50D Viewfinder blurred when subject in focus (not diopter)

Discussion in 'Canon EOS' started by dmorgan, Apr 5, 2010.

  1. Hi,
    I recentally had my 50D cleaned by canon at their service centre in Hertfordshire. Since then I have noticed that in focus subjects are blurred in the viewfinder.
    To clarify, the camera will autofocus, with the autofocus indicator lights highlighting the in-focus areas. However, in the viewfinder the in-focus areas look clearly out of focus. The resulting picture is perfectly in focus. If i manually adjust the focus on the lens I can make the image tack sharp in the viewfinder, however the resulting photograph is out of focus.
    I have adjusted the diopter to make the image in the viewfinder as unblurred as possible, but it is still not clear enough through the viewfinder when the subject is in focus (according to the autofocus). This makes it virtually impossible to manually focus.
    I have had another person who has 20-20 vision check (with the diopter adjusted for them) and they can confirm that they are having the same problem - that is in order to get the image in the viewfinder in focus they have to manually focus the lens - which then results in a perfectly sharp image in the viewfinder but an out of focus photograph.
    I have removed the focus screen and put it back in place, to make sure it is positioned correctly, but the problem remains.
    This happens with all my lenses.
    When using Live view, the in focus areas are perfectly sharp on the LCD and in the resultant photograph.
    Are there any other suggestions, or would I need to take it back to the service centre?

  2. You need to reseat the focusing screen. It is out of alignment. Used to happen to my EOS 3 if I ran with it across rough terrain.
  3. Hi Puppy Face,
    Thanks for your response. However, I have already removed the focussing screen and placed it back into position - this doesn't seem to have any effect.
    Any other ideas?
  4. Might be missing a shim, or have it wedged in wrong.
  5. Something is out of alignment, and we can immediately rule out the following components:
    • The lens, including the alignment of the lens mount: photographs and live view depend on this, and you've already demonstrated that they both work perfectly well.
    • The sensor: ditto
    • The AF system, which is mounted in the base of the mirror box: you've already tested and proven that the AF system remains accurate.
    • The mirror assembly, including the sub-mirror on its back: a mirror which is out of alignment could indeed produce viewfinder problems, but as all of the light reaching the AF system is dependent on the mirror assembly, it would also throw off AF.
    • The dioptric adjustment. What you are looking at in the viewfinder is not the subject; it's an image that's projected onto the focusing screen. Other than the fact that the focusing screen is transmissive while the screen in a movie theatre is reflective, the situation is the same in both cases: one set of optics (the camera lens; the projector lens) projects an image onto the focusing screen and is responsible for making sure that the image on the screen is in focus; a completely separate set of optics (in both cases, your eyeball and any corrective eyewear you may be using, which in the case of the camera includes the setting of the dioptric adjustment) lets you view that image and is responsible for making sure that you can focus on the screen. If the guy in the projection booth tweaks the projector's lens and you can now see the image in focus, then the problem cannot have been that you are wearing the wrong prescription glasses; likewise, if you can tweak the camera's lens and the image comes into focus, then the problem cannot have been that you have the dioptric adjustment set incorrectly.
    • So, the only things that could be the problem are the bits that (following the path that the light takes) are after the mirror and before the dioptric correction optics. Of those, the only part that is not reasonably firmly fixed in place is the focusing screen, which makes it by far the most likely culprit.
      And at that point, I can't tell you why it's not right or how to fix it, particularly as you've already removed and reinstalled it. But that's almost certainly the part that is causing the problem. I suspect the repair centre accidentally caused this; I would be in touch with them about it.
  6. There is the slight chance when they cleaned the camera that , the screen you came in with is not the screen you took home, it literally only takes a spec of dirt or oil , or film substance that you cant see with the necade eye to screw up the screen, and i bought two new screens , and used the tool to put it in and one of the ones i purchased was defected right out of the box, outside of the screen i cant think of a thing, but if the canon reapir place is close by , id go back and let them look rather than drive yourself crazy.
  7. For really critical MF some people shim their focusing screen for perfect alignment.
  8. Is it possible that the focusing screen is upsidedown?
  9. Hi,
    Thanks for all the responses. I took it to the service centre and they repaired it while I was waiting. Turns out the indicator plate was not aligned correctly.
  10. I am having the same issue...where did you go that you could have this done in store..
    They want me to send it out and it will be an arm and a leg and $$$$$$$! Thanks!

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