Over two decades ago, Tamron created very straightforward system of nomenclature to describe the inherent features found within their lenses. Tamron's lens nomenclature utilized very logical abbreviations or designations along with full descriptions for these abbreviations. As a result, Tamron has simply added to their established nomenclature in order to describe the inherent features of their current lenses as well.
Original (1980) Nomenclatures
The "CF" Designation:
Many people misinterpret Tamron's "CF" designation to stand for "Close Focus". Tamron's "CF" designation actually stands for "Continuous Focus", meaning that the lens has the ability to continuously focus from infinity to macro mode. Some CF zoom lenses had this CF ability regardless of the set focal length, while other CF zoom lenses featured internal cams which would automatically zoom the lens towards a specific zoom setting as the focus ring was turned. This latter feature was referred to as the Minimum Object Distance (M.O.D.) Selector System. The M.O.D. feature was certainly much more convenient than having to press a "macro" button, as found on many similar competing lenses, in order to go into macro mode. Needless to say, M.O.D. increased the cost of a Tamron lens due to the extra internal focus/zoom coupling mechanisms. But once you used a Tamron CF lens which featured the M.O.D. Selector System, you were hooked due to the extraordinary convenience of the Tamron design. The CF designation has now been discontinued by Tamron, but older CF lenses were simply marked with the letters "CF MACRO" somewhere on the lens barrel (usually above the aperture ring).
The "Macro" Designation:
It appears that Tamron designated lenses as "Macro" lenses only if the lens was capable of achieving considerably closer focusing compared to many similar lenses, or if the lens featured either a macro button or some other form of specific mechanism in order to get into macro mode. If the lens merely featured continuous focusing to a very short focus distance, then it appears that Tamron gave the lens a "Macro" designation only if the lens could achieve a macro reproduction ratio of 1:6 or better. Lenses with a macro feature are marked with the letters "MACRO" somewhere on the lens barrel. Lenses with a telephoto macro feature are marked with the letters "TELE MACRO" somewhere on the lens barrel.
The "SOFT" Designation:
Tamron's "SOFT" designation stands for "Soft Focus". Tamron lenses with a SOFT desination incorporate special lens elements and a control ring to introduce varying amounts of spherical aberration. The spherical aberration produces a very nice softening of details within the image. Tamron produced only one lens with the SOFT feature the SP 70-150 F/2.8 SOFT lens.
The "SP" Designation:
Tamron's "SP" designation stands for "Super Performance". Tamron's original SP symbol is shown above left. Tamron's current SP symbol is shown to the right of the original symbol. In the past, Tamron's lenses received the SP designation for any of or a combination of the following reasons:
Today, many lenses produced by Tamron and other manufactures feature low dispersion elements and internal focusing. It appears that Tamron currently reserves its SP designation for lenses which meet any or a combination of the following criteria:
Older Tamron SP lenses were simply marked with the letters "SP" somewhere on the lens barrel (usually above the aperture ring), and many SP lenses also had "TAMRON SP" marked on the front element retaining ring and/or on the included built-in or standard accessory lens hood. Today's modern Tamron SP lenses are distinctively marked with a thin gold ring about the top of the lens barrel.
The "LD" Designation:
Tamron's "LD" designation stands for "Low Dispersion". Tamron lenses with a LD desination incorporate one or more very low dispersion elements. Almost always, Tamron used two low dispersion elements to achieve apochromatic performance which was similar to lenses which incorporated a fluorite element. Tamron's older LD lenses were distintively marked with a thin bright green ring around the top of the lens barrel and featured the letters "LD" somewhere on the lens barrel. Tamron has done away with the thin bright green ring for designating its modern lenses which incorporate LD lens elements.
