Steve-

Since you are the optics guy, could you tell us the optical design and compatability between the new 300 f4 ED for the Pentax 6x7 and the design of the 1.4 teleconverter (mine works very well on the new 200mm, sharper than the old 300 Takumar by itself). Combined with a decent TC the 300 ED shouldn't lose much resolution, eh?

Thanks, Charles

-- Charles Shoffner (chasmn@aol.com), February 26, 2001

Answers

The 300ED is typical of the modern telephoto-like designs. It has many elements along the optical path and not just a front and rear group as in the days of old. It does not appear to have much of a telephoto ratio(negative rear group)that is used to shorten the lens. This 300 should be a great performer because of this and the use of ED glass. It is very important to have ED elements at the beginning of the optical train but having them in the rear is not all that important. The 1.4x converter is not ED but since it is at the end of the optical system, it shouldn't be a problem. The 1.4x would turn the lens into a telephoto since it magnifies the image from the front system. It should work great. SR

-- Steve Rasmussen (srasmuss@flash.net), February 27, 2001.

I just saw something interesting about the 300ED on the German website for Pentax. The ED is 210mm in length while the old one was 186mm. This is more evidence that the ED is NOT a telephoto design. A true telephoto design uses a positive group in front of a negative group, where the negative group is used to shorten the lens but maintain the focal length of as if it were longer. SR

-- Steve Rasmussen (srasmuss@flash.net), February 28, 2001.