Archived from groups: rec.photo.digital (
More info?)
On Sun, 04 Sep 2005 01:33:45 GMT, Charles <ckraft@SAMTRAP.west.net>
wrote:
>On Sat, 3 Sep 2005 20:26:01 -0500, "PanHandler"
><panhandler@emptyhat.net> wrote:
>
>>
>>"Charles" <ckraft@SAMTRAP.west.net> wrote in message
>>news:fnhkh1htgm30dmnecs8hs7m2dure9ske33@4ax.com...
>>> On Sat, 3 Sep 2005 19:39:04 -0500, "PanHandler"
>>> <panhandler@emptyhat.net> wrote:
>>>
>>>>
>>>>"Charles" <ckraft@SAMTRAP.west.net> wrote in message
>>>>news:9kbkh19ftugu4hok2thrltgl7st5dgrfs9@4ax.com...
>>>>
>>>>> is that F4-5.6 or 1.4-5.6? If the latter, it sounds like my lens.
>>>>
>>>>Huh?
>>>>
>>> Never mind, I can't read. the lens says 1:4 5.6. The 1:4 must mean
>>> the zoom ratio.
>>>
>>> I've been having trouble reading things today, must be getting old.
>>
>>It means that the max aperture varies from f4 at 28mm, and to f5.6 at 105mm.
>>The zoom ratio is determined by dividing 28 into 105 (3.75). Zoom ratio has
>>nothing to do with aperture.
>>
>
>
>I wouod have guessed that I would divide 70 into 300. Shows what I
>know.
>
>The connection between zoom ratio and aperture comes from the way
>Sigma wrote it on the lens.
The "1:4 5.6" is written that way because the F/ number is a ratio of
the focal lens to the aperture opening. It's a very common way of
putting the aperture on a lens.
F/4 means the aperture opening is 1/4 the lens' focal length, while
F/5.6 means the aperture opening is 1/5.6 the lens' focal length.
Thus: 1:4 5.6 describes the F/ numbers for the lens at its widest and
longest focal lengths.
It follows, then, that on a prime lens (for example, a 50mm lens) only
one F/ number would be shown, and that would be the smallest F/
number, or the widest aperture opening. So, a 50mm 1:1.8 lens would be
a 50mm lens with a widest aperture of F/1.8.
--
Bill Funk
Replace "g" with "a"
funktionality.blogspot.com