50mm prime lens why can't I get my main subject in focus?

Discussion in 'Digital Discussion & Q&A' started by 391615, May 4, 2008.

  1. 391615

    391615 TPF Noob!

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    I've been taking some shots with my prime lens. Its a 50mm f1.4 I was shooting in f4.5. I focussed in auto on a persons face about 3 metres away. when I looked at the shots on the computer later, the people behind the subject I was photographing was in focus instead. I am absolutely sure I focussed on the main subject so why was that out of focus, and teh background probably 4-5 metres were in focus more? is this something all camera lenses do, using auto focus?
     
  2. Battou

    Battou No longer a newbie, moving up!

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    Try getting a little closer, a 50mm lens a 3 meters is right on the boarder of distanced focus and infinate focus for that lens if is anything like mine. Being right on the border like that might be confusing the AF and it's subject search.
     
  3. 391615

    391615 TPF Noob!

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    I know I do have a bit of dust on my lens, I tried to get off but couldn't. I noticed I couldn't focus on the sky, or anything really bright white. I get so frustrated when my camera won't focus in and won't shoot, on auto. I was taking some shots today and I only had one camera, otherwise I would have taken out my 18-55, and I had to make sure I got some close up portraits.

    I'm not sure what lens you had that was 3metres, for max focus distance, but mine goes to about 10 then infinity.
     
  4. Battou

    Battou No longer a newbie, moving up!

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    Canon FD, 50mm 3.5 macro....My mistake, I looked at the wrong 50mm lens, my other two FD 50mm's and my MD 50mm go up to 10 as well...disreguard my post.
     
  5. 391615

    391615 TPF Noob!

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    Thanks...

    If I look at the shots again, I think I was more 7-9metres so yeah you could actually be right, I did notice it wouldn't focus in on the sky. I definitely know with this lens, the best shots are head and shoulders from 1metre, I love the detail in the shots, but I'm realising that near infinity is not good.

     
  6. Flash Harry

    Flash Harry TPF Noob!

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    Have you got focus area selection set right, seems strange to me that something distant was focussed on instead of the subject. H
     
  7. Battou

    Battou No longer a newbie, moving up!

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    I actually encounter this quite often with my POS P-Shooter, but that thing is a different ball game prolly not the same cause
    .
     
  8. JustAnEngineer

    JustAnEngineer TPF Noob!

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    Check the diopter adjustment on your viewfinder.
     
  9. kellylindseyphotography

    kellylindseyphotography TPF Noob!

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    have you tryed manually focusing?
     
  10. DeadEye

    DeadEye TPF Supporters Supporting Member

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    Yep That ^^^ I blew a ton of shots that way. Was shooting through marsh weeds so the auto focus was no good at all . The diopter was set for no glasses and I had on glasses.. :DOH: Every shot was sharp looking in the viewfinder and worthless in the can.
     
  11. djacobox372

    djacobox372 No longer a newbie, moving up!

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    Sounds like a back-focus problem to me.

    It's not uncommon for the autofocus to be out of allignment, my nikon d200 and d70 both had this problem which is obviously more noticable when shooting with a narrow DOF like you described.

    I had to send my d200 to nikon to have it adjusted, luckily the d70 was adjustable via a hex screw in the body. My d70 now has perfect focus, my d200 is still off--I wish I could fix it myself like the d70 because nikon service seems to lack a bit of attention to detail.

    Some bodies like the nikon d300 are adjustable on a per lens basis via the menu--a feature all digitals should have IMO!
     
  12. Kegger

    Kegger TPF Noob!

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    Make sure that your focus isn't set on dynamic area. Put it on nearest subject or spot and you shouldn't have that problem, well, unless your past the focus range of course.
     

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