Hi everyone, Tony Dae here.
follow up videos:
I got a question about what the crop factor would be for the Blackmagic pocket cinema camera 4k and what would happen to their lenses if they were to adapt them to the camera.
So of course, instead of answering simply, I made a video featuring MATH so that you all can figure this out yourselves by creating your own spreadsheet in Excel or Google sheets. Knowledge is power!
I hope that this video is not too confusing, as it is made for people who do understand what a crop factor is and isn't.
Keep in mind that the data regarding the crop factor is in relation to shooting the BMPCC4K in 4K, not 1080P or windowed high speed 120p.
Also, when I talk about the sensor size of the bmpcc4k, I am in now way referring to the mount type. The mount type of the camera is m43 and is irrespective of the sensor size. I also state one sensor as a micro 4/3 and the BMPCC4k as a 4/3 sensor, because thats what BMD calls it. I am using this to indicate the difference between the size shown in the cvp website and the size of the BMPCC4K. Both could be technically classified as "four thirds" sensor, and I hope you understand my meaning in context to this video.
*PLEASE READ BELOW IF YOU ARE CONFUSED OR IF YOU ARE GETTING ANGRY AND WANT TO FIGHT IN THE COMMENTS*
The lens itself isn't affected exactly by the crop, but it does in fact affect the field of view, which is important when you want to frame your shots a certain way. The more the sensor is cropped, the further you have to back up from the subject to match the same framing you would have had with the same lens on a full frame 35mm camera.
Because you have changed the location of the lens, the depth of field will appear deeper. There's no magic, its science. And the figures used in this video, and elsewhere, are meant to help people understand what a shot will look like when trying to match the same framing on a camera as full frame 35mm.
Keep in mind that the crop factor is not only determined by the sensor size, but also any additional crops that may be happening in camera. Some cameras have additional crops when recording in 4k or 1080p or at certain frame rates. This should also be taken into account when you make your own spreadsheet.
Also, keep in mind that I use terms like Relative Focal Length (RFL) in mm and Relative Minimum Depth of Field (RMDOF) in f stops. These terms are used to help you to understand the focal length and shallowest depth of field achievable by the lens are both relative to trying to get the exact same framing as if you were using Full Frame 35mm.
Different focal length calculations does not mean that the lens is changing focal length, only that you will have to back up farther AS IF YOU WERE using a longer lens.
Although the depth of field will appear different when you back up, the aperture/iris (f stop) of the lens itself DOES NOT change at all when determining a crop factor. The diameter is exactly the same and the exposure will be the same as if the lens were used on a full frame camera.
A focal reducer/speedbooster widens the field of view relative to its magnification factor and also increases the T stop by about a stop by concentrating light from the edges toward the center but does not affect the actual diameter of the aperture (f stop). Exposure WILL be different when using a focal reducer/speed booster.
If you need more help, resources are below.
Music credit: bensound.com