just share what I have learnt over years ... maybe more professional people like brother wah, brother FR can correct me if I am wrong?
Hologon is for superwide, it is based on a very curved front lens element to capture the very wide angle of field. the design philosophy is to produce a superwide lens with second to zero distortion, so a symmetrical design is adopted. however, coz of the very curved front lens, light loss at corner is often serious especially if aperature is wide open. that's why for hologon, the aperature is usually small and/or a gradation filter is supplemented. eg. Contax G H16/F8
Distagon is wide-angle lens of which the rear lens is a "distance" from the film. Hence Distagon is specially designed for SLR to allow for the mirror distance. That's why you do not find Distagon in G series. On the other hand, if this "distance" constraint is removed, then Biogon design will replace Distagon. eg. Biogon in Contax G series, the famous Biogon 38/2.8 in SWC. And you do not find Biogon in C/Y series too. Hence we can conclude that in theory, the Biogon design should be better than Distagon in terms of optical performance. B28 better than D28? B21 better than D21?
Normally Distagon has large aperture while the front lens surface of is not curved. eg. D25/2.8, D28/2.0, D35/1.4. It adopts a non-symmetrical design which means more distortion. To reduce the distortion, more lens elements is required. More lens elements mean more lens-air interfaces so that more internal flares will be produced. Hence if a Distagon is pointing directly at strong light, the performance would be dropped significantly. eg. D21/2.8. The T* coating can reduce such internal flares but not completely.
Planar is similiar to Distagon. Planar has the meaning of "bright". They are high aperature standard to mid-range lens. eg. P50/1.4, P45/2, P85/1.4, P135/2.0 and the design philosophy focussed on the high apertures and adopts non-symmetrical design. However unlike Distagon wide-angles, as as the need for distortion correction is not as much a concern in standard or mid-range, less lens element is needed in Planar design and so internal flare problem is of less concern.
Tessar focusses on light weight and uses the least possible lens elements (only 4). The word Tessar means a 4-elements lens. It is a symmetrical design and so distortion is minimal. On the other hand, it does not aims at big aperture. eg. T45/2.8
Comparing to Planar, Sonnar sacrifices big apertures for light weight, less elements and lower productionn costs. They are non-symmetrical design.
Tele-Tessar is the tele-version of Tessar.
S-Planar, Makro Planar is macro lens with Planr design philosophy.
Others like Mirotar, APO-Tessar, Vario-Sonnar are self explanatory.
Hope it helps.
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