blackest Loc: Ireland

Hi All
I've just been playing round with a speedbooster and figuring out it's effect the one i'm using is a Pixco and has a 0.72 crop factor
I paired it with a sigma 18-30mm lens f3.5 - f4.5 which is f4 + or - 1/3rd of a stop so pretty much an F4.

With the speed booster multiplying the crop factor by the f-stop gives the boosted aperture which is pretty much 1 stop difference
so f4 becomes f2.88 or just f2.8 really (about 2.52 to 3.24 for my sigma).
Field of view is a combination of lens crop factor x booster crop factor.
M43 (2x) x 0.72 = 1.44 100mm lens 144mm
bmpcc4k (1.9) x 0.72 = 1.37 100mm lens 137mm
bmpcc6k (1.588) x 0.72 = 1.14 100mm lens 114mm
bmpcc (2.88) x 0.72 = 2.07 100mm lens 207mm

Field of View is probably something you can work with the 100mm lens field of view can be from 114 to 207mm for video it depends on resolution which also maybe a windowed mode which makes the sensor effectively smaller. F-stop is not the same as T-stop it's not just aperture that controls how much light gets through but the lens elements and coatings will reduce the light reaching the sensor as well.

The Speedbooster can also increase flaring and a loss of contrast, so not entirely a free lunch but does make manual lenses more useful.
I hope this was interesting. crop factor can be a calculated a couple of ways it's easiest to use the width, if you use the diagonal then you have to allow for the aspect ratio of different sensors.

burkphoto Loc: High Point, NC

MetaBones SpeedBoosters are the only ones I'm familiar with. They work great with the Sigma 18-35mm f/1.8 ART lens, especially in Canon mount. That combination is very popular with indy filmmakers. It retains all automation of the lens and camera, although autofocus performance is abysmally slow.

Unfortunately, the MetaBones SpeedBoosters are quite pricey! $650 to $700 is probably worth it if you have a lot of dSLR glass, though.

blackest Loc: Ireland

There are quite a few brands making speed boosters, Viltrox is the main alternative but there are others I bought the Neewer pixco .72x for less than 100 euro and I use it for Pentax lenses. I'm also using a Gimbal with a rod mount focus motor. It can be easily programmed for A B moves or controlled from the handle. What can be handy with the more expensive adapters is they can power optical image stabilization thats built into the lens, if the lens has it of course. If you are using manual lenses non of that applies to the speedbooster The Sigma 18-35 Art is a great lens but pretty expensive and heavy.

The main thing really is that it helps bring the lens into a more useful focal range. For my Panasonic , BMPCC 4K and BMPCC they have crop factors of 2x 1.9x and 2.88x respectively so the 18 has the effective view of 36mm on the Panasonic with the speed booster its about a 26mm field of view and the extra stop of light is pretty useful.

Native lenses are lighter and cheaper and more useful if you want features.
For my Panasonic my f2.8 70-200 becomes effectively an F2 140 - 400 but doesnt get stabilization , although there are bodies with IBIS these days. ...