FA 31mm f1.8 vs A 50mm f1.7 Help!

[jerry thirsty]

Actually, there is a way to get the autofocus adjustment mode on the K-x. Instructions are here:

 

http://www.scribd.com/doc/23723765/Pentax-Kx-Pentax-K-x-AF-adjustment-through-undocumented-debug-mode

 

I would clarify the instructions a little bit:

 

1) Make sure you hit return after the line of text inside the file.

2) Make sure you save it as "MODSET.492", not "MODSET.492.txt" (but upper or lower case doesn't seem to matter)

[michael_elenko]

<p>Marius,<br /> There are a lot of methodology holes in your approach here. Andrew G. is spot on. Hand-held has way too much margin of error. Also, at least in your original post you noted that you are using the built-in flash. I'm assuming that this will trigger a P-TTL protocol and the lighting will not be as uniform for each lens. Thus you will be examining images lighted differently, especially if you are maintaining standard aperture and shutter settings for lenses of differing focal lengths. That can affect perceived focus. Since the area seems quite dark to me, how can you be sure that you focused each lens by hand correctly to begin with? If you have to do this kind of testing indoors, use stable, consistent modeling lights, the camera on a tripod, MLU, and a remote control. The MLU will disable anti-shake. And as Michael K. says, try to equalize the target for both focal lengths. This difference alone, is sufficient enough to make me question any judgments about sharpness here.</p>

<p>This may help you determine if you have a fine lens here (and to me the odds of that are very very high): read Mike Johnston's <a href="../columns/mjohnston/pentax-35mm-lens/optical-discussion">review</a> of the DA 35mm that was posted on PNet in August 2008. I think Mike is one of the most coherent photography writers anywhere. Ignore the specific findings about that lens (though I agree with Mike), for your purposes, I would examine <em>how</em> he evaluates the lens. He functionally tests for factors besides simple sharpness. Then read his <a href="http://theonlinephotographer.typepad.com/the_online_photographer/how-to-stress-a-camera-le.html">article</a> about How to Stress a Camera Lens. May I suggest that you then take the 31mm outside and follow Mike's steps, taking notes along the way to help your evaluation? My guess is that you will better appreciate what a fine tool you have purchased.</p>

<p>ME</p>

[shots worth sharing]

<p>I engaged in a similar exercise in the delirium of cabin fever last winter. I came away with some vague, probably half-baked, impressions regarding relative sharpness but I learned a lot about shooting technique and lens qualities. My key finding was that, despite my attempts to control variables, there were significant differences between shots using the same lens with the same settings at the same distance: in essence, that my relationship with the gear was fairly dynamic, even in controlled circumstances. I came away with a deepened appreciation of the need for multiple takes of the same shot whenever possible and a sense that lenses need to be evaluated in terms of their suitability and performance in real world shooting situations.</p>

[laur1]

<p>Marius: to me, none of the shots you posted seem very sharp to me. They also seem shot in low light and underexposed quite a bit. The information that Andrew asked for is also important - are these 100% crops or shots that were resized? For proper comparison, you should focus on the same area and then post 100% crops of that area.<br>

Frankly, while the K-x is a great camera, its viewfinder is not that nice to use for manual focusing in low light. I was thinking of recommending focusing via Live View, but due to the smaller resolution of the LCD screen, I didn't find that to be as precise as it could be either.<br>

I think the simplest test is to use as target some piece of cloth. Shoot it at an angle and you'll certainly get some part of it in focus - look for that area and then you can test how much detail you captured about its threads. To eliminate camera shake, put it on a tripod, use a remote shutter, and set the shutter delay so the mirror is raised some time before the image is exposed. <br>

Hope this helps.</p>

[marius_mirea]

<p>Thanks all, you have been very helpful. In the meantime I have used the lens more extensively and I think it is a good copy :)<br>

I admit that my testing methods were ...let's say... approximate and there is more to a good photo than sheer sharpness.<br>

Anyway I will try sometime whet I'll have the time to set up a more proper test but not to evaluate the FA 31mm (which now I am now convinced has no fault) but to try to compare all my lenses, because I think it would be very interesting to test a very different bunch of lenses and see how they compare.<br>

Overall I am very impressed by the speed and the usefulness of the responses I have got and I think that this forum is among (if not the most) friendly and usefull for a dslr beginner like me<br>

Cheers to you all!</p>

[michael_kuhne]

<p>You can easily check the photozone website, which runs testing under very well-controlled lab conditions. They will provide specific lines of resolution figures for lenses.</p>

<p>Actually, Hin Man reports that in shooting high-quality JPEG images with his K-x, the default results are slightly soft. He has increased sharpness setting by a notch or so, which I believe will mean +2, as the default bright mode would likely already be at +1. The camera is deliberately engineered this way to allow more leeway for adjustment.</p>