Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
01-13-2010, 03:16 PM   #1
Senior Member
Stefan Carey's Avatar

Join Date: Nov 2008
Location: Melbourne
Photos: Gallery
Posts: 190
New Pentax 16-45mm F4 cannot autofocus near infinity

1. While testing out the brand new lens I find that it has a lot of trouble, and is often completely unsuccessful focusing on anything near infinity, from say 100 metres and further away. I am using center auto focus point with a K-m. I know how to help the camera focus by trying to find an edge to focus on.

Is this endless hunting normal? Is this a faulty lens? Do you have have trouble with the Pentax 16-45mm getting focus at longer distances?

I do not mind using manual focus, and for using hyperfocal distance, manual focus might be better than using the focus lock anyway (?). (Last night I used the focus chart and the camera and lens seem to be fine there.) But there are times when I need to take a quick shot where this gets in the way.

2. I have notice a dramatic difference in sharpness of fine detail at long distance (2-3km) between some shots taken on the same tripod (RAW). The distant detail, like a large steel electriciy tower, is blurry and on some shots not, and I am beginning to think that even with a two second mirror lock up, the tripod is still vibrating after I have pressed the shutter. My theory is that where I have been extra careful to press the shutter gently and not move the tripod, the shots are sharper. (Especially where the tripod head is extended.) Has anyone moved from a lightweight tripod to a heavier tripod because of this? I willpost some samples tonight.

01-13-2010, 04:51 PM   #2
Loyal Site Supporter
imtheguy's Avatar

Join Date: Mar 2009
Location: Virginia Beach
Photos: Gallery | Albums
Posts: 2,950
I use my da16-45mm mostly at 20mm or so and f/13 to shoot landscape panoramics. I have had zero issue with hunting or focus at infinity, including trials at any other focal lengths and f-stop. Not able to explain your problem other than it ain't normal for that lens on a K20D anyway. Focus charts? Something is broken, I don't think focus charts are a good long term solution. I recommend you try a second 16-45mm lens.
01-13-2010, 04:55 PM   #3
Senior Member
Stefan Carey's Avatar

Join Date: Nov 2008
Location: Melbourne
Photos: Gallery
Posts: 190
Original Poster
Many thanks for taking the time to reply and the suggested settings which I will try.
01-13-2010, 04:57 PM   #4
Veteran Member




Join Date: Jan 2009
Location: Canada
Posts: 1,255
You can also try a shutter release cable and as you suggested a sturdier tripod.

01-13-2010, 05:04 PM   #5
Senior Member
Stefan Carey's Avatar

Join Date: Nov 2008
Location: Melbourne
Photos: Gallery
Posts: 190
Original Poster
Hi there ASDF, thank you for the suggestion, sadly the K-m has no shutter release. I will try a tabletop and see what happens. I will post some samples tonight (its 11 am here at work now)
01-13-2010, 05:11 PM   #6
Damn Brit
Guest




There's always the possibility of minute vibrations extending beyond that two seconds.
Especially with a lightweight tripod and especially with the centre column extended.
Is there a hook at the bottom of the centre column that you can hang something from to further dampen it? There's also other variables (like wind) that may have an affect.
Last thing you want to do is send it back if there is a simple explanation for what's happening.
Do you have another lens that you can test in the same conditions?
01-13-2010, 05:19 PM   #7
Senior Member
Stefan Carey's Avatar

Join Date: Nov 2008
Location: Melbourne
Photos: Gallery
Posts: 190
Original Poster
Hello there Damn Brit, these are excellent suggestions, and I agree the last thing I want to do is send back what might be a good copy of a lens (shorter distance shots are razor sharp).

I have a feeling you are right about the minute vibrations: when shake reduction is turned off any of these will be problem. I will try another lens (18-55mm ot the 35-70mm) at the same focal length and see what happens.
01-13-2010, 07:45 PM   #8
Senior Member
Stefan Carey's Avatar

Join Date: Nov 2008
Location: Melbourne
Photos: Gallery
Posts: 190
Original Poster
Just took another few shots at lunchtime: to my surprise I found that at beyond 28mm the lens will autofocus perfectly. If I reduce focal length to below 28mm (which is where I will use it most), auto focus fails, from even about 5 metres and further. I also notice a slight irregularity while turning the lens at around the 24mm mark, does this all sound normal? (I really would like to keep it but...)

01-13-2010, 10:08 PM   #9
Pentaxian
Just1MoreDave's Avatar

Join Date: Feb 2007
Location: Aurora, CO
Photos: Gallery | Albums
Posts: 4,863
I'm pretty sure my DA 16-45 autofocuses fine, even on my camera, which is probably last in Pentax DSLR AF speed. I'll check it again in the morning, too dark for infinity focusing now.

