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07-08-2008, 09:06 PM   #1
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Something wrong wiith my Tamron 19AH, or am I a yutz?

I bought this lens brand-new from B&H ($250, but the only way I could find a copy that didn't have dust that interfered with macro shots) more than a few months back and used it on and off with my K100d with no real problems that I can recall. I just got a K20d last week but really didn't have time to finagle with it until tonight. Shots with my Sigma 17-70mm & my Pentax K 50mm 1.4 came out fine, but when I popped on my Tamron and took a wide-open shot, I was getting pics like this:

(full-size crop-iso200 at 210mm at f3.5)

And this shot was after I cleaned both my lens and my UV filter with a new lens cloth, and re-mounted my Adaptall-2 adapter to make sure the aperture was being properly operated (and the blades were clicking fine, too) and refocusing. The diffusion-effect wasn't visible through the viewfinder, so I don't think it was the light (400 watts of Reveal tungstens in a fixture almost directly overhead). Using the lens hood didn't change anything, nor did using a paper to block some of the light. I started taking shots while stepping-down, and the effect lessened, and was pretty much gone by the time I hit F8 (1/2sec at iso200):

So I'm debating whether or not I'm either missing focus by just a bit (the "I'm a yutz" part) or somehow something got screwed up in the lens (which would be really annoying, considering I don't abuse my stuff).

07-10-2008, 06:15 AM   #2
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So I'm guessing I'm a yutz??
07-10-2008, 07:49 AM   #3
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It might be the tungsten lights but that's a guess. I would also remove the UV filter. I heard and experienced some of what you are seeing on my K10D with a few older 3rd party lenses. I can't offer a true explaination.

But I'd try just shooting in normal sunlight with and without the filter. See what you get at various apertures and post back.
07-10-2008, 08:36 PM   #4
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Well, it turns out that I am, indeed, a yutz, but not quite for the reason I originally thought. I was taking a few more shots tonight with the lens under different lighting as Zack suggested and still getting the same fuzzed look when zoomed in all the way and wide-open. Then I zoomed out & shot wide-open and got a normal-looking shot. Then I realized what was going on. Basically, I forgot about all the rules that apply to depth-of-field, especially with a close-focusing macro lens like the 19AH. While I remembered that shooting wide-open makes for a shallow DOF, I forgot that shooting from a short distance away from the focus point also makes for a shallow DOF, which gets even more shallow combined with a wide aperture. In other words, the fuzziness I was getting was being caused by the fact that I was missing focus by just a tiny bit with a DOF that would've been almost paper-thin due to the fact I was shooting a bit less than 3 feet away. So, to summarize:

Lens is fine.
Camera is fine.
I'm a moron.

07-10-2008, 08:44 PM   #5
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QuoteOriginally posted by Grimlock Quote
Lens is fine.
Camera is fine.
I'm a moron.
But an honest moron

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