Blackmagic Forum

Hey All,

I just got the chance to take the BMMSC4KG2 out for a spin. I have a Metabones .64X that gives me a Stop and a third more light. So a 1.4 should be 1.1 on the display wide open. It only goes to 1.4 on the display wide open. It does communicate with the lens as I see it knows it is a sigma 35mm 1.4 in the menu system. Not sure if it is calculating the Speedbooster...

So my concern is - does the camera only open the lens to 1.4 and not opening it wide open because it thinks that it should only open to 1.4, or is it opening it wide open and instead of displaying 1.1 it is displaying 1.4?

Does anyone have any insight on this? It would be greatly appreciated.

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That lens is still a F1.4 but the camera is receiving more light. F Stop isn't exact like T Stop.

I can appreciate that. I have owned so many different cameras and brands. This is the first one that does not calculate for the Speedbooster. Just wanting to know if my aperture is getting to the full open position.

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If the lens is communicating to the camera via the speedbooster, I'm pretty confident that the camera is giving you the actual aperture of the lens (f1.4) via the electronic contacts; it has no way of calculating the larger effective aperture after it has gone through the speedbooster's optics.

One way to verify is to shine a light into the lens; if it's wide open you won't see the aperture blades. Stop down even one stop and you should see them.

Brad Hurley wrote:If the lens is communicating to the camera via the speedbooster, I'm pretty confident that the camera is giving you the actual aperture of the lens (f1.4) via the electronic contacts; it has no way of calculating the larger effective aperture after it has gone through the speedbooster's optics.

One way to verify is to shine a light into the lens; if it's wide open you won't see the aperture blades. Stop down even one stop and you should see them.

Awesome, thank you. I will try that and see

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***So I do have an update***

When I use the Sigma 18-35mm Art 1.8 it does calculate the Speedbooster gain of light by displaying that it opens to 1.19, which is a stop and a third more light. However it did not calculate for the Sigma 35mm art 1.4 lens. Maybe it has something to do with the crop lens verses the FF. I will continue to investigate and I also have sent BMD an inquiry as well.