F5.6 and DOF question

I was just talking to sombody ( friend taking photo corse at colage) that was telling me that opening you AV larger that f 5.6 does not affect your DOF at all because 5.6 is neutral. Is this true and if so why? I have been stopping my lenses down from 2.8 to like 3.5 thinking it would give me slightly sharper pic's even with the flash. I understand that the 2.8 would still give me a faster Tv and better AF but aI had no idea tha the DOF at 5.6 and 2.8 would be the same. Confused

DOF certainly continues to decrease as you open up the apeture from 5.6 to 2.8, and on beyond that if your lens will do it.

It will also give you a faster Tv as larger apetures emit more light, thus the shutter doesn't need to stay open as long for proper exposure. With a given lens AF likely won't be affected by f2.8 versus f5.6, because your lens is operating at maximum apeture during focusing and only stops down when you take the shot.

Often lenses with larger maximum apetures will focus faster simply because they can emit more light, but there are many other factors affecting focusing speed.

Don't think so. Check this out:

http://www.dofmaster.c​om/dofjs.html

I'd tell your friend to drop that class and try a to get his money back. . . =) He's being mislead. Starting at say F1.4 - DOF [Is always dependent on distance the further you are from your subject the larger it is] is very narrow - stopping down to say F 4.0 makes the DOF larger etc etc - Stopping down means increasing Fnumbers 2.0 is stopped down for my 50 F1.4 - but its wide open for my 35 F2.0 - 5.6 is stopped down considerably for both of those lenses.

Its true that AF is better on 2.8 lenses or larger because the lens is used wide open to focus and stopped down to the set AV just as soon as you pull the trigger. . . so if you have a 2.8 lens and you are shooting in AV mode with the f stop set to F4.0 - the camera will focuse with the lens set at its widest aperture, 2.8 but when you take the image the lens stops down to F4.0.

i wouldnt talk to him about photography... at least until he has finished his course

AF will not be affected by the aperture you select, the lens will focus at the widest aperture setting, regardless of the aperture you use. it stops down at the point of taking the photo - see for yourself, look into the lens when taking a pic stopped down.

got beaten to it.. hehe

There is no neutral, the larger your aperature number (2.8,4, 5.6, 8, etc), which actually means the smaller your aperature the more DoF you have.