click photo to enlarge
The outline of most arches was constructed using a straight edge and a pair of compasses. It's quite easy to see how a round-headed arch might be drawn using these tools, but pointed arches were drawn in this way too.
The simplest pointed arch - the "pointed" or "two-centred arch" was drawn using two arcs that met at the apex of the arch, with the compass point located outside, to the left and right, of the vertical lines that form the jambs. This is easier to show using an explanatory drawing than it is to describe in words.
I mention this because when I came to look at my photograph of an arched doorway through which a spiral staircase can be seen, I couldn't decide what kind of arch it was. The photograph was taken in Tattershall Castle, Lincolnshire, a tall, brick structure built in 1434, a time when castle building was on the wane. The arch is of the Tudor/four-centred variety. Some authorities class these arch shapes as one and the same, though others maintain that the Tudor arch is more depressed than its the four-centred sibling. Either way, I was definitely depressed after I'd consulted my books and the internet and come to no definite conclusion!
The photograph was taken using natural light, and the effects that might suggest the use of flash come from artificial light sources that are designed to make the tourist's passage safer, and natural light penetrating through small windows.
photograph & text (c) T. Boughen
Camera: Olympus E510
Mode: Aperture Priority
Focal Length: 11mm (22mm/44mm equiv.)
F No: f3.5
Shutter Speed: 1/13 seconds
Exposure Compensation: -0.7 EV
Image Stabilisation: On