This is yet another field test but this time not about a lens. I have found the helicoid to be quite useful in macro work due to its variable offset ability. It's like having two extension tubes in one. It works quite well with the 135mm macro lens or the regular lenses. The results with non-macro lenses have been very sharp, especially with the 105 and the 200mm. With the 300mm, the lens is extended so far from the body that it could cause excess stress on the body tripod screw mount. It can be done but be careful. It seems that the 135 needs some extension even though the lens is made for macro work. There is room for improvement with the 135mm lens because of this. The biggest advantage of the helicoid is that once you have your tripod set, you probably won't have to move it unlike when you use fixed extension tubes. The helicoid gives you so much more focusing range. Its disadvantage is that you lose the automatic metering and have to stop down to the shooting aperture to meter. Overall, a good piece of equipment.

-- Steve Rasmussen (srasmuss@flash.net), March 06, 1998

Answers

Benson, thanks for the magnification numbers on the Helicoid. I have never used the reverse adaptor mainly because my macro work doesn't require the kind of magnification provided by this accessory. I noticed that the 67mm reverse adaptor is meant for the 90, 105 and 135mm lenses. All of these are symmetrical(or very close to it)in optical design. This is no accident, because reversing an asymmetrical lens would cause unsharpness for many reasons. It is obvious that Pentax has put a lot of thought into the entire P67 system. SR

-- Steve Rasmussen (srasmuss@flash.net), March 09, 1998.

Thanks for the test report. I wanted to add that the helicoid's maximum magnification (with a 105mm lens) is 0.63X as opposed to the tube set, which allows 1.07X

Any experience with using the helicoid tube with a reverse adaptor??

-- Benson (btw@vnet.net), March 08, 1998.

The Bogen Telephoto Lens Support (3420) seems like a good tool for use with the 300mm lens with or without the helicoid extender. The front strap can probably hold on the sun shade so focusing is not inhibited. (Don't have one yet but planning on it soon.)

-- Tom Goodrick (tgoodrick@earthlink.net), May 14, 1999.