Originally posted by 1r0nh31d3 I had not even considered the sigma, I'm going to see if I can check one out. I went through about 2000 photos I have taken with the 50mm to check out the exif data to see how I was shooting. The majority of my keepers were all shot at f2.8 I am not camera savy but the reason seems to be that anything much lower than 2.8 and the DOF is quite narrow, narrow enough that I can only get a portion of someones face in focus. So the shots I have taken that are lower than 2.8 are for very special or unique circumstances and not with kids as I could not get their whole face in focus.
I think this is normal but does the DOF change with focal length as well as f-stop. So would shooting at F 2.0 have the same depth of focus shooting with a 50mm or 35mm or 28mm or 21mm? With my limited lenses and knowledge it seems like the answer is yes.
I guess what i am getting at is that if the lowest f-stop I am shooting with moving objects is 2.8 maybe I am better off with my fast lens being a manual and my AF lens is more of an all rounder. Sorry to blabber but I don't have many camera friends and I feel I need to talk this out with someone before pulling the trigger. Thanks in advance for any help and time put into contemplating this.
As I understand it, DOF is a combination of focal length, focus distance, and aperture. The longer the lens focal length, the less DOF. The shorter the focus distance, the less DOF. The larger the aperture (smaller the f/#), the less DOF.
Thus a 30/1.4 would have a larger DOF at 1.4 than my 58/1.4 at 1.4 if taken from the exact same distance to subject. Where you have to be careful is that with the 30, since your FOV is wider, you would likely move closer to the subject to fill the frame. I may be off here, but I think if you fill the frame with your subject with both lenses (by moving closer with the 30), the DOF will be the same.
Can I get an affirmation on this from another member? I'd hate to steer this guy wrong.
As for AF vs manual, it's really just about what you're comfortable with. My personal preference is manual focus fast primes and AF slow zooms, and it works for chasing my kids around, but what may work for me may aggrevate you.
Don't worry about blabbering, most of us are in the same boat as you.