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Question on focal reducer/booster for M43

Discussion in 'Adapted Lenses' started by Steve In Converse, May 6, 2015.

  1. Steve In Converse

    Steve In Converse New to Mu-43

    2
    May 6, 2015
    Steve Sprague
    Hey all,

    I have a (probably dumb) question regarding using a focal reducer/booster. I have several different mount lenses ...Pentax K, M42, Contax etc. and I know I would need a booster for each different mount, but two of my favorite lenses for my Blackmagic Pocket camera are native M43 mounts. What would I purchase to use a focal reducer/booster for those lenses? As I understand it, even though I am using M43 lenses on a M43 mount, there is still a crop factor. I would love to be able to boost these lenses a bit though and also get back some of my lost fov. Am I nuts? Thanks!

    Steve
     
  2. tkbslc

    tkbslc Mu-43 Hall of Famer

    You cannot use a focal reducer with m4/3 lenses or even 4/3 lenses. Use of a focal reducer requires two things. First, the lens you are adapting has to have a larger imaging circle than the camera you want to use it on. Second, the lens mounts have to be different depths to allow for the focal reducer to fit in between. So you couldn't have a focal reducer for m4/3 to m4/3, even if the black magic sensor is a little smaller. There isn't room to fit a focal reducer in there without turning it into a macro lens.
     
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  3. tkbslc

    tkbslc Mu-43 Hall of Famer

    Just thinking some more, one thing that would be possible is a front mounted wide angle adapter. They typically have issues with sharpness and CA at the edges, but since the BM Pocket is a 3x crop, you'd not be seeing those edges in the final video anyway. And 1080p is more forgiving than 16MP for minor issues to begin with.

    What lenses do you have that you are hoping to use and make wider?
     
  4. dwig

    dwig Mu-43 Top Veteran

    621
    Jun 26, 2010
    Key West FL
    ... and typically they produce a noticeable increase in barrel distortion.
     
  5. tkbslc

    tkbslc Mu-43 Hall of Famer

    Which would also likely be outside the frame since the camera is 3x crop.

    It would really only make sense if you were talking wide angles. If you had a 45mm, then you might as well just use a 30mm lens instead of a WA adapter. But even a 12mm is only 35mm equiv on the Black Magic. So you don't have a lot of options other than fisheyes and expensive UWA to go even moderately wide.

    I think the Black Magic Pocket probably should have been Nikon CX mount since it is close to the same size sensor.
     
  6. dwig

    dwig Mu-43 Top Veteran

    621
    Jun 26, 2010
    Key West FL
    No, only the most extreme edges would be cropped. Rectalinear distortion, both barrel and pincushion, span the whole image. They will still be present in the cropped portion. Also, while the BM cameras have a 3x crop factor relative to 35mmFF, they have more like a 1.5 crop factor relative to m4/3 which is the proper reference for this thread's topic.
     
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  7. tkbslc

    tkbslc Mu-43 Hall of Famer

    I understand it is not a perfect solution, I am just throwing that out there, since as I said, there are not many options for wide angles on the Black Magic. I don't find WA adapters to be particularly great in most cases.

    Typically barrel distortion is more pronounced at the edge of the frame due to cumulative effect of the curvature. It would be much less obvious on a cropped image. Crop a fisheye photo for an extreme example of this.

    1.5x crop vs regular m4/3 is very significant. That's like the difference between APS-C and FF. You are losing 60% of the sensor area and almost 20% on each edge of the frame.
     
  8. Steve In Converse

    Steve In Converse New to Mu-43

    2
    May 6, 2015
    Steve Sprague
    Thank you so much for your concise explanation!

    I have a Rokinon 8mm...not looking to make it wider, just want all of the 8mm. :) The other lens is a Lumix 14-42 which is pretty much my go-to lens right now. I love it.