Camera and Lens

[cikguyan]

Dear Moderators,
At the moment I am using Nikon D40x and Nikon 18-200mm VR lens to take school activities' photos, group photos, church indoor photos, landscapes and wedding photos at times. I thought of buying a fast lens for indoor activities and low lighting condition at a minimal cost. Should I buy a Sigma 18-50mm f/2.8 EX DC Hsm Macro ? Should I buy another camera Nikon D80 and Tamron 17-50mm f/2.8 lens ? Please kindly advise me. I thank you.