[baro-nite]

[UPDATE: ISSUE SOLVED by adding shims; see page 2]

I've been missing focus on a lot of shots with my new DA* 200 2.8. I'm trying to figure out how much of this is due to my focusing technique and how much, if any, to equipment. I did some testing, perhaps not in the most scientific way but I've gotten pretty consistent results. Autofocus is fine. When I focus manually with this lens I am consistently focusing behind the subject (I don't say 'back focusing' because I gather that is meant to refer to AF problems only).

My only other relatively fast lens is my Sigma 1:2.8 70mm macro. It's possible I have the same issue to a slight degree but I'm not sure. I've attached some examples, two from the DA* 200 and one from the Sigma. I also tried my DA 50-200 at 200mm, but at f5.6 the DOF was too large for me to be sure of the results. I did at least confirm that the DA* is massively better than my 50-200 at 200, no surprise there.

In the DA* shots I am attempting to focus on the DA* box (with post-it notes on it). The post-it notes indicate whether MF or AF was used. The front of the box is at about 14" on the ruler (where the box meets the ruler). The objects are receding from right to left. These are 100% crops, f2.8, from about 9m away.

In the Sigma shot I was attempting to make the center of the 10" line the point of focus. It's pretty close but I think slightly off from what I saw in the viewfinder. This is a 1:2 shot, uncropped.

Do I just need to improve my MF technique, or is my focus screen mis-aligned? Or something else?

[A curiosity, and not relevant to the main question: I was shooting in Av mode (as usual), and with AF the actual shutter speed was as indicated in the viewfinder. But with MF I would usually get a faster shutter speed and an underexposed shot. (I've adjusted the exposure in PP.) I do not have AF point linked to AE, and am using multi-segment (green dial setting) metering.]

I probably shouldn't start this discussion now as I will only sporadically be online for the next few days, but this is driving me crazy.

Edit: When I say I am 'consistently focusing behind the subject', I mean I am nearly always behind it, but not always by the same amount -- no question, my MF technique isn't perfect.

Attached Images

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Last edited by baro-nite; 08-29-2011 at 12:23 PM. Reason: Added a note (indicated as an edit). 2nd edit: issue is solved.

[Canada_Rockies]

I have manually focused using Pentax equipment since 1961, and yet had trouble manually focusing my K10D when I first got it. This was not good in my mind, particularly since two of my best lenses are from the M series. I was also having exposure meter inaccuracies, and Lowell Gouge among others pointed out that the stock focusing screen was too bright and actually only worked properly with A series lenses with the aperture set on the [A] setting.

I gambled on purchasing a screen (LL-60) from the *ist days, and that corrected the exposure problems. I also found that it corrected my focusing to a large extent. The grain of the screen was coarser as on my older cameras, and enabled me to manually focus with much less difficulty. I have since added the O-ME53 1.2X focusing magnifier to my K10 and the little bit larger view helped some more, to the point that my manual focusing errors are back to my normal level.

I envy you your DA* 200, BTW. What a gorgeous piece of glass.

[Marc Sabatella]

It's an unfortunate fact of life that the focus screen will show shallower DOF than it should for sufficiently fast lenses. That is easy to verify by shooting some text on an angle wide open and comparing how many lines appear in focus in the viewfinder versus in the shot. That means that some things that appear to be in focus in the viewfinder *cannot* be in focus in the picture. I think this is the cause of a lot of MF problems. It's possible through practice to get better at focusing in such a way that your subject is not within that zone that is not actually in focus when it appears to be in focus in the picture. Beyond that, though, a split prism screen is probably the answer.

[baro-nite]

Thanks for the answers.

Albert -- I recently installed the focusing magnifier. My tests shown above were using that, so at this point I don't think it's helped me. Although it does make it easier to see. (Yes, the DA* 200 is great glass. When I get it in focus!)

Marc -- I guess you mean the apparent viewfinder DOF is too large with a fast lens? I understand that, but it is the consistent direction of the MF errors I am getting that has me wondering about a mis-aligned focusing screen. I'll have to do some more testing when I get the chance.

[nathancombs]

i am having back focus problems my self i think that i need to just have my K10D sent in for a tunup i use mine a LOT not felling let down it my K10D gets beat up a lot its just time to get some thing new or replace it, the problem is not bad but its hard to hit any thing with a 1.4 or 1.7 M

[Marc Sabatella]

See my comments above. There's most likely nothing wrong the the camera, it's just an infortunate fact of life that the design of the focus screen is such that it shows too much DOF, so some things that appear in focus in the viewfinder will not and cannot be in focus in the picture.

[baro-nite]

In both of these images I am attempting MF on the word indicated by the arrow.

With the DA* 200 @ f2.8:



and with the Sigma 70mm @ f2.8:



Marc, I feel very confident that the result does not match the view from the viewfinder, even when taking the greater DOF of the viewfinder into account. That is, I am confident that I had the subject (the word indicated by the arrow) in or nearly in the center of the in-focus range. From what I have gleaned from the many forum threads about focus issues (yes, I read many of them before starting this thread) the logical answer seems to be that my focus screen is mis-aligned. I say that because AF is working well. But before I pursue getting this corrected I'd love to have any other opinions as to whether or not I am on the right track.

