This may be a dumb question

[mattbowen]

<p>Like I said this may be a dumb question (and I think I know the answer but I want to make sure), <br>

I know that the numbers on the front of the lens that say (1;2.8-4) means F2.8 to F4 but when it says (1:2.8 (22)) does that mean F2.8 to F22 or is there another meaning? </p>

[parv]

In the second case, f/22 is the smallest achievable aperture for that lens. While in the first case, f/4 is the largest possible aperture at the long end of the focal length of that (zoom) lens.

[gregory_king1]

<p>Right. The number in parenthesis is the minimum aperture, which is (usually?) constant on all lenses, and rarely important.</p>

<p>Any numbers stated as a range, with a dash, are the maximum apertures available at the end of the zoom range. Some zooms (and obviously all primes) have a single number for maximum aperture, since it never changes.</p>

[mattbowen]

<p>Thank you all for the reply that is what I thought but wasn't positive.</p>

[craigd]

<blockquote>

<p>The number in parenthesis is the minimum aperture, which is (usually?) constant on all lenses...</p>

</blockquote>

<p>On zoom lenses with variable maximum apertures, the minimum aperture often varies too. See this review of a Sony 18-55mm f/3.5-5.6 zoom lens, for example:</p>

<p><a href="http://www.slrgear.com/reviews/showproduct.php/product/1272/cat/83">http://www.slrgear.com/reviews/showproduct.php/product/1272/cat/83</a></p>

<p>The chart near the top of the SLRgear review shows the minimum aperture varying from f/22 at 18mm down to f/36 at 55mm. Not surprisingly, their test results show pretty bad diffraction-induced softness at f/36! Canon's 18-55mm f/3.5-5.6 kit lens does the same thing.</p>

[paul_de_ley]

<blockquote>

<p>Right. The number in parenthesis is the minimum aperture, which is (usually?) constant on all lenses, and rarely important.</p>

</blockquote>

<p>It's rarely important in the sense that most of us would never go beyond f16 for most of our lenses, but it's nevertheless a useful piece of information about the versatility of the lens for particular kinds of subjects & shots. For the better quality closeup-capable lenses (not to mention true macro lenses) and for wide angles capable of attaining or approximating hyperfocality it will tell you how far you can go in trying to maximize DOF. I assume it also matters if you're into shooting long exposures of flowing water, crashing waves etc etc where maximum sharpness is less important than a lens' ability to draw out shutter speeds without necessarily having to stack on multiple ND filters.</p>

[mattbowen]

<p>Thanks for the replies. I have a 28 to 70mm with a 1:2.8 and it can stays at 2.8 from 28 through to 70 as to where on mt 55 to 200mm changes the F stop as you change focal length, will that happen with a lens that is says 1:2.8 (22) or will the F stop stay the same as you change focal length?<br>

I am wanting to get a new lens for portraits and like the ability to keep the same F stop through out the spectrum. </p>

[parv]

Thanks Craig D for something new (to me).