For a few months now I have been shooting macros using my P67II with a Pentax Helicoid extension tube and both 90f2.8 and 45f4 lenses. Of course I always shoot with the lens stopped down using the manual lock on each lens. Generally, for depth of field I shoot at f11 to f16. Shutter speeds are generally 1/2 to 1/15 with iso 100 print film. Mostly I am shooting flower closeups. I have been bothered by finding the prints seem generally soft in focus. I have attributed that to subject motion as I check focus and depth of field and always use a sturdy tripod (Bogen 3036). Today I was shooting without any wind a flower that had interesting detail of pollen on its stamen. I could see this clearly with my eyes and with my Nikon using a 35f2 on a TC-2 extender. The 90f2.8 with helicoid, which covered the same field as the 35f2/2X combination did not show a sharp image through the viewfinder at f16 or f14 (half between 16 and 11). I moved the camera manually to make sure I was focusing on the stamen. At f2.8 the image appeared sharp. But at shooting aperture it appeared very soft. Is this a basic limitaion of the aperture? If so how do we deal with DOF in macro shooting? Would a glass close-up lens be sharper?

-- Tom Goodrick (tgoodrick@earthlink.net), August 22, 1999

Answers

Tom: First of all I should mention that symmetrical or near symmetrical lenses are best for close up work. The 90 should be fine for work with the Helicoid. I have used the Helicoid for ten years now with both the 105 and 200 with no problems with sharpness. Even though the 200 is asymmetrical, it does ok because the distances used are not really close. I have used the 45 and 75(both asymmetrical) with the Helicoid and can say that the working distances are just too close for me. Also, they are not well corrected at macro distances. Spherical aberration is the problem. With your 90 stopped to f/16 or f/22, diffraction should not be visible through the finder. You will see focusing screen grain when you stop down, so it is hard to tell if the image is actually soft. This is what makes macros so difficult in general with MF. The DOF using 35mm format is much better and therefore much easier to get sharpness. My 105mm/Helicoid combination at f/22 is tack sharp. You are shooting with lens stopped down using the maual lever on the lens locked? SR

-- Steve Rasmussen (srasmuss@flash.net), August 22, 1999.

Tom, even with good eyes and much experience using the Helicoid, I still make mistakes. DOF scales cannot be used nor can the focus be accurately be seen. There is bound to be errors. BTW, my print film work with flower macros has not been to my satisfaction and so switched to slide. There seemed to be some kind of color overload where the saturated colors would cause a bleeding and lack of edge sharpness. SR

-- Steve Rasmussen (srasmuss@flash.net), August 22, 1999.

Yes, I shoot with the manual lens lever locked down. I suppose it could be my matte-finish grid screen making it appear soft. Unfortunately, my vision is not the greatest. I use bifocals, one pair set for computer screen distance on the top part. Half the time I forget and go out shooting with those glasses. The astigmatism in the right eye keeps me from using just the diopter. Some prints look fairly sharp but few are "tack sharp". On the other hand I always get tack sharp prints with the 35 mm (on 4x6 glossy prints as opposed to 4x5 matte prints for the 6x7). I have wanted to do an 11x14 of one of the 6x7 flower macros but have not seen any that look sharp enough using a 5x loupe. Maybe I'll just pick the best and have a go at it.

-- Tom Goodrick (tgoodrick@earthlink.net), August 22, 1999.