Da*16-50 vs. Tamron 28-75

FotoPete · 08-13-2007, 08:21 PM

To my knowledge decentering is kinda what it implies. Like..say a certain lens element wasn't installed correctly and was left slightly off the axis or tilted or something. This could explain why your open aperture images seemed 'biased' to the right edge.

Another way to think about 'decentering' is the every popular Lens Based Image Stabilization. It is a common application where the gyro sensors in the lens detect your handshake and then deliberately decenter the IS/VR/OS/MEGA OIS lens group in an attempt to keep the image stable on the sensor plane.

If you live within driving distance to B&H, it will save you the phone calls, shipping, repair, and return shipping times from Pentax USA. Or for anyone else, their Pentax Div. HQ.

Wethphotography · 08-13-2007, 08:25 PM

Originally posted by FotoPete

To my knowledge decentering is kinda what it implies. Like..say a certain lens element wasn't installed correctly and was left slightly off the axis or tilted or something. This could explain why your open aperture images seemed 'biased' to the right edge.

Lens Based Image Stabilization is a common application where the gyro sensors detect your handshake and then deliberately decenter the IS/VR/OS/MEGA OIS lens group in an attempt to keep the image stable on the sensor plane.

Thanks. Your explanation fits with what I found at photozone:
"Q: What is a centering defect ?
A: A centering defect originates in a misaligned lens element or lens group. The result is a blurry corner, an off-coplanar projection (symmetrical blur) or object edge shadows. A centering defect is normal to some degree - there's simply no perfect lens out there, not even a Leica. Generally centering problems are more obvious with large aperture lenses and they're more frequent with budget (third-party) lenses."

FotoPete · 08-13-2007, 08:32 PM

Haha note...budget/third party. I know it is statistically wrong to judge from Photozone given the many factors invovled in lens submission for reviews, but it seems like the Pentax reviews are commonly plagued with decentering issues.

If this is poor quality control on Pentax's part, they had better get their act together haha especially with something as prestigious as their DA*...cuz from what I've been reading on this forum, it seems like Tamron's lenses are more consistent..even the budget 70-300mm. (CA aside, almost everyone has good things to say about its sharpness.)

Adam · 08-13-2007, 10:01 PM

Wow, the low quality of the 16-50mm sure seems disappointing. I was planning on having it replace by DA 12-24mm and my FA* 28-70mm for trips, but I guess that's not happening.

Adam
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SloPhoto · 08-13-2007, 10:38 PM

wow

that is one sad lens. When only looking at the top image, I thought I was looking at a 100% crop!

Harald · 08-13-2007, 11:43 PM

Originally posted by Wethphotography

... I was in centered AF mode and I checked before each photo that the sensor was illuminating on a small juniper planted in the middle between the front and rear wall. ...(

I am not an pixelpeeper, but when checking the new copy of lens I never use first AF. This is because using MF you can exclude one reason for bad results immediately.

My prosedure is that using MF the particular point that should be focused correctly is hunted, usually taking several pictures. Otherwise set up is similar than used by OP. From this picture the sharpness can be seen and possible AF problems doesnt affect.

But remember when you look at the corners wide open correctly center focused pictures that there should be something in the corner in the very same focusing distance. DOF is very very narrow at f:2.8 and wider.... if the items are even in slightly different distance, you cannot make any conclusions about corner sharpness. It would be better take separate pictures for this purpose and using MF be sure that items in the corner area are focused properly.... only few centimeters difference make your conclusions useless ;-)

Use DOF calculator if phenomena is not familiar to you. I have seen very many posts telling "honest" opinion about wide open performance (especially corner sharpness) basing to scenery pictures having no items in the picture corner even close the actual focusing distance... from these pictures you can only see the corner bokeh :-)

That said, from these OP:s pictures you cannot say anything about misalignments, because you cannot be sure that the picture plane is completely parallel with the main scenery, the wall for example. Even small angle can cause non-focused other side of the picture when DOF is so narrow as it is at f:2.8.

Second phase is evaluate AF in same situation as the "sharp" picture is taken. But now I have a properly focused pictures to what the AF result can be compared.... and with these two sets of pictures I know exactly if possible problem is in optical performance or AF.....

Harri

borno · 08-14-2007, 02:56 AM

My 2cents for that money I'd send it back it should be sharp at f2.8 if it is a * lens. I don't see anything sharp at 28mm. just my opinion of course- bummer after waiting so long (you didn't pray for patience did you?

