New XT Aperture question

[learjet035]

Hello 1st post, total newb to slr's so get ready for 1000's of questions. I just got my first non point n shoot so I am blown away with all the adjustments that can be made. I was reading the book that came with the camera and noticed that while using the "AV' manual mode I should be able to stop down to 1.0, I think this would create the largest amount of depth of field??? I think. Anyway, I have not been able to go lower than 4.5 so my questions is, what am I doing wrong. I am assuming the XT is smart and not letting me go lower due to the pic will not come out. If you guys have any input that would be great. The pics that I am taking look amazing, and that's with umm no skill, so your stuff must be awesome! Thanks :D

[etaf]

the aperture is dependant on the lens - so if you have the kit lens then 4.5 is the largest (low numbers = large aperture) aperture you can get.
Also the low number will give the smallest DoF
I have posted lots of information and tutorials on DoF and photography etc here
http://www.dpforums.com/forum/forumdisplay.php?f=38
I'm sure theres lots of info on this forum too.

[Belmondo]

The lowest you can stop down is whatever the maximum aperture is on the lens you have installed.

If you have an f/4.5 lens installed, you'll never be able to stop down below that number. The fastest lens currently available from Canon is the 85mm f/1.2 lens.

This is why as a general rule, lenses with larger apertures (lower number) are much desired and usually more expensive.

[learjet035]

cool, I see. I just bought a cheap Tamron AF75-300 that says F/4-5.6 LD
so I guess I'll still be seeing 4-5.6 then. Makes perfect sense, thanks.
And thanks for the link, thats great.

[etaf]

at the 75mm end you will see F4 and at 300mm F5.6