Does zooming the lens moves the aperture setting on my camera body too?

Question

just bought a canon xsi and its my first dSLR. when i'm adjusting the lens on this 18-55mm IS the f-sotp setting on lthe LCD also moves.

can i take a photo with a blurred background using this lens? can you pleasen help me with the settings.

Answer 1

Changing the focal length will not change the aperture UNLESS you have it set at the maximum. For most zoom lenses, the maximum aperture changes with the focal length. In your case, the maximum aperture at 18mm is f/3.5, but the maximum at 55mm is f/5.6. As you increase the focal length, the maximum aperture is forced to increase as well.

This is why you should check your exposure every now and then.

And by blurred photos, you mean with a shallow depth of field? Yes, you probably can, with some practise and playing with the settings. You should probably stay with a focal length whose maximum is more than f/5.6, though.

Answer 2

for maximum aperture there are two types fixed and variable. The most common is variable f/3.5-5.6 what means you can only use maximum aperture 3.5 at 18mm and 5.6 at 55mm so if you camera is setting up 18mm and aperture 3.5 when you zoom the aperture will change but if you have fixed maximum aperture it won't matter if  you zoom.

And for taking pictures with blurred background put priority on aperture and open it to the maximum.

Answer 3

There are two type zoom lenses .. the one you have is more traditional and as your lens is zoom to a longer focal length the maximum aperture becomes smaller.

There is a relatively new lens design that has the same aperture at all focal lengths of the lens (these are much more expensive).

Your 18-55 mm is a traditional zoom.  You can get some Bokeh using that lens at 55 mm wide open.  You will just have to do some tests to see if you like the results or not.

On Bokeh:

http://www.kenrockwell.com/tech/bokeh.ht...