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02-19-2016, 01:21 PM   #1
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manual focus question

I use manual focus lenses quite often on my K10D. My eyesight is still good (I wear glasses when shooting) and I'm using the stock focusing screen, with the diopter set correctly for my eyes. The camera focuses correctly using AF lenses. However, when using MF lenses, there's a small problem. When focusing, the image in the VF will be sharp to my eyes, but the green hex focus confirmation doesn't correspond to what I perceive as sharp focus. When it lights up, the VF image seems just a bit off from perfect focus.

Using the green hex indicator usually assures an in-focus shot, whether or not it appears that way in the VF. Relying on my eyesight, and ignoring the green hex does not. It's most often slightly out of focus. I don't have this problem with my other cameras (ist D, K-7, K100D). I just find I have to rely on the focus confirmation using the K10D, which leaves me uncertain I got the shot in focus.

Is there something I'm overlooking? Or are my eyeballs out of alignment? Thanks.

02-19-2016, 01:35 PM   #2
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Double check the diopter setting.

If that is for sure good then the focusing screen might be off a bit. Not familiar with the K10D but on other cameras I have it can be shimmed to adjust the apparent focus. Not something to do lightly without lots of testing though.
02-19-2016, 01:37 PM   #3
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QuoteOriginally posted by paulh Quote
I use manual focus lenses quite often on my K10D. My eyesight is still good (I wear glasses when shooting) and I'm using the stock focusing screen, with the diopter set correctly for my eyes. The camera focuses correctly using AF lenses. However, when using MF lenses, there's a small problem. When focusing, the image in the VF will be sharp to my eyes, but the green hex focus confirmation doesn't correspond to what I perceive as sharp focus. When it lights up, the VF image seems just a bit off from perfect focus.

Using the green hex indicator usually assures an in-focus shot, whether or not it appears that way in the VF. Relying on my eyesight, and ignoring the green hex does not. It's most often slightly out of focus. I don't have this problem with my other cameras (ist D, K-7, K100D). I just find I have to rely on the focus confirmation using the K10D, which leaves me uncertain I got the shot in focus.

Is there something I'm overlooking? Or are my eyeballs out of alignment? Thanks.
Sounds like your focus screen needs shims added or removed to get it just right. The focus screen "stands-in" for the sensor when the mirror is down, and so the reflected path of light needs to be the EXACTLY the same distance as it would be if it (the light) were hitting the sensor instead. So there are tiny little shims in the focus screen bracket that can be added/removed to change this distance ever so slightly. If it is off, what appears sharp on the screen will be out of focus on the sensor.
02-19-2016, 01:42 PM   #4
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I imagine it's really a tedious process shimming the focus screen


QuoteOriginally posted by vonBaloney Quote
Sounds like your focus screen needs shims added or removed to get it just right. The focus screen "stands-in" for the sensor when the mirror is down, and so the reflected path of light needs to be the EXACTLY the same distance as it would be if it (the light) were hitting the sensor instead. So there are tiny little shims in the focus screen bracket that can be added/removed to change this distance ever so slightly. If it is off, what appears sharp on the screen will be out of focus on the sensor.


02-19-2016, 01:45 PM   #5
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The diopter setting can already be ruled out. If it was off, then the image would never appear fully sharp, no matter at what point the lens is focused , and the sharpest appearing (yet still blurry) point would still be at the same focus level, since what she's viewing is a 2 dimensional projected image on a screen, not light directed directly through the lens into his retina.

It's like looking at your TV with your glasses on or off - it has no effect of how sharp the picture is at the screen itself, and making the TV picture blurrier is not going to help you see it from far away.

QuoteOriginally posted by jatrax Quote
Double check the diopter setting.

If that is for sure good then the focusing screen might be off a bit. Not familiar with the K10D but on other cameras I have it can be shimmed to adjust the apparent focus. Not something to do lightly without lots of testing though.
02-19-2016, 02:02 PM   #6
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QuoteOriginally posted by paulh Quote
When focusing, the image in the VF will be sharp to my eyes, but the green hex focus confirmation doesn't correspond to what I perceive as sharp focus. When it lights up, the VF image seems just a bit off from perfect focus.

Using the green hex indicator usually assures an in-focus shot, whether or not it appears that way in the VF.
have you run multiple rounds of focusing tests, using both methods, and compared 'em at 100%, on the computer screen? it's the only way to be sure.

if the k10d had liveview, it would be helpful, but afaik it doesn't.

i replaced the focusing screen in my k10d, and it was off, so i tried shimming it with paper strips, but dropped a piece of it into the bowels of the camera, lol, where it still resides to this day.
02-19-2016, 02:08 PM   #7
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Thanks for the quick replies everyone. Shimming my focus screen doesn't sound like a fun way to spend the day...but I may try it eventually. Meanwhile I guess I'll stick with the green hex and continue testing.
02-19-2016, 02:11 PM   #8
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QuoteOriginally posted by Spodeworld Quote
I imagine it's really a tedious process shimming the focus screen
Yes. My K5IIs needed a really thin shim to be perfect, very floppy to install, check and adjust. I made a shim myself out of brass shim stock for another camera, which worked out eventually. It's a little worse on the K10D because it lacks live view. Maybe the tethering software would help there?

Stevebrot posted something about shimming maybe 3 months ago that was worded perfectly for me. He described it in a way that avoided the terms front- and back-focus. I'll try to find this post, which I copied to a text file so I could tackle the procedure again. The other reason to mention Steve is that he has hinted recently that he can help you acquire shims. I regret not doing this when the Pentax source was just a mile away. Now it's easier to get marijuana than Pentax shims.

