Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
10-31-2010, 10:33 AM   #1
Forum Member
bpjod's Avatar

Join Date: Apr 2009
Location: Wetaskiwin, Alberta
Posts: 82
K5 front/backfocus - WOW!

Picked up my K5 last night. First thing I decided to do this morning was do the AF adjustments for all of my lenses with my new body.

My K7 was all over the map in this regard. In fact when I got my new DA15 a couple of months ago I almost sent it back because the images were so horrible before realizing that it was just very badly front-focused. On the K7 I needed a body adjustment of +8 and my lenses varied from -5 to +9. On top of that, every time I focused, there was enough variability in the focusing endpoint that I was never entirely certain if I was setting the adjustments correctly, but in the real world the pictures were far better than before adjusting so I was obviously improving things by doing the adjustments.

Well I just finished doing the focusing adjustments for my new K5. Not a single lens required adjustment. I'm stunned. Not a single one!!!

Frankly with the variability in the K7's results I figured the variance was all in the lenses, but that doesn't appear to be the case now. I can offer you no explanation, just my findings but needless to say I'm thrilled!

For further information, the method I use for adjusting front/backfocus is explained here. The lenses I own are all of the DA Ltds (15/21/35/40/70), FA 135/2.8, DA 55-300 and DA 12-24.

EDIT: Oh, I also tested the lenses at two different distances (40mm and less at 1m and 3m, longer than 40 mm at 3m and 5m) and the zooms were tested at all the different marked focal lengths (i.e. 55-300 was tested at roughly the 55, 70, 100, 200 & 300 settings).


Last edited by bpjod; 10-31-2010 at 10:40 AM.
10-31-2010, 11:09 AM   #2
Pentaxian




Join Date: Mar 2009
Location: Perth Australia
Photos: Albums
Posts: 1,511
I've never understood how a lens could front or back focus.

Regardless of the lenses calibration the camera should not stop moving its focus ring via the screw or electrical impulses to the sdm until its in focus. If a lens was 'out' all that should be noticeable to the end user would be the markings on the barrel would be inaccurate.

Just does not make sense to me.

I can totally understand how a camera can be out of calibration because the sensor is not in the same place as the focus detector...

Maybe someone can explain it to me.
10-31-2010, 11:13 AM   #3
Veteran Member
Eruditass's Avatar

Join Date: Jul 2009
Location: Pittsburgh, PA
Photos: Gallery | Albums
Posts: 2,206
QuoteOriginally posted by WerTicus Quote
I've never understood how a lens could front or back focus. Just does not make sense to me. I can totally understand how a camera can.
Same here, especially if the system runs one more check before confirming. Open loop I can understand. Different apertures I can also see since AF is done wide-open. I swear someone answered it for me, but I cannot remember.
10-31-2010, 11:31 AM   #4
Veteran Member
cbaytan's Avatar

Join Date: Nov 2008
Location: Trabzon/Turkey
Photos: Gallery
Posts: 1,010
In my knowledge is (might be wrong though), AF system including an AF sensor is different from the image recording sensor, and AF system tells the lens where to stop. A micro-metric wear or misplacement on the lens' screws or aligning point makes the lens stop at the wrong place. Thats my guess.

10-31-2010, 11:34 AM   #5
Raylon
Guest




Doesn't sound like the K-5 is awesome in this regard, simply sounds like you had a bad K-7.
10-31-2010, 11:55 AM   #6
Forum Member
bpjod's Avatar

Join Date: Apr 2009
Location: Wetaskiwin, Alberta
Posts: 82
Original Poster
I don't know enough about this to know how it works. I had heard of it before but never worried about it until I switched to Pentax a couple of years ago. I started with DA 21 & DA 70 and the DA 21 seemed soft until I adjusted it's focus. As my lens collection grew, because of the experience with the DA 21, I tested and corrected each lens as I acquired them with my results being all over.

I could see how a body would be slightly miscalibrated and that one universal adjustment would correct for this, but in that case I would think that one adjustment would be all that was required for all lenses. Given the variability I was seeing between lenses I figured that there must be some lens component too, although how this could be I am at a loss to explain. Maybe my K7 was unusual in that regard, I don't know but I'm happy to see these results with my new K5.
10-31-2010, 12:04 PM   #7
Veteran Member




Join Date: Aug 2009
Photos: Gallery
Posts: 1,236
Sounds like the K-7 could have used a tune-up. To my knowledge all Pentax DSLRs have the AF alignment screws on the bottom near the tripod screw which are visible once the bottom body panel is removed. Never tried tweaking it myself though, but I'm just saying that it isn't a problem that can't be fixed with a simple change and the ability to properly align the screws (eg. sending the camera to Pentax).
10-31-2010, 12:21 PM   #8
Pentaxian




Join Date: Mar 2010
Location: SW Washington
Posts: 814
I don't think the K-5 is anything special in this regard, just a matter of manufacturing tolerances. For what it's worth, my K-5 required some minor adjustments to dial in a couple of my lenses. It took just 15 minutes, and they were a well spent 15 minutes, because now all of them are dead centered.

I really love how you can set each lens individually. With the K-x, not only did I have to deal with that annoying debug mode, but you could only set a global adjustment, so you had to pick a compromise where nothing was quite dead on.

