Need pointers on sharper focus

Discussion in 'Photography Beginners' Forum' started by Renol, Oct 7, 2009.

  1. Renol

    Renol TPF Noob!

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    I've noticed when using my 50mm lens that I often have pictures that are out of focus (see examples below). Since its quite a pain to try and focus right through the viewfinder manually I use the autofocus. In these I have the autofocus set on the center point as I find I have issues getting good focus with all of them at times.

    All shots were done on a my Rebel XT with a 50mm f/1.4. Oh I also have a Canon UV filter mounted on the lens too.

    Example 1: [​IMG] Aperture too wide?
    Exposure Time: 0.0080 s (1/125)
    Aperture: f/1.4
    ISO Equiv.: 400
    Exposure Bias: -0.33
    Whitebalance: Auto
    Metering Mode: matrix
    Exposure: aperture priority (semi-auto)

    Example 2: [​IMG] Shutter too slow?
    Exposure Time: 0.033 s (1/30)
    Aperture: f/11.0
    ISO Equiv.: 100
    Exposure Bias: -0.33
    Whitebalance: Manual
    Light Source: Daylight
    Exposure: aperture priority (semi-auto)
     
    Last edited: Oct 7, 2009
  2. UUilliam

    UUilliam TPF Noob!

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    eh... your hands are shaking too much?

    Shouldn't do this!! especially at 1.4 at 1/125

    the minimum shutterspeed recommended for that lens on your body is 1/90 (focal length = shutter speed since 50mm on a 1.6x crop sensor is 1.6x50 = 80mm then shutter ideally would be 1/80 but since canon doesn't have this option you would use 1/90, you are using 1/125 which is a whole stop quicker
    your image is also to warm and it is underexposed!
    Try using a flash to make the target "freeze"
     
  3. Dao

    Dao No longer a newbie, moving up!

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    Photo #1: Did you try to focus on her eyes? It seems you focused on her left shoulder.

    Photo #2: You need a faster shutter speed as mentioned.
     
  4. Renol

    Renol TPF Noob!

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    Could be my hands...I'm more inclined to blame myself or technique rather than the hardware. I've had shots as low as 1/5 turn out alright without a tripod, but that's rare and takes too much effort to stay still.

    I was unaware of a minimum recommended speed...er rather I've read about it before recently but it hasn't sunk in yet. Also I absolutely hate the built in flash especially indoors but if a flash helps stabilize a shot of a person or subject I'm willing to try it.

    Not sure where I was focused honestly. Usually I try to focus on the face, lock it, and move the camera to the right angle (if it isn't already).
     
  5. tirediron

    tirediron Watch the Birdy! Staff Member Supporting Member

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    Hmmm... a tough one. I wonder if you're not just missing the focus. The string on the top of the bag in #2 seems relatively sharp. Don't forget that your DoF is VERY shallow; at f1.4, wit the subject 6' away, it's something in the order of 2"! I would suggest re-shooting and perhaps trying to manually focus just to confirm whether or not there is a potentinal camera/lens issue.
     
  6. Renol

    Renol TPF Noob!

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    I see. I don't always have this problem with the lens, but it seems more common than I want it to be. Looking through my photos of the last shoot I did a lot of them are out of focus due to slow shutter speeds. I have gotten a number of photos that are in focus with that lens so I'm not sure. Noob question, but how does one test a lens to make sure its not off? (I cringe even asking that so apologies in advance).
     
  7. tirediron

    tirediron Watch the Birdy! Staff Member Supporting Member

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    Print on a sheet of paper as many 10 or 12pt letter 'X's as you can, and tape the sheet to a wall. Set your camera on a tripod, and make sure that it is level and completly square to the sheet of paper. Position the camera so that it is a couple of inches inside the minimum focusing distance of the lens (ie if the lens will focus down to 2' than make sure the camera is 2' 2" from the paper) and take a series of exposures starting at wide open and working to progressivley smaller apertures. Look at 100% crops of the resulting images and see how sharp the results are. An OOF image will be immediately apparent.
     
  8. Renol

    Renol TPF Noob!

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    Thanks a lot! I'll give that a try. Fully expecting there to be no issues with the lens though so we'll see.
     
  9. fiveoboy01

    fiveoboy01 TPF Noob!

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    Lookin at the pic, I'm wondering if it's a DOF issue as well. I've taken plenty of shots wide open with a 50/1.4 that have one rinky-dink sharp area and the rest not so sharp... Gotta be careful with such a large aperture, I've learned to stop it down a bit if conditions permit.

    Not sure if I'm reading your post right or not, but 1/125 is not a stop quicker than 1/90. Just want to clear up that bit of misinformation.
     
  10. Renol

    Renol TPF Noob!

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    As I suspected the lens is fine in terms of focus. There is some vignetting from F/1.4-1.8 that gets worse the wider open you go. And it's interesting to see the difference in exposures from each photo. Some are darker and lighter than others...and I really need to clean my sensor too ><
     

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