angle. The DX camera (a D5100) covers a smaller area. It has been given a green cast to make it stand out from the two other photos. The CX camera (a J1) covers just a small fraction of the FX area. (The photos have been resized to overlap, so the density of the pixels does not correspond to the size of each photo.)
If I had wanted to cover the same angle of view with each photo, I would have had to choose different focal lengths. If the FX camera uses 200mm, the DX camera would need to be 133mm and the CX camera 74mm to give the same angle of view (or zoom factor or magnification). A table with conversions of some common values can be found here.
Advantages with large sensor cameras:
Advantages with large sensor cameras:
- Less noise, better dynamic range and colour depth. This is basically because the sensor has a bigger area to gather information from. However, note that a new camera with the latest technology and a small sensor can perform better than an old camera with a big sensor in these respects.
- Wider angle of view. To get the same angle as a 14mm lens on an FX camera, you would need a 9mm lens on a DX camera.
- Narrow Depth of Field and more appealing bokeh. This is actually a tricky one. If you look at the three superimposed photos above, you will notice that they have more or less the same amount of bokeh on the background. That is because they were taken with the same focal length and the same aperture. In this case the bokeh is identical, but the image area is different. It is only when you try to cover the same image area with different sensors that the difference in depth of field is apparent. The FX camera has a focal length 200mm. To cover the same area, the DX needs 133mm. With a smaller focal length, the same aperture value (e.g. f/1.4) actually corresponds to a smaller physical aperture hole measured in millimeters. A smaller aperture hole means a sharper picture overall. Therefore, to get the same depth of field at a smaller focal length, the aperture hole needs to get bigger. If an FX camera has focal length 200mm with aperture f/1.4 with a target at five meter, a DX camera will need to be set to 133mm to get the same angle of view. To get the same depth of field, the aperture may need to be set to something as large as f/1.0. As hardly any Nikon lens has an aperture f/1.0, the same depth of field is impossible on the DX camera. Ergo, FX has a narrower depth of field.
- Smaller, lighter and cheaper lenses possible.
- Smaller camera. (This is not always the case, but an FX sensor will not fit into a really small camera.)
- Cheaper than big sensor cameras.
- Wider choice of lenses.
- Less vignetting in some cases. (If you use an FX lens that has visible vignetting on an FX camera, the DX sensor will cut that part out.)
- Bigger magnification. (To get the same zoom as a 200mm lens on a DX camera, you need a 300mm lens on an FX camera.)
3 comments:
I know I wrote the above myself, but that was several months ago, and today I had actually forgotten the explanation about depth-of-field. I'm so grateful to myself that I wrote it down, so I now can read it again and get reminded on how it works. Thank me, very much!
I realize this is an old post, but I want to gently object to this statement: "However, the same 50mm lens magnifies more on a small sensor than on a big one."
If the sensor densities are the same (e.g. each has the same "micron pitch" or "Pixels per inch") then there is no magnification at all the DX and CX images would be exactly the same as corresponding crops of the image from the larger FX format. In other words, it's not the CX or DX'ness of the sensor that matters, but the number of pixels packed onto that sensor. By extension, the depth of field would be the same across all sensors. Depth of field is a function of the Focal length, distance from the subject and aperture - it's not related to the sensor geometry. I understand that what you're getting at is that you must use a wider angle field of view on a crop sensor to get the same image (or stand farther away from the subject). The depth of field changes because of either the change in distance to the subject, or the change in focal length (or both).
Great comments.
Both are the same phenomena, but from different viewpoints to explain the same effects.
Post a Comment