[apisto]

Please help me understand if I have a "bad copy" of the DA*55, or if the below behavior is normal.

I recently bought a new DA*55. At f1.6 and smaller, the aperture blades do not seem to close down evenly as shown below in a photo at f1.6. Part of the circle is nice and rounded, but part is ugly because the aperture blades are not even, or not closing evenly. So I returned it for another copy. But the second copy exhibits the exact same behavior on the exact same part of the circle! I know this is something that will not often come up in normal shooting conditions. But I intend this as my "artsy-fartsy" lens, so it will affect photos from time to time.

Is this effect normal? Are these bad copies?

Also, on both copies, while the lens IQ is good at f1.6, at f1.4 the sharpness is low, and the contrast very low. I guess this is to be expected, though?

Thank you in advance for everyone's time.

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[dms]

Did you check the serial number--maybe the goofed and sent the same lens again?

[apisto]

LOL, good point. Unfortunately I was not bright enough to record the first serial number.

[zbrueningsen]

I've never had any sharpness issues or contrast issues. Let me check some photos and see if I have have that blade shape issue. But as far as the sharpness and contrast have you focus calibrated it? Early on some of the production had focus issues. Because I've owned mine for a few years and mine is super sharp.

[dms]

I don't have the 55mm f1.4 but what you show is on one of my inexpensive (3rd party) lenses--but I would not expect it on a more costly Pentax lens. I haven't seen it on any of my other couple of dozen lenses--and for a fast 50 where you want a full circle wide open, it seems problematic. Not a problem on my 50mm f/1.7 (M) or f/1.4 super takumar.The indent does appear (as an example) on my 50 M f/1.7 closed down slightly--except it is symmetrical. 1/3 stop closed down can make a noticeable improvement--again my 50 mm f/1.7 is fine wide open.

[JinDesu]

https://www.flickr.com/photos/jindesu/sets/72157647736916351

Here are some sample shots (with full size images linked) with my older k-x. The k-x being 12MP will not show as much as your k-5IIs, but I never felt it was a slouch even wide open.

I don't have a lot of good F1.4-1.6 samples on my k-3, but I could shoot some tomorrow.

[Just1MoreDave]

I just got one used, that I didn't expect to be perfect. The aperture blades look even to me until maybe f11, but it's hard to tell a regular nonagon. I get a little more flare than I expected, f1.4 from a bright highlight in the frame so a hood wouldn't fix it. That is on the edges of the frame. It's sharper than my F50/1.7 in test shots. Focus seems to be the same as Youtube video focus tests. In ten days I've taken 400 shots with it. I wouldn't return it even if I could.

[apisto]

I really appreciate everyone's feedback and the photos posted. It sounds like I need to try out copy #3.

To answer the question about focus tuning, I have not formally tested it, but it "seems" spot on. Also, when testing sharpness and contrast, I snapped photos of the back of a dollar bill at an angle. There is a lot of fine detail in the texture of the paper and the printing.

[apisto]

I sent back the second copy and will get the third copy in about a week. I will report back how the new copy performs.