Nikon D40 Apeture woes

Discussion in 'Photography Beginners' Forum' started by Amphoteric, Oct 12, 2007.

  1. Amphoteric

    Amphoteric TPF Noob!

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    Hello everyone,

    It seems I am posting alot of topics here recently. Anyway, I am trying to do various things with Depth of Field. I use a Nikon D40 camera and am shooting in Apeture mode. I have shot things from a close distance with both f3.8 (largest setting) and f28 (smallest), yet the items in the background are in focus on both pictures. It would seem that no matter what my apeture size, I cannot get my depth of field to change. Does my shutter speed affect this? Any help would be appreciated.

    Thanks
     
  2. andrew07

    andrew07 TPF Noob!

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    there are 3 things that affect DOF

    aperture
    focal length
    and distance from the subject



    have you checked your focal length?
     
  3. Sw1tchFX

    Sw1tchFX TPF Noob!

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    beat me to it.
     
  4. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    Aperture, focal length and distance to subject will all play a factor.

    Try setting up something (or someone) and getting close to it. For example, a can of Coke on a table. If you shoot it from two feet away and use an aperture of F3.8...the wall on the other side of the room, should be fairly out of focus. If you stop down to F22, both the can and wall should be in focus...or at least the wall should be much more in focus.

    If you back up from the can...the effect of using a shallow DOF will be lessened because the difference between the camera and the subject will be closer to the distance from the subject to the background.

    You can try the same experiment outside with a distant background. Take a photo of someone with a wide aperture and background quite far away. The background should be out of focus. If you move closer to the background and or use a smaller aperture, the background will become clearer.

    As for focal length, the longer the lens, the more shallow the DOF...so when you want to blur out the background, use a longer focal length.
     
  5. Helen B

    Helen B TPF Noob!

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    Could you post examples, with the EXIF data intact. I suggest f/3.8, f/8 and f/28, to show the difference between f/8 and f/28 caused by diffraction, just as a side issue.

    Thanks,
    Helen
     
  6. Mike_E

    Mike_E No longer a newbie, moving up!

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    Just an exorcise to give you a feel for it- go to a train track -a straight section- and snap off all of the different combinations of aperture and focal length that you have (the closer to the track/ground you are the easier it will bee to see). Take notes so that you will know which shot is what. Don't use anything but Manual and be sure to still pay attention to the meter and adjust with shutter speed.

    You should then be well on your way to getting it straight. ;) (especially if you remember to measure how far the cross ties are apart.)
     
  7. Amphoteric

    Amphoteric TPF Noob!

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    Alright, so you are saying that the closer I am to the object (and thus the background) the shorter my focal distance and thus the more clear the background will be?

    me-------------->can---------------->background = fuzzy
    ...........me------>can---------------->background = clearer

    Is that right?

    PS: Mike E. Dont know where any train tracks are near me.
     
  8. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    No, you've got that backwards. The closer you are to your subject, the fuzzier the background will be.
     
  9. Mike_E

    Mike_E No longer a newbie, moving up!

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    You don't have to have train tracks, a straight road with a gravel shoulder would do- as long as you have the camera close to the ground so that the distance from the lens to the ground doesn't become an issue. What you are looking for is something that is fairly straight so that you can tell where good focus starts and stops. Marking off the distance in these will help to learn what you will have as far as DoF on other shots.
     
  10. Amphoteric

    Amphoteric TPF Noob!

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    Alright, here is an example (I dont know how to get the exif data). I took this photo with my camera practically touching the railing. I took one at f3.8 and one at f28. In both the backgrounds are about as sharp as in this image.

    http://img523.imageshack.us/my.php?image=angledstepsyc1.jpg

    And just so I got this straight:

    f3.8 = fuzzy background
    f28 = clearer background
     
  11. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    I think I see your problem...it looks like you may be focusing on the background....so no matter what aperture you use...it will be in focus. However, the railing that is close to the camera should be more out of focus with a large aperture and it should be more in focus with a smaller aperture.

    That's correct...provided that you are focused on something that is well in front of the background.
     
  12. Amphoteric

    Amphoteric TPF Noob!

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    Hmmmm, I did focus on the railing, not the background. However, it would seem riddiculous to argue that I didnt do something wrong since the laws of physics didn't just up and decide to mess with me. I guess I will just chalk it up to a "my bad" and try it again on something a little further away.
     

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