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04-30-2013, 10:59 PM   #1
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16-45 Tilted Off Focus Plane?

The camera problems just don't seem to end this year. I'm really running out of gear to break or fail on me. So in need of a walk around zoom I ended up with a used 16-45. Initial inspection seemed ok on my k-5, but then my k-5 started to fail this past weekend. My k-7 needed a good mount ring so I took the one I had off the k-5. As a side note, getting ahold of the parts department is nearly impossible. Now with a good ring I should have good focus registration right? The mirror box was never moved. With a 50mm on the k-7 it looks sharp across the frame. The 16-45 is a wholly different story. First of all I had to adjust focus to +7, where my k-5 needed no adjustment. Then I the slightly soft right side I noticed with my k-5 seemed greatly magnified to the point of uselessness. It is only at infinity though which tells me that the lens isn't decentered (actually at close focus it is superb), but instead maybe tilted off the focal plane. I'm thinking I can just shim it? Anyone have any experience with shimming lenses? Also if I sent it into pentax does anyone know what they would charge to align the lens? I'm guessing its probably about the amount that it is worth. If I focus on the right side, it gets sharper but never sharp at infinity. The left side starts to lose focus then, so I'm guessing the planes aren't lining up. It is most certainly distance related. It would seem that if a 50 prime looks sharp across the frame that I could rule out the body, though without a k-5 to also test with some more (and looking back at the k-5 shots with the same mount ring they have similar problems to be honest) its kind of hard to say my mount swap didn't introduce any problems. Oddly the focus shifts are somewhat random. At times the right side doesn't look so bad, but it could be that I was just at infinity where it looks best at any distance. If it moves off infinity even stopped down it looks awful until the subject starts getting close. I know its a zoom and not the greatest ever to say the least, but where it is sharp in the frame it is actually very nice. If I could just the whole frame sharp....

I guess I experiment with some shims.

Here is a link to the last picture I took.

imgur: the simple image sharer

Its full resolution for the pixel peepers. Thats at 16mm and f10. Everything should be sharp. Even a decentered lens sharpens up a bit at high fstops. I focused on the right side and it threw the left out. If I focus at infinity the left sharpens more, but the right goes soft. At first I thought it was field curvature, but the 16-45 doesn't have many issues with curvature. This is maddening. I just want a camera with a zoom that works. My 18-55 and 28-80 both have decentering issues. Of my k-5 was out of alignment. Hard to say. I should test them on my k-7. I'm tempted to just round up everything and send it to pentax and say "make it work" but hate to think what that would cost right now. I also can't be without a working camera on my person and the k-7 was my backup. I'll unseat the mount tomorrow and reseat it and make sure that its sitting in there as best as possible. Wide angles make alignment issues more apparent. So my options are try shims, send lens and camera back to pentax for pairing, or toss lens in trash and lose a few hundred dollars. I'll just add it to the list of things to fix along with my k-5, 12-24 (broken mount), M 28 3.5 (sticky blades), M 50 1.4 (filter ring fell off and is now damaged..looking for a parts donor), metz 54mz4i (blown bulb). That's been my year so far. If it weren't for bad luck, I'd probably have none by now.

Sorry for the long post. Wish I was just out shooting pictures again and not worrying about why half my image is mush.

Oh I tried a zeiss star and the out of focus donut looked decent. Aparantly if a lens is decentered the donut hole will not be aligned in the center. In this case it was at both extremes. As one user has pointed out, moving the barrel that is wobbly does not seem to shift the focus plane or alter sharpness at all. I am convinced that this lens has somewhat complex field curvature, but I should not be getting the border I am getting on the right at F8-F11 at infinity. Would have been a half decent picture too. :/

04-30-2013, 11:11 PM   #2
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http://imgur.com/TtpkssS

Also from the k-7 and 16-45. This was at f8.

Last edited by zosxavius; 04-30-2013 at 11:43 PM.
05-01-2013, 03:44 AM - 1 Like   #3
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The mount rings sometimes are shimmed between the camera mount surface. You are looking at only a few thousands of an inch + -.
05-01-2013, 05:25 AM   #4
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QuoteOriginally posted by bobpur Quote
The mount rings sometimes are shimmed between the camera mount surface. You are looking at only a few thousands of an inch + -.
yeah, I was reading another thread on dpreview where they suggested shimming the lens.

The good news is that it looks like when I reseated the mount ring on my k-7 last night it must have seated better because low and behold my focus adjustment was off. its looking much better after I tested some in the daylight this morning. I dropped my focus adjust to +3 and its now stopping hard at infinity like it should. I do believe the field curvature at 16mm is somewhat pronounced, so it seems that closer objects may appear slightly out of focus at infinity. I'm going to have to just go out and shoot and check it as I go along.

