Blackmagic Forum

Hello everyone,
I need some quick help with a formula for calculating the right focal length for a lense that I have to buy for the BlackMagic micro Studio 4k.

If possible could someone give me a simple solution for the following scenario. I have x meters distance to a subject that is y meters wide so I need z millimeters focal length lense with the bmm studio 4k. The camera will be installed at the theatre where I work for the stage manager as a live Monitor.

Ive tried to Google this but I am finding a number of different formulas and i simply don't have the time right now to learn what knowledge is actually necessary. Need to have the camera and lense here by Friday and I just don't want to make a mistake here right now. I never went to college for this stuff , I am more self-taught. I promise I will make an effort to learn more about this but right now it just gets a little too complicated for me when you add the whole cropfactor and sensor-size dilemma to the equation.

A simple and quick answer would be very much appreciated.
Thanks a lot in advance.

And greetings from Germany!

Christopher, welcome to the BM Forum, however, we use real names here not handles, just a heads up.

To answer your question, a BM Micro Camera has roughly a 1-inch sensor, with a S16 size area used to get the image. So for reference only, a 16mm lens on the Micro Studio is approximately the save angle of view on on the Micro Camera, as a 50mm lens on a full frame 135mm Camera.

Specific angles of view for a given focal length lens can be computed, but it is quicker to use a look up table application like PCAM used on a IOS Mac platform (IPhone IPad).
Here are some angle of views for common focal lengths at a 10-foot distance from the camera to give you a starting point. AOV is angle of view in degrees, distance is 10-feet and width of coverage is imperial measurement in feet/inches:

Lens AOV. Width of coverage
15mm. 26.34. 8’ 3.8”
20mm. 19.9. 6’ 3”
25mm. 16. 5’
35mm. 11.45. 3’ 6.8”

Since all camera to subject distance is 10-feet, you can double the results for 20-feet distance, etc
A formula can be worked out, but so using PCAM is quicker.
Hope this helps
Cheers

There is a pretty simple formula for FOV and you can do most of the math in your head. Basically when the focal length of the lens is equal to the horizontal size of the sensor the distance to subject and FOV are the same.

For your application a 13mm lens would yield a 1:1 ratio. Once you have that number the rest is simple multiplication or division.

There is a handy tool for that:

https://dofsimulator.net/en/

It has the Blackmagic cameras (including the BMMSC4K) and lots of lenses as presets

cheers,
Daniel

Denny Smith wrote:Christopher, welcome to the BM Forum, however, we use real names here not handles, just a heads up.

Denny in case you didn´t notish yet.. Different names are allowed since an update of PHPBB forum a week or 3 back....
There real name is displayed at the side bar under total posts etc..

Thanks Daniel, I didn’t see that.
Cheers