Hi there, I just bought my self a pentax 67 with a 105mm lens and loaded the camera with Fuji Provia. When i got my slides back they looked great until i checked closely with a loupe. The problem is depth of field is lacking. eg if i focus on 20 meters and set the lens f/11 i should get depth of field from 9 meter's to infinity, my problem is that everything look's sharp except infinity. i did another experiment where i set the lens on focus on 20 meters and set the lens on f/11 and f/16/ and f/22 and still i only got a bit of improvement(infinity still wasn't in focus enough) by the way the lens does focus on infinity. Is this method wrong. Should i focus on infinity and forget about hyperfocal distances. Is the scale marking on the lens inaccurate,this problem also happens with the 45mm.

I dont have this problem with my 35mm, and i think 35mm has greater depth of field.

I would appreciate if someone could tell me what is the problem.

thanks for your help

by the way this 67 forum is a great idea.

-- pedro mendonsa (pedrom@ozemail.com.au), April 18, 1998

Answers

Pedro, my 105 takumar is sharp at infinity when shot like you described (focus at 20 meters, f/22). I can understand one lens having a mismarked depth of field scale but two? Could be pilot error. It's time to call Pentax. SR

-- Steve Rasmussen (srasmuss@flash.net), April 29, 1998.

Pedro My calculations say that the f/no has to be f/22 to have a 20 m hyperfocal distance. (Computed for 40 lp/mm blur). For f/11, my calculator says the close focus is 31 feet and the far focus is 132 feet when focused at 66 feet. Hyperfocal distance is 132 feet (40 m). Bill

-- Bill Kelly (gklent@ix.netcom.com), September 17, 1998.

I too had problems w/depth of field with my Pentax 67, where the portions of the image at infinity were not tack sharp like they should have been. So I decided to run some tests with both the 105mm and 300mm lens. My conclusions were that the D.O.F scale on the 300mm doesn't seem to be accurate, (the 105mm seemed to be okay), and that if you want the sharpest images, it's best to set the DOF at least one stop less than the scales indicate (or more if you can). EG: if you're shooting at f/22, set the hyperfocal distance as though you were shooting at f/16. I've since been using this technique on my 45mm, 105mm and 300mm lenses and my images are now as sharp as I was expecting to get from these expensive lenses.

BTW: most photography books don't mention the technique just described, but I have since asked one professional photographer and he affirmed that he routinely uses the more conservative hyperfocal distance. It really depends on how large a print you're going to make, or perhaps more accurately, the viewing distance to the print. Using the DOF scales on the 105mm, for example, might be fine for 8x10's, but *not* for 16x20's. On the 300mm, the scales don't seem to be very accurate at all, and it's best to always set the hyperfocal distance at least one stop less than you're actually shooting. The 45mm lens I have seems to have fairly accurate scales, (but it's hard to tell since it has a large DOF to begin with), but I've gotten in the habit of shooting a more conservative hyperfocal distance even with this lens, unless the scene I'm shooting forces me to make compromises.

-- Bryan Flamig (bryanflamig@home.com), March 29, 1999.