Sigma 50-500 mm lens

[spinner]

My Sigma mounting ring appears to have loosened. The lens has quite a bit of movement when mounted on either of my Nikons. So much so that if I don't twist them to make the connnection tight the lens won't focus and I get an F err message. Does anyone know if, or how I can tighten the ring on the lens? Or is it a job for Sigma's repair unit?

[Oldboy]

If you mean the collar that attacheds the lens to the tripod/mono pod, you can tighten that yourself. Focus error is the Aperture ring problem and would require fixing by Sigma. Are you sure the Aperture ring is locked in the correct position? 

[Simple]

Exactly the reason I had to send my Bigma to Sigma. It is possible to tighten but I am afraid you have to take the ring at the mount end of first and you risk damaging the electronics.
The loosening of the Bigma is a well known problem. Harry had his shaken apart in a Landrover when on Safari, mine shook loose while I pulled it in a Pelican hardcase on solid wheels over a gravel path. The outer coating on the lens has a habit of coming of, making the lens look rather tattered. Sigma service is very good, but because mine was an old model, (they don't make the non OS anymore) they had to send it to Japan for repair. 8 Weeks turnaround and around £200. They would have also replaced the outer barrel for that price, but they could not find one even in Japan, so I just have the old battered one back, but at least it will be working and is calibrated.
Hope that helps.
Simon 

[spinner]

Sorry Fellas, I guess I wasn't clear in my description. It's the mount for lens to camera. And the basic problem is the whole lens can move in a rotational manner, enough that the electric connection breaks and I get error message. I literally have to rotate the camera until it reads the inputs.

I guess a run to Sigma is in order, thankfully they're only 55 kms away off one of our major motorways.

[spinner]

Exactly the reason I had to send my Bigma to Sigma. It is possible to tighten but I am afraid you have to take the ring at the mount end of first and you risk damaging the electronics.
The loosening of the Bigma is a well known problem. Harry had his shaken apart in a Landrover when on Safari, mine shook loose while I pulled it in a Pelican hardcase on solid wheels over a gravel path. The outer coating on the lens has a habit of coming of, making the lens look rather tattered. Sigma service is very good, but because mine was an old model, (they don't make the non OS anymore) they had to send it to Japan for repair. 8 Weeks turnaround and around £200. They would have also replaced the outer barrel for that price, but they could not find one even in Japan, so I just have the old battered one back, but at least it will be working and is calibrated.
Hope that helps.
Simon

Looks like I'm in the same boat. They don't have parts to repair anymore. They'll try to tighten the screws, but if any parts are broken I'm out of luck.