How to REALLY describe a camera's "zoom"?

Started Dec 15, 2012 | Discussions thread
Contributing MemberPosts: 698
Re: How to REALLY describe a camera's "zoom"?
In reply to ata3001, Dec 18, 2012

There are several possible problems with the OP's  description.

OK we know that if by turning a barrel or pressing a button you see your subject getting bigger or smaller  you have a zoom.. That is regardless if it is a wide to wide, wide to tele or tele to tele zoom... (first point of confusion : zoom does not mean telephoto) So say a 10-30mm is a 3x zoom just as a 100-300mm is a 3x zoom (that is the angle of view is 3x narrower or wider from one end to the other)
Now what is twice as close ? If you take a shot of a person (well anything)  with a 55-200mm lens set at 55mm and then one at 110 from the same point, you should on the 110 shot have the face of the subject twice as large(your object appears twice as close) The same for a 100mm compared to 200mm or 15mm compared to 30mm regardless of the format. The reason you may not get exactly that is very simple. A 55-200mm  3.5/5.6 lens may be so in numbers but, say,  a 58.3-194mm F3.9-5.7 in reality. Now of course I just made up the above  numbers , what I meant is that the numbers on the lens are close enough not necessarily the exact numbers. (close enough to the popularly recognised figures, so 28mm and 35mm in FF not 28.5 and 37.3...) Usually the number is exaggerated towards the more desirable one, so F3.5 rather than F4 and 200mm and instead of  194mm. And that is why if you have the popular 18-55mm and 55-200mm combo and take the same picture at the 55mm end of both lenses most likely you will get two slightly different photos (in angle of view...)
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