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11-26-2012, 10:37 AM   #1
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K5 Focus Problem on one lens

Hi All,

I'm having an issue with my K5 using a Tamron 28-75 lens. I've had this lens for a few years and have used it both with my K5 and K20d and have loved it, however, it seems to have developed a strange focus issue. I noticed last week that I was losing a lot of shots. I was taking pictures of my daughter two days ago, and I lost them all, they are totally unusable. I tried recalibrating the lens with my Spyder Lens Cal and adjusted to what appeared to be a close AF adjustment - it's actually clear on -10 right now. I am getting reasonably sharp pictures, up to about 3 feet, but from anywhere from 3 feet or greater, it's out of focus. I tested my 70-200, and it's absolutely fine. I've used this set up for going on three years with little issues (this past year with my K5 and a K20d before that). I had some problems during the summer prompting me to get the Lens Cal, and after that, it looked great until last week. No matter what adjustment I'm making, it's very soft focus.

I've added photos to my flickr account. I messed up a little when I shot the k20d for comparison, it was at f3.5 and the k5 is in 2.8, I know it will make a little difference, but I just really need to know if it's time to get a new lens or if this would be worth trying to fix, and what it could be (maybe an internal lens slipped or something??). The titles of the pictures should let you know what I was shooting. Thanks!


Flickr: jenniferrd73's Photostream

11-26-2012, 12:02 PM   #2
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Hi, sorry to hear you are having problems.

Sorry I don't have that lens but is it capable of being focussed at distance with Liveview? This would tell you if the problem was more likely optical or a focus system system problem (within lens presumably).
11-26-2012, 01:25 PM   #3
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I just did a few side by side tests, and while the live view seems a little better, it's not substantial. If the live view had been sharper, what would have that meant? I also leaning towards the glass is dirty because it's giving me that hazy look as well, so it might be two issues all at once, even though we are very good about cleaning it before every shoot. Am I wrong in assuming that if another lens is acting fine with the camera, that it's something to do with the lens in question (process of elimination)? This is just frustrating, I don't know if I need to buy a new one, ship this off to Tamron, or what.
11-26-2012, 01:51 PM   #4
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I'm no expert but have had some problems with older lenses I have had here.

If the lens can't be focussed properly manually (and I'm suspecting this might be the case if LV is still having issues), then there is something optically wrong with the lens. I would try manually focussing on a target a moderate distance away. Use LV and 10 x magnification (press INFO button a few times) and see if you can manually achieve a good focus. If you can't focuss manually then its likely something has gone optically wrong with the lens. At that point I would have a good look through the lens to see if I can spot anything (like haze, condensation or fungus).
If you can manually focus, is the manual focus movement free moving (i.e. is it sticky)?

11-26-2012, 05:24 PM   #5
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QuoteOriginally posted by kiwi_jono Quote
I'm no expert but have had some problems with older lenses I have had here.

If the lens can't be focussed properly manually (and I'm suspecting this might be the case if LV is still having issues), then there is something optically wrong with the lens. I would try manually focussing on a target a moderate distance away. Use LV and 10 x magnification (press INFO button a few times) and see if you can manually achieve a good focus. If you can't focuss manually then its likely something has gone optically wrong with the lens. At that point I would have a good look through the lens to see if I can spot anything (like haze, condensation or fungus).
If you can manually focus, is the manual focus movement free moving (i.e. is it sticky)?
Thanks, I will test it out tomorrow outside and see. I did call Tamron, but they couldn't tell me what it might be. I probably will send it in and at least get a quote to see what it will cost to fix it.
11-26-2012, 06:09 PM   #6
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Over time the lens may have taken a light knock somehow, in a camera bag or in use. That could have bumped a lens element slightly out of alignment, or the focus gear mechanism could have a tiny grain of dirt in it, or something. It doesn't take much to throw a lens out sometimes.

Do you notice whether the lens is visibly softer only in particular areas of the image, and apertures (eg only the left side of an image is softer at 40mm @f2.8, but everything is sharp on the right) or is the softness uniform across the lens no matter what? Uneven sharpness could be a symptom of a de-centred lens element or two.

Plus - are you using an UV or protection filters on that lens? Sometimes they can cause unpredictable problems with a lens, including softness. Remove the filter and see what happens.
11-26-2012, 06:20 PM   #7
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It does indeed sound like the lens has an element slightly out of kilter. It is more likely if all your distance shots are blurry rather than just some.
11-27-2012, 08:58 PM   #8
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Thanks all. Yes, I now suspect an element out of alignment. It's very soft at f2.8 and slightly soft f4 at 70mm, though some shots have been lost at other focal lengths at both 2.8 and 4. I had a skylight filter on it that I removed and it also seemed to help with the few test I was able to run today, especially on the f4 shots (not sure why, just reporting what I found, lol). I have two shoots coming up, I believe if I keep it at at least f5.6 or higher, I'll be fine for them, then I'll send it to Tamron to be fixed. It's still appears super sharp except for the problem shots, so if I'm careful, and keep checking, I think it should be fine. Part of the one shoot will be outside, so I can use my other lens for that.

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