When I use Tamrons 90mm macro lens as well as some other lenses, the open aperture value displayed on the camera is smaller than designated on the lens. Is my lens defective?
The 90mm macro lens is designed to extend its front group largely toward the subject in close-up macro photography. In that situation, the amount of light reaching the film decreases. The aperture displayed stays the same in most cameras, but some SLR cameras are equipped with a feature that shows the effective f-values, and smaller open aperture values are displayed when the lens barrel is extended for close-up photography. This phenomenon is not a lens defect or flaw, but is a camera characteristic.
