I am considering buying the updated 800 mm ED lens. Has anyone had experience to help answer these questions:

1. How sharp is the lens? Does it have to be stopped down 2 stops to become sharp?

2. Do you see any image degradation using the dedicated 1.4X?

3. How much image degradation do you see with the 2X [which Pentax does not recommend using with lens over 400 mm]?

4. With ideal technique, how much degradation do you see when stacking the 1.4X and the 2X tele-converters?

5. How does the Zoerk adapter to Contax 645 work with these combinations?

6. Is there any chromatic changes?

7. What do these sell for used? Anyone have one for sale?

Thank you

Jerry

-- Jerry Stein (jerrysteinmd@mac.mail.com), April 28, 2002

Answers

You are talking about a very rare lens, mostly due to its cost. I don't own one but have pieced together info on the 800ED from various sources over the years. It is reportedly very sharp, even wide open. The 1.4x has good reports as well. The 800 cross section is similar to Fluorite lenses with the first element being negative. This is done to protect the delicate positive Fluorite element. I'm not 100% sure it is Fluorite but it has that configuration. One thing is for sure and that is that it has at least two super low dispersion elements. Its quadruplet front group can be an indicator of superachromatic correction but is not a guarantee. I doubt that anything beyond the 1.4x on the 800 (1120mm)would be usable due to the shutter shake issue. Pushing the lens to 2240mm even with a Wimberly head would be a mistake. Stacking converters is not a good idea optically anyway.

-- Steve Rasmussen (srasmuss@flash.net), April 28, 2002.