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02-05-2010, 01:00 AM   #1
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Surpising IQ results: 55-300mm. Thoughts?

I spent a few hours today taking pictures of my bookshelf with two telephoto lenses. I was surprised by the difference in sharpness. My K2000 was mounted on a Manfrotto tripod w/ a fluid head and locked off. Both lenses spent the day at 300mm aimed at the spines of several books and the compacted page edges of a stack of old "Journal of Foreign Affairs". Distance from subject was @ 80 inches. Shots were taken with no filters, wide open, and a shutter speed of 1/180 synced to a hotshoe mounted Metz flash bounced off a diffused white ceiling. Since I'm buying either lens for the reach I'm not interested in testing any other focal lengths. Either lens will either live or die based on it's IQ at 300mm in my world.

Auto-focus was tested starting from both extremes, an arbitrary midpoint, and one manual focus shot for a total of four shots. The session was repeated thrice. The images were captured sRGB, PEF, then viewed and compared as such with no processing in CaptureOne at various magnifications not exceeding 100%. It certainly was not scientific but definitely good enough to see differences between two lenses.

I was shocked to see being resolved some of the actual paper fibers in the stack of Journals. I was more shocked to discover that the Pentax 55-300mm was not as sharp as the Sigma 70-300mm and I also saw some slight fringing in the Pentax shots. In addition, The Sigma focusing ring had a solid smooth feel to it and the Pentaxís felt as if there was grit in the gears and seemed to have a tiny bit of slack. The Sigma felt much more solidly built than the Pentax but that may be an illusion because of the weight difference. Build aside, the Pentaxís IQ wasnít consistent with the numerous reviews Iíve read over the past few weeks. Iím hoping itís just a bad sample because I donít like the Sigmaís revolving barrel and I do like circular polarizers. On the other hand I hope Iím not sending back a great Sigma sample because I may be able to learn to live with the spinning barrel (how bad can it be?).

I have to send both back because UPS mishandled both boxes and they will always be suspect to me as a result. The box containing the Sigma had clearly come very close to being completely crushed and the Pentax... well, I had to go to the shipping center to pick it up and when the clerk picked it off the shelf he began nonchalantly tossing it in the air and spinning it in his hands like a basketball before smacking it down on the counter as if he'd made a dunk shot right in front of me. His unbelievable ignorance and lack of respect was immediately reported to his supervisor (Iím sure to no avail).

Since I'm returning both I feel like I'm back to square one one with regard to placing an order to replace one or the other. I'm inclined to try another Pentax. I've kept both sets of pix for comparison with the next lens sample, whatever that may be. I'm genuinely perplexed by today's IQ tests. They fly in the face of every review Iíve read. Any thoughts?


Mick

02-05-2010, 01:49 AM   #2
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try again. if the Sigma is still better, then get the Sigma.
02-05-2010, 02:06 AM   #3
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You must have mixed up the lenses. I was glad to see the last of my Sigma 70-300 and the missus has kidnapped my 55-300 because she's kind of smitten with it.
02-05-2010, 02:12 AM   #4
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Bear in mind that the Sigma like the similar Tamron lens have been designed with close up ability and so short working distance will have been designed into the lens at the optimisation stage. The Pentax on the other hand has not been designed for close up work. As your test was at fairly short object distances (for a 300mm telephoto) I'm not really supprised that the Sigma performed better. If you get the chance to repeat the test try it at a greater distance.
If you are only interested in the 300mm end why not get a prime which should perform better than either?

02-05-2010, 03:04 AM   #5
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Using two different lenses from the same manufacturer could give you completely different results. When you try a lens and you like the results, that's the one you keep, not another one from the same manufacturer. There is some sample variations when the lenses are assembled.
02-05-2010, 07:49 AM   #6
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It is also possible that it is not an IQ issue, but a focus issue. Did you do a FF/BF test on them?
02-05-2010, 10:48 AM   #7
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come to think of it, Matt has a point. I suggest that testing at such focal length should be done at varying distances (minimum working distance to infinity) inorder to see a fair comparison. the Sigma, being a pseudo-macro, is optimized for close-up shots just like the test that you did. farther shots would be an enigma if it still could produce a same consistent result.
02-08-2010, 08:01 PM   #8
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I didn't think about the possibility of optimization differences, food for thought. As far as a prime goes, well, its about $800.00 more (the price of a ticket to somewhere picturesque where I can use whatever lens I purchase). I have to make compromises. I also didn't think about the idea that the 300mm focal length is the one I should have tested since that is the focal length that I want to be the sharpest.

Thanks for the replies. I've return both lenses so your opinions are appreciated since I will be ordering the replacement soon.

02-08-2010, 09:18 PM   #9
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just an addition, the DA55-300 seems to perform the strongest at 55mm.
02-09-2010, 11:37 PM   #10
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How weak is 300mm wide open???
02-10-2010, 12:13 AM   #11
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I ain't shot no books from a few feet away. And I ain't used no tripod yet. But I wanna see this sigma that is better than this DA 55-300 at 300mm in real world shootin'. In fact I think I might even put this little old Da 55-300 up agin my 300mm prime. haha hehe hoho

Just kidding of course... we all know the sigma 70-300 is a fine lens, and the primes are way better than this little consumer zoom.








Last edited by Igilligan; 02-10-2010 at 10:25 AM.
02-10-2010, 12:25 AM   #12
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QuoteOriginally posted by MD Optofonik Quote
I was more shocked to discover that the Pentax 55-300mm was not as sharp as the Sigma 70-300mm and I also saw some slight fringing in the Pentax shots. ... Any thoughts?
Yes, your shots were out of focus.
02-10-2010, 01:22 AM   #13
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QuoteOriginally posted by MD Optofonik Quote
How weak is 300mm wide open???
Hand held, it is this weak wide open...

Attachment 53900

and a crop
Attachment 53901

Attachment 53902
02-10-2010, 02:29 AM   #14
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Photozone.de test results show that at 300mm, wide open, the DA-55-300 on a Pentax is significantly sharper than the Sigma 70-300 on a crop Canon both center and edges.

If both of you are correct (which is not unlikely), I must conclude there is substantial sample & testing variation.

Last edited by newarts; 02-10-2010 at 02:35 AM.
02-10-2010, 06:20 AM   #15
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fwiw... like gus, the only results that me anything to me ( a devout amateur) are the ones i see... i used to use the tammy 70-300mm, and have been using my 55-300mm for some time now.... and primarily at 300mm for bird shots.... but when used at the short end, i've been surprised at the quality of the results afforded me...... yes this is subjective, but i would've graded my tammy about a b-, and my pentax 55-300mm a b+ to a-.... and no, i'm not a teacher... (the tammy lens suffered from fringing)....
just a couple of 55-300mm shots.....
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