Auto focus will not focus. lens problem or camera problem?

Communication contacts needs to be checked.

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.

The problem sounds like the camera did not reset properly after the last exposure. Minolta deigned the camera to keep the aperture fully open except during exposure.
During exposure it snaps the aperture down to the selected opening, then opens it again to allow enough light for proper focusing. If it did not fully open the blades after the shot, much less light would pass through the lens. The viewfinder would be darker and look murky.
Most likely cause? Dried up lubricants in the camera.
Next likely cause? Teeth broken on a plastic gear.
Get it to a camera repair place. Get estimates first.

No but you can get a converter for it

there is a locking ring you have to remove and then the front optic may fall out if it sticks you may need to heat up the barrel that might work

The lens may not be a dynex type so it wont work on your 700

Hey sunnibeach4,
On SLR cameras the filters are attached to the end of the lens via threads inside the end of the lens barrel. Without knowing exactly what lens you are using I can't tell you what filter diameter you need but most lenses list that information on the inside rim of the front of the lens. I hope this helps!

Sincerely,
Allan
Go Ahead. Use Us.

It takes either: Energizer 475 or Duracell 245........if camera still will not fire, your camera has a problem. www.flcamerarepair.com

If it has a Minlota mount, yes!

Sorry, the mounts of Minolta manual focus lenses are different than their auto focus series. Sigma, Tokina and Tamron all make compatible zoom lenses to fit the Maxxum series cameras