)

Edwood · 08-16-2007, 01:22 PM

Looks like I made a good decision in cancelling my DA* 16-50 preorder and jumping ship to Nikon.

FotoPete · 08-16-2007, 01:30 PM

Well if you guys are intending to compare the DA*16-50 lens, use the Tamrom 17-50/2.8 as comparison!

I'm sure its just decentering from quality control issues/overhype/pentax rushing the lens.

Haha Edwood...it was nice know ya the one post I read. Hope you get a better deal on the other side!

;-P

the only reason I'd ever swtich to Nikon is to make use of all those darn f-mount Vivitars collecting dust at the camera store. Then again, Nikon nerfed the aperture couplers (aka backwards compatibility) on all but their D200 and D2.

Edwood · 08-16-2007, 01:37 PM

Originally posted by FotoPete

Well if you guys are intending to compare the DA*16-50 lens, use the Tamrom 17-50/2.8 as comparison!

I'm sure its just decentering from quality control issues/overhype/pentax rushing the lens.

Haha Edwood...it was nice know ya the one post I read. Hope you get a better deal on the other side!

;-P

the only reason I'd ever swtich to Nikon is to make use of all those darn f-mount Vivitars collecting dust at the camera store. Then again, Nikon nerfed the aperture couplers (aka backwards compatibility) on all but their D200 and D2.

Well, I haven't completely abandoned Pentax. I still have my *ist DS and 35mm f/2. Most of Nikon's Primes suck. But their Zooms are much better.

-Ed

mopar_man · 08-16-2007, 02:22 PM

That Tamron is very nice. If I ever get the money to buy another AF zoom, that'll be it.

Artymous · 08-16-2007, 03:44 PM

Originally posted by FotoPete

Well if you guys are intending to compare the DA*16-50 lens, use the Tamrom 17-50/2.8 as comparison!

I'm sure its just decentering from quality control issues/overhype/pentax rushing the lens.

Haha Edwood...it was nice know ya the one post I read. Hope you get a better deal on the other side!

;-P

the only reason I'd ever swtich to Nikon is to make use of all those darn f-mount Vivitars collecting dust at the camera store. Then again, Nikon nerfed the aperture couplers (aka backwards compatibility) on all but their D200 and D2.

Pentax *rushing* the lens? It was delayed forever... and now many of the initial reports range from "eh" to "ack!"

I am quickly losing confidence in Pentax myself, and it's too bad.

Wethphotography · 08-16-2007, 03:51 PM

Originally posted by Artymous

Pentax *rushing* the lens? It was delayed forever... and now many of the initial reports range from "eh" to "ack!"

I am quickly losing confidence in Pentax myself, and it's too bad.

I share your disappointment on the DA*16-50, but must say that I really like the DA* 50-135. Thank goodness, they got the second right or might have been selling all my gear and going to the dark side!

Assuming my DA *16-50 lens wasn't a bad copy, I hope they will make a second attempt at designing a 16-50 f2.8.

Artymous · 08-16-2007, 04:05 PM

Originally posted by Wethphotography

I share your disappointment on the DA*16-50, but must say that I really like the DA* 50-135. Thank goodness, they got the second right or might have been selling all my gear and going to the dark side!

Assuming my DA *16-50 lens wasn't a bad copy, I hope they will make a second attempt at designing a 16-50 f2.8.

I am hearing more positive things about the 50-135mm, and it's the lens that covers my own needs better, but my confidence with Pentax extends to far more than just a couple of extremely-hyped lenses taking forever to come out and then being nothing special when they do.. heh.

I'm giving the company until next Summer to do something to change my mind... so unless they do more than minor body upgrades, constant announcements that lead to not much of anything, refusal or inability to get lens production and production of other vital components (such as batteries and flash-guns et al.) to a point where they are easily obtainable and not "out of stock" for months and moths at a time, and everything else that Pentax seems to be doing lately...

Well.. I'm just hoping that they can pull the socks up.

