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Thread: How to force autofocus to focus on a specific object?

  1. #1
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    Default How to force autofocus to focus on a specific object?

    Hi,

    I took this picture and i want to focus on Penguin but using autofocus it is impossible.
    Or only answer is manual focus?

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    Senior Member Diavonex's Avatar
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    Default Re: How to force autofocus to focus on a specific object?

    Use spot focusing; watch out for camera shake.
    Last edited by Diavonex; 28th August 2009 at 04:12 PM.

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    Moderator Octarine's Avatar
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    Default Re: How to force autofocus to focus on a specific object?

    Use single AF point that is directly above the penguin. See manual for further details.

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    Senior Member ricleo's Avatar
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    Default Re: How to force autofocus to focus on a specific object?

    or use the centre focus point, focus on the penguin and then recompose the framing while your finger is half-depressed on the shutter button.
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    Default Re: How to force autofocus to focus on a specific object?

    Quote Originally Posted by Diavonex View Post
    Use spot focusing; watch out for camera shake.
    Quote Originally Posted by Octarine View Post
    Use single AF point that is directly above the penguin. See manual for further details.
    Quote Originally Posted by ricleo View Post
    or use the centre focus point, focus on the penguin and then recompose the framing while your finger is half-depressed on the shutter button.
    Thank you guys.
    ricleo i will try you method .
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    Moderator Octarine's Avatar
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    Default Re: How to force autofocus to focus on a specific object?

    Quote Originally Posted by ricleo View Post
    or use the centre focus point, focus on the penguin and then recompose the framing while your finger is half-depressed on the shutter button.
    This could throw off the focus, especially with such a shallow depth of field. Nobody is a born tripod, chances are good to shift in more than one direction. That's the point where multiple AF points come in handy.

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    Default Re: How to force autofocus to focus on a specific object?

    Quote Originally Posted by Octarine View Post
    This could throw off the focus, especially with such a shallow depth of field. Nobody is a born tripod, chances are good to shift in more than one direction. That's the point where multiple AF points come in handy.
    Will keep in mind.
    I was looking at this picture, aperture is only 2 and it very sharp/clear.
    Does it mean increasing .2 will make picture that clear?

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    Last edited by ziploc; 28th August 2009 at 04:49 PM. Reason: Please post url for photos not belong to you.
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    Moderator ziploc's Avatar
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    Default Re: How to force autofocus to focus on a specific object?

    Quote Originally Posted by commonjunks View Post
    Will keep in mind.
    I was looking at this picture, aperture is only 2 and it very sharp/clear.
    Does it mean increasing .2 will make picture that clear?
    No. The problem with your pic is not due to the aperture but because you've gotten too close to the subject. All lenses have minimum focusing distance (check the manual of your camera/lens); if you're closer then the minimum focusing distance the lens/camera will not be able to focus. E.g. if a lens' min focusing distance is 0.5m, you can only focus starting from 0.5m or more.

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    Default Re: How to force autofocus to focus on a specific object?

    TS,

    No part of your photo looks sharp to me... How near are you to the subject? Do you know that if you are too near to the subject, you are not able to focus anything at all, even with manual focus?

    Also, did you take that photo with autofocus or manual focus? let us know so we can help you...

    The f/1.8 allows your subject to be sharp too... Just that you need to know how to focus...

  10. #10

    Default Re: How to force autofocus to focus on a specific object?

    Many first-time DSLR buyers tend to think that using the kit lens will be just like a point-and-shoot and immediately give tham a "macro" mode. it does not; you need to take your minimum focus distance into consideration.

    As for selecting your focus point, there is a section in your camera manual that details how to switch to spot focus and then select the point.
    Alpha

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    Default Re: How to force autofocus to focus on a specific object?

    Quote Originally Posted by Rashkae View Post
    Many first-time DSLR buyers tend to think that using the kit lens will be just like a point-and-shoot and immediately give tham a "macro" mode. it does not; you need to take your minimum focus distance into consideration.

    As for selecting your focus point, there is a section in your camera manual that details how to switch to spot focus and then select the point.
    Thank you i will look at my manual. Maybe i give example of wrong picture, i will try to post some of my sons picture (those pictures are taken from distance and taken handheld 1/200 @ 1.8 aperture).


    Quote Originally Posted by hongwen37 View Post
    TS,

    No part of your photo looks sharp to me... How near are you to the subject? Do you know that if you are too near to the subject, you are not able to focus anything at all, even with manual focus?

    Also, did you take that photo with autofocus or manual focus? let us know so we can help you...

    The f/1.8 allows your subject to be sharp too... Just that you need to know how to focus...
    Sorry it is taking autofocus (camera was able to focus), distance about 25~30 centimeters.
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  12. #12

    Default Re: How to force autofocus to focus on a specific object?

    Quote Originally Posted by commonjunks View Post
    Thank you i will look at my manual. Maybe i give example of wrong picture, i will try to post some of my sons picture (those pictures are taken from distance and taken handheld 1/200 @ 1.8 aperture).
    If you're at f/1.8, you need to consider how thin your depth-of-field will be.
    Alpha

  13. #13
    Senior Member zac08's Avatar
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    Default Re: How to force autofocus to focus on a specific object?

    Quote Originally Posted by commonjunks View Post
    Thank you i will look at my manual. Maybe i give example of wrong picture, i will try to post some of my sons picture (those pictures are taken from distance and taken handheld 1/200 @ 1.8 aperture).




    Sorry it is taking autofocus (camera was able to focus), distance about 25~30 centimeters.
    It's too close to autofocus. Your lens has a minimum focusing distance. Do watch for that.
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    Default Re: How to force autofocus to focus on a specific object?

    What focusing point are you using?

    You need to tell the camera where to focus at by selecting the focus point in order to test front/back focus. Otherwise, with auto focus-point selection, the camera might not focus on where you want it to focus or sometimes it will focus on in between the two points it thinks you want to capture. It is not a problem at smaller aperture, but at f/1.8, you really need to pin point the focus point on where you want it to focus at.

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    Default Re: How to force autofocus to focus on a specific object?

    Quote Originally Posted by NewbieInCS View Post
    What focusing point are you using?

    You need to tell the camera where to focus at by selecting the focus point in order to test front/back focus. Otherwise, with auto focus-point selection, the camera might not focus on where you want it to focus or sometimes it will focus on in between the two points it thinks you want to capture. It is not a problem at smaller aperture, but at f/1.8, you really need to pin point the focus point on where you want it to focus at.
    I think tonight i need to read manual. I was hoping to skip it but seems . Funny thing is last month i got 50mm f1.8 lens and result was very clear but i returned it (due to misunderstanding between me and shop) and now i buy from another shop and not that good result. But again, i will read manual and try to keep the things in mind for my next shot.
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