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Mitakon lens Turbo, Speed Booster analog, available
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  • sorry still this a failing of the lens turbo or all focal reducers with the sigma 18-35? does it vignette on the gh5 throughout the range or only at 18?..

  • @kmackreath
    I think it is only the Lens turbo failing. The Sigma 18-35 is designed to cover a Nikon DX sensor with a diagonal of 28.4mm. 28.4*0.726=20.6 which is still larger than the GH5's 19.9mm with 16:9 crop. The actual image circle of the lens at 18mm seems to be around 33mm, so an ideal focal reducer would produce a circle of 24mm. I measured only 19.2mm through the lens turbo.

  • @htpzt thanks.. so are we saying the lens turbo is useless at all Focal ranges on the sigma or only at the wide end?

    I don’t mind losing the first few mm and zooming if I have to

    And I assume the metabones ultra does not have this problem at all?

    And what full frame lens would work well With the lens turbo 2?

    Like would the nikkor 50mm 1.8 lens be suitable for this adapter?..

    [VK] Merged

  • @lmackreath The sigma becomes useless at everything smaller than 28mm and even then it vignettes with faster apertures. I don't have any wide Nikon lenses on hand, but if I hold a M42 35mm lens in front, is seems to be a lot better than the sigma at 35mm with basically no vignetting. I will return my lensturbo and get a used Metabones ultra tomorrow.

  • Is there not a cheap alternative to metabones then that like the ultra does not vignette?

  • would the sigma art 24 1.4 ff work?

  • @htpzt do you have actual hands on experience with the lens turbo vignetting with the gh5 and the sigma 18-35 as I have conflicting reports to whether it vignettes or not?

  • @lmackreath I don't have a GH5 but a Nikon mount Sigma 18-35 F1.8 and both a Lensturbo 2 and a Speedbooster. Here is the Vignetting wide open at top to bottom 18-20-24-28-35mm on a GH2. Speedbooster is on the left.

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  • @htpzt very useful tests!

    If not asking too much, could you do the same comparison with lens in f16, to see the black parts in corners?

    also, which version of speed booster you have?

  • @apefos Here it is at F16. My Speedbooster is the old 0.71x version, the same as the new ultra.
    The Lensturbo also gets a weird bright spot in the center and a bright ring around when stopped down (slightly exaggerated):
    On the Metabones side it actually is a different picture everytime.

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  • @htpzt Many thanks! I hope the Mitakon does not vignette with full frame lenses.

  • @htpzt this is a great comparison! You must have a good eye for detail! -Many thanks!

  • @htpzt Very nice test. What is happening with the Lens Turbo is caused by the exit pupil distance of the Sigma 18-35. In this lens the exit pupil distance varies by a huge amount, from 70mm at the 35mm end to 150mm (e.g., nearly telecentric) at the 18mm wide end. Long exit pupil distances put big demands on focal reducers because they require larger element diameters. In order to achieve the larger element diameters you need to use the highest possible refractive index glass to reduce lens curvatures.

  • Canon FD to Fujifilm FX



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  • @brianc1959 From this very old post, thanks for your very good and through explanation!