08-13-2007, 11:43 PM	#21
Harald Senior Member Join Date: Sep 2006 Posts: 259	Originally posted by Wethphotography ... I was in centered AF mode and I checked before each photo that the sensor was illuminating on a small juniper planted in the middle between the front and rear wall. ...( I am not an pixelpeeper, but when checking the new copy of lens I never use first AF. This is because using MF you can exclude one reason for bad results immediately. My prosedure is that using MF the particular point that should be focused correctly is hunted, usually taking several pictures. Otherwise set up is similar than used by OP. From this picture the sharpness can be seen and possible AF problems doesnt affect. But remember when you look at the corners wide open correctly center focused pictures that there should be something in the corner in the very same focusing distance. DOF is very very narrow at f:2.8 and wider.... if the items are even in slightly different distance, you cannot make any conclusions about corner sharpness. It would be better take separate pictures for this purpose and using MF be sure that items in the corner area are focused properly.... only few centimeters difference make your conclusions useless ;-) Use DOF calculator if phenomena is not familiar to you. I have seen very many posts telling "honest" opinion about wide open performance (especially corner sharpness) basing to scenery pictures having no items in the picture corner even close the actual focusing distance... from these pictures you can only see the corner bokeh :-) That said, from these OP:s pictures you cannot say anything about misalignments, because you cannot be sure that the picture plane is completely parallel with the main scenery, the wall for example. Even small angle can cause non-focused other side of the picture when DOF is so narrow as it is at f:2.8. Second phase is evaluate AF in same situation as the "sharp" picture is taken. But now I have a properly focused pictures to what the AF result can be compared.... and with these two sets of pictures I know exactly if possible problem is in optical performance or AF..... Harri Last edited by Harald; 08-13-2007 at 11:55 PM.

08-14-2007, 02:56 AM	#22
borno Veteran Member Join Date: Nov 2006 Location: md-usa Photos: Gallery \| Albums Posts: 2,580	My 2cents for that money I'd send it back it should be sharp at f2.8 if it is a * lens. I don't see anything sharp at 28mm. just my opinion of course- bummer after waiting so long (you didn't pray for patience did you?)

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08-13-2007, 08:21 PM	#16
FotoPete Veteran Member Join Date: Feb 2007 Location: Toronto Photos: Gallery Posts: 1,774	To my knowledge decentering is kinda what it implies. Like..say a certain lens element wasn't installed correctly and was left slightly off the axis or tilted or something. This could explain why your open aperture images seemed 'biased' to the right edge. Another way to think about 'decentering' is the every popular Lens Based Image Stabilization. It is a common application where the gyro sensors in the lens detect your handshake and then deliberately decenter the IS/VR/OS/MEGA OIS lens group in an attempt to keep the image stable on the sensor plane. If you live within driving distance to B&H, it will save you the phone calls, shipping, repair, and return shipping times from Pentax USA. Or for anyone else, their Pentax Div. HQ.

08-13-2007, 08:25 PM	#17
Wethphotography Inactive Account Join Date: Dec 2006 Location: Washington, D.C., USA Photos: Gallery Posts: 417 Original Poster	Originally posted by FotoPete To my knowledge decentering is kinda what it implies. Like..say a certain lens element wasn't installed correctly and was left slightly off the axis or tilted or something. This could explain why your open aperture images seemed 'biased' to the right edge. Lens Based Image Stabilization is a common application where the gyro sensors detect your handshake and then deliberately decenter the IS/VR/OS/MEGA OIS lens group in an attempt to keep the image stable on the sensor plane. Thanks. Your explanation fits with what I found at photozone: "Q: What is a centering defect ? A: A centering defect originates in a misaligned lens element or lens group. The result is a blurry corner, an off-coplanar projection (symmetrical blur) or object edge shadows. A centering defect is normal to some degree - there's simply no perfect lens out there, not even a Leica. Generally centering problems are more obvious with large aperture lenses and they're more frequent with budget (third-party) lenses."

08-13-2007, 08:32 PM	#18
FotoPete Veteran Member Join Date: Feb 2007 Location: Toronto Photos: Gallery Posts: 1,774	Haha note...budget/third party. I know it is statistically wrong to judge from Photozone given the many factors invovled in lens submission for reviews, but it seems like the Pentax reviews are commonly plagued with decentering issues. If this is poor quality control on Pentax's part, they had better get their act together haha especially with something as prestigious as their DA*...cuz from what I've been reading on this forum, it seems like Tamron's lenses are more consistent..even the budget 70-300mm. (CA aside, almost everyone has good things to say about its sharpness.)

08-13-2007, 10:01 PM	#19
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,595	Wow, the low quality of the 16-50mm sure seems disappointing. I was planning on having it replace by DA 12-24mm and my FA* 28-70mm for trips, but I guess that's not happening. Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

08-13-2007, 10:38 PM	#20
SloPhoto Inactive Account Join Date: Apr 2007 Posts: 133	wow that is one sad lens. When only looking at the top image, I thought I was looking at a 100% crop!

