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Thread: Problem with focusing

  1. #1

    Question Problem with focusing

    I'm using the Sony SAL-50M28 macro lens with a Sony alpha 350. I'm trying to shoot a 140mm x 40mm white piece of paper in front of a white background. Everything is very white. On autofocus mode, it never finds the focus, so I'm using manual. The shooting distance is about 45cm. Because everything is so white, I find it very hard to get a sharp focus through the viewfinder, if I use the LCD the screen all I see is a white screen.

    I tried to shoot through a range of focus by turning the focus a little at a time. Took about 20 shots but none of them are sharp. I'm using tripod, without remote. The tripod isn't that steady and camera does move a teeny weeny tiny bit when I press the shutter. What should I do?

  2. #2
    Senior Member zac08's Avatar
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    Default Re: Problem with focusing

    The AF module requires a definite difference to work.

    Try drawing a cross on the paper and make sure it is far enough from the sensor. Each lens has a minimum focusing distance. Look on the lens, it's written there.
    Michael Lim
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  3. #3

    Default Re: Problem with focusing

    white on white is an autofocus system's nightmare.

    Why are you trying to take a picture of a white piece of paper?
    Alpha

  4. #4

    Default Re: Problem with focusing

    Yeah, I'm wondering why you would need a white on white image too?
    If I'm not mistaken, a camera needs some contrast so as to AF. Not sure about this.

  5. #5
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    Default Re: Problem with focusing

    google is your friend howstuffworks

  6. #6
    Member boombox's Avatar
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    Default Re: Problem with focusing

    Smooth White Paper doesn't have any contrast to work on, and thus you cannot focus - probably not with any system today, and definitely not the A350. Even the A700 with its dual cross center + f2.8 Sensor - a very sensitive combo that can lock focus on stuff like a white walls or smooth white table tops (which is a feat that many bodies can't do) wouldn't lock either - if your paper's too smooth and has no contrast.

    Given the difficulty of you focusing manually because you don't know how sharp it looks, so you now know how hard it is for the machine yeah?

    Well,

    Trick is to make a temporary marking on your white paper, maybe just placing a paper clip on the white paper (provided that you're shooting from top down, or paste it on with a light adhesive if it's not and you don't want to clip on the paper for fear of crumpling it), then removing it after you locked focus.

    Alternatively, you can use the distance scale on your macro lens, and adjust your focus according to the distance.

    But just making a temporary making should help a ton, even a pencil dot marking that can be easily clone stamped in post processing can save you a world of trouble. How to make it is up to you.

  7. #7

    Default Re: Problem with focusing

    I think I'm going for the cross then heal it away in PS. I'm shooting a product which I'm selling which is a plain bookmark. Thanks a bunch. Why didn't I think of that?

  8. #8
    Moderator catchlights's Avatar
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    Default Re: Problem with focusing

    just put a new 2 dollars note down, you will be able to focus liao
    Shoot to Live, Live to Shoot
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  9. #9
    Member boombox's Avatar
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    Default Re: Problem with focusing

    Quote Originally Posted by AenTan View Post
    I think I'm going for the cross then heal it away in PS. I'm shooting a product which I'm selling which is a plain bookmark. Thanks a bunch. Why didn't I think of that?
    Great to hear! Good luck!

  10. #10

    Default Re: Problem with focusing

    Here's my new attempt with an X in the center to help focusing. The X has been digitally removed in this image.

    Taken with f/16. I realise that gave the entire bookmark more clarity. Any lower and the top and bottom starts to blur. First time using Manual Exposure mode. Pretty fun.
    Uneven lighting of the background and a bit of the subject, hope the light tent I ordered will fix that.

    Original size: http://flickr.com/photos/aentan/3115990858/sizes/o/

    Last edited by AenTan; 18th December 2008 at 01:22 AM.

  11. #11

    Default Re: Problem with focusing

    Not sure what is the attempt, but what I see can be done by drawing a rectangle on a white background.
    |SonyA700|T180mmf3.5|M70-210mmf4|S30mmf1.4|T17-50mmf2.8|T90mmf2.8|M5600hsdX2|

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