Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
08-13-2007, 08:21 PM   #16
Veteran Member
FotoPete's Avatar

Join Date: Feb 2007
Location: Toronto
Photos: Gallery
Posts: 1,710
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
Veteran Member
Wethphotography's Avatar

Join Date: Dec 2006
Location: Washington, D.C., USA
Photos: Gallery
Posts: 417
Original Poster
QuoteOriginally posted by FotoPete Quote
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
Veteran Member
FotoPete's Avatar

Join Date: Feb 2007
Location: Toronto
Photos: Gallery
Posts: 1,710
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
Administrator
Site Webmaster
Adam's Avatar

Join Date: Sep 2006
Location: Arizona
Photos: Gallery | Albums
Posts: 40,957
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's high server and development costs are user-supported. You can help cover those costs by donating. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

08-13-2007, 10:38 PM   #20
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!
08-13-2007, 11:43 PM   #21
Senior Member




Join Date: Sep 2006
Posts: 259
QuoteOriginally posted by Wethphotography Quote
... 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
Veteran Member
borno's Avatar

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?)
08-16-2007, 01:22 PM   #23
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
Veteran Member
FotoPete's Avatar

Join Date: Feb 2007
Location: Toronto
Photos: Gallery
Posts: 1,710
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
New Member




Join Date: Mar 2007
Location: SoCal
Posts: 14
QuoteOriginally posted by FotoPete Quote
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
08-16-2007, 02:22 PM   #26
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
Senior Member




Join Date: Nov 2006
Location: Kamloops, B.C.
Photos: Gallery
Posts: 226
QuoteOriginally posted by FotoPete Quote
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.
08-16-2007, 03:51 PM   #28
Veteran Member
Wethphotography's Avatar

Join Date: Dec 2006
Location: Washington, D.C., USA
Photos: Gallery
Posts: 417
Original Poster
QuoteOriginally posted by Artymous Quote
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.
08-16-2007, 04:05 PM   #29
Senior Member




Join Date: Nov 2006
Location: Kamloops, B.C.
Photos: Gallery
Posts: 226
QuoteOriginally posted by Wethphotography Quote
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.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
28mm, da*, f2.8, k-mount, lens, pentax, pentax lens, slr lens, tamron
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Tamron 17-50mm, Tamron 28-75mm, Sigma 17-70mm, which lens for my trip to Greece? macky112 Pentax SLR Lens Discussion 15 11-20-2011 03:08 PM
For Sale - Sold: K10D, Tamron 28-75 F2.8, Tamron 75-300 F4-5.6, Super-Tak 50/1.4, AF-360 Flash maconmatt Sold Items 5 10-25-2010 06:18 AM
For Sale - Sold: Sigma 24-60mm F2.8 (K mount) and Tamron Adaptall 24mm F2.5 with Tamron P/K ada pxpaulx Sold Items 4 08-27-2010 08:47 PM
For Sale - Sold: Pentax K100d + 18-55mm + Tamron 70-300mm; Tamron 90mm Macro jake123 Sold Items 4 11-09-2009 12:51 PM
For Sale - Sold: Tamron SP 70-210mm f/3.5, Tamron SP 28-135mm f/4.0-4.5 28A, Tamron pk/a adapta hinman Sold Items 14 05-08-2009 05:35 PM



All times are GMT -7. The time now is 01:30 AM. | See also: NikonForums.com, part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top