Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
01-09-2013, 05:19 PM   #1
Senior Member
telly0050's Avatar

Join Date: May 2011
Posts: 233
My tamron 17-50mm generally expose brighter wide open, is it normal?

I have a tamron 17-50 f2.8, and it seems to have some exposure problem.

When shooting wide open at f2.8, i almost always get an image of 1/3 to 2/3 stops brighter than other aperture setting such as f3.5 or f8.
I used the same framing and Av mode.
Also when using f2.8, it does not look as sharp as I expect from reviews (however stopping down to f4 is extremely sharp)

My copy is a cheapo $360 version purchased from eBay, shipped from taiwan. (price is over $400 anywhere else when I bought it, but now there seem to have some japanese seller selling around $370 in Amazon)
Even though the box says manufacture from Japan, the lens itself has "made in china" painted on it (just saying, nothing against chinese product).

Does anyone has any thought?

01-09-2013, 05:27 PM   #2
Pentaxian
LeDave's Avatar

Join Date: Jun 2009
Location: Minneapolis - St. Paul
Photos: Gallery
Posts: 2,895
It's normal for a photo to look brighter when shot wide-open compared to stop down. However 2/3 stops brighter seems a bit too much. Can you post photos?
01-09-2013, 06:17 PM   #3
Pentaxian
VisualDarkness's Avatar

Join Date: Nov 2011
Location: Uppsala, Sweden
Photos: Gallery
Posts: 4,439
Maybe vignetting is tricking the exposure metering?
01-09-2013, 06:29 PM   #4
Senior Member
telly0050's Avatar

Join Date: May 2011
Posts: 233
Original Poster
i see, i guess 1/3 is normal.
i just took some shots and test it, it is not so noticeable here, but more noticeable when i am shooting outdoor (so i always use -1/3 or lower just to be safe).



here 100% crop of the focused area, do you find it sharp enough, or a bit on the soft side?


01-09-2013, 06:40 PM   #5
Pentaxian
VisualDarkness's Avatar

Join Date: Nov 2011
Location: Uppsala, Sweden
Photos: Gallery
Posts: 4,439
If you look at the corners they still look darker wide open than stopped down so I still think the vignetting is tricking it to slightly overexpose the center. Have you tried comparing spot, center-weighted and multi-segment with different aperture settings?
I don't own that lens but to me that looks pretty sharp for cheepish fast zoom, will you trade it for my blooming Sigma 24-70/2.8?
01-09-2013, 06:53 PM   #6
Senior Member
telly0050's Avatar

Join Date: May 2011
Posts: 233
Original Poster
thanks, i guess i just expected too much from a cheapo lens (i use prime lens most the time)
and i think u can easily trade off your sigma and get 2 of this lens with that fund
01-09-2013, 07:11 PM   #7
Site Supporter




Join Date: Oct 2011
Location: Temple City CA
Photos: Gallery | Albums
Posts: 726
mine is 1/3 darker in all range, I don't really care about it tho, same thing happened with the old tokina 70-210, for some reason most for 3rd party lenses, Pentax made are spot on
01-09-2013, 07:14 PM   #8
Pentaxian
VisualDarkness's Avatar

Join Date: Nov 2011
Location: Uppsala, Sweden
Photos: Gallery
Posts: 4,439
QuoteOriginally posted by telly0050 Quote
thanks, i guess i just expected too much from a cheapo lens (i use prime lens most the time)
and i think u can easily trade off your sigma and get 2 of this lens with that fund
I got the old version, not the newer really good ones. Though it's good enough for me (surprised me actually for the price) and was really really cheap. Most zooms vignette when pushed to their extremes quite heavily, even more expensive ones, and many primes too. Look here to see your lens: Tamron AF 17-50mm f/2.8 SP XR Di II LD Aspherical [IF] (Nikon) - Review / Test Report - Analysis
It looks perfectly acceptable to me when I think about the lenses I use that have way worse vignetting as I really don't care about it in most cases.

01-09-2013, 07:33 PM   #9
Senior Member
telly0050's Avatar

Join Date: May 2011
Posts: 233
Original Poster
new lens coming out every year, it's hard to avoid all those temptation.
so better stick with what we have and master it until the gear can't provide us enough room for our creativity.
01-09-2013, 08:11 PM   #10
Site Supporter




Join Date: May 2012
Location: Adelaide
Photos: Gallery | Albums
Posts: 1,081
Personally, I think the Tamron 17-50 is a very good lens. Ok, it may not have the build quality of some of thje others, but optically it can produce very good results.

