snegron7 wrote:
The first dslr's all had APS-C sensors. Since then the big manufacturers (Canon, Nikon, Sony, Panasonic, Pentax) have developed "full frame" sensors to match (roughly) the size of old 35mm frames found in film cameras. Lenses were designed for 35mm (full frame) at first, then subsequently designed for APS-C.
Here is my gripe; APS-C lenses advertised as "equivalent to" whatever their multiplier is for full frame sensors (1.6, etc) in terms of field of view. For example:
Sigma 18-50mm = 27-75mm (35mm equivalent)
Sony 11mm = 16.5mm (35mm equivalent)
Fuji 23mm = 35mm (35mm equivalent)
Viltrox 13mm = 20mm (35mm equivalent).
I understand that these are field of view numbers, but why not advertise or describe the lens as what it will truly capture images as? If it's really a 27-75mm field of view lens, why advertise it as an 18-50mm lens? If the field of view is 20mm, why bother stamping on it "13mm"?
Well, for one, since we don't live in a 2-dimensional world, the field of view isn't actually equivalent. Sure, if you only considered the X and Y axes they would be, but using a smaller sensor doesn't negate the fact that a 23mm focal length is still a 23mm focal length.
For example, shoot a subject with a 23mm lens on a crop sensor. Then shoot the same subject with a 35mm lens on a full-frame body, while having the subject occupy the same amount of the frame. The 23mm lens on the crop sensor camera will have more of the background in the image and less bokeh. Whether that's a good thing or a bad thing depends on what you're trying to achieve, of course.
Even though the 23mm lens is considered to be a 35mm "equivalent," it's not - it's still a 23mm focal length.
