In article , Eric Stevens
wrote:

Lower down the Wikipedia article says

"For still photography, a lens with a focal length about equal to
the diagonal size of the film or sensor format is considered to be
a normal lens;

which means that anything longer than that is a long lens. very simple.

that's also consistent with wikipedia:
https://en.wikipedia.org/wiki/Long-focus_lens
In photography, a long-focus lens is a camera lens which has a focal
length that is longer than the diagonal measure of the film or sensor
that receives its image.

it's also in agreement with what ken said, which tony confirmed was
correct (contradicting his initial claim), up until he realized that
meant i was also correct, at which point he quickly changed back to
long lens is an opinion idiocy and then lied about it.

its angle of view is similar to the angle subtended
by a large-enough print viewed at a typical viewing distance equal
to the print diagonal;[12] this angle of view is about 53°
diagonally. For cinematography, where the image is larger relative
to viewing distance, a wider lens with a focal length of roughly a
quarter of the film or sensor diagonal is considered 'normal'. The
term normal lens can also be used as a synonym for rectilinear
lens. This is a completely different use of the term."

It is clear that even for constant image dimensions the focal length
ascribed to a 'normal' lens is very much a moveable feast dependent on
the viewer and their circumstances. That is why I wrote "what is long
is an opinion".

you're moving the goalposts again.

different formats (including your graflex) will have different numbers,
and video will obviously be different yet since the image is projected
with viewers further back, plus most video is now widescreen.

nothing about it is opinion, just different sets of numbers.

once again:
"For still photography, a lens with a focal length about equal to
the diagonal size of the film or sensor format is considered to be
a normal lens;

for 35mm full frame still cameras, 50-55mm is considered normal, which
is actually a little longer than the frame size (~43mm) because 50mm is
a simple lens design and therefore cheap to manufacture as well as
being long enough to not need a retrofocus design due to the fixed
flange distance of the mirror box, which for nikon f is 46.5mm.

and then there's tolerances. focal lengths are within 5% of stated, so
a 50mm lens is actually anywhere from 47.5mm to 52.5mm.

nikon dx, including the d300 mentioned early in the thread, has a 1.5x
crop factor, so normal is 35mm (52.5mm effective).

tl;dr lenses longer than normal are long lenses. very simple.