[octavmandru]

Hehe, I was getting similar results with a camera. AF was saying something, but I was seeing different.
Then I remembered, all started after I was playing with the focusing screen. The bastard had moved, so I was seeing wrong.

Ok, I'm a mechanical engineer, so keep trying to find the mechanical error. But this sounds like one.
I believe the reason is either the alignment of the focusing screen, or the mirror limiter. So the registration distance has increased (wear and missalignment caused by vibrations). Or the camera is just like that since ... forever, but now the shallow depth lens is revealing everything.

Octav

[Canada_Rockies]

Hehe, I was getting similar results with a camera. AF was saying something, but I was seeing different.
Then I remembered, all started after I was playing with the focusing screen. The bastard had moved, so I was seeing wrong.

Ok, I'm a mechanical engineer, so keep trying to find the mechanical error. But this sounds like one.
I believe the reason is either the alignment of the focusing screen, or the mirror limiter. So the registration distance has increased (wear and missalignment caused by vibrations). Or the camera is just like that since ... forever, but now the shallow depth lens is revealing everything.

Octav

Have you removed the focus screen? There is possibly a shim that is out of place between the screen and the prism.

[lmd91343]

The K10D has a fine focus adjustment in the controls with firmware 1.30. I had to use it for mine. Mine was so far out that the dim (wide DOF) kit lenses were off. I was ready to swear off Pentax. The images were MUCH better after the adjustment.

The unfortunate thing is that there is only one adjustment for the camera. I was lucky because my three good lenses (50-135 2.8; 17-50 2.8; & 10-17 3.5-4.5) all measured the same. I set the camera at that. My two kit lenses and my 50 1.4 were all different from each other and the first three.

Your two lenses look similar to each other. Perhaps split the difference in the fine adjustment.

The instructions are here:
Blog

This is not normally user accessible as it is in the K20 and K5. Proceed at your own risk!
The K20 and K5 allow for 20 adjustments directly by the user.

Good luck,
Lance

[octavmandru]

Excuse me, but how is the AF adjusting going to help, since AF is fine and manual optical focusing is crooked?
He can ruin the AF too.

OP clearly said: "AF is fine, manual focusing is giving bad results". This means clearly enough that the optical path for the VF is different to the one on the IS (Imaging Sensor) and AF sensor.
Now, I have to come back to my original assumptions: The optical path is determined by the mirror for both VF and AF. So if it works for one (AF), should work for the other (VF), too.
But, the VF image is actually created on the matte screen, also known as focusing screen. The mirror is OK, only the FS (focusing screen) position can be the problem.

Octav

P.S.
To clarify:
OP, when you auto focus, does the image look clear in the viewfinder or not?
Then, when you use AF to take a picture, is the focus where it should be, or not?


Octav

[freddykrueger]

I think that your focusing screen is misaligned. But if you use the focus confirmation light, you should be fine. I know that the focus areas are quite big, they're not just points, but I get very good results by using the confirmation light with my K-x and M 50mm f/1.7. And if your shot is a bit off, just move the focusing circle a bit to the right direction. The only other solution for you would be to send it to factory for calibration.

[opfor]

I have only one thing to say, diopter adjustment........:-)
You did say manual focus problems, right?

[baro-nite]

Thanks very much to all for your replies.

Or the camera is just like that since ... forever, but now the shallow depth lens is revealing everything.

Exactly; (although I've had the Sigma nearly as long as I've had the camera and usually manually focus it for macro shots, but usually stopped down) I suspect I've had this problem all along and hadn't noticed.

Have you removed the focus screen? There is possibly a shim that is out of place between the screen and the prism.

I've never attempted to adjust it, and indeed I had never even cleaned the sensor until recently (after all this became noticeable). But I agree with your idea that it is a focus-screen shim problem.

The K10D has a fine focus adjustment in the controls with firmware 1.30. ... The images were MUCH better after the adjustment.

Yes, but that is for AF, correct? My AF is fine.

OP, when you auto focus, does the image look clear in the viewfinder or not?
Then, when you use AF to take a picture, is the focus where it should be, or not?

Just did another test, this time with AF. I had to set it up again so it's not the same perspective as the test above, but I think it shows the same issue with the viewfinder. This is with the DA* 200, and after auto-focusing I moved the arrow to what I thought was the most in-focus line. I used the remote on a 3 second delay to trigger the shutter to make sure I didn't move the camera.

Edit: Again, in real-world shooting where it is obvious what the AF is locking on (large object, more or less planar and perpendicular to the line of sight), AF works accurately.

I have only one thing to say, diopter adjustment........:-)
You did say manual focus problems, right?

Yes, MF only. But I believe I have the diopter adjustment correct, and my understanding is that the diopter doesn't affect where in the image the focus appears to be sharpest, but rather whether or not anything appears in focus.

So now the question is whether I try installing a new shim myself, or send the camera back to the mother ship, or take it to a local shop. I saw a video on replacing the focus screen that made the process look dead easy, so I'll see if I can order the shims from Pentax and try it myself. I know some PF'ers have made their own shims so I suppose that's an alternative, but I'd prefer the real deal. Any tips appreciated.

[octavmandru]

tip: since you fancy the ideea of manual focus, why don't you order a katz eye screen (think that's correct) and order the shims set from them?
Of course replacing the screen is dead easy. It is supposed to be replaced, so don't sweat on it.

Octav