Hello everyone. Relatively new Pentaxian here who a few months ago bought a kx with the 18-55 and 55-300 kit lens. Just a short while ago, I was fortunate to acquire the vaunted FA31 f1.8 lens from our marketplace in top condition, used.
I should like to share my comments about my new prized FA31 and notes about some comparison tests that I did with it and my 18-55 kit lens at 31mm. Before I begin, I am in no way trying to imply that the kit lens is as good as the FA31. Additionally, I am strictly an amateur who has a lot to learn in the world of photography. The majority of you have forgotten more than I probably will ever know.
But, I suspect that there are some of you out there like me who are hooked on great Pentax lenses. So here goes:
1. I tested each of the two lenses with two Imatest charts printed on 8 1/2x11 paper that I downloaded and taped to a box. The tests were indoors with natural lighting and two overhead ceiling fan lights turned on. Manual focus using Liveview, ISO 400, aperture priority. At f1.8, 2.8 4.0, 5.6, 8.0, 11.0 for the FA31 and 4.0, 5.6, 8.0, and 11.0 for the 18-55 at 31mm. (Hereinafter, I will refer to the 18-55 at 31mm as "55S." To attain 31mm, I guestimated the zoom ring to what I thought would be as near 31mm as I could --- about halfway between 24mm and 35mm.)
Bottom line: At f4.0 and up, the FA31 had better sharpness and less fringing than the 55S. Verdict: Definitely FA31.
2. I next tested the two lenses with pics of a pot and vase sitting on the edge of our fireplace, with a french door facing north behind the fireplace. That gave me an opporunity to judge pic IQ and purple fringing through the door frame. Same parameters as for the above: ISO 400, manual focus, aperture priority, f4.0, f5.6, f8.0, f11.0.
Bottom line: slight edge to the FA31. What really got me here was just how the 55S hung in there in a real world picture setting. FA31 better at the edges; 55S either equal to or slightly not as good as the FA31 in the center. Since the 55S at 31mm fastest setting is f4.0, it came as no surprise that the edge sharpness was not as good as the FA31 at f4.0. (I have read the Photozone reviews of the FA31 probably two dozen times, fyi.)
3. This morning I took some pics facing north from our upper deck here in south central New Mexico. ISO 200 with Auto Focus, aperture priority. Apertures compared: f4.0, f5.6, f8.0, f11.0, f16.0.
Bottom line: At all apertures, the FA31 appeared better in terms of overall IQ, in my opinion. For several pics, the results were somewhat close though. Again, I note just how decently the 55S hung in there.
4. As a means to amplify my notes about how the 55S competes fairly well, I should like to share 6 pics from test 3. above, at f4.0. The first two are the pics right out of the camera. In my eyes, the FA31 is better. But, again, the 55S hangs in there pretty good for this scene. The other four pics are crops, two of which are some houses near the center and the last two are at the right hand edge of the scene. I was surprised at just how decent (and even a bit better) the 55S crop looks for the two houses near the middle. Of course, no surprise that the FA31 is sharper at the edges.
Summary conclusions and comments. I very much like my FA31. It will stay on my camera most of the time. But, the 18-55 kit lens is not chopped liver. I am amazed at just how good the over 600 pics are that I have taken. I will keep it for sure. Interesting at how a $50 lens hangs in pretty good for decent lighting pics compared to a hall of fame $1000 lens. No bokeh comparisons, but just a small sampling of ordinary real-world pics with good lighting conditions.
I suppose some of what I am saying parallels Ken Rockwell's essay:
Your Camera Doesn't Matter.
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Here are the uploaded pics. FYI, the FA31 pics resulted in a shutter speed of 1/2000 and -1 exposure bias. For the 55S --- 1/1250 and 0 exposure bias. As you can see, the FA31 pics were exposed a bit less. Not exactly sure why they are different in the same light, but it is what it is.
1. FA31:
2. 55S:
3. FA31 scene crop 1:
4. 55S scene crop 1:
5. FA31 scene crop 2:
6. 55S scene crop 2:
Last edited by altovintner; 10-07-2011 at 02:04 PM.