Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
05-18-2008, 06:21 PM   #1
Veteran Member
volosong's Avatar

Join Date: Sep 2006
Location: Antelope Valley, SoCal
Photos: Gallery
Posts: 660
req advice - send 16-50 for repair? - warning, large images within (9 img, ~1Mb each)

I wanted to do one more test, so on Friday, I made up my own "test chart" to check the focus on
my DA* 16-50/2.8 lens. I used Excel to create the chart. Each box is one quarter inch square
and printed with a laserjet on white bond stock. I taped the chart to a window on the house in
the backyard. Sun was from the right, but test area was in complete, open shadow.

I shot RAW+ at 16mm, 29mm, and 50mm at apertures f/2.8, f/4.0, f/5.6, f/8.0, and f/11. 29mm is
pretty close to the mid-zoom range for this lens. Only the f/2.8, f/5.6, and f/11 images are posted
here. The images are the full resolution images. All shot at ISO 100 in Av mode, AWB.

I mounted the K20D on a tripod and set the exposure mode to infrared wireless remote with a
three second delay. I reset the aperture, pressed the wireless remote, and moved about 10 feet
(3 meters) away from the camera so that I wouldn't influence the exposure or amount of light
falling onto the chart. At 16mm, the front element of the lens was pretty close to the chart. Pretty
close to the minimum focus distance. Focus mode was AF-C. Without the hood, because of
being in shade and the closeness of shooting at 16mm.

I loaded the PEF files into Adobe Photoshop CS3 which loaded the images into Adobe Camera
Raw. Only thing I did to the images was to change the white balance to "shade" from the AWB
that I normally use. Within Photoshop, I applied an automatic contrast stretch
(image/adjustment/auto levels), changed the bit depth to 8-bits (image/mode/8 Bits per
Channel), then saved as JPEG quality "low", or quality level "3". I did this to keep the images
sizes near or below 1Mb, which is the limit for imageshack. EXIF data should still be attached.


Could those of you who have the 16-50 take a look at the images and tell me if in your opinion,
you think this lens is acceptable and I should just keep it and be happy, or is it a candidate to
send in for "repair". Especially notice the right hand side of the images, and the apparent
vignetting at f/11. Wouldn't think that would be a problem at 50mm. It is to be expected at
16mm, but not the longer focal lengths. Too much time has passed to exchange the lens
at the shot, so I need to send it to Pentax while it is still under warranty.

Thank you for any advice you can offer. Right now, I'm not happy with the performance of this
lens. Is it a lemon, or is this the best I can expect from any copy of this lens? (This quiery
cross posted to dpr because not everybody here visits there also.)

16mm, f/2.8, 1/1250s



16mm, f/5.6, 1/400s



16mm, f/11, 1/100s



29mm, f/2.8, 1/1600s



29mm, f/5.6, 1/500s



29mm, f/11, 1/125s



50mm, f/2.8, 1/1600s



50mm, f/5.6, 1/500s



50mm, f/11, 1.125s




Last edited by volosong; 05-18-2008 at 07:00 PM. Reason: grammar typo in title
07-09-2008, 10:16 AM   #2
Veteran Member
volosong's Avatar

Join Date: Sep 2006
Location: Antelope Valley, SoCal
Photos: Gallery
Posts: 660
Original Poster
bump.

no comments? Is this a trash copy, or acceptable?
07-09-2008, 11:36 AM   #3
Veteran Member




Join Date: Mar 2008
Location: CT / NY
Photos: Gallery
Posts: 822
I understand why post them at full resolution but it is really HARD to visualize whats going on.. so maybe thats why you are not getting much responses...

i know it is a PIA, but i'd try to resize them to the biggest size you could fit in the forums for a 19" monitor.. so people can see the images without scrolling down and up and forgeting which image is which etc etc....
07-09-2008, 01:09 PM   #4
Pentaxian
jsherman999's Avatar

Join Date: Dec 2007
Photos: Gallery
Posts: 8,228
.


I hate to say it, but it's next to impossible to really judge those images, they're
just too large and cumbersome.

I always suggest doing some real-world tests - go out in daylight and take some
flora/people/landscape/architecture shots. In the evening, do some low light
tests, while keeping in mind that *any lens is going to have at least some
problems focusing in low light, especially low tungsten light.

Then, look at the results. If you didn't underexpose, the daylight shots should be
terrific. Same with the low-light shots, although your keeper ratio is going to be
lower there, so keep that in mind. Try to determine if any 'bad' shots are the
result of the situation/photgrapher vs. the lens.

And when the I-expect-them-to-be-bad shots are weeded out, look at what's
left - whats left should all be really great, sharp, pleasing to the eye, a few
should even floor you. That's how you know you've got a good lens.

Often these grid/brick wall tests are counterproductive. Real-world shots!

Here are some links to shots from a 'good' lens - would my lens pass
your grid test? I don't know, and I don't care, these images make the lens
worth every penny to me --->

16-50 #1

16-50 in the West



.

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!
16mm, 50mm, chart, f/11, f/2.8, f/5.6, images, k-mount, lens, pentax lens, shot, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Req: Advice on unfamiliar K mount 50/1.7 MF. Hypocorism Pentax SLR Lens Discussion 10 10-13-2010 11:40 AM
please - your thoughts on this DA* 16-50 (large img) tlfaust Pentax SLR Lens Discussion 2 04-23-2008 05:34 AM
Warning: if you don't like spiders, please move on... (1MB) Marc Langille Post Your Photos! 21 01-27-2008 05:47 AM
New hummingbird images... (warning- some large files) Marc Langille Post Your Photos! 24 09-29-2007 09:57 AM
A few from my new Bigma (3 large IMG) rfortson Post Your Photos! 2 02-20-2007 06:11 PM



All times are GMT -7. The time now is 11:09 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