Inconsistent focusing with new Canon 50mm and 85mm F1.8 lenses. A distressing problem

Discussion in 'Beyond the Basics' started by JonHornsby, Mar 14, 2009.

  1. JonHornsby

    JonHornsby TPF Noob!

    Joined:
    May 21, 2008
    Messages:
    13
    Likes Received:
    0
    Can others edit my Photos:
    Photos OK to edit
    My daughter has a Canon Rebel XT and recently purchased a Canon 50mm F1.8 and a Canon 85mm F1.8 lens for this camera. She had two reasons for wanting these lenses: (a) to take pictures when ambient light levels are low without having to use flash and (b) to use the shallow depth of field of these lenses at large apertures to separate the subject from the background. The two lenses are quite sharp but unfortunately, 64% of the images taken at a wide aperture (F2) are out of focus regardless of the focusing mode used. We took a series of photos of a stationary object with the camera/lens mounted on a tripod, using the self timer to eliminate vibration caused by mirror slap. We photographed the subject using Manual Focus override, AI mode, and One-Shot mode.

    The overall result was that 64% of the time, the camera focused in front of the subject – far enough in front to create an unacceptably blurry picture of the subject. (To be precise, only 20% of the images were sharply focused in AI mode, only 40% in One-shot mode, and only 50% in the manual “tweaking” mode) This is very annoying. Actually it’s more than annoying, it’s downright unsatisfactory. The problem does not occur with the standard 18-55mm zoom kit lens because the maximum lens opening is only F3.5-F5.6 (greater depth of field) with the kit lens. which takes amazingly sharp pictures.


    The problem is apparently caused by the camera's sensor and/or mirror alignment or positioning, and could presumably be corrected by Canon for a "mere" $210. But is it worthwhile to have this camera repaired, or should my daughter get an upgraded Canon camera with more megapixels and the stabilized kit zoom lens? Also, what is the likelihood that Canon would fix the camera free, since this appears (maybe it is, maybe it isn't) similar to the problem that prompted the technical advisory and free repair for EOS-1D cameras which experienced focus tracking problems?
     
  2. 250Gimp

    250Gimp TPF Noob!

    Joined:
    Oct 3, 2006
    Messages:
    1,031
    Likes Received:
    0
    Location:
    Chelsea, Quebec
    Can others edit my Photos:
    Photos OK to edit
    How old is the Xt?

    If it is out of warranty I doubt that Canon will fix it for free.

    If you send it in you should probably send the lenses in as well so they calibrated with the body.
     
  3. JonHornsby

    JonHornsby TPF Noob!

    Joined:
    May 21, 2008
    Messages:
    13
    Likes Received:
    0
    Can others edit my Photos:
    Photos OK to edit
    Thanks, 250Gimp.

    A quick follow up. My daughter has sent the new Canon lens back and will sell her Canon XT, which is a couple of years old and out of warranty. She will get a Nikon D300 with 18-135mm lens and a Nikon 85mm F1.8 lens.
     
  4. Jaszek

    Jaszek No longer a newbie, moving up!

    Joined:
    Oct 7, 2008
    Messages:
    2,177
    Likes Received:
    25
    Location:
    Brooklyn, NY
    Can others edit my Photos:
    Photos OK to edit
    can you post some sample shots? maybe you should've checked where the focusing point was set to.
     
  5. AlexColeman

    AlexColeman TPF Noob!

    Joined:
    Dec 13, 2008
    Messages:
    1,732
    Likes Received:
    1
    Can others edit my Photos:
    Photos OK to edit
    She will be much happier with the Nikon.
     
  6. JonHornsby

    JonHornsby TPF Noob!

    Joined:
    May 21, 2008
    Messages:
    13
    Likes Received:
    0
    Can others edit my Photos:
    Photos OK to edit
    The vertical type was 1 inch in front of the horizontal type (the thickness of two gum wrapper boxes). Hopefully, the effect will show up at the resolution of the photos in this reply. I'm very new at doing this and had to get help in placing an image in the message.

    [​IMG]

    [​IMG]
     
  7. JonHornsby

    JonHornsby TPF Noob!

    Joined:
    May 21, 2008
    Messages:
    13
    Likes Received:
    0
    Can others edit my Photos:
    Photos OK to edit
    Thanks, Alex. I am certainly not condemning Canon products as a result of this one "glitch." Canon makes fine cameras and lenses. But I think you are right. She will be very happy with the Nikon.
     
  8. 250Gimp

    250Gimp TPF Noob!

    Joined:
    Oct 3, 2006
    Messages:
    1,031
    Likes Received:
    0
    Location:
    Chelsea, Quebec
    Can others edit my Photos:
    Photos OK to edit
    Were these shots taken with a tripod?

    The DOF is very thin at f2, so if you lean into the shot the least little bit after aquiring focus you will get an out of focus shot.

    To do this test properly you need to use a tripod, or at least put the camera on something solid so it doesn't move at all.

    Cheers
     
  9. JonHornsby

    JonHornsby TPF Noob!

    Joined:
    May 21, 2008
    Messages:
    13
    Likes Received:
    0
    Can others edit my Photos:
    Photos OK to edit
    Yes, the photos were taken with a tripod, using the self timer to eliminate vibration caused by mirror slap.
     
  10. Flash Harry

    Flash Harry TPF Noob!

    Joined:
    Jun 26, 2006
    Messages:
    1,918
    Likes Received:
    1
    Location:
    Durham, UK
    Can others edit my Photos:
    Photos NOT OK to edit
    The money spent on these cameras/lens there should be no such issues and if there is whether in or out of warranty should be corrected free, its time these mega rich companies were brought to book a camera that can't focus is about as much use as a chocolate fireguard.

    Canon have had focus issues for years now on some models, I first read of such issues in 2001, my Niks however work with all nikon lens perfectly, the d300 even have a built in calibrator just for this reason, not that I've had to use it yet, so I think another nikon convert will be very happy with the new tool. H
     
  11. JonHornsby

    JonHornsby TPF Noob!

    Joined:
    May 21, 2008
    Messages:
    13
    Likes Received:
    0
    Can others edit my Photos:
    Photos OK to edit
    Most interesting. I had no idea the D300 had such a feature. My daughter will be glad to hear that.
     
  12. JerryPH

    JerryPH No longer a newbie, moving up!

    Joined:
    Oct 14, 2007
    Messages:
    6,111
    Likes Received:
    15
    Location:
    Montreal, QC, Canada
    Can others edit my Photos:
    Photos NOT OK to edit
    D700 and D3 also have this feature... though I am happy to say that none of my lenses need any adjustments, even my 85mm F/1.4 is spot on set at F/1.4 and minimal focus distance.

    Before I blame any lens, my first is to blame the person behind the camera. At F/1.8, as mentioned, a tiny lean in or out after teh focus is locked in can cause this effect. Set it on a tripod, and I think we will see that 1 of 2 things will happen:

    - Lens will be consistently perfectly focused
    - Lens will be consistently out of focus

    If it is consistently out of focus, sending it to Canon for adjustment is the answer, if its not out of focus... user technique needs work.
     

Share This Page

Search tags for this page
blurry pictures with canon 85mm lens
,
canon 50mm 1.8 backfocus
,

canon 50mm 1.8 front focusing

,
canon 50mm f/1.8 focusing problems
,
canon 85 1.8 focus problem
,

canon 85mm focus problem

,
canon f1.8 50mm focus problem
,
having trouble focusing my canon 50mm 1.8
,
inconsistent focus canon xti
,
trouble focusing on multiple objects with canon 50mm