Latest Review Posted | SMC Pentax-FA 28-105mm F4-5.6 [IF] I have two copies of this lens. Both are sharp across all focal lengths. 28-105 on an APS-C body gives a very useful range, from mild wide angle to medium telephoto. It's great as a walk around lens with nice image quality.
Resolution
Results of an informal resolution test are shown below. Lacking an AF 1951 chart, I used a barcode from a battery blister pack. The field of view was 38 inches. At 105mm f5.6 (wide open), 1.5 lp/mm on the subject was just barely resolvable. This turns out to be about 61 lp/mm on the K-x sensor. At 105mm f7.1 (2/3 stop down), 2 lp/mm on the subject was again barely resolvable. This is about 82 lp/mm on the sensor. These numbers are limiting resolution values, so contrast is fairly low at maybe 3% or so.
https://www.pentaxforums.com/forums/members/eddieamzel-albums-misc-images-picture14246.jpgClose up shot of barcode.
https://www.pentaxforums.com/forums/members/eddieamzel-albums-misc-images-picture14247.jpg
38 inch width.
https://www.pentaxforums.com/forums/members/eddieamzel-albums-misc-images-picture14248.jpg
100%crop at f5.6 (check out the thin line above the 2 in "40293")
https://www.pentaxforums.com/forums/members/eddieamzel-albums-misc-images-picture14249.jpg
100% crop at f7.1: (check out the lines above the 3 in "02381")
Build Quality
I've noticed two things, on both copies. One: the front element was slightly loose when I purchased it (used). This is apparently a common issue with similar Tamron designs as we... |