When it comes to camera lenses there is a difference between lenses enhanced for use on digital cameras and those that are not. Digital camera technology brought with it some new issues that manufacturers have had to resolve. One prominent issue is called sensor flare.
Internal light flare was an unexpected consequence of using an image sensor inside of a camera rather than film. The emulsion side of film is mostly non-reflective. Light entered through the lens and hit the film which caused very little light scatter. However an image sensor is very shiny and reflective. Light from the lens strikes the sensor surface and reflects and scatters back up the lens. This scattered light causes ghost images in the final picture.
We should note that this kind of internal flare is strongest when the camera is pointed toward a light source. The sources doesn't need to be very large or bright for flare to result; Christmas tree lights, burning candles and even sun glare off of glass or metal will create flare.
Manufacturers found that the most efficient way to combat internal flare was to add special coatings to the rear elements of the lens. Both lens coating technology and the anti-reflective materials required were readily available which made this an easy choice.
Camera lenses have had special optical coating applied to them for decades. However seldom were those coating applied to any surface other than the front lens element. In addition to rear element coatings flare is further reduced by blacking internal metal components as well as the edges of lens elements.
Tamron digitally enhanced lenses are designated with a "Di" marking. This shouldn't be confused with "digital only" because a Di lens will function on a DSLR, film camera or a full-frame digital body. Tamron uses the Di-II designation to identify digitally enhanced lenses made expressly for APS-C digital cameras only.
By selecting a digital camera lens from Tamron designated as Di the photographer will have the most effective tool for reducing internal sensor flare. By preventing light reflected from the shiny sensor from refocusing on the image sensor ghosting is controlled and prevented.
Can a digital camera use lenses that aren't enhanced for digital? Yes, of course it can. However the certainty of ghosting caused by sensor flare would seem to indicate that a digitally enhamced lens is a better choice. The cost of a digitally enhanced lens is essentially equal to one that is not which makes the choice even easier.
Stu Eddins is blogger, instructor, merchandiser, and is generally in charge of a lot of things for Porter's Digital Cameras and Imaging. Visit their site at http://www.porters.com/. Years of experience over the counter and in classrooms have turned Stu into an evangelist for image preservation, capturing and sharing memories, and helping people understand digital cameras, digital camera lenses.
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