GH4 M4/3, speed booster, and lens questions

[tiki988]

Hi everyone,

I've been searching around the internet trying to find the questions below, but have had no luck. I just bought the metabones ef speedbooster and have a 24-105 f4, but have not had much time to play with it. These questions should apply to any speedbooster and m4/3 camera.

1) Does the speedbooster only give me 1 stop of extra stop of light and widen my FOV? Will an f4 lens still behave like an f4 lens in terms of DOF? (assuming distance and focal length are not factors here) I will get the DOF of an f4 lens and not the DOF of a f2.8 lens with the speedbooster?

2) Given the wider FOV, does the m4/3 sensor still behave like normal in terms of DOF? Will f2.8 m4/3 still be equivalent to f5.6 on a full frame camera, in terms of DOF?

I'm asking because my next lens purchase will most likely be the sigma 18-35 f1.8, to be able to get a shallower DOF.

Hopefully these questions make sense, and if anyone can provide some info, that would be much appreciated.

Thanks!

 

[yslee]

Sensors don't affect DoF per se; it's focal length, subject distance, aperture and your final output (CoC basically). Your questions are a little off, but assuming if you use the 24-105 on the Speedbooster and m43 camera like you would on a FF camera, you will get a 1 stop difference in DoF.

 

[TheDingo]

With the SpeedBooster your 24-105mm f/4 lens becomes a 17-74mm f/2.8 lens.

On a Micro 4/3 camera this combination is equivalent to a 34-148mm f/5.6 lens on a 35mm Full Frame still-photo camera.

 

[VMT]

1) Does the speedbooster only give me 1 stop of extra stop of light and widen my FOV? Will an f4 lens still behave like an f4 lens in terms of DOF? (assuming distance and focal length are not factors here) I will get the DOF of an f4 lens and not the DOF of a f2.8 lens with the speedbooster?

2) Given the wider FOV, does the m4/3 sensor still behave like normal in terms of DOF? Will f2.8 m4/3 still be equivalent to f5.6 on a full frame camera, in terms of DOF?

1. With any lens, your DOF decreases with higher f-stop, increases with lower f-stop. SB increases your non-4/3 lens by 1 stop, so your DOF is decreased by 1 stop.

2. The SB has no effect on the sensor. The change in FOV is a combined function of the SB and lens reducing the focus of light onto the 4/3 sensor, resulting in a wider FOV (and brighter image).

 

[c3hammer]

...On a Micro 4/3 camera this combination is equivalent to a 34-148mm f/5.6 lens on a 35mm Full Frame still-photo camera.

Except that we get 4 times the light gathering of the f/5.6 at the actual f stop of f/2.8. DOF and FOV are as stated, but the f/2.8 allows much more light for that DOF. I believe this to be a significant advantage to the m43 systems.

On the OP's topic, I've found that native primes are hugely important to get what I consider to be shallow enough depth of field with the m43 system. My main kit these days is a 12mm f/2, 17mm f/1.8 and the 25mm f/1.4 then a 100-300 for wildlife work. The only place I use a speed booster is with a vintage OM 50mm f/1.4. That yields an equivalent of 88mm f/1.0 in 4k UHD mode. Obviously others millage may vary if you were to get the speed boosted 18-35 f/1.8. I just don't want to carry that pig of a combo around

Cheers,
Pete

 

[refocusedmedia]

It also takes away a stop of light on the far end of your f-stop range as well, as I recently discovered. So now your f/16 minimum aperture becomes f/11.

 

[Sol M.]

It also takes away a stop of light on the far end of your f-stop range as well, as I recently discovered. So now your f/16 minimum aperture becomes f/11.

Just so there's no confusion, the Speed Booster does not only affect the extreme ends of a lens' aperture, it shifts the entire aperture range by 1 stop.

The Speed Booster is effectively a lens itself-- it affects how light is focused. As a result, when you use the Speed Booster with a lens, its properties are changed, including aperture range, FOV, angle of view, etc. As TheDingo noted, using the Speed Booster with a 24-105mm f/4 results in a 17-74mm f/2.8 lens. I would encourage forgetting about FF equivalence and just focus on how lenses work on the MFT sensor, but you can apply any crop factor/FOV calculations you want to this lens.