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<blockquote data-quote="aroy" data-source="post: 229365" data-attributes="member: 16090">The focal length mentioned in any lense is always real. What differs with the sensor size is the Field of View - FOV. As DX sensor is shorter, about 24mm long verses 36mm for the FX sensor, image gets cropped. So you get a cropped image with respect to FX sensor, hence the FOV is less, as though the lens focal length was more. So in effect what you see with a 300mm lens in a DX sensor is the FOV that would have been in a 300x1.5=450mm lens on an FX sensor.OT.If the sensor is half the length, that is 18mm instead of 36mm, then the crop would be even more and the FOV would be same as a lens with double the focal length.What makes the DX more interesting is when you have the same MP in both DX and FX, say D7100 and D610. Here the DX sensor has more resolution (pixels/mm of image), so if your image is small, say half the sensor width - 12mm, then the DX image will have more resolution, that is why for wild life, where the animal/bird rarely fills up the frame DX, will have more resolution, but at the expense of higher noise.</blockquote>

[QUOTE="aroy, post: 229365, member: 16090"] The focal length mentioned in any lense is always real. What differs with the sensor size is the Field of View - FOV. As DX sensor is shorter, about 24mm long verses 36mm for the FX sensor, image gets cropped. So you get a cropped image with respect to FX sensor, hence the FOV is less, as though the lens focal length was more. So in effect what you see with a 300mm lens in a DX sensor is the FOV that would have been in a 300x1.5=450mm lens on an FX sensor. OT. If the sensor is half the length, that is 18mm instead of 36mm, then the crop would be even more and the FOV would be same as a lens with double the focal length. What makes the DX more interesting is when you have the same MP in both DX and FX, say D7100 and D610. Here the DX sensor has more resolution (pixels/mm of image), so if your image is small, say half the sensor width - 12mm, then the DX image will have more resolution, that is why for wild life, where the animal/bird rarely fills up the frame DX, will have more resolution, but at the expense of higher noise. [/QUOTE]

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