Have you checked the focus accuracy on it and worked out if the camera needs a calibration adjustment? As you move to wide open, any slight inaccuracy will be come more obvious (smaller apertures will increase DOF and hide small focus errors). My Tamron 17-50 needs +50um adjustment om my K-x, and then it is very sharp. I can see from my images when it is mis-calibrated (such as when I have used another lens with different calibration and have forgotten to reset the camera focus calibration when I put the Tammy back on, grrrr).

Also, with you sample, it is not clear exactly what point the camera may have focussed on if it was on multi-point focus. Again, F2.8 with its reduced DOF will reveal autofocussing on something away from your main point of interest.

Also, only very few (of the very best) lenses hold their sharpness all the way to wide open.
01-09-2013, 08:20 PM   #11
Pentaxian
VisualDarkness's Avatar

Join Date: Nov 2011
Location: Uppsala, Sweden
Photos: Gallery
Posts: 4,439
I would say that it's focused right or slightly to the right of the "12" judging from the Longitudinal Chromatic Aberration (the colorshift of the numbers right and left of the "12"). Though it's a bit harder to tell due to the tilting plane I'm pretty sure it's around the "12".
01-10-2013, 03:26 AM   #12
Site Supporter




Join Date: May 2012
Location: Adelaide
Photos: Gallery | Albums
Posts: 1,081
QuoteOriginally posted by VisualDarkness Quote
I would say that it's focused right or slightly to the right of the "12" judging from the Longitudinal Chromatic Aberration (the colorshift of the numbers right and left of the "12"). Though it's a bit harder to tell due to the tilting plane I'm pretty sure it's around the "12".
Yes, now that I am home and using a higher res screen, I think you are right, the purple/green colour shifts support a conclusion that the focus aligning pretty well on the central column of numbers. I couldn't distinguish this so well on the work pc.
01-10-2013, 04:08 AM   #13
Veteran Member
glasbak's Avatar

Join Date: Apr 2009
Location: Netherlands
Posts: 343
I also noticed that my sample underexposes a bit on all apertures, except 2.8.
Detected this doing flash test exposures, stopping the lens down and doubling the flash power every step.
01-10-2013, 08:16 AM   #14
Senior Member
telly0050's Avatar

Join Date: May 2011
Posts: 233
Original Poster
QuoteOriginally posted by southlander Quote
Personally, I think the Tamron 17-50 is a very good lens. Ok, it may not have the build quality of some of thje others, but optically it can produce very good results.

Have you checked the focus accuracy on it and worked out if the camera needs a calibration adjustment? As you move to wide open, any slight inaccuracy will be come more obvious (smaller apertures will increase DOF and hide small focus errors). My Tamron 17-50 needs +50um adjustment om my K-x, and then it is very sharp. I can see from my images when it is mis-calibrated (such as when I have used another lens with different calibration and have forgotten to reset the camera focus calibration when I put the Tammy back on, grrrr).

Also, with you sample, it is not clear exactly what point the camera may have focussed on if it was on multi-point focus. Again, F2.8 with its reduced DOF will reveal autofocussing on something away from your main point of interest.

Also, only very few (of the very best) lenses hold their sharpness all the way to wide open.
yes you are right, this lens is hard to focus sometimes.
my copy has front focus issue and i have AF -8 adjustment on my k5, and it still missed quite a bit of shots, unlike my trusty 35/2.4 which has over 85% accuracy.
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!
f2.8, k-mount, pentax lens, slr lens, tamron, tamron 17-50mm
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
New DA 15, is it problem or it is normal ? krendel154 Pentax SLR Lens Discussion 12 04-03-2012 03:55 PM
Da16-50mm vs Tamron 17-50mm .. or is my kx faulty? kxr4trids Pentax SLR Lens Discussion 4 11-13-2010 05:14 PM
Tamron 17-50mm .. is it REALLY worth it? Nightwings Pentax SLR Lens Discussion 36 08-17-2010 06:35 AM
Is the DA* 16-50mm 2.8 sharp wide open? hamidlmt Post Your Photos! 13 02-23-2009 04:13 PM
Wanna see how sharp the Tamron 17-50 is wide open? PentaxPoke Pentax SLR Lens Discussion 16 10-15-2008 02:31 PM



All times are GMT -7. The time now is 11:41 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