You’d first have to know a bit more. What is the flange distance of the lens? That data can generally be found for large format lenses on the Internet. I label the flange distance Fg. When the bellows is fully extended on your camera, you need to know the distance from the front of the ground glass to the front surface of a lens board.
This can be safely measured by using a small diameter wooden dowel rod that can be bought cheaply from Home Depot, Lowes’s, or other hardware store. Fully extend the bellows with a lens board (no lens). Insert the dowel and carefully and gently push it until its end touches the front of the ground glass. Use a pencil to mark the dowel where it meets the front of the lens board. Remove the dowel and measure the distance. Designate it L.
Most standard lenses have a flange distance that is less than the focal length.
Wide-angle lenses usually have a flange distance that is greater than the focal length.
Telephoto lenses have a flange distance significantly shorter than the focal length.
Now we need to know Emax, the maximum extended distance of the second nodal point of the lens.
For a standard or telephoto lens, Emax = L + Fg.
For a wide-angle lens, Emax = L – Fg
Example 1:
I’ll use a 300/5.6 Nikkor W as an example of a standard LF lens and suppose that when the bellows on your camera is fully extended, the front of the lens board is 360 mm forward of the ground glass.
The relevant data for the Nikkor LF lenses can be found in the following PDF:
https://www.mr-alvandi.com/downloads/large-format/nikon-large-format-lenses.pdf
For this lens, Fg = 284.9 mm. The 2nd node is forward of the flange (front of lens board) by the distance
Δ = f – Fg = 300 mm - 284.9 mm = 15.1 mm
That means that with the bellows fully extended, the total distance from the image plane (and front of ground glass) to the 2nd node is L + Δ = L + 15.1 mm = 360 mm + 15.1 mm = 375.1 mm, so
Emax = 375.1 mm
Using the standard formula s = if/(i - f ) where i is the image distance and s is the subject distance measured from the image plane to the first nodal point of the lens, and replacing i with Emax, we get
s = Emax*f/(Emax – f)
Then s = (375.1 mm)(300 mm)/( 375.1 mm – 300 mm) = 1498 mm
Or about 1.5 meters (4.9 feet).
This is really the same as the answers given in the previous posts above. I chose a particular 300 mm lens for which I had specific data and I made some assumptions as stated to illustrate how you could go about taking the measurements and doing the calculation.
Example 2:
Now do this for a telephoto lens of about the same focal length capable of 5”x 7” coverage (at f/22). Recall, that telephoto lenses are generally used without movements due to their narrow angle of view and the fact that both nodal points usually fall forward of the front element.
I’ll chose the Nikkor-T ED 360mm f8 whose flange distance is Fg = 261 mm (so it will work on a camera with a maximum front-of-lens-board position of L = 360 mm from the ground glass).
The second node is Δ = f – Fg = 360 mm – 261 mm = 99 mm forward of the front of the lens board.
That gives
Emax = L + Δ = 360 mm + 99 mm = 459 mm
s = 459 mm(360 mm)/(459 mm – 360 mm) = 1669 mm
So, the closest subject distance with bellows fully extended is about 1.7 meters or 5.5 feet.
