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02-13-2014, 08:05 AM   #1
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Diffraction on K30?

I seem to have trouble getting consistently getting sharp landscape photos. How far can you stop down on the K30 before diffraction is a real limiter? This question would be for landscape photos enlarged to 30"x20",

I usually stick with F/8, for landscapes using my DA15, and DA21, making sure to focus on the background, preferably near the edge of the image.

I recently made an 18"x12" enlargements from the DA55-300, and I was unhappy with the soft corners at 170mm, F/8, but I didn't try focusing on the edge, instead of the center. Could I have gotten better results stopped down to F/11 or F/16 (with tripod)?

I have learned that with the DA15 and the DA21, I can get sharp corners at F/8 but that it really helps to focus on the edge of the picture instead of the center due to field curvature, or alternatively, to just know where infinity for the corners is on the lens. I have some DA15 pictures that had soft corners at F/8, and other that were very good. But I haven't experimented with F/11 or F/16.

Here's the DA55-300mm photo at 170mm F/8, which has soft corners when enlarged; although I have another at 150mm F/8, the Los Angeles skyline from the Griffith observatory, that looks pretty good (sharpened a bit).


Here's the disappointing soft lower/left corner at 1:1

- Sheldon


Last edited by sheld; 02-13-2014 at 08:29 AM.
02-13-2014, 09:05 AM - 1 Like   #2
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Are you sure the problem is diffraction? Could be many things that make an image soft: atmospheric conditions, filters, anything on the lens, high ISO, misfocusing (try taking a shot using live view focusing?), not using a tripod, not using 2 sec timer (SR disabled), not using remote, lens just being soft in the edges at that focal length.. and at 170mm, even if you use a tripod, a breeze can cause blur. Also, keep in mind that the field of focus is not perfectly flat, so a wall in front of you might be sharp in the middle but misfocused in the edges.

In regards to diffraction, some say that f9 is the limit on APSC (I forget where I read this), but I personally go up to f14 if I need to (for the DoF). f16 and above is where it gets really bad.

However, I think that shot looks pretty good. Too bad you are making large prints, because for web use, it would be good enough. On large prints, at close inspection, photos quickly start to look shaky
02-13-2014, 09:56 AM   #3
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QuoteOriginally posted by Na Horuk Quote
Are you sure the problem is diffraction?
I usually shoot at F/8, where there is little to no diffraction, but I haven't tried any landscapes at F/16, or even F/11, so I don't know what aperture it is best to use for enlargements.
02-13-2014, 11:54 AM - 1 Like   #4
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You may find tuning the AF micro adjust for each lens could help. The only lens I've really gone to town getting the AF right on is my 35/2.4, a great lens in a lot of ways but for long distance shots my copy definitely has a curved focal plane which is totally unnoticeable at closer than roughly 25 metres. After centre AF 'perfect' adjustment, taking a shot of a lone tree (about 250m away I would guess) at the far end of a wheat field clearly showed the plane of focus curving back towards me at the left and right edges of the frame (not the corners) probably 40m away roughly. I could tweak the AF the get these edges in sharp focus at the tree's distance but then the centre suffered, so in the end I set it halfway between and got a better consistency across the frame but not quite as sharp as possible if tuning for centre alone. It's still very good with this compromise though.

A zoom lens might be a bit tricky to get good results across the range though but I would say it's worth a go.

02-13-2014, 12:18 PM   #5
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QuoteOriginally posted by SteveB Quote
You may find tuning the AF micro adjust for each lens could help. The only lens I've really gone to town getting the AF right on is my 35/2.4, a great lens in a lot of ways but for long distance shots my copy definitely has a curved focal plane which is totally unnoticeable at closer than roughly 25 metres. After centre AF 'perfect' adjustment, taking a shot of a lone tree (about 250m away I would guess) at the far end of a wheat field clearly showed the plane of focus curving back towards me at the left and right edges of the frame (not the corners) probably 40m away roughly. I could tweak the AF the get these edges in sharp focus at the tree's distance but then the centre suffered, so in the end I set it halfway between and got a better consistency across the frame but not quite as sharp as possible if tuning for centre alone. It's still very good with this compromise though.

A zoom lens might be a bit tricky to get good results across the range though but I would say it's worth a go.
I think with the live-view autofocus, one can focus the edges, or even the corners, and that might work really well, but I haven't tried it on the DA55-300. I originally thought the Curved Focal plane thing was only a problem for wide angles, like the D15/DA21.
02-13-2014, 03:09 PM   #6
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Personally, I found that f/8 to f/11 is the limit before diffraction sets in most lenses. In some cases, I see diffraction beginning to set in at f/5.6 like my FA 50mm f/1.7. Other lenses like my Tele-Lentar 135mm can go seemingly go to f/16 before I see degradation (huge drop in IQ at f/22). I get increased perceived sharpness due to a deeper DoF but center sharpness starts tapering off.

I agree with Na Horuk and say that what you are seeing is not diffraction but a softly focused corner.

Try setting up your camera on a tripod and take a similar picture (unless you can take this same one over) at every major f/-stop. It's not as tedious as it sounds. Go for f/4, f/5.6, f/6.3, f/8, f/9, f/11, f/16, f/22, and f/29. If you want to do more then all the better. Open all the images in a viewer that allows you to cycle through them in sequential order with your keyboard's arrow keys. Apple's Preview is good at this. It even remembers if an image was zoomed and panned. Zoom and pan to a corner and cycle through the images at the same location. I'd say an exercise like this is worth doing once just to get familiar with your lens and what the limits are.
02-14-2014, 11:31 AM   #7
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QuoteOriginally posted by sheld Quote
I think with the live-view autofocus, one can focus the edges, or even the corners, and that might work really well, but I haven't tried it on the DA55-300. I originally thought the Curved Focal plane thing was only a problem for wide angles, like the D15/DA21.
No, I've seen it mentioned in a few reviews of longer lenses including zooms. In fact, I just bought a Sigma 17-50/2.8 in preference to a Tamron 17-50/2.8 partly because one review of the Tamron mentioned a curved focal plane at infinity, the Sigma being better. It's not usually a big problem, but it does exist to an extent.
02-18-2014, 08:53 AM   #8
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It certainly isn't a body problem.

It could be lens decentering, or an otherwise soft optic in the corner. Frankly, at that middle of the range focal setting and f/stop it appears to be more than field curvature related. The image might have a bit of motion, as well. What shutter speed was used, and could mirror slap been part of the problem? Try a range of f/stops. Try a different lens - wider is best. Landscape shooting at long focal lengths generally is a challenge if you are expecting the entire field to be sharply focused.

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