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Q. Are Tamron lenses compatible with digital SLRs?
A. Tamron’s Di-II lenses are designed exclusively for digital SLR cameras with APS-C size imagers (24x16mm or smaller). The optical systems of our Di lenses are matched to the performance characteristics of digital SLR cameras as well as film cameras.
Q. High power zoom lenses such as 18-250 or 28-300 seem to cover angles of view wider than those covered by equivalent telephoto lenses. I suspect the focal lengths at the telephoto ends might actually be shorter than designated.
A. High power zoom lenses use Internal Focus (IF) systems to shorten the Minimum Focus Distance. When an IF system is used in the optical system of a lens with a wide to tele range, the magnification ratio at telephoto is shortened when you shoot closer to the MFD. When pictures are taken at a close focusing distance with a zoom lens at its telephoto end, the zoom lens covers a wider angle of view than would a fixed telephoto lens. However, since the focal length of any lens is based on the focusing distance at the infinity setting (and Tamron’s high power zoom lenses provide the same angles of view as other telephoto lenses at the infinity setting), this phenomenon is not a defect or flaw in a zoom lens.
Q. When I use Tamron’s 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?
A. 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.
Q. Is there a difference between the designation MACRO on a 90mm macro lens and a zoom lens?
A. Tamron puts the MACRO designation on all lenses that have a maximum close-up capability of 1:4 (0.25x) or larger, regardless of the lens type. However, there is a difference between a macro lens and a zoom lens in the image quality for close-up photography. In designing a macro lens, the emphasis is put on image quality and performance to provide a high image quality and an attractive out-of-focus background effect in close-up photography, while maintaining sufficient performance in general photography for portraiture or scenery. On the other hand, in designing a zoom lens with a macro feature, emphasis is put on high image quality in general photography while equipping the lens with a convenient close-up capability.
Q. Other than Di-II Lens Series, all Tamron’s AF lenses for Nikon and Pentax are equipped with an aperture control ring, but Di-II lenses do not have the ring. Why is that?
A. Di-II Lens Series are for exclusive use with digital SLR cameras. All Nikon and Pentax digital SLRs are designed to control apertures with a dial on the camera, not with a control ring on the lens. An aperture control ring is unnecessary for AF lenses designed for exclusive use on digital SLR cameras.