I wanted to see how sharp a picture my ZX-M could take with my three lenses. I have a 50mm f/2.0 SMC-A, a 135mm f/3.5 SMC-M and a 200mm f/4.0 SMC-M. I used Elite Chrome 200, mounted the camera on a tripod and shot a section of brick wall with each lens. They were all of the same section of wall so the distances were approximately 4 feet, 10 feet and 15 feet respectively. I set the aperture to f/8 and let the meter determine shutter speed, which showed in the viewfinder as 1/15 second.
The good news is that all the pictures were sharp from edge to edge and in the corners. Also, I bracketed focus just a small nudge too shallow and a small nudge too deep on each shot and the slides with the "correct" focus was the sharpest, although the differences were pretty small and in some cases indistinguishable (since I was at f/8, I suppose). The bad news is that the exposures were not the same. The shot at 50mm was a perfectly exposed slide. The shot at 135mm was just a tiny bit darker, barely perceptible. The shot at 200mm was noticably darker than the other two. Now I know that my SMC-A lens let the camera use matrix metering on the 50mm shot. But both the 135mm and 200mm ones used the center-weighted metering since they are pre-A lenses, right? If I weren't comparing the 50mm and 135mm slides side by side on a light table they would each look "well exposed" but the 200mm one is not a well-exposed slide, it looks dark. The 135mm and 200mm lenses were purchased used through KEH and the 200mm one was a "bargain" that has no marks on the glass but you can tell it's been around the block a time or two exterior-appearance-wise. So is it possible that its aperture setting is off by a half or two-thirds of a stop? How should I try to test that further? - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
