Distagon is the name Zeiss gives to its wide-angle lenses that use a retrofocus design. Short focal lenses are typically composed of glass elements whose shapes are symmetrical in front of and behind the diaphragm. As focal length decreases, the distance from the rear element to the film plane or digital sensor decreases and could even protrude into the mirror box requiring the camera to be in mirror lock-up mode to use the lens. A retrofocus lens solves this problem by using an asymmetrical design that allows the rear element to be further away from the plane of focus than its effective focal length might normally suggest.
The Distagon T* 18mm f/3.5 lens, that I used to make the above photograph, is surprisingly small and light for its wide 90 degree angle-of-view with full-frame sensor cameras where’s it capable of delivering true wide-angle lens performance.
This digital IR shot was made at Barr Lake State Park the day before a big snowstorm was due to blow most of those leaves away. Camera was an LifePixel IR-converted EOS Digital Rebel Xti and 18mm Distagon T* f/3.5 and the balance on the lightweight Xti body was superb. The Digital Rebel’s 1.6x multiplication factor changes the angle-of-view to the equivalent of a 29mm lens (on 24x36mm format.) Exposure was 1/125 sec at f/16 and ISO 400 with a plus one-stop exposure compensation.
If you want to save a few bucks when converting your camera to infrared when ordering a conversion from LifePixel, use the coupon code “farace.”