Some things I'm wondering are:

Is there a default aperture to the Sigma (like wide open)? Or can I set it to whatever I want on a different camera--say, f/3--then attach it to the pocket 4k with a cheap dumb adapter and have it stay at f/3?

What about dumb adapters with a manual aperture control, like the Fotodiox PRO IRIS Lens Adapter? Can I just leave the Sigma wide open then stop down the Fotodiox to change exposure and DoF according to taste? The product listing on the Fotodiox website says this will cause severe vignetting--but does anyone know how high the f-stop has to be before that happens with an APS-C lens on the 1.9x crop sensor?

Are there smart EF-MFT adapters which actually work with the Pocket 4K that don't cost anywhere near $400, and that also are not speedboosters? I'm very limited on funds, and I particularly like the equivalent focal range that the 1.9x crop would give me with the 18-35mm.

The main goal is to find the cheapest POSSIBLE adapter for the Sigma EF to the Pocket 4K while not being forced to use the Sigma at f/16. A secondary goal would be to have some degree of control over the f-stop. Thanks in advance :)