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07-04-2012, 06:17 AM   #1
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40mm XS fringing

I just got a K-01 with its 40mm XS and have been using this lens on the K-01 and my K-r now. Its focus is fast, the lens is very sharp, but I have a problem with it wide open. It appears to fringe, more than my other lenses (the DA L kit, 35mm f2.4 and M 50mm f1.7).

Attached is a 100% crop of a shot taken with my K-r. Now, true, the conditions are not ideal - it is midday and the lens is wide open, so some fringing is expected, but it seems excessive. This even happens in dark situations without a huge contrast, even indoors under artificial lighting. Is this just how the lens is designed or is there something wrong with this particular copy? The fringing can be clearly seen in the highlights of the table and the chair (they are not normally purple), but also around the legs. Post processing can only do so much.

Edit: Apparently the forum resized the attachment, but you can still see the purple cast over the highlights and around the furniture frames

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Last edited by Na Horuk; 07-04-2012 at 06:30 AM.
07-04-2012, 06:28 AM   #2
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It's not really evident from this shot, so I'm inclined to say it's not excessive, but could you post 100% crops of the affected areas?

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07-04-2012, 06:43 AM   #3
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There most likely is some if you shoot wide open, thats with almost any lens the case.
07-04-2012, 07:27 AM   #4
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That is a harsh test , Na
So using its grandparent, the Pentax-M 1:2.8 40mm wide open I did a chair in the nearly full sun
2MB camera jpg: You can full screen it.
https://www.box.com/s/1e103b12d36069846ef0

07-04-2012, 10:09 AM   #5
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Nice hats. In that photo the fringing is much better controlled than what I saw with my lens, but I am a bit 'allergic' to chrom abs.
Here, I shot some branches against the bright sky, the easiest way to get fringing. This is not the edge of the frame, its near the center. With the chairs in the OP, the furniture is not purple at all, but in the photo it appears to be. But now that I've been shooting with the K-01 and 40mm XS for a while (practically went on a shooting spree at a local park), I think the great sharpness and very fast AF make up for this. I was just worried I might have gotten a bad lens because it was the window-front camera with a huge discount, even though the sellers assured me it was fine.
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07-04-2012, 12:07 PM   #6
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It does more have that issue then the 40mm Ltd and that was my main reason not to keep the xs-version.
07-04-2012, 03:54 PM   #7
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Strange since the optics are the same right?
07-04-2012, 04:46 PM   #8
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On the Pentax-M 1:2.8 40mm I see that wide open at f/2.8, the diaphragm (which is between the elements) is right out of the way, so the lens is effectively stopped by another fixed aperture behind the lens.
However this old lens is still good wide open.
I read , and learned by experience making waterhouse stops etc, that longitudinal stop position is critical to sharpness and color fringing.
The 40 pancake is often condemned but i regard it as one of my 4 best M lenses for versatility and sharpness and travel, although it is difficult to rotate the small ap and focus rings.
https://www.box.com/s/h7v10vzyyr1yjsb4p1xq
Maybe Na could try another shot with the diaphragm down one stop.

07-05-2012, 06:05 AM   #9
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QuoteOriginally posted by Anvh Quote
Strange since the optics are the same right?
Maybe on paper, but the lenses are not the same. Different materials?

Last edited by RonHendriks1966; 07-05-2012 at 06:17 AM.
07-05-2012, 06:16 AM   #10
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Might be... but find that actually unlikely why use different parts if you've already parts that fit?
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