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04-12-2013, 03:21 PM   #1
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K-5 soft/glowy wide open

I picked up a couple of primes and was surprised how bad the images look wide open. One is a pawn shop special - an "Access" P-MC WIDE-AUTO MACRO 28mm f/2.8, and the other is a Sigma 30mm f/1.4 EX DC (HSM, yeah right). The Sigma is a refurb from the Sigma outlet store, and the other from a local pawn shop.

Even my 18-135 WR is a bit soft & glow-y wide open, but not nearly as bad as these third-party primes.

By the way, this 28mm lens is fantastic close-up @ f/8! Anyway ... these images were show in RAW and processed in Lightroom with sharpening and clarity added, and chromatic aberration removed. THESE ARE PROCESSED IMAGES, not straight out of the camera. Why? Because this is how bad the look even with processing!

The pawn shop special wide-open:



And stopped down:



The Sigma 30/1.4 wide open:



And stopped down:



I'm surprised to be seeing this glow and smeared detail in all my lenses (to repeat, my 18-135 WR does it a bit, but not this bad). This has me wondering if I have a camera problem. Thoughts?

04-12-2013, 04:00 PM   #2
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The images looks like they are mostly lacking contrast (rather than just a bit of sharpness) and there are signs of some CA.

A few points that may be of help:
1. The wall you are using as a subject appears to be a very light colour and in fairly bright light. This can be bad for showing up contrast and CA problems for just about any lens.
2. Did the lenses have hoods on? A hood would certainly help.
3. Have you tried darker test subjects with these lenses.
4. The older 28mm coatings will not be as good as modern lenses and will particularly benefit from a hood and not being pointed at bright subjects.
5. As you are no doubt already aware most lenses perform better stopped down (f8 should be good) so I would expect them to be softer wide open. The Sigma is a bit softer than I thought it would be but this appears to be mostly contrast / CA and might be exaggerated by the subject matter.
6. I don't think there is any problem with your camera (that would more likely show up with the lens was stopped down rather than wide open).
7. Did you use liveview to with 10x magnification find the best focus (looking at the images you may well have).

Last edited by kiwi_jono; 04-12-2013 at 04:07 PM.
04-12-2013, 04:02 PM   #3
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I doubt you have a camera problem. As you probably know, lenses generally perform better at moderate apertures (f/5.6 or f/8ish) than they do wide open (with the exception of very expensive lenses, that is, especially exotic telephotos like a 600/4 that's designed to be shot wide open).

Hence the old newspaper photographer adage: "F/8 and be there."
04-12-2013, 04:04 PM   #4
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It is a lens thing, not the camera. Doesn't look like you quite nailed the focus -- it is not surprising the Access cheapie is crap wide-open, but the Sigma should look better. Focus precisely, use a hood.

04-12-2013, 04:21 PM   #5
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Your camera is fine, and the lenses look acceptable. Try again with a lens hood.
04-12-2013, 04:38 PM   #6
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Yeah, the wall is a very reflective surface actually and it looks like the focus is slightly off.
The CA you see appears to be axial or bokeh CA, which means the old Lightroom and most software can't fix it. This is also why the whole wall looks like it is glowing neon. If you nail the focus, this won't be such an issue. Pentax lenses have a bit of a reputation for this kind of CA, but it disappears if you stop down, even a little.
Most lenses perform best stopped down two steps or so.
Try doing this test and focusing using AF, then Live view, then manually. You can also try using a focus chart and then AF adjust accordingly. The DoF is very shallow wide open, and if you are photographing a reflective bright surface, it can appear as blur. Other reasons for reduced sharpness can be filters or slow shutter speed, but probably not in this case.
04-13-2013, 10:48 AM   #7
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The Sigma 30mm is not HSM in Pentax mount !
04-13-2013, 11:11 AM   #8
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You also look like you were shooting awfully close to the wall with those shots. That 30mm f/1.4 wide open means you probably could measure your depth off field in centimeters at close range. The grout looks to be in better focus than the bricks themselves, and I'd bet you were probably still backfocusing a bit.

