Sigma 70-200 f/2.8 lens- have to push down to get it to work

Hi,
I have a Sigma 70-200 f/2.8 lens, which I love. Recently when connected, the top lcd screen flashes F-- and it won't focus. I have to push the lens down to get it to work.

Any idea what the problem could be please?

Thanks,
Pa.

I have always said Sigma lenses were rubbish, which is why I only buy Pentax lenses.

It's a bit unfair on them to say they're totally rubbish haha

I'd say Pentax only need to get one mount right whereas Sigma need to get four mounts and systems right to be successful (with reverse engineering too).

The bit that gets me is that they do this with three mount screws instead of the five that Pentax lenses have.

Some of the old lenses from when Sigma competed only on price are poor but then so are many Pentax lenses from the same era.

These days Sigma lenses are every bit as good as Pentax ones.

I had a similar issue with a Sigma 70-300. Each time is happened I had to remove the lens and clean the contacts with a soft cloth. That used to fix it until next time the fault occurred.

Michael