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Thread: Focus Issues

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    Default Focus Issues

    Hi. I'm pretty new to photography and have lots to learn. One issue I usually stumble upon is focus. Even though I think I have the camera settings correct, when I reviewed the photos, it doesn't look sharp or focus at all.

    Here are some example photos from my school open gym. Lighting was poor and had to use some 'extreme' camera settings. Only edits I did was using auto settings in CS2 Camera RAW. No crop, but resized though.

    1) Face doesn't look sharp


    2) Face does look somewhat sharp but can be better?


    Here are the equipments I used:
    - Canon Rebel XTi w/grip
    - Canon 50mm f/1.8

    Here are the settings I used:
    - Manual Exposure
    - Shutter : 1/250th
    - Aperature: f/1.8
    - ISO: 1600
    - AI Servo AF
    - Manual Focus Point: Center Focus

    The issue I'm having is that even though I have the center focus point on the player's face, I can't seem to get a sharp photo. I'm pretty sure it has to do something with DOF(depth of field) but I don't know much about this. From what I know(hopefully this is correct) that a large fstop such as f/1.8 would produce a shallow DOF which mean objects would appear sharp if they are closer to the camera and anything beyond a certain distance will be blurry. A small fstop such as f/22 would produce deep DOF which mean everything from a short to long distance would be sharp. I'm hoping this is correct. Please correct me.

    I also know that some lenses has a sweetspot at some aperture. I think on the Canon 50mm f/1.8, the sweetspot is around f/2.8 but I wished I could use that. I could try to slow down the shutter to 1/200th and raise the aperture by one stop but not sure if the shutter speed would be fast enough to "freeze" the shot.

    Or my last idea is that I pushed my equipments to their limits and it's the best quality I can get. Even that's the case, I still want to get some opinions on DOF and how that effects focus. I think that is my problem that I don't understand how DOF works. I also heard something about focusing 1/3 on the subject? Maybe that could help?

    And finally, any general tips, advices, suggestions or comments to a new photographer would be grateful too

    -Thanks
    Last edited by zasboy; 01-19-2007 at 05:31 AM.

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    to be honest, that's quite acceptable. usually lenses are noticably less sharp when it is wide open.

    but you pretty much understood the situation yourself from you description.

    btw, which gym is that? is it los altos HS?

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    Kwun, indeed the photos are acceptable but I was wondering if I could improve on it?

    I did some photoshop edit on the photos and it looks much better now. Here's my badminton gallery: Click Me

    The gym in the photos was taken at the UC Santa Cruz West Field Gym. The school has two gyms, West and East. I was a student, club officer, and team member on the UCSC Badminton Club/Team until I graduated in 2006. I still go back to play and take photos
    Last edited by zasboy; 01-19-2007 at 04:36 PM.

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    on the topic of whether it can be improved, i think for some situations, it can be improved. those include more stationary shots like serving. in that case you can try f/2.8. and you will be using 1/125s for shutter speed. both settings will be within the safe margin and you might get slightly better sharpness.

    for action shots, i don't think you can expect much more. f/1.8 gives a really shallow depth of field as you said, that means the range of distance where object is in focus (centered around the focus distance) is very small. any small movement will knock the subject outside of this focal range. furthermore, 1/250s is really very borderline when it comes to stopping motion. motionblur will cause in-focus subject to look more blurry.

    from your setting, it looks like the gym is better lit than average. ISO1600, f/1.8 and 1/250s and you still get a decently exposed photo (i assume you haven't tweaked the exposure on Camera Raw). there are gyms around with much worse lighting and there is very little hope of getting anythign in focus!

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    another thing that can be done is to push the exposure. use faster shutter (1/500s) or larger aperture (f/2.8). the photos will come out underexposed and then you can compensate it in Camera Raw. the result is that the contrast and noise level will suffer. but it will at least give you better DoF and less motion blur, you can experiment to see if that produce a more acceptable photo.

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    Good advices kwun. I'm going back to the UC Santa Cruz West Gym on Sunday and will try to underexpose some shots. I'll report back with some results.

    Some additional informations helps. The West Gym has high open ceilings. There are windows on the roof but the photos I took were taken a night. The photos I'll be taking on Sunday will be during the daytime. Not sure if that is going to make a difference in lighting.

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    Since you use the 50/1.8, here are some opinions I have of it.

    At aperture f1.8, it is quite soft.

    f1.8 also gives low depth of field.

    It doesn't focus very fast so your subject may have moved and the AF mechanism hasn't caught up.

    When the AF changes the lens, the incremental steps may be large enough that the centre will not be quite in focus. The 50/1.4 has smaller incremental steps so the accuracy of focus will be better. (this point is sometimes mentioned in the camera forums).
    Last edited by Cheung; 01-20-2007 at 09:29 AM.

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