Hi @andypandi - this video is pretty useful at explaining cone of vision. https://www.youtube.com/watch?v=OSUnr3gWbYY

For me to visualize this I think it would help to think of the 360 degree circle around me, on the floor, if I were in the center. 180 degrees exist in front of me, and of that 180, 60 is a wedge that's the center one-third. I could use my arms to replicate this imaginary edge, to approximate what area of my field of vision to draw from observation A simpler answer is, just draw... and if the edges are way too distorted then either crop the outer parts, or of it's two-point or three-point, move the vanishing points farther away

Scott is a great artist, and this page about perspective is correct (I can vouch for that) and definitely has its own uses. But I will say to read it in moderate, because it is very much technical, and you'll need to understand photography as well (that's why Scott talks about photography as well). The only thing that differs 60 and 90 degree vision is their respective coverage (or in photography lingo, field of view). The smaller degree vision creates smaller coverage, while bigger degree vision creates bigger coverage. Coverage is how big physically (this is important, physically, not visually) the object needs to be to fit into the frame. Face is physically small, while a sky crapper building is physically big. This is basically what 'short lens' and 'long lens' is all about, the coverage (Long lens are also called telephoto, while short lens are also called wide lens), For small things like portraits, we'd use long lens, while for landscape like buildings, we'd use short lens. Long lens produce a range of 20 to 5 degree of vision, normal lens (like 50mm) produces something around 45 degree of vision (I think Scott makes mistake calling 50mm to have 60 degree of vision), while short lens produces 60 to 140 degree vision. Now you start to see why when we're taking portraits we'd use a long lens, because the fact that it produces small (only 20 to 5) degree of vision, fits with the physical size of a face in portraits that is also small. If you try to use short lens (60 to 140 degree) for portraits, this is what Scott also notices, you'll get distortion, because you're trying to use big degree vision to frame a small thing. The face will look wider than it should be (this is what many Instagram shooter complain about their cheeks look large, because our phone normally have short lens). As I mentioned, however fascinating the numbers are, this information will have less use when it comes to actual drawing, If you want to put this information to use, get a DSLR and start taking pictures by yourself, and then learn the photographs your DSLR takes. That way, you can learn how these numbers work, and not only that, also see how those numbers affect the visual of things you take the pictures of.

You mesure the cone of vision from the station point. A 60 degree cone of vision is a 60 degree angle (30 degrees on each side) that you extend to the horizon line. Using the center vanishing point (CVP) draw a circle which will be your cone of vision. I drew an example of a 60 degree cone of vision, but it’s basically the same thing for a 90 degree one (it’s just a 90 degree from the station point, 45 degrees on each side). Hope this helps!

This is exactly like the choice of lenses in photography. You are free to pick a lens with wide angle and short focal distance, which offers you a broad view which emphasises perspective, or a lens with narrow angle and long focal distance, which brings things closer to you, at the cost of flattening things out.

The wider the angle the more dramatic is the perspective. For example, with a telescope lens, you have an extremely small angle in the cone. https://images.squarespace-cdn.com/content/v1/543ea9d5e4b05588d7c5b8fd/1610914278016-MDWGXRA70O9BAOEZT13L/ke17ZwdGBToddI8pDm48kJUlZr2Ql5GtSKWrQpjur5t7gQa3H78H3Y0txjaiv_0fDoOvxcdMmMKkDsyUqMSsMWxHk725yiiHCCLfrh8O1z5QPOohDIaIeljMHgDF5CVlOqpeNLcJ80NK65_fV7S1UfNdxJhjhuaNor070w_QAc94zjGLGXCa1tSmDVMXf8RUVhMJRmnnhuU1v2M8fLFyJw/moment-telephoto-lens-sample-photo-new-york.jpg?format=1000w like in this picture, the cone is very small therefore the perspective is nearly isometric. On the other hand, you have something like a fisheye lens. There you have a really wide angle on the cone, but you will face distortion and dramatic perspective. What type of lens you choose to draw is up to you. If you want to increase the angle bring the vanishing points closer together. (Imagine you zooming out) I'm no expert correct me if I'm wrong :D

This is for when you need precise measurement. and typically I don't determine the FOV (cone here) from the start, but rather have 4 equal length perpendicular lines of the same length of a cube to represent the spatial focal that I'd like to picture the scene with (which means "okay I want the scene to behave as when a cube is placed here it should have such perspective"), then with those 4 lines you can plot 3 vanishing points, and those 3 can give you 3 horizon lines, the distance of each pair of those two points represents 90 deg FOV at your view direction. Gah... it's so hard to explain with words...... sorry