sorry still confused..is 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?..

@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

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

@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?

@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?

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

@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.

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