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Old Jun 2, 2009, 10:02 AM   #11
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Look at the magnification value of the lenses. Lens manufacturers have often used "macro" with zoom lenses that can do anything larger than 1:4 (a 4" object will cast a 1" image on the sensor). The Tamron (at least according to B&H's website) can do 1:3.5, so it's just under that unofficial 1:4 criteria (there is no actual standard for when a lens becomes a macro lens). If you look at the Pentax specifications, it says it can do 1:3.5 also (as can their DA 55-300, by the way). Pentax seems to reserve the word "macro" for their primes that can do 1:2 or 1:1. So both the Pentax and the Tamron have the same magnification abilities, what you look for in a macro lens.
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Old Jun 2, 2009, 2:43 PM   #12
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To add to what Harriet says: a true macro lens has a lens element design that allows you to take a picture that is sharp from edge to edge, if the object is flat. For example a print sheet. Other lenses should rather be called "close focusing lenses". For most purposes this is of little or no importance, the magnification ratio is more interesting.

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Old Jun 3, 2009, 6:49 AM   #13
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Well, I had decided to go ahead and get the Pentax. Unfortunately, I got a response back from him this morning that he sold it since he hadn't heard from me. He'd only contacted me last Wednesday and I wrote him back asking him to let me wait until I got home. Oh, well. Should have acted quicker.

Thanks for all the input. I'll keep my eyes open for another.

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Old Jun 3, 2009, 12:47 PM   #14
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Patty, true macro is 1:1 or greater - anything less is merely close-up. As has been pointed out, most true macro lenses are flat-field, the "pseudomacros" are not.

As Goldwinger can testify, fixed equipment can fail again, especially when it was that way originally, so you may be better off in the long run. I am sure the Pentax lenses are no less reliable than the Tamron, but anyone can get a bad example I hadd to send my Sony mount Tamron back for exchange because right out of the box it made horrible grinding noises in manual mode.

Here is best of three recently posted threads in the close-up forum, so you can see what the lens can do close up - they are from the Sony, so I didn't post them here. I haven't mastered either the camera or the lens yet, and bear in mind that the a350 is not a K20.

Sage advice
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Old Jun 3, 2009, 12:57 PM   #15
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Originally Posted by jelpee View Post
Another option is the recently released, but not yet available Sigma 18-250 HSM). The HSM is really attractive to me and I want to wait for some feedback before deciding. Now if they will only match Tamron's 6 year warranty, I'd be willing to pay a premium for it.
I can't speak to anything Pentax specific, but I can speak to the Sigma HSM lenses. I personally have the APO 70-200mm F2.8 II EX DG MACRO HSM, and I'll tell you, the focus motor is AMAZING. Though I'm fairly new to the SLR game, I have tried a fair number of lenses and I've never used a lens that would focus that quickly and quietly. (I use my Sigma 28-70 non-HSM driven by the motor in my D50 as a basis for comparison)
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