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Stacking lenses for macro - a few questions

Discussion in 'General Technical Discussion' started by BostonRott, Jun 12, 2007.

  1. I just received my 52-52mm adapter today from B&H ($8) so that I can stack my 50mm onto the front of my 105mm.

    There are some things that I'm unclear about:

    1. Do I set the 50mm to focus at infinity? Or to closest?
    2. Do I leave the 50mm wide open at f/1.8 (it is a 1.8, not a 1.4), or do I stop it down if I want more DOF?

    3. If looking for more DOF, do I stop down both lenses or just the 105mm?

    4. What is the light loss with the 50 stuck on front, 1 stop? Or more than that? Or dependant upon the 50mm's aperature?

    I appreciate the help! :smile:
     
  2. gvk

    gvk

    388
    Jun 17, 2005
    Mystic, CT
    The reversed 50 mm will act like a supplementary close-up lens. It reduces the effective focal length in combination with the 105 mm primary lens to a bit over 34 mm, depending on the actual seperation between the lenses. An object at around 40 mm or so in front of the combination will be in focus with the main lens set at infinity.

    When using stacked lenses, you should usually set the focus of the supplementary lens at infinity and open the aperture to its widest setting. Then use the primary lens to focus and its aperture to set exposure. Stopping down the 50 mm lens in front will likely introduce vignetting by restricting transmitted light from filling the entrance pupil of the main lens. In theory there is no light loss except for reflection and absorbtion by the added glass elements. In practice there can be a bit of reduction depending on how well the entrance pupils match (the normal entrance pupil of the reversed lens is actually acting as an exit pupil to illuminate the entrance pupil of the main lens. The magnification of the combination should be about 2X when focused at infinity and somewhat higher when at close focus.
     
  3. Gerry,

    What wonderful insight, thank you for your help and time!! :smile:

    Tomorrow's weather looks decent and I have newly blooming Peonies and Iris. Hopefully I'll get out to play! :smile:
     
  4. You can vary the focus on the 50mm actually, It will actually give you a tiny bit more zoom if you focus closer.
    if you have the 18-55 I find it to be a more convenient macro add on lens, Since you can zoom out (to 55mm) And zoom in to 18mm (for some amazingly close focusing), And a quick DOF preview is simply holding the little aperture control lever on the front of the lens (when reversed)

    Quality might not be as good (can't really test that myself)
     
  5. I don't have an 18-55. I do have the 35/2 and will play with that also. :smile:
     
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