One way to check your tripod system is to take night photos of an airplane crossing the frame. I live close enough to Denver International Airport to have a regular supply of test planes. If the photo shows the plane's lights squiggling up and down, the camera is moving too much.
01-13-2010, 10:45 PM   #10
Senior Member
Stefan Carey's Avatar

Join Date: Nov 2008
Location: Melbourne
Photos: Gallery
Posts: 190
Original Poster
Thanks Dave for your thoughts. Airplane test is a good one to remember. I have decided to send it back. I will still post some samples here tonight fo what I took at lunchtime.
01-13-2010, 10:47 PM   #11
Ash
Community Manager
Loyal Site Supporter
Ash's Avatar

Join Date: Mar 2007
Location: Toowoomba, Queensland
Photos: Gallery | Albums
Posts: 22,695
Stefan, I had a 16-45 that gave me the same issue, but when I replaced it with the 16-50, I continued to have the same thing happen, and all at the wide end of the lens.

Sounds like to me it's the camera not able to adjust and lock infinity focus well. The lens is probably fine. Just a speculative guesstimation...
01-13-2010, 11:05 PM   #12
Senior Member
Stefan Carey's Avatar

Join Date: Nov 2008
Location: Melbourne
Photos: Gallery
Posts: 190
Original Poster
Thank you Ash, H'mmm, now I am confused!
01-13-2010, 11:44 PM   #13
Senior Member
Frank B's Avatar

Join Date: Aug 2009
Location: San Diego, California
Posts: 149
I've had the DA16-45 since about July of 2007, and it often has trouble locking autofocus at distances as well. Sometimes if I rotate the camera 90 degrees it will then lock, other times I have to rotate back and forth a few times for it to lock. I never paid much attention but now that I think about it, it always happens when the focus should be at infinity. It does this on both K10D and K20D, but I mostly only use it anymore on the K10D. I've always only used the center AF sensor.
01-14-2010, 01:34 AM   #14
Senior Member
Stefan Carey's Avatar

Join Date: Nov 2008
Location: Melbourne
Photos: Gallery
Posts: 190
Original Poster
Expecting too much of infinity?

OK here is a 1200px sample taken today at 1600th of second. JPG resized from the RAW using Silkypix 4.0 with no sharpening, but exposure bumped up.
Camera was sitting on a masonry wall. Two-second shutter release, center focus, set to F5.6, manually focussed on infinity, center weighted average exposure (original RAW file was much darker). Exif says focal distance is 36mm

Zenfolio does not seem to allow me to upload the RAW file, but am happy to email, but is 16MB.
Here is a link to a crop taken from the image displayed at 100%. I do not like the indistinct detail

Am I expecting too much at infinity?
And here's an example at F16, same location same settings, this time at 16mm, focus manually set to infinity

and a 100% crop

Last edited by Stefan Carey; 01-14-2010 at 02:12 AM. Reason: added photos
01-14-2010, 02:28 AM   #15
Pentaxian
gazonk's Avatar

Join Date: Feb 2009
Location: Oslo area, Norway
Photos: Gallery | Albums
Posts: 3,512
QuoteOriginally posted by Stefan Carey Quote
And here's an example at F16, same location same settings, this time at 16mm, focus manually set to infinity[/IMG]
Well, that's definitely front focused. Did you set it to the infinity marker? My 16-45 focuses a bit past the infinity marker, did you try that?

About the shutter release: Try the Pentax IR Remote, I'm pretty sure your K-m works with that. When I use my K10D on a tripod, I almost always use the IR remote with 3s delay.

EDIT: Btw. I was referring to the crop below the f/16 shot. I was wondering if that really could be f/16, but it's not, it's f/5.6 according to the EXIF.
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!
16-45mm, camera, detail, focus, k-mount, lens, pentax 16-45mm f4, pentax lens, shots, shutter, slr lens, tripod
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
My Pentax SMC-A 70-210/4 won't focus to infinity, what to do? pasipasi Pentax SLR Lens Discussion 5 04-15-2014 11:22 AM
Pentax 85mm f/2 -- does yours focus past infinity? deadwolfbones Pentax SLR Lens Discussion 10 04-30-2010 10:32 PM
Pentax fa 80-320 4.5-5.6 - can't infinity focus? flippedgazelle Pentax SLR Lens Discussion 4 06-13-2009 04:31 PM
pentax 18-250 not focusing to infinity hitechrr Pentax SLR Lens Discussion 6 08-25-2008 03:10 PM
For Sale - Sold: FS: Autofocus film cameras and autofocus lenses Not Registered Sold Items 15 03-17-2008 07:08 AM



All times are GMT -7. The time now is 09:46 AM. | See also: NikonForums.com, CanonForums.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