Same Focal Length / NOT same angle of view ?? Panasonic 14mm, Olympus 12-40

Guy Parsons wrote:

kdouglas7 wrote:

thanks Guy!

I'm chocking it up to the effect of the 'nodal point' , as you mentioned.

After some more tests, I realized that by moving the camera (w/zoom lens attached) back by a few increments I was able to achieve the same FOV as the 14mm prime lens.

'nodal point' ... good to know!

I may have been giving misleading info after doing a bit more reading.

Maybe the nodal point is not the answer but the front entrance pupil. Anyway, whatever it is called I find it when needed (for panoramas) by rotating the camera on a tripod head and observing the background in relation to a vertical stick or string held close to the lens.

Shift the camera back and forwards in respect to the point of rotation until the stick/string always obscures exactly the same part of the background. It may change position with zooming and focusing the lens.

I always called that the nodal point but now I think my terminology is wrong.

Have a read of this page http://www.johnhpanos.com/epcalib.htm to see my confusion and maybe get the right names.

I note your further reference, but I just wanted to say that where the sensor sees one 'nodal point' (i.e. where the 'rays' come from) is not the same as where the 'scene's rays' apparently converge to!

All theory for amateurs is based on a 'thin lens' that assumes there's a point in the centre of the construction through which all light rays pass. Useful. but just ain't so with modern complex designs. As you pointed out correctly that can be resolved.

Mike