Distance Lens - Film pane

[Rogier]

Wandering what the relationship is between focal length and distance to film pane.
Is it the focal length in mm from front element to the film pane?
The distance from the rear element to the film pane?

Something else?

 

[ferider]

Wandering what the relationship is between focal length and distance to film pane.
Is it the focal length in mm from front element to the film pane?
The distance from the rear element to the film pane?

Something else?

Focal length is the distance from lens' "nodal point" to the film plane (when lens is set to infinity). Typically the nodal point is where the aperture is.

Roland.

 

[Rogier]

Hmm thanks, think I will have to establish it by experimentation given the primitive "aperture" the Holga camera. Compared to the one inside the Linhof lens that I want to put on it...

 

[ferider]

Compared to the one inside the Linhof lens that I want to put on it...

🙂

 

[Dwig]

...Typically the nodal point is where the aperture is.
...

True with simple designs and symmetrical designs, but not always the case.

True telephoto designs (as opposed to simple long focus designs) and retrofocus designs (inverted telephotos, usually used for wide angle lenses on SLRs) project the nodal points forward, in the case of telephotos, or rearward, in retrofocus designs, of the physical center of the lens system and the iris.

A very simple test can be done by focusing the lens at infinity and measuring forward from the image a distance equal to the rated focal length.