05-01-2013, 05:31 AM - 1 Like   #5
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I was able to correct an old zoom that had a side to side register alignment problem and it is quite good now.
(reposted images)
Before: showing right side is sharp and left is not focussed
https://www.box.com/s/98e8559cccbd0d0e83a4

With some tests it is possible to detemine which way to correct.
this was a repetitive process involving partial re-assembly and test shots
Dismantle, Very carefully hand grind the high side on a fine flat stone with water. This will take the register past infinity.
https://www.box.com/s/edb6960a3a2a8ae738f2
Then shim back to infinity using a gasket made of cooking parchment ( 0.02 mm, 0.8 thou inch) between the original brass shims

After tuning:
https://www.box.com/s/8bd668f7368a02e3dc68

However if the lens has any reasonable value I would recommend a pro repair where hopefully, the bad parts would be replaced.
05-01-2013, 05:31 AM   #6
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imgur: the simple image sharer

I think that is looking better. I'm going to have to test this some more and figure out how much of what I'm looking at is misfocus and how much is field curvature.
05-01-2013, 05:38 AM   #7
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QuoteOriginally posted by wombat2go Quote
I was able to correct an old zoom that had a side to side register alignment problem and it is quite good now.

After tuning:
https://www.box.com/s/8bd668f7368a02e3dc68

However if the lens has any reasonable value I would recommend a pro repair where hopefully, the bad parts would be replaced.
that is a good result. the more I think about it. the more I want to see this on a 2nd body to see if I am having the same issues. maybe I will meet up with my friend and use his k-5 for a few moments. I did the best I could reseating the mount ring. It was from the k-7 originally, so in theory it should have gone right back into place where it should be. I tightened the screws in a star pattern hoping to get it as even as possible. I have to shoot a parade later on today, so I will be out using this lens some more. I'll post back after I shoot a few hundred images. Hopefully all will be nice and sharp.
05-01-2013, 05:40 AM - 1 Like   #8
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Yes, definitely confirm the problem on 2 cameras.
Also a "fence test" at wide ap is an easy way to see the problem

05-01-2013, 05:47 AM   #9
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QuoteOriginally posted by wombat2go Quote
Yes, definitely confirm the problem on 2 cameras.
Also a "fence test" at wide ap is an easy way to see the problem
also brick walls.

though its hard to test infinity with a wall that's close.
05-01-2013, 07:49 AM   #10
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I think I mostly cured it. I wanted to be sure I seated the ring correctly, so I pulled it off the camera and reseated it with a good deal of force from my hands. I then made sure all the screws were tightened correctly and in a star pattern again. It seems to have helped a bit. I also made sure the ring was perfectly flat. The ring itself is very snug, any variation from the plane is not what we want. I set the lens to infinity and tried some more. It's looking better to my eyes. Anyone want to look at these crops? It seems the right side is still possibly less sharp but not nearly by as much. Again these are from the center at the extreme edge, so I would expect some softness there anyways at 16mm. The 16-45 is not known for being the sharpest edge to edge at its wide end. It's also known for being somewhat inconsistent due to a variety of factors. I know some of you pixel peep. What's your opinion? The crops are from a picture taken at f9. I find the lens gets sharper across the frame at f11, but at a slight loss to center resolution. Nearly wide open at 5.6 the center and most of the frame are actually pretty darned sharp. There is likely some field curvature hurting softness at the edges at 16mm as well as CA also hurting sharpness. This lens does indeed have a dark soul as photozone puts it lol. I could probably return it to the buyer, or sell it and trade up for another one, but quite honestly I don't know if I will really find a better sample anyways. I know a bunch of you have this lens, so I'd gladly listen to anything you all have to say. My experiences so far are mixed. Love the color rendition and contrast. I also like the sharpness across the frame when it is present. Dislike the field curvature (seems more than the 12-24), though it is better than the 18-55 in that respect. Also dislike the borders at 16mm. For what the lens costs I know I can't expect * quality optics, but this lens does surprise me at times. I've gotten some great flower shots with it already. Its better optically than my 18-55 and 28-80 were, so I guess I keep it? Can't decide lol.

I attached crops on this post. imgur seems to recompress jpegs and make them a smeary mess. My apologies.
Attached Images
   
05-04-2013, 10:24 AM   #11
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Before you start grinding the mount flange or taking it to bits to 'fix' it, have a look on PixelPeeper at some full size images taken with this lens - you'll see that your copy is probably as good as is to be expected
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