Does any have you any experience with the mutar I extender? I,m contemplating to use it with the 50 mm 1.4 (still have to buy that one too) and with the 85 mm Planar. Is it good. What's the effect on image-quality?
I use the Mutar I with the VS 80-200 and Provia 400F slide film. It works well. There is no noticeable quality loss at small print sizes up to 8 x 10 in my experience.
Please keep in mind that a teleconverter is just a magnifying glass. It magnifies the middle portion of the image to stretch it out to the full frame. Therefore it magnifies any softness of the main lens. If the main lens is soft wide open, then the image with the Mutar will look softer. I think the Mutar itself is not soft, but it simply magnifies the softness of the main lens. So as long as your main lens is good and sharp at the operational aperture, then the image after the Mutar will still be acceptably sharp.
Carrying a Mutar around is much easier than two extra lenses, in terms of size, weight, and cost. One Mutar plus one 50mm plus one 85mm gives you four focal lengths: 50, 85, 100, and 170mm. It's much cheaper too, so as long as you can work with the two stops of light reduction through the Mutar, I can recommend it's use.