With the larger negative size the field of view of medium format lenses is much wider than the field of view with the same focal length on 35mm. To make a comparison with 35mm film SLR fields of view multiply the focal length by 0.48. For instance, 90mm is ~44mm in 35 film SLR terms.

I do not see a consensus on which lens series is the best. The non-C single anti-reflective coating lenses seem to be the “worst”, but the optical difference between the K/L and C lenses is not so clear. Some commentators have indicated that the C series had poor quality control, whereas the K/L lenses–being optically the same–are better by virtue of better quality control.

Original

Single anti-reflective coated lenses released in 1970 with the original Pro

NB

These lenses are optically identical to the original lenses, but have a newer barrel design (NB) that matches the later C lenses. They only were produced briefly and are comparatively rare on the market.

C

C, apparently, stands for “Design Improvement”. These lenses are multi-coated. Released with the Pro-S in 1974. Has a “C” on the front name ring.

K/L

Most recent. These lenses are, apparently, a slightly newer design with better coatings than the C lenses. The K/L is a code to indicate which bodies the lenses are compatible with. K indicates the Pro/Pro-S bodies and L indicates the Pro-SD bodies. KL lenses all shipped with an adapter attached to the lens so that they can be mounted to Pro-SD bodies. This adapter should be removed to mount to Pro/Pro-S bodies. This adapter is a fairly simple rubber O-ring for light sealing rather than for any mechanical reason. I, personally, have not had any issues using C lenses on my Pro-SD body without the small adapter ring.

Has a “K/L” on front of the barrel.

L lenses

Совместимы только с версией Pro-SD; это 75mm Shift lens и 500mm APO.

APO/L

Apochromatically corrected lenses. Sometimes known as A lens. More expensive, heavier, but chromatic aberrations are better corrected.

Фото	Фокусное расстояние (мм)	Максимальная диафрагма	Поколение	Угловое поле (градусы)	Вес (г)	Описание	Notes
	37	f4.5	C	180	1240	Construction: 9 elements, 6 groups Field of view: 180 deg Minimum focus: 6.4mm Filter size: 40.5mm (has a filter holder between the lens and the body) Weight: 1,240g Minimum aperture: 32	fisheye distortion
	50	f4.5	C	82	960	More details
	50	f4.5	Original	82	960	Details
	65	f4.5	C	68	0
	65	f4	K/L	68	1070	Details	This is a new, different optical design than the earlier original and C 65mm lenses
	65	f4.5	Original	68	840	Details
	75	f3.5	K/L	61	980	Details
	75	f4.5	S/L	61	1700	Details
	90	f3.8	C	52	0
	90	f3.5	K/L	52	960	More details
	90	f3.8	NB	52	0
	90	f3.8	Original	52	705	Details
	100	f5.2	C	47	1660	Details	100mm-200mm Zoom
	127	f3.8	Original	38	655	Details
	127	f3.8	C	39	0
	127	f3.5	K/L	39	780	More details
	140	f4.5	C	36	800	Details	Macro lenses with floating element to adjust plane of focus curvature.
	150	f4	C	33	790	Details	Soft focus lens
	150	f3.5	K/L	33	840	Details
	180	f4.5	C	28	0	Details
	180	f4.5	K/L	28	900	More details
	180	f4.5	Original	28	875	Details
	210	f4.5	APO/L	24	1020	More details	Apochromatic correction
	250	f4.5	K/L	20	1130	More details
	250	f4.5	Original	20	1310	Details
	250	f4.5	APO/L	21	1370	More details	Apochromatic correction
	250	f4.5	C	21	1020	Details
	350	f5.6	APO/L	15	1440	Details
	360	f6.3	C	14	1040	Details
	360	f6.3	Original	14	1360	Details
	360	F6	K/L	?	0	Details
	500	f6	APO/L	10	2360	Details
	500	f8	C	10	1980	Details

Lens Accesories

Auto Extension Tubes

Two extension tubes–for use in close up photography–were produced, the No. 1 (45mm) and No. 2 (82mm).

Extension tubes were produced for the Pro and Pro-S and a different model for the Pro-SD. The Pro-SD extension tubes fit the larger lens throat of the Pro-SD body. Because of this the Pro-SD extension tubes do not fit on Pro or Pro-S bodies.