08-16-2007, 01:22 PM	#23
Edwood New Member Join Date: Mar 2007 Location: SoCal Posts: 14	Looks like I made a good decision in cancelling my DA* 16-50 preorder and jumping ship to Nikon.

08-16-2007, 01:30 PM	#24
FotoPete Veteran Member Join Date: Feb 2007 Location: Toronto Photos: Gallery Posts: 1,774	Well if you guys are intending to compare the DA*16-50 lens, use the Tamrom 17-50/2.8 as comparison! I'm sure its just decentering from quality control issues/overhype/pentax rushing the lens. Haha Edwood...it was nice know ya the one post I read. Hope you get a better deal on the other side! ;-P the only reason I'd ever swtich to Nikon is to make use of all those darn f-mount Vivitars collecting dust at the camera store. Then again, Nikon nerfed the aperture couplers (aka backwards compatibility) on all but their D200 and D2.

08-16-2007, 01:37 PM	#25
Edwood New Member Join Date: Mar 2007 Location: SoCal Posts: 14	Originally posted by FotoPete Well if you guys are intending to compare the DA16-50 lens, use the Tamrom 17-50/2.8 as comparison! I'm sure its just decentering from quality control issues/overhype/pentax rushing the lens. Haha Edwood...it was nice know ya the one post I read. Hope you get a better deal on the other side! ;-P the only reason I'd ever swtich to Nikon is to make use of all those darn f-mount Vivitars collecting dust at the camera store. Then again, Nikon nerfed the aperture couplers (aka backwards compatibility) on all but their D200 and D2. Well, I haven't completely abandoned Pentax. I still have my ist DS and 35mm f/2. Most of Nikon's Primes suck. But their Zooms are much better. -Ed

08-16-2007, 02:22 PM	#26
mopar_man Senior Member Join Date: Aug 2007 Location: SK, Canada Posts: 108	That Tamron is very nice. If I ever get the money to buy another AF zoom, that'll be it.

08-16-2007, 03:44 PM	#27
Artymous Senior Member Join Date: Nov 2006 Location: Sechelt, B.C. Photos: Gallery Posts: 229	Originally posted by FotoPete Well if you guys are intending to compare the DA16-50 lens, use the Tamrom 17-50/2.8 as comparison! I'm sure its just decentering from quality control issues/overhype/pentax rushing the lens. Haha Edwood...it was nice know ya the one post I read. Hope you get a better deal on the other side! ;-P the only reason I'd ever swtich to Nikon is to make use of all those darn f-mount Vivitars collecting dust at the camera store. Then again, Nikon nerfed the aperture couplers (aka backwards compatibility) on all but their D200 and D2. Pentax rushing* the lens? It was delayed forever... and now many of the initial reports range from "eh" to "ack!" I am quickly losing confidence in Pentax myself, and it's too bad.

08-16-2007, 03:51 PM	#28
Wethphotography Inactive Account Join Date: Dec 2006 Location: Washington, D.C., USA Photos: Gallery Posts: 417 Original Poster	Originally posted by Artymous Pentax rushing the lens? It was delayed forever... and now many of the initial reports range from "eh" to "ack!" I am quickly losing confidence in Pentax myself, and it's too bad. I share your disappointment on the DA16-50, but must say that I really* like the DA* 50-135. Thank goodness, they got the second right or might have been selling all my gear and going to the dark side! Assuming my DA *16-50 lens wasn't a bad copy, I hope they will make a second attempt at designing a 16-50 f2.8.

08-16-2007, 04:05 PM	#29
Artymous Senior Member Join Date: Nov 2006 Location: Sechelt, B.C. Photos: Gallery Posts: 229	Originally posted by Wethphotography I share your disappointment on the DA16-50, but must say that I really* like the DA* 50-135. Thank goodness, they got the second right or might have been selling all my gear and going to the dark side! Assuming my DA *16-50 lens wasn't a bad copy, I hope they will make a second attempt at designing a 16-50 f2.8. I am hearing more positive things about the 50-135mm, and it's the lens that covers my own needs better, but my confidence with Pentax extends to far more than just a couple of extremely-hyped lenses taking forever to come out and then being nothing special when they do.. heh. I'm giving the company until next Summer to do something to change my mind... so unless they do more than minor body upgrades, constant announcements that lead to not much of anything, refusal or inability to get lens production and production of other vital components (such as batteries and flash-guns et al.) to a point where they are easily obtainable and not "out of stock" for months and moths at a time, and everything else that Pentax seems to be doing lately... Well.. I'm just hoping that they can pull the socks up.