Freelensing by definition is exposing an image while the lens is removed from the camera body.
This allows you to selectively bring areas of the image in and out of focus.
Selective focus is obtained by hand holding the lens close to the sensor and moving the lens in a certain direction for the effect. Any camera with a detachable lens will do.
Before you begin….
Any lens will do but a focus length of around 50mm is ideal
Set your ISO and shutter speed before detaching the lens from your camera while you become comfortable with the lens being hand held.
One hand will be on the body, and one cupping the lens.
Set your lens to manual focus, and open it to infinity.
Turn your camera to Live View mode if your camera has this feature to see the effects in real time and watch your focus.
1. Remove the lens from the camera. Try your first few attempts seated if you are nervous about shooting without the lens attached. You don’t need to make big movements with the lens to get something in focus.
2. Rotate the lens left to right and up and down directly in front of the camera sensor, as close to being connected to the body as can be. Move your lens in and out and all around and watch the image in Live View, spend time playing with what you see.
3.Turning the lens to the right allows for the right half of the image to be in focus and vice versa for the left. Try moving it tilted up, down, and different angles and watch where the focus lands.
4. Hold the lens too far away from the body and you will expose a lot of light to the sensor. This creates a soft glowing haze and is fun to play with. Open it too much and you will blow out the frame. Slightly let in a little bit of light at a time by opening one edge towards the light source and create light leaks.
When you become a little more comfortable with the technique, you can adjust ISO and shutter speed to allow more or less light.
(from the website-blog - https://www.clickinmoms.com/blog/the-art-of-freelensing-a-step-by-step-guide/)