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08-31-2013, 08:04 PM   #1
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Focus problem, maybe?

There are so many forums to choose from I'm not sure this belongs here, but this is a good place to start.
I've a brand new K-30 w/ 18-35 kit, and though I haven't taken 100s of pictures I've take a bunch of test shots and I just don't feel the focus is right. I can't say exactly what is wrong, it just doesn't seem sharp. I've heard people use the word "soft", that might be what it is. What I'd like is a procedure to properly determine whether it is a focus problem or me. I have a tripod, but I'd still have to fire it by pressing the button as I've no remote or cable release.
Should I test at any particular ISO or at any particular aperture setting? Should I use a particular type of subject? Indoors, outdoors? What should I look for in PS Elements or Lightroom (trial version) to say definitively there is a focus problem? Should I expect sharpness at 100% enlargement or is that expecting too much?
I've got the DA 1.8 limited 50 mm lens coming, but I'd like to proceed with a legitimate test now with the kit lens.
Thanks in advance for any direction anyone can offer.

08-31-2013, 08:14 PM   #2
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Testing:
Lowest ISO possible
On a tripod
Use a remote or the 2 second delay drive mode
Use a middling aperture, maybe f/8 (Particularly on the kit lens but many lenses will be a bit 'soft' wide open, so stop down at least 2 stops for 'sharpest' results)
Use a high resolution test target like:ISO 12233 Test Chart print it on good glossy paper.
Make sure the camera is precisely aligned both vertically and horizontally with the target.

Here is an article about fixing focus issues. I'm not sure you have an issue but this has good info on testing: https://www.pentaxforums.com/reviews/lens-align-front-back-focus/introduction.html


QuoteOriginally posted by Catscradle Quote
I've got the DA 1.8 limited 50 mm lens
Just FYI but the DA 50 f/1.8 is not a Limited lens. That's a different series which costs quite a bit more. Nothing wrong with the DA 50mm, it's just not a limited.
08-31-2013, 08:50 PM   #3
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QuoteOriginally posted by jatrax Quote
...
Just FYI but the DA 50 f/1.8 is not a Limited lens. That's a different series which costs quite a bit more. Nothing wrong with the DA 50mm, it's just not a limited.
I'm new at Pentax, thanks for the correction. Is "prime" the right word?
08-31-2013, 08:55 PM   #4
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Biggest cause of soft photos for beginners is using too slow of a shutter speed. I'd be checking that first before worrying about AF fine tuning.

08-31-2013, 09:41 PM   #5
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QuoteOriginally posted by twitch Quote
Biggest cause of soft photos for beginners is using too slow of a shutter speed. I'd be checking that first before worrying about AF fine tuning.
Yes, and posting sample photos with the exif information intact or at least copied into your post would be most helpful in our giving advise. Exif info will have things like shutter speed, aperture used, focal length etc so we can look at your photo and settings and see if it's just a settings issue or if using focus charts and more involved trouble shooting is necessary.
09-01-2013, 05:21 AM   #6
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Thanks for the comments and links.

I've printed the chart linked to by Jatrax and also the chart at this link: Jeffrey Friedl's Blog . The second link seems to be an excellent article on focus checking. Let me know if I'm wrong. I will take tripod pictures of these images and evaluate. Unfortunately today is rainy and cloudy so I can't use outdoor light and I don't have studio lighting. I'll try using standard lighting, but I don't think it will suffice.
09-01-2013, 06:09 AM   #7
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Jartax has some great comments

"Testing:
Lowest ISO possible
On a tripod
Use a remote or the 2 second delay drive mode
Use a middling aperture, maybe f/8 (Particularly on the kit lens but many lenses will be a bit 'soft' wide open, so stop down at least 2 stops for 'sharpest' results)"

I would like to add just 1 item, when shooting an image using the above comments shoot a 2nd identical image same subject and settings but use Live view. Then compare the 2 images. LV uses a different AF method and if the LV shot is sharper it's time to think about AF adjustment.

Hans
09-01-2013, 09:29 AM   #8
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The light wasn't good, so the shutter speeds were slowish. I set the aperture at f/8 and the ISO at 200. The back/front focus had a shutter speed of 1/30 with the telephoto at 35 mm and I thought looked pretty good, though I thought focus deteriorated more quickly coming forward. The detailed image was shot at 1/13 w/ the telephoto at 55 mm, I wasn't as happy with that. I took both of these with the timer. I didn't see any difference between viewfinder and live view focusing.
Opinions?

