Sigma has released a list of zoom lenses that could be affected by an autofocus defect, offering owners a modification service, free of charge, the firm says.

The lenses affected are the APO 50-500mm F4.5-6.3 DG OS HSM (Serial Numbers between 10633051 and 10972000), APO 120-400mm F4.5-5.6 DG OS HSM (Serial Numbers between 10574001 and 10972000) and APO 150-500mm F5-6.3 DG OS HSM (Serial Numbers between 10674301 and 10972000). Sigma is advising users to check serial numbers to determine whether their lenses might be affected.

"To overcome this issue, we will be offering our customers an inspection and where applicable, a modification service, free of charge. In the case of any autofocus problem becoming apparent on inspection, we will rectify the situation and make every effort to minimise delay and inconvenience," says Sigma.

"If you are the owner of one of the above three focal lengths but your serial number is different to those specified above, then you need take no further action. If however you are in possession of one of the lenses with a serial number mentioned above, please contact us on our special helpline 01707 376 795 and we will arrange to collect your lens at no cost to yourself."

It adds: "In the unlikely event that the inspection uncovers a potential problem, your lens will be modified and returned to you absolutely free of charge with the minimum of delay. We deeply apologise if any inconvenience has been caused to our customers."

For more information,  visit www.sigma-imaging-uk.com/returns, call Sigma's helpline on 01707 376 795 or email them at support@sigma-imaging-uk.com.