Edit: here's the post that describes when to add or remove shims:

https://www.pentaxforums.com/forums/58-troubleshooting-beginner-help/272076-f...ml#post3448227

The post's procedure for checking focus relies on live view so it's not good for the K10D. I like to do it this way:
  • Camera on tripod.
  • I tape a newspaper to the floor as a focus target.
  • Sensor is roughly 45 degrees to newsprint.
  • I choose tripod height and a lens so wide open, my depth of field is one line of newspaper text or less (stock screen will show more DOF than image)
  • A long focus throw is better. I like a 90/2.8 macro because it's sharp wide open.
  • Focus on one line of text right in the center of the VF and take a shot.
  • Text is good because I can remember where the focus was supposed to be when I look at the shot on a large screen.
  • Sports page results usually have small text.
  • Then repeat until you decide it's close enough.
  • Repeating is annoying because it's hard to fiddle with shims without disturbing the focus ring, tripod, target, etc.



Last edited by Just1MoreDave; 02-19-2016 at 02:43 PM.
02-19-2016, 02:39 PM   #9
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QuoteOriginally posted by paulh Quote
Thanks for the quick replies everyone. Shimming my focus screen doesn't sound like a fun way to spend the day...but I may try it eventually. Meanwhile I guess I'll stick with the green hex and continue testing.


Yes shimming is a challenge but when done properly well worth the effort. When changing focusing screens on booth the K-5II and K-3 I had to put in the hours but never regreted it.
02-19-2016, 02:48 PM   #10
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It also should be pointed out that with the stock screen, super-accurate manual focusing is literally impossible with fast lenses (like an f/1.8 or faster, and maybe even some f/2.8s) no matter how well shimmed...
02-19-2016, 03:08 PM   #11
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QuoteOriginally posted by jatrax Quote
Double check the diopter setting.
What he said. adjust so that the AF brackets lines are sharp.

QuoteOriginally posted by jatrax Quote
If that is for sure good then the focusing screen might be off a bit. Not familiar with the K10D but on other cameras I have it can be shimmed to adjust the apparent focus. Not something to do lightly without lots of testing though.
The K10D screen calibration was pretty good if my memory serves me correctly. I confirmed mine using moire pattern before I pony'ed up for a Katz Eye. The main issue on that camera was poor focus precision overall and one of the symptoms was that the green hexagon and the manual focus would often not coincide. Both manual and PDAF systems were fairly imprecise with the AF system being somewhat more so (focus sensitivity of about f/3.5-f/4 with stock screen vs. f/5.6 for the PDAF). Given the full set of variables for both systems, agreement on a real subject is not always guaranteed. I found this to be true even after switching to and confirming accuracy of the Katz Eye.


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02-19-2016, 03:20 PM   #12
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QuoteOriginally posted by vonBaloney Quote
It also should be pointed out that with the stock screen, super-accurate manual focusing is literally impossible with fast lenses (like an f/1.8 or faster, and maybe even some f/2.8s) no matter how well shimmed...
I would draw the line for manual focus sensitivity somewhere around f/3.5 on the K10D and subsequent flagship models. I was somewhat aware that I was getting poor manual focus results from my A 50/1.7, but it was not until I bought the Jupiter-9 85/2 that I realized how severe the issue was with my K10D (no live view as a check). The Katz Eye literally changed my life in regards to manual focus. Suddenly I got good results!


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02-19-2016, 03:21 PM   #13
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I used to have problems manually focusing my K10D. I also wear eyeglasses and the standard screen is installed. I made sure the diopter was adjusted optimally and practiced. Now I can usually nail the focus rather well. I normally turn off AF as I find the focus lock restriction on shutter release a pain - with manual focus lens the slightest shift can lose confirmation.

To adjust the diopter I first focused the image until I got a good confirmation. Then I adjusted the diopter for the sharpest view checking against the etched lines on the screen.
Then I trained myself to recognize what focus looked like according to the camera - focus until you get the green hex and study the image in the viewfinder - rinse and repeat.
Next step - focus first without using confirmation - don't half-press the shutter until after you think you have focus. Then half-press and adjust focus until the green hex locks on. After awhile you will learn how to nail the focus so that the green hex locks on the moment you turn on the meter and focus system.
You might even be able to skip the second step above.
02-19-2016, 06:34 PM   #14
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QuoteOriginally posted by paulh Quote
Using the green hex indicator usually assures an in-focus shot, whether or not it appears that way in the VF. Relying on my eyesight, and ignoring the green hex does not. It's most often slightly out of focus

Perhaps you could just adjust the viewfinder diopter adjustment to suit what the camera sees rather than your eyes. When the hex is lit, adjust the diopter setting until you see a crisp in-focus image.
02-19-2016, 06:45 PM   #15
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QuoteOriginally posted by pjv Quote
Perhaps you could just adjust the viewfinder diopter adjustment to suit what the camera sees rather than your eyes. When the hex is lit, adjust the diopter setting until you see a crisp in-focus image.
That will not work. Even though you are looking "through" it, the image is focused on the focusing screen -- it might as well be printing on a piece of paper. To adjust the diopter, you shouldn't be looking at the image at all, but the lines etched on the screen. Purposely misadjusting it will serve no purpose other than to give you a headache.

Last edited by vonBaloney; 02-19-2016 at 09:54 PM.
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