Novice trying to get to grips with the complexities is puzzled why some of
the smaller dslr have zoom lenses labelled as X28 and even X35, whilst the
larger dslr have lenses rated in focal lengths such as say 18 - 200mm.
The latter whilst generally more expensive seem to have far less powerful
Would anyone be able to clarify why these lenses are labelled in this
different way please, and especially how the zoom factor label can be
calculated from the focal length label?
It's a marketing ploy. People buying cheap compact and bridge cameras
are deemed to be impressed by big zoom numbers, while people buying
DSLRs are deemed to be used to 35mm film cameras.
Most compacts and bridge cameras seem to start from about a 35mm focal
length equivalent lens, but due to the sensor size, it's actually only
about 5 or 10 mm. Multiply by the zoom factor, and you get, for a 10x
zoom, about 35 - 300mm equivalent. They also have 'orrible distortions
at the extreme ends of the range.
To go the other way, divide the large number by the small one, and
that's the zoom factor. It'll be much smaller than for a compact camera,
as it's actually bloomin' expensive to make a decent zoom lens to cope
with the larger sensor in the DSLR. A typical range will be 35 - 105mm,
or 70 - 200mm. If you want a decent 10x zoom on a decent DSLR, you'll be
paying both arms and, probably, a leg too. The extreme zooms the
paparazzi use are often well into four figures just for the lens, and
another couple of thousand for the body.
I was looking at a display of compacts in a supermarket and had to laugh
because the accompanying blurb on stand-up cards headlined the digital
zoom range and failed to even mention the optical zoom at all.
Indeed, 3:1 is the limit for acceptable quality if you really want accuracy.
the 11:1 is a reasonable compromise for 'happy snappers'
More is plain rubbish.
And, of course, the actual picture angle depends fairly largely on the
sensor dimensions as well as the focal length.
A 50mm lens on a 35mm camera is roughly like a 35mm lens on my DSLR for
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