Carl Zeiss T* Mutar III
Carl Zeiss has introduced a new Mutar Tele-Extender, the Mutar III 1.4X. Tele-Extenders will provide added focal length to a Carl Zeiss T* lens. This is an excellent way to save the cost of an occasional use lens.
A tele-extender will multiply the focal length of a lens by the amount noted on the extender. In the case of the 2X it multiplies the focal length by 2 times, with the loss of two f stops.
The 1.4X multiplies focal length by 1.4 X while losing only one f stop of lens speed. This means that your Carl Zeiss T* Sonnar 180mm f2.8 will be an effective 252mm in focal length at f4. That is an appreciable gain in focal length without a prohibitive loss in lens speed.
When the effective f stop changes by the introduction of a tele-extender or with bellows extension, the exposure changes but the depth of field stays the same as the original lens f stop.