No blur/same focus everywhere.

Discussion in 'Digital Discussion & Q&A' started by Karl, May 10, 2009.

  1. Karl

    Karl TPF Noob!

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    Heya,

    Complete beginner's question..

    I'm starting to understand focus and depth of field, how the lens focuses on one point (my subject) and blurs whatever's in front of at the back..

    Now my question is, how do I make it so EVERYTHING in the image is clear, no blur, no focus on anything in particular?

    My gear is in my signature although this is a question mainly for my D90.
     
    Last edited: May 10, 2009
  2. MelodySoul

    MelodySoul TPF Noob!

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    By stopping down (using a smaller aperture).
     
  3. Karl

    Karl TPF Noob!

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    But won't using a too low aperture make the images way too dark? Thus forcing me to use flash?
     
  4. dcclark

    dcclark TPF Noob!

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    If you use a smaller aperture, you will need to choose a correspondingly longer shutter speed -- so as to let the same amount of light in. Alternately (or in addition), you can increase your ISO to make your sensor more sensitive to light.

    But setting your aperture to its maximum (say, f/22) is not enough. It's all about where you focus -- the idea you want to learn about is called hyperfocal distance. Here's a link: Hyperfocal distance. Read it, understand it. The basic idea is: the hyperfocal distance is the distance which, given an aperture and focal length, if you focus at that distance, you will have "perfect" focus from 1/2 of the hyperfocal distance, out to infinity. This is as close as you're going to get to what you want.
     
  5. Karl

    Karl TPF Noob!

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    Thanks a lot dcclark!!

    I made a few tests.

    I set two objects on a table distanced by about 30 cm one from the other.

    I used my 35mm manual focus (although honestly, I don't know what each of my lenses does.. Consequences of "inheriting" a photography kit and throwing myself in the art)

    Then to get a clear focus of both the objects, no blur, I had to set about 22 aperture.. which made the picture really dark. In consequence, I lowered my shutter speed a lot, down to 2, and got a really clear picture. Bingo! Just learnt something new:

    If I want to get a clear focus in my whole scene, I need a higher aperture (still don't know why aperture affects that). Thus, high aperture causes less light to come in, hence I need to keep my shutter open for longer to capt more light and brighten the picture up.

    As for ISO, I don't know what that is, haven't started to fiddle with that yet, but your link will certainly come in handy, I'll be doing some reading. :]
     
  6. Josh66

    Josh66 Been spending a lot of time on here!

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    ISO is the sensor's sensitivity to light.

    Instead of lowering the shutter speed, you could have increased the ISO to get the same result. (You won't be able to do this on your film body though - you can't adjust the ISO of film whenever you feel like it.)

    The way you did it is better though - high ISOs generally have a lot more noise. If you were taking a picture of a moving subject (where a long exposure time would show motion blur), increasing the ISO would be the better option. A noisy picture is better than no picture.
     
  7. Karl

    Karl TPF Noob!

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    Ahh, understood. ^^

    Now to figure out how to change ISO on a D90.
     
  8. KmH

    KmH Helping photographers learn to fish Supporting Member

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    Hold down the ISO button on the back left side of the body, rotate the main wheel under the right thumb as you watch the numbers change in the LCD screen top right.

    If you go to this blog you'll find an explaination of why a smaller aperture results in a deeper depth of field.
     
  9. Karl

    Karl TPF Noob!

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    Thank you so much KmH. ^^;
     

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