Hyperfocal distance with Speed Booster

[Sami Sanpakkila]

Hi,

When calculating hyperfocal distance while using the Speed Booster what is the circle of confusion one should use?

Sami

[Tim Dashwood]

You should still use the f stop as read from the lens, and its actual focal length with CoC for Super-35 (.025mm). The size of the aperture is not physically changing, only the transmittance is being increased with the reduction.
If you look at the before and after sample videos of the Speed Booster you will notice that the DoF characteristics of the lenses are unchanged, only the magnification and luminance change.

[Sami Sanpakkila]

I didnt even think about the f-stop, that's a good point. I was actually asking should I use Super 35mm or Full Frame as a starting point for my calculations?

[Alister Chapman]

The lenses transmittance is not being changed, the f-stop is changing.

The F-Stop is the ratio between the focal length of the optical system and the lenses entrance pupil diameter.

Change the focal length of the optical system by adding a multiplier element and that ratio changes, as a result the f-stop changes. When you use the adapter the pictures get brighter because the ratio between focal length and entrance pupil is changing, ie the f-stop is changing.

The DoF doesn't appear to change as the adapter simultaneously makes the focal length shorter (increasing DoF) and makes the f-stop larger (decreasing DoF). The two cancel each other out resulting in the same DoF assuming you don't adjust the exposure and simply look at the original darker image compared to the brighter adapted image.

Use the same true f-stops as opposed to the lens indicated f-stops and the images with the adapter would show a deeper DoF. So if you exposed the shots with and without the adapter exactly the same just using the aperture control on the lens, the with adapter images would have a slightly deeper DoF. For any DoF calculations you should use s35 as this is what the optical system is tuned for when using the adapter.

[Sami Sanpakkila]

Cool, thanks Tim and Alister! That definitely clears it up. :)

[Sami Sanpakkila]

Anyone using these? OptimumCS-Pro; TrueDoF-Pro; VideoDoF

I'm going to be shooting a scene next weekend that will have tree falling towards the camera. I imagine I'll be some 30-60 meters away from the 5-9 meter high tree. We will try to have the tree fall straight towards the camera and there will be an actor 3-6 meters from the camera looking towards the tree. I think Ill use a 24mm lens for this.

I'd like to have everything in focus all the time during the scene. Any hints how to achieve this would be welcome!