10-31-2010, 12:41 PM   #9
Senior Member




Join Date: Nov 2009
Location: Marin, CA
Photos: Gallery | Albums
Posts: 281
Is the process linked to in the first post the best way to adjust your lenses? Is there a best established way to adjust on Pentax bodies?
10-31-2010, 12:55 PM   #10
Pentaxian
Asahiflex's Avatar

Join Date: Jan 2008
Location: Netherlands
Photos: Gallery
Posts: 2,754
QuoteOriginally posted by Raylon Quote
Doesn't sound like the K-5 is awesome in this regard, simply sounds like you had a bad K-7.
Indeed. I have many AF lenses (see my sig) but none of them needed correction on my K-7. And I'm VERY picky in this regard.
10-31-2010, 01:59 PM   #11
Pentaxian




Join Date: Mar 2010
Location: SW Washington
Posts: 814
QuoteOriginally posted by qtopplings Quote
Is the process linked to in the first post the best way to adjust your lenses? Is there a best established way to adjust on Pentax bodies?
Dunno, that method linked seems rather tedious. I use a much simpler, "low tech" method.

Get something with a dense/consistent texture. I use the fur on a stuffed animal. Set it at a shallow angle (to get a large distance gradient). Get the camera as close as you can to it and set the aperture to wide open to get as small a DOF as possible. Set focus to center point. Take a picture. In playback mode, zoom in with the e-dial to about 8x magnification (don't move it around, just zoom straight down the middle). Check if the in focus area is right in the center. If not, adjust according, one step at a time, until the in focus area moves into the center of the frame. Very fast, only takes me 1-2 minutes to dial it in, and very accurate.

For longer lenses that don't focus close enough, I have to do the "trial and error" method, which is just picking a target and adjusting the focus step by step until I get maximum sharpness. Slower (~5 minutes), but still works fine.

Always be sure to manually move the lens off focus after every shot to force the camera to refocus. If you leave it where it is, the camera will usually decide that despite the adjustment, where it is right now is "good enough" and won't do anything. Good thing we have Pentax and quick-shift!

Last edited by Cannikin; 10-31-2010 at 02:21 PM.
10-31-2010, 02:21 PM   #12
Veteran Member
Andi Lo's Avatar

Join Date: Jul 2008
Location: Halifax, Nova Scotia
Posts: 2,925
This seems to be a very common problem for owners of bodies with AF adjustment though. First time we hear someone complaining about this is on K20d. Lenses that would focus perfectly (or reasonably) will badly FF / BF on it.
10-31-2010, 04:35 PM   #13
Veteran Member
Eruditass's Avatar

Join Date: Jul 2009
Location: Pittsburgh, PA
Photos: Gallery | Albums
Posts: 2,206
QuoteOriginally posted by Cannikin Quote
Dunno, that method linked seems rather tedious. I use a much simpler, "low tech" method.

Get something with a dense/consistent texture. I use the fur on a stuffed animal. Set it at a shallow angle (to get a large distance gradient). Get the camera as close as you can to it and set the aperture to wide open to get as small a DOF as possible. Set focus to center point. Take a picture. In playback mode, zoom in with the e-dial to about 8x magnification (don't move it around, just zoom straight down the middle). Check if the in focus area is right in the center. If not, adjust according, one step at a time, until the in focus area moves into the center of the frame. Very fast, only takes me 1-2 minutes to dial it in, and very accurate.

For longer lenses that don't focus close enough, I have to do the "trial and error" method, which is just picking a target and adjusting the focus step by step until I get maximum sharpness. Slower (~5 minutes), but still works fine.

Always be sure to manually move the lens off focus after every shot to force the camera to refocus. If you leave it where it is, the camera will usually decide that despite the adjustment, where it is right now is "good enough" and won't do anything. Good thing we have Pentax and quick-shift!
I don't see how the moire test is tedious. With the moire test, you don't have to rely on zooming in all the way and sharpness because you just look for artifacts seen in LV (you can zoom in a bit to have LV just display the image). I keep mine in LiveView set to use phase-detect autofocus. I focus with phase detect, switch to MF (I just hold the lens release in), and then see if adjusting the focus forward or backward gives more or less artifacts. Then I adjust the setting and repeat (setting the focus back to infinity or MFD). Don't even need to take a picture.

Also, you can do this indoors without having to worry about incandescent lighting messing it up.

Last edited by Eruditass; 10-31-2010 at 05:27 PM.
10-31-2010, 05:06 PM   #14
Site Supporter
filmamigo's Avatar

Join Date: Aug 2007
Location: Toronto
Photos: Gallery
Posts: 678
Andi Lo, if you check the forums for different brands and go back a few years, you see that front focus/back focus issues were common. But the recommended solution was to keep returning lenses and try again and again until you got one that focussed perfectly on your body. I'd much rather have AF fine tuning. This was a key reason I upgraded my K10D to a K20D. I had a lens that I loved, and it was in perfect agreement with my *ist DL. With my K10D, the same lens was soft... actually, it was sharper than ever but it was backfocusing. The K20D rescued that lens for me.
10-31-2010, 07:13 PM   #15
Veteran Member




Join Date: Jan 2007
Location: New Mexico
Photos: Albums
Posts: 1,125
I had to return my first K-7 body, because I could barely calibrate my lenses with maximum adjustments. The second body was much easier to calibrate.

Rob
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!
adjustments, body, camera, da, dslr, k-5, k-5 ii, k-5 iis, k5, k7, lenses, pentax k-5
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Front to Back Sharpness: Distance setting on front of lens yoon395 Troubleshooting and Beginner Help 18 09-08-2010 04:33 PM
Sigma 70-200 with both front and backfocus nobbsie Pentax SLR Lens Discussion 6 01-12-2009 05:42 PM
Backfocus/frontfocus on K10d? dresden_phoenix Pentax DSLR Discussion 13 05-02-2008 01:06 AM
k100d backfocus help k100d Pentax DSLR Discussion 0 02-15-2008 11:25 AM
Question: backfocus on *istDS stern Pentax DSLR Discussion 3 01-10-2007 08:44 AM



All times are GMT -7. The time now is 01:30 PM. | 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