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07-01-2011, 01:35 PM   #1
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Is the kit 18-55mm IQ really this bad? FF problem?

Bought a K-5 with the 18-55mm WR kit lens recently. I also bought a used Auto Revuenon 50/1.4 mf lens. I found it nearly impossible to take pictures through the viewfinder with the Revuenon, if I take the shot when I hear the in-focus beep, there is heavy front focus, and if I try focus relying only on my eyes I have consistent FF problems too. My eyes should be fine, and the diopter adjustment should be correct. Focusing is easiest with LV magnification, but I hate taking pictures this way.

I was also wondering if there is something wrong with the kit lens or the AF system, since I'm surprised how bad the IQ is with the kit lens.

I took some test shot from my balcony and uploaded them to web, please take a look and post your comments. All shots are ISO400, handheld & SR on. The shots with the Revuenon are f2.8 1/125 and 1/100, kit lens was ~50mm, f5.6. and 1/20. Focal length was inputted correctly as 50mm with the Revuenon.

Pics can be found at Index of /pentax. Original DNG files included. No PP except for conversion to JPEG at Lightroom.

07-01-2011, 01:42 PM   #2
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Haven't seen your photos - they're too big - better to resize them for web and post them here.
Anyway, I had the kit lens for a while and it surprised me how sharp it was - but mostly at f/8. Venture outside by more than a stop each way, and you may find IQ dying out considerably. Nevertheless, it should be a good performer. Have you tested under normal sunny conditions?

Here are some examples of the 18-55 WR on the K-5 I managed to get:




07-01-2011, 01:45 PM   #3
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Can't say about FF, but with the kit lens you're basically shooting "wide open" (remember at the long end the minimum aperture is 5.6) and at a speed that might show blur, so hardly the ideal test conditions.

That said, it's not a bad lens, but it won't be stellar either.
07-01-2011, 01:51 PM   #4
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The kit lens is surprisingly good for what it is - cheap, commonly produced, and low quality. Under ideal conditions, the lens can take some amazing shots. Unfortunately, ideal conditions do not occur with this lens too often. I would never fault it though, considering it's a kit lens, and by all accounts, it does far better than kit lenses from other brands. But you can't expect the world from it.

Best shots from it generally come from the 35mm end at F8. Wide open, it takes F11 to get it cleaner, and even then it isn't that special. 55mm end is alright at the F8 end. That's been my experience, and if you check out:

Pentax SMC-DA 18-55mm f/3.5-5.6 AL - Review / Test Report

You can see a bit more info on what settings you should aim for.

07-01-2011, 02:47 PM   #5
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Thanks for the feedback. Guess I had my expections a bit high. What about the focus beep and vewfinder focusing trouble when shooting with the 50mm? Shouldn't it be correctly focused when I hear the beep and see the icon? It's every time focused too near, no matter if I start focusing from too near or far.
07-01-2011, 02:53 PM   #6
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QuoteOriginally posted by Phoenix_ Quote
Thanks for the feedback. Guess I had my expections a bit high. What about the focus beep and vewfinder focusing trouble when shooting with the 50mm? Shouldn't it be correctly focused when I hear the beep and see the icon? It's every time focused too near, no matter if I start focusing from too near or far.
You need to calibrate the AF for each lens attached to the camera. It's in the custom menu

The K-5 stores the calibration for 20 separate lenses. There's loads of threads here on how to do it.
07-01-2011, 02:55 PM   #7
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should be, is your diopter set correctly? The focus beep is generally correct on my k-x and on my brother's k20d. Also, remember that in that mode, you're stuck with the center focusing point.

as for the kit lens, it is NOT in any way a bad lens. I went through several different standard zoom "upgrades" before i settled on my current one (sigma 18-50 f/2.8) because i actually found all of them to be softer than my little kit. If you're getting bad pictures from it, its probably due to incorrect technique more often than not. Look at this thread to see what some people have done with theirs:
https://www.pentaxforums.com/forums/lens-clubs/45425-kit-lens-club.html
07-01-2011, 11:03 PM   #8
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QuoteOriginally posted by Phoenix_ Quote
Thanks for the feedback. Guess I had my expections a bit high. What about the focus beep and vewfinder focusing trouble when shooting with the 50mm? Shouldn't it be correctly focused when I hear the beep and see the icon? It's every time focused too near, no matter if I start focusing from too near or far.
Regarding the focus beep - it's not perfect on my k-x, and I believe this will be a good thread for you:

Mastering manual focus on Pentax DSLRs « robertsdonovan.com

The focus beep when approaching from infinity and when approaching from 0 on my 50mm manual allows for quite a bit of leeway in between. You just got to test where the actual focus will land

07-01-2011, 11:30 PM   #9
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Based on the exif data for the picture, I wouldn't blame the kit lens as bad. It's hard to compare it with the revuenon when shooting with different shutter speeds/apertures. For one the kit lens photo was taken at 1/20 of a second versus 1/125 with the revuenon. Even if you're on a tripod, just the slightest breeze will cause the leaves to blur a little. Also zoom lenses vs prime lenses is like comparing apples to oranges. No consumer level zoom lens will ever be as sharp as a decent prime lens. Period. That's the price you pay for convenience and flexibility.

With that said, in my experience the Pentax kit lens is an excellent performer. Perhaps try taking some more shots in better light and posting them here if you still see a problem.
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