The "IF" Designation:
Tamron's "IF" designation stands for "Internal Focusing". Tamron lenses with an IF desination incorporate internal focusing wherein the length of the lens does not change while the lens is being focused. This is because a group of internal focus elements are moved, in order to acheive focus, rather than moving the frontmost lens elements. Movement of these internal focus elements is very similar to moving the variator and compensator lens groups within a zoom lens, but instead the lens is being focused rather than being zoomed. Some Tamron IF lenses also featured a variable IF cam, much like the variable zoom cams found within zoom lenses, which produced a faster and much more natural focusing collar movement at very close focus distances. This is a useful feature in close-up and macro photography since it allows the photographer to quickly focus the lens while in macro mode. Tamron's older IF lenses were marked with the letters "IF" somewhere on the lens barrel.
Additional (mid 1980s to present day) Nomenclatures
The "AF" Designation:
Tamron's "AF" designation stands for "Auto Focus". All Tamron AF lenses feature fixed mounts for autofocus camera bodies rather than using the Adaptall-2 mount system. Note that some "AF" lenses were also made available in manual focus Adaptall-2 mount versions.
The "MF" Designation:
Tamron's "MF" designation stands for "Manual Focus". After Tamron introduced its various AF lenses, Tamron needed a new designation to clearly distinguish either the manual focus Adaptall-2 version of the AF lens, or to distinguish other Adaptall-2 lenses which were still in production.
The "AD" Designation:
Tamron's "AD" designation stands for "Anomalous Dispersion" lens optics. Conventional optical glass has very even dispersion for different wavelengths or colors. Most people are familiar with using a prism to split sunlight into a rainbow of colors, and many will recall that the colors are fairly evenly distributed across the width of the rainbow. AD glass doesn't spread the colors evenly. Instead, AD glass speads the colors at each end of the rainbow by very little compared to the colors in the middle of the rainbow. AD glass is a special type of optical glass which isn't cheap. Optical engineers use AD optics to control chromatic aberration in the deep blue and deep red portions of the color spectrum. This greatly reduces the dreaded color fringing for deep red and deep blue-violet colors, and greatly reduces lateral color. AD lens elements are particularly useful for minimizing chromatic aberration and lateral color in very wide angle to telephoto zoom lenses.
The "ASL" Designation:
Tamron's "ASL" designation stands for "ASpherical Lens" optics. ASL lenses utilize one or more hybrid aspherical lens elements within their optical designs. A hybrid aspherical lens element consists of a conventional lens element onto which a resin based aspherical surface is applied. Aspherical optical elements allow the optical designer to better correct for inherent spherical aberration and chromatic aberration without having to utilize additional optical elements. The aspherical surface obviously corrects for spherical aberration, but chromatic aberration can also be corrected for since the lens element is really a hybrid which is composed of two materials which have different refractive indexes. The application of aspherical elements within zoom lens designs allows for the creation of lenses which have any of or a combination of the following features: a larger zoom range, fewer lens elements, aspherical elements in place of LD glass, a very large maximum aperture.
The "LAH" Designation:
Tamron's "LAH" designation stands for "LD Aspherical Hybrid" lens optics. Lenses with LAH optics feature Tamron's proprietary low dispersion (LD) aspherical hybrid lens optics. LAH lenses utilize one or more LD aspherical hybrid lens elements within their optical designs. A LAH lens element is composed of a low dispersion (LD) element onto which a resin based aspherical surface is bonded. Apparently only Tamron has developed the proprietary technology to accomplish this feat since LD elements are fragile by nature.
The "XR" Designation:
Tamron's "XR" designation stands for "Extra Refractive Index" lens optics. Lenses with XR optics for the frontmost elements are somewhat more compact than similar lenses which use optics with less powerful refractive indices. XR optics allow wide angle lenses, wide angle zooms and wide angle to telephoto zooms to have a somewhat smaller overall diameter. XR optics can potentially allow long telephoto lenses to be shorter in overall length, thus reducing weight.
The "ZL" Designation:
Tamron's "ZL" designation stands for "Zoom-Lock" mechanism. Many of today's zoom lenses utilize two or more zoom cams and feature large front elements which also move when the lens is zoomed. In some zoom lens designs, it is simply unavoidable for the zoom setting not to creep when the lens is tilted up or down. Tamron neatly solved this problem by incorporating a zoom-lock mechanism which locks the zoom setting in place.