28-80 mm sigma won't auto focus

Check compatibility with Sigma representative in you area.

Sigma makes their lenses with a variety of mounts. A lens with a Canon mount, for example, will not fit onto a Sony camera. Assuming you get the Sigma lens with a Sony mount then yes, it will be compatible with the Sony alpha.

Minolta had two lens mounts. One for manual focus SLR film cameras and one for Auto Focus SLR Maxxum film and digital SLR cameras. Sony uses Minolta Maxxum lens mount.
If the Sigma 400 f5.6 lens was made for Minolta X-700 series, XG, series, XD series, SRT series, then it will not fit on your camera.

Having gone over a month with no response, I assume this is no longer a problem.

Usually the gears will strip the lens gears which tend to be plastics whereas Sony a cameras themselves have metal driven cogs....I once stripped a sigma zoom using an
A700 simply because the motor on that camera had no feedback on torque...put a different lens to check this out first...then check the faulty lens the cog is visible once you remove the rear mount.

I was focusing to close to the subject & too much glare from a church window.

Are you using a DX lens. Do you know if you have the camera's auto focus set to AF (auto focus) or M (manual)? There are many things that effect the focus and as an added note, any shots over 1/60 shutter speed in normal light should be in focus without the need of a tripod.

I shoot a D80 and a D70 and I have excellent results and very clear pictures, I'd be will to bet that either your lens is incompatible with the camera or it's just a setting. I'd be happy to help if you could give more info to your settings.

well after a week in the shop it came back working. the guy at the shop could only tell me that the repair people had fixed a problem in the auto focus (he had no other information). So the solution here is going to a place to repair your lens. if someone finds the cause of this problem it would be great

A dirty filter, front, or rear optic can cause the lens to seek

It will not focus on anything closer than 5 feet.

(From Sigma lens literature) Capable of macro photography, this lens has a 1:2 maximum close-up magnification at the 300 mm focal length. It's the ideal high performance lens for portraits, sports photography, nature photography, and other types of photography that frequently use the telephoto range. It also has a switch for changeover to macro photography at focal lengths between 200mm and 300mm with a maximum close-up magnification from 1:2.9 to 1:2. The minimum focusing distance is 1.5m / 59 in. at all zoom settings.