Try standing back a bit further and try again - I bet you'll have better results.

04-14-2013, 07:21 PM   #9
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QuoteOriginally posted by kiwi_jono Quote
The images looks like they are mostly lacking contrast (rather than just a bit of sharpness) and there are signs of some CA.

A few points that may be of help:
1. The wall you are using as a subject appears to be a very light colour and in fairly bright light. This can be bad for showing up contrast and CA problems for just about any lens.
2. Did the lenses have hoods on? A hood would certainly help.
3. Have you tried darker test subjects with these lenses.
4. The older 28mm coatings will not be as good as modern lenses and will particularly benefit from a hood and not being pointed at bright subjects.
5. As you are no doubt already aware most lenses perform better stopped down (f8 should be good) so I would expect them to be softer wide open. The Sigma is a bit softer than I thought it would be but this appears to be mostly contrast / CA and might be exaggerated by the subject matter.
6. I don't think there is any problem with your camera (that would more likely show up with the lens was stopped down rather than wide open).
7. Did you use liveview to with 10x magnification find the best focus (looking at the images you may well have).
1. Perhaps.
2. Yes, I did.
3. No, not in any reliable fashion.
4. Yes, but this wasn't a situation where flare would be an issue, as the sun was behind the camera (high & to the right)
5. Yep. I didn't expect the pawn shop special to be sharp wide open, but I did expect the Sigma to be (per the reviews in the database). Agreed the subject (and lighting) are poor.
6. I don't think so either, but for all my lenses (so far) to be glow-y wide open seems odd.
7. No, just the center point with the Sigma and the focus confirmation in the viewfinder for the pawn shop special.

The sad part about questions of contrast and CA is that these images are processed in Lightroom, with contrast added and CA removed. The original raw files looked much worse (as they should, raw files should be somewhat low contrast and in need of sharpening).
04-14-2013, 07:24 PM   #10
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QuoteOriginally posted by Sagitta Quote
You also look like you were shooting awfully close to the wall with those shots. That 30mm f/1.4 wide open means you probably could measure your depth off field in centimeters at close range. The grout looks to be in better focus than the bricks themselves, and I'd bet you were probably still backfocusing a bit.

Try standing back a bit further and try again - I bet you'll have better results.
This was about 6-8 feet away, as far away as I could get in this location. The focus could certainly be off, too.
04-14-2013, 07:26 PM   #11
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QuoteOriginally posted by Na Horuk Quote
Try doing this test and focusing using AF, then Live view, then manually.
Yeah, I would love to get a LensAlign or something, as I'm fairly sure the Sigma could use just a bit of autofocus fine adjustment.
04-14-2013, 07:34 PM   #12
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Thank you all for your advice. I'll try this again, with better subject and lighting, and proper focus. I must say, I'm still a bit worried that shooting a brick wall just before noon could make the Sigma perform so poorly.
04-14-2013, 11:05 PM   #13
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QuoteOriginally posted by kevwil Quote
make the Sigma perform so poorly
Look at any test of the Sigma - eg Photozone's. Wide open it is not at it's sharpest, and has poor to absolutely no resolution at the edges of the frame wide-open, according to them. Maybe your copy has some minor decentering or something to make it appear even softer in the centre than usual. If in doubt, send it back.

Oh, and I trust you are not using any [UV or anything else] filters on those lenses while you are testing them...
04-15-2013, 06:21 AM - 1 Like   #14
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QuoteOriginally posted by kevwil Quote
Yeah, I would love to get a LensAlign or something, as I'm fairly sure the Sigma could use just a bit of autofocus fine adjustment.
Get an evaluation copy of FocusTune (by the same maker as LensAlign). Works great to fine tune your lenses.

FocusTune

Pat
04-16-2013, 09:13 AM   #15
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QuoteOriginally posted by ve2vfd Quote
Get an evaluation copy of FocusTune (by the same maker as LensAlign). Works great to fine tune your lenses.

FocusTune

Pat
Thanks!

But it seems there is no demo/trial with Pentax support. What download did you use?
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