Macro Focus Question

Discussion in 'Macro Photography' started by Noah212, Feb 10, 2010.

  1. Noah212

    Noah212 TPF Noob!

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    I'm using a cheap macro technique where you put a 50mm lens (focused to infinity) head first onto a telephoto lens (also focused to infinity). This is shown here: [ame="http://www.youtube.com/watch?v=2F_xfKcxvro"]http://www.youtube.com/watch?v=2F_xfKcxvro[/ame]

    Anyway, I am having a lot of trouble getting the camera to focus on a whole area. From what I know as a semi-begginer photographer, that this has to do with the f- button or f-stop (I'm not really sure). I have set the f- button on the forward lens to as high as it will go, but the telephoto lens won't allow me to turn the f- button any higher. Is there anything I can do to make the "focus area" bigger? Thanks so much.
     
  2. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    This is not really a focusing problem, instead what you describe is a depth of field problem and its something that is inherant with higher magnifiaction (macro) photography. It won't matter what setup you use (within reason) the depth of field will always be very small.

    To give yourself more depth in a shot you can use a smaller aperture (that means bigger f number and less light getting into the camera). That will give you more depth to a shot since the smaller the aperture (bigger the f number) the more depth of field you will get in a shot. However there is a limit to this and its called diffraction. As a process of the lens and camera there is a point where decreasing the aperture (making the f number bigger) the image will result in a greater depth of field, but the overall sharpness of the shot will be less. It's for this reason that f13 is normally as small as people go with the aperture - f16 is sometimes ok, but its around this point that diffraction starts to appear with most setups (specific camera bodies and lenses might have different tollerances for this and you would have to test this yourself if you wanted a more accurate result).

    In addition for the reversed setup you don't want to be adjuting the aperture on the reversed lens - leave it so that the aperture blades are always open (smallest f number). And thus control the aperture with the lens that is attached to the camera (this way focusing is easier since the blades on both lenses are open for focusing and then its only the attached lens which has its blades close for the taking of the shot)
     

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