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09-03-2014, 04:37 PM   #16
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QuoteOriginally posted by Zafar Iqbal Quote
Question: If I'm getting front focus, would I need to add or remove (use thinner) shin?
How are you checking for front/back focus ?

09-03-2014, 04:52 PM   #17
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By doing test shots. It may not sound as a reliable method, but I'm having so much FF going on that even some inaccuracy on my behalf doesn't matter.
09-03-2014, 04:58 PM   #18
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Just a thought but do you have any fine focus adjustments applied? If so those would no longer be accurate once you start swapping shims around.
09-03-2014, 05:01 PM   #19
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No, It's in fact completely disabled.

09-03-2014, 05:02 PM   #20
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QuoteOriginally posted by Zafar Iqbal Quote
if I use the lower part of the viewfinder, I'd get accurate focus but not when using upper half.
Your focus screen is either not seated or your mirror is out of adjustment. It needs to be ALL the way back and resting on the two tabs in the photo linked below:

http://www.katzeyeoptics.com/images/k7_inst_12.jpg

The reason I know this is because I failed to do so on the first half dozen tries. The frame should snap shut with very little resistance.


Steve

---------- Post added 09-03-14 at 05:05 PM ----------

QuoteOriginally posted by jatrax Quote
Just a thought but do you have any fine focus adjustments applied? If so those would no longer be accurate once you start swapping shims around.
The shims don't affect the fine focus adjustments of the AF system. They are (fortunately) completely different systems.


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09-03-2014, 05:10 PM   #21
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QuoteOriginally posted by stevebrot Quote
The shims don't affect the fine focus adjustments of the AF system. They are (fortunately) completely different systems.
Correct. Not sure what I was thinking
09-03-2014, 05:21 PM   #22
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QuoteOriginally posted by kh1234567890 Quote
How are you checking for front/back focus ?
QuoteOriginally posted by Zafar Iqbal Quote
By doing test shots.
I would test against the AF system (focus confirm) initially. That should give you some indication as to whether you should add/subtract shims.
  • Flat target (I use the lens test target from Mark Roberts' Web site printed to heavy photo paper) taped securely to a wall
  • Camera on tripod
  • 50mm manual focus lens (if you have one)
  • 1 meter distant
  • sensor parallel to target
  • target at center of viewfinder
The flow:
  • Use focus confirm to attain focus. Is the viewfinder image in focus? If so, the screen calibration is very close and you are done with this flow.
  • Move the focus ring toward infinity in an attempt to attain viewfinder focus
  • Success? The lens is back focusing. If not, front-focus is the problem.
  • If back focusing, increase shim thickness. If front-focus, decrease shim thickness.
  • Repeat
Once you are close you can do a similar calibration against a taken image of the target or magnified live view (if supported on your camera).


Steve
09-03-2014, 05:23 PM   #23
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I've tried both with and without having the screen rest on top the two tabs.

Right now, the S-Type screen is resting on the tabs and I'm not using any shims. If I use the very bottom in the viewfinder to focus, I get slight BF. If I use the very top in the viewfinder, I get severe FF.

09-03-2014, 05:29 PM   #24
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QuoteOriginally posted by jatrax Quote
Correct. Not sure what I was thinking
You are not the first person who has added that cautionary note on a focus screen calibration thread.


Steve
09-03-2014, 05:33 PM   #25
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QuoteOriginally posted by Zafar Iqbal Quote
Seems I might have bent the tray and have tried to straighten it up again. Its a mess now :/
If the tray is bent or damaged all bets are off and you'll probably have to have the camera serviced to replace the tray and alignment of the components checked.
09-03-2014, 05:36 PM   #26
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QuoteOriginally posted by Zafar Iqbal Quote
Right now, the S-Type screen is resting on the tabs and I'm not using any shims. If I use the very bottom in the viewfinder to focus, I get slight BF. If I use the very top in the viewfinder, I get severe FF.
Dang! Possible causes:
  • Screen thicker on one side
  • Leading edge of screen lower than trailing edge (bent frame or something in the way)
  • Mirror out of alignment
The slight BF is what we are after with no shims present.


Steve

---------- Post added 09-03-14 at 05:38 PM ----------

QuoteOriginally posted by Not a Number Quote
If the tray is bent or damaged all bets are off
Ooops! I missed that part. If bent, it would not be a good idea to attempt to set it right with the frame still in the camera. Replacement would be the best option.


Steve
09-03-2014, 06:10 PM   #27
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QuoteOriginally posted by Not a Number Quote
If the tray is bent or damaged all bets are off and you'll probably have to have the camera serviced to replace the tray and alignment of the components checked.
I do not think that is the cause any longer, because I have been getting consistent results, rather than randomly varying accuracy across the screen, which should be the case when I started to "fix" the tray.

Even after all that, and a very long evening (and now night as well), I'm back to square one where upper VF part is giving me lesser accuracy than the lower VF part.

QuoteOriginally posted by stevebrot Quote
Dang! Possible causes:
  • Screen thicker on one side
  • Leading edge of screen lower than trailing edge (bent frame or something in the way)
  • Mirror out of alignment
The slight BF is what we are after with no shims present.

Steve
I honestly can't say whats up and I'm once again giving up.

It could be the screen is at fault here and it could also be, that the camera is showing age signs. It's currently at 80,903 exposures. The reason I think the latter might be true is because when I revert to the stock screen and shim, the focusing is still very inaccurate.

When I focus on something and recompose (all corners), I can tell by looking through the VF alone that the focus is shifting. It's not related to the bad-focus-because-you-recomposed thing, which is subtle in comparison.

What I might do, is to swap roles between my two K-30's. My other K-30 is much less used and still have stock focusing screen on it, because I've only been using it with AF.
09-03-2014, 11:18 PM   #28
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QuoteOriginally posted by Zafar Iqbal Quote
When I focus on something and recompose (all corners), I can tell by looking through the VF alone that the focus is shifting. It's not related to the bad-focus-because-you-recomposed thing, which is subtle in comparison.
Bent frame or maladjusted mirror.


Steve
09-04-2014, 11:08 AM   #29
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The changes in what are in focus and not appear to be constant, so I have question:

Is the image flipped or anything like that when it goes through the pentaprism? I'm thinking I could try compensating with only aplying thickness where needed, so focus will be more even across VF.

Does the edge of the screen that is closest to the cam mount correspond with the top of the VF?
09-04-2014, 11:57 AM   #30
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The image from the lens on the sensor is upside down so the portion of the image nearest to the camera mount would be the "top" of the image.

Last edited by Not a Number; 09-04-2014 at 11:59 AM. Reason: oops
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