This is part one of two for this lens. This is a big lens and noticably larger than the 300mm. The 400 Takumar is a strange combination of designs. It is like a mini 600mm as far as diaphragm, lens caps, camera mounting and tripod mount are concerned. But, it is like the 300mm in optical design and helical focusing. The finish and workmanship is just outstanding. The lens hood will lock in position if rotated to the right spot. It took me awhile to figure this out. The outer bay mounting is no problem if one is used to this system. If not, there will be a learning curve. You can over tighten the lens ring and cause the camera/lens to separate. You can under tighten the ring and the two could separate also. The optical design is composed of a Cooke Triplet up front and a condenser element and field flattener in the rear. I am quite sure the lens is corrected for blue, red and yellow, making it APO. Given that it was designed in the early 70s, it used glass that is not super low dispersion. My guess is that it will fringe at f/4 but I will report on this later after more field work. Going to different f-stops on the aperture ring is not as smooth as the 600mm. The clicks are difficult to go over quickly as they want to stop the movement of the aperture ring. Close focusing is 25.5 feet so you can tell this is not a newly designed lens. With outer bay tubes, it will go down to around 8 or 9 feet, depending on your f-stop. The tubes allow for some nice close up work that without, you would be quite limited. The tripod mount seems to allow for excellent balance of the camera/lens combination. I will report about shutter shake with this lens in my next report. BTW, this lens has an f/45 stop and is f/4 wide open. I feel Pentax could have gotten away with an f/64 stop with this lens because even at that ratio, the aperture would still be 6.25mm. The lens uses an outstanding 12 blade diaphragm that allows for nearly circular openings. As far as I can tell, the last year of production for this lens was 1987. More to follow-- SR

-- Steve Rasmussen (srasmuss@flash.net), February 06, 2000

Answers

The change in infinity focus when using the rear filter is at the last zero of the 600 foot mark on the barrel. This may vary slightly depending on the thickness of your filter.

-- Steve Rasmussen (srasmuss@flash.net), October 24, 2000.