First medium format purchase

[swifty]

Hi Jon, I may be completely wrong with my assumptions in my post above.
Do you know how the angle of view is measured and can you shed light (pardon the pun) on my above theoretical model comparing a tiny sensor/film and a giant one?

I think it would be useful to identify we're not talking about things like barrel/pincushion/moustache type distortions which are related to lens design.
For lack of a better term, it's 'perspective distortion' that's the subject of contention here. The type you see between a wide angle vs telephoto lens. If there's a better term for it, please let us know.

- - - Updated - - -

Could the angle of view be measured from the lens nodal point in which case it is irrespective of sensor/film size?

[jjphoto]

...Could the angle of view be measured from the lens nodal point in which case it is irrespective of sensor/film size?

It's my understanding that this is the case, however there are two nodal points in every lens (because the lens has two sides and effectively can be used in either direction although obviously with a different result).

...
I think it would be useful to identify we're not talking about things like barrel/pincushion/moustache type distortions which are related to lens design.
For lack of a better term, it's 'perspective distortion' that's the subject of contention here. The type you see between a wide angle vs telephoto lens. If there's a better term for it, please let us know...

Re perspective distortion. Whether or not there is 'distortion' in the final image depends on the size of the print and viewing distance relative to the perspective in the original image. The reason images shot with wide angle lenses appear distorted is often because the distance from which we view the resulting image is at odds with the perspective in the image itself. If you view the image from closer than the normal viewing distance, or the finished image is much larger (having the same affect as viewing it from closer), you will see that the perspective looks natural or realistic and the 'distortion' has disappeared. So I don't think the 'distortion' happens when the image is taken rather when it is viewed at the wrong print size/viewing distance. Try it. It's explained much better by Rudolf Kingslake (Director of Optical Design at Eastman Kodak) in 'Lenses in Photography' (1951) where the entire first chapter is called and is about Perspective. It's a superb book and worth reading if you're into that kind of thing (optics, lenses etc) although there are lot's of good books on the subject.