Speedboster on BMPCC only controlling first 5 1/2 F-Stops

Dear Forum,

I am currently testing a Nikkor 50mm/1.4 on my Nikon G Speedbooster for BMPCC. In the process of determinig which Number on the Aperture Ring of the Speedbooster corresponds to which "real" aperture, I found out that the Speedbooster is only controlling the apertures from 1.4 to 5.6 1/2. Either way I mount the Lens on the Speedbooster (SB set to "7" or to "F", lens wide open or fully closed) I will always only control the first few apertures, unable to reach even f8.

At first I thought that the 6 Steps, from "1" to "7" on the Aperture Ring correspond to the first 6 Apertures meaning: 1.4, 2, 2.8, 4, 5.6 and 8. That is not the case, f2 is only reached when the SB is set to "3", f8 is never fully reached.

I really want to be able to use a Lightmeter with my BMPCC + SB, because of that I need to know the "real" apertures.

Anybody has a clue how to get a calibrated SB with full aperture range?


Best Wishes,

Viktor

You need to review the instructions for mounting a Nikon lens on the Metabones Speed Booster, on the Metabones site. The lens (if it has an iris ring, like the older AiS lenses) the lens and SB need need to be set correctly when mounting them together. With G lenses, just set the iris ring on the Speed Booster per Metabones instructions.

That said, the f/stop ring on the Speed Booster, is designed to increase by 1/2 stops for every hash mark, depending on the lens you are using. Some Nikon lenses will give you a 1-stop change. Stopping a lens down past f/8 on the Pocket Camera is going to make your image appear softer due to refraction, and is not recommend, unless yiu want a soft effect.

I do not use G lenses because you can not really tell what f/stop you are really at. The older Nikon F lenses with an actual iris ring, are easier to calibrate. Set the lens to its second f/stop from max (say f/2.8), and turn the SB ring until the image dies on change, at the point the change in brightness stops, not the index mark on the SP, then with this lens, that index mark will be f/2.8. Go to f/3.5 and do this again. Record your findings.

A quicker way, is just to set the lens at the f/stop you want and use the ring on the SB to open the iris to focus, and close it back down to the preselected f/stop. This is what I do, to make a click stop lens, declicked from thr max f/stop to the preselected f/stop.
Cheers