Sigma 18-50mm f/2.8-4.5 sld for canon 50d issue

<p>I just bought a canon 50D before Christmas so I'm very new to this, its my first DSLR camera. It came with a kit lens and I also bought this Sigma lens to go with it. <br>

The question I have, on the lens it says F/2.8 but my camera won't take it lower than F/3.2. Is there something I have to do besides putting the lens on the camera if it isn't a canon lens, or should the camera already know the range? I've tried changing it in all of the creative modes and none will go below f/3.2.<br>

any ideas? hopefully the answer is so obvious as to make me feel silly !<br>

thanks in advance :),<br>

kristen</p>

 

<p>It could be that you are at greater than 18mm focal length. The lenses you have are not fixed focal length. They are variable, and your sigma will be f2.8 at 18mm only. Its a f2,8 to f4.5. At 50mm you will not be able to go under 4.5. Invest in a good photography book to learn more or browse through photo.net's tutorials.</p>

<p>oh! i did not know that it had to be at 18mm. i bet that is what my problem is. I have invested in about 6 good photography books and am in the process of reading them all. The amount of info is a bit overwhelming but so so interesting. i will check out the tutorials, thanks so much for your help!</p>

<p>Just to clarify: there is 'fixed focal length,' and there is 'fixed aperture.' This lens is neither. Zooms are by definition not fixed focal length: that is the 18-50mm part. Your lens is also not fixed aperture, which is the f/2.8-4.5 part. The size, weight, and cost of a zoom are determined partly by the size of the glass needed for the maximum aperture at their longest focal length, in this case, f/4.5 at 50mm. In most cases, unless you pay more $$ and are willing to lug around more weight, you will get variable-aperture zooms. A competitor that is fixed focus is the Tamron 17-50mm f/2.8.</p>

<p>so the Tamron 17-50mm f/2.8: are you saying that will that give me a maximum aperture of 2.8 at any zoom length?<br>

thanks!</p>

 

<p>yes, it will give you a maximum aperture of f/2.8 (or approximately that) at any focal length. Normally, if a zoom has a fixed aperture, the name will end with that single aperture. If it has a variable aperture, it will end with both the max aperture at its shortest focal length and its max at the longest.</p>

<p>If you look at a bunch of lenses, what you will find is that in general, fixed-aperture zooms cost more--often a lot more--and are larger and heavier, because of the size of the needed glass. That's why my longer zooms are both variable-aperture...</p>

<p>I too have a Sigma 18-50 f2.8. Actually on my 40D at the moment. It's f2.8 all the way through the zoom range. The on-lens typography describes it as:<br>

Sigma DC 18-50mm 1:2.8 EX Macro.<br>

If that's the lens the OP has, it should go to f2.8 throughout.</p>