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09-01-2013, 09:45 AM   #9
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QuoteOriginally posted by Catscradle Quote
The light wasn't good, so the shutter speeds were slowish. I set the aperture at f/8 and the ISO at 200. The back/front focus had a shutter speed of 1/30 with the telephoto at 35 mm and I thought looked pretty good, though I thought focus deteriorated more quickly coming forward. The detailed image was shot at 1/13 w/ the telephoto at 55 mm, I wasn't as happy with that. I took both of these with the timer. I didn't see any difference between viewfinder and live view focusing.
Opinions?
Catscradle, to get a handle on any front/back focus issue, you have to have the aperture set to wide open. The objective is to narrow the depth of field as much as possible.
09-01-2013, 10:03 AM   #10
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QuoteOriginally posted by IchabodCrane Quote
Catscradle, to get a handle on any front/back focus issue, you have to have the aperture set to wide open. The objective is to narrow the depth of field as much as possible.
Ok. Is there no end of learning.... The first post said to shoot around f/8, but I guess he meant for an overall focus test. I just tore all that down and I'm not going to bother setting it up again right, maybe give it another shot tomorrow. If I can get some good sunlight I think the results may be more meaningful anyway.
09-01-2013, 11:44 AM   #11
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QuoteOriginally posted by Catscradle Quote
Ok. Is there no end of learning.... The first post said to shoot around f/8, but I guess he meant for an overall focus test.
Correct. Your original post suggested you were not happy with overall focus, not necessarily front/back focus. IMHO the kit lens is too slow to benefit much from AF fine tuning. Not saying it won't benefit at all, just that other factors come into play. To test a lens to see if it CAN be in focus, test it at it's best: f/8 and middle focal length on zooms. Every lens has a 'sweet spot' but in general middle of everything is going to be best. As you get closer to the far ends of the range (on your lens the 18mm and the 55mm lengths) you will start to lose some quality. If you cannot get a good sharp picture with a lens at it's best spot then likely something is wrong. And then you start to look at AF fine tuning or other adjustments.

A really good (and expensive) lens like for example the DA*60-250 will give you good results wide open and at both extremes of focal length but you pay for that. Even on very good lenses it is usually recommended to stop down at least 1 stop from wide open and to back off the longest focal length just a bit.

Now if you are testing for front/back focus then Ichabodcrane is correct, shoot at the largest aperture you can to narrow the depth of focus so you can see where the best point is. But before you start down the AF fine tuning route make sure you have eliminated all other factors, such as shutter speed, technique, stopping down a bit and so on. Without precise testing AF fine tuning can make things worse because the margin of error in a sloppy test is more than the original error. So you are just guessing what the adjustment should be. I guess I opened the AF fine tuning can of worms by posting that article but you should really check everything else before going to that.
09-01-2013, 12:30 PM   #12
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QuoteOriginally posted by jatrax Quote
...

Now if you are testing for front/back focus then Ichabodcrane is correct, shoot at the largest aperture you can to narrow the depth of focus so you can see where the best point is. But before you start down the AF fine tuning route make sure you have eliminated all other factors, such as shutter speed, technique, stopping down a bit and so on. Without precise testing AF fine tuning can make things worse because the margin of error in a sloppy test is more than the original error. So you are just guessing what the adjustment should be. I guess I opened the AF fine tuning can of worms by posting that article but you should really check everything else before going to that.
I appreciate your help in this effort. My intention is NOT to fine tune the AF, at least at this juncture in my photographic journey and current level of expertise. As this is a new camera for me and the world of digital SLRs is a new world for me, my only intention is to discover where the machine's limitations end and mine begin. From that point I can start to address my limitations and later the machine's. That is unless the machine turns out to have some limitations that are not normal for the k-30 w/18-55 mm lens. At any rate I want to evaluate BOTH front to back and overall focus. If nothing else I figure the endeavor is a good way to get more familiar with the camera.
I might yet bring this back and get it with the 18-135mm lens kit, but that hardly seems worthwhile as that kit is priced 450 more than this kit which is the cost of the 18-135 stand alone lens.
09-01-2013, 12:32 PM   #13
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Just to complicate an already complicated issue, it's not always ideal to conduct focus tests fully wide open, it depends on the lens and the camera's AF sensor. Due to lens aberrations, the focal point can move a bit at different apertures; also, the AF sensor may only work at an actual f5.6 no matter what aperture the lens is wide open - I think the K-30 is one such camera. So, try wide open tests but if things look a bit off at f5.6 for instance, then the reason could easily be one of the 2 mentioned.
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