85mm f1.8 D RF vs 85mm f1.4 D IF
I read somewhere that mentioned CRC (close range correction) means the same thing as RF (Rear focusing) in telephoto lenses but what about IF (internal focusing) ?
#1. "RE: 85mm f1.8 D RF vs 85mm f1.4 D IF" | In response to Reply # 0f8bthere Basic MemberThu 19-Jul-01 09:46 AM
Close range correction (CRC) MAY involve the shifting of the rear elements, but it is not the same thing as rear focusing. The 24mm f/2.8 lens has CRC but it is a standard helicoid focusing system. The 85mm AF f/1.8 is a internal focusing system (rear group focusing), but it does not have CRC.
CRC may involve the shifting of only certain element groups out of the overall optical configuration to ensure good performance over the entire focusing range. It is not the same as internal (rear) focusing, but a feature that is incorporated in lenses that are deemed to need it regardless of the focusing system. Looking through the catalog, most of the lenses with CRC have conventional focusing, in which the lenses get longer when focused to its minimum focusing distance.
You can read a review between the two current 85mm lenses f/1.8 and f/1.4 at the following site: