Rob Adams a Painter's Blog painter's progress

July 25, 2018

Sun Cast Shadows

Filed under: Drawing,How to do,Perspective,Uncategorized — Tags: , , — Rob Adams @ 6:04 pm

This is a brief tutorial on the construction of shadows as they are cast from the sun. We all know how descriptive they are, the long shadow of a fence over a path, a telegraph pole over a road, spreading from the feet of people on the beach at the end of the day. Shadows in a painting tell the viewer more about the day than you might expect. A shadow crossing a road shows how high the verges are relative to the road, describing the shape of the land. We instinctively understand from shadows what time of day it is, even which season. If you understand how they are cast and how to get them correct you have quite a powerful tool in your painting box.

Here I want to deal briefly with the simplest of possible cases, but hopefully give you an idea of how the same methods might be used in more complex scenarios.

So our first example, a set of posts.

shadows, tutorial

The time is 1pm. See the changing angle of the shadows and how although in reality all the shadows are the same length in our perspective view they vary in thickness and length. Let’s move the clock on an hour.

 

Shadows, tutorial

Here we are at 2pm the sun is at it’s highest due to the magic of daylight saving summer time! People often imagine the shadows are splayed because the rays radiating from the sun, but this is not the case. The sun is 93million miles away so if we looked straight down from the top all the shadows would be the same length and parallel. So the effect of the shadows splaying is due to perspective and nothing else. On one more hour.

shadows

No surprises here at 3pm the shadows have swung round and lengthened again as the sun has dropped nearer the horizon. So let us look at 2pm again and look at how things got to where they are.

shadows, tutorial

A very tall skinny illustration since we have to get the sun in!

First the Red lines. If we drop a line vertically down to horizon we find it hits exactly at the point where the shadows converge at the horizon IE, the shadow’s Vanishing Point. If we had the shadows and no sun (as we might have in a reference photo) we could extend the shadow lines to the horizon and then project that point vertically up. We know the sun must be on that line… but where?

For that we need the Green lines. If we start from the sun again and fire a ray from the sun so that it skims the middle of the very top of the pole. Where that ray hits the ground marks the length of the shadow. Once again if we work backwards we can draw a line from the end of our shadow and through the middle of the top of the pole, extending it on we find it crosses our red line at exactly the sun’s position.

Shadow, tutorial

Here is a simplified version with  just a plank. As you see it also shows how the shadow gets wider in perspective as it gets nearer. Now a more complex example, a sculptor’s table with hammers upon it. First a quick video.

You can drag the slider and watch the shadows in motion. Once again here are a few times of day.

shadow, tutorial

Here is our table at 10am.

shadow, tutorial

…and at 12pm. Compare the two images and see how the various parts have moved. On 2 more hours.

shadow tutorial

Finally here we are at 2pm with the sun at its highest. Time for another tall skinny illustration with coloured lines!

shadow tutorial

Starting with the red lines. A line from one corner of the tabletop shadow then taken through the real corner and extended up crosses the same line drawn from another corner (any corner will do) at the point where the sun is. The blue lines show the splay of the shadow of the table legs and obey exactly the same rules as the posts did. The two vanishing points of the sides of the table top shadow are exactly the same as the vanishing points for the table top itself.

Similar rules govern how shadows from artificial lights are placed. If the ground is sloping or the posts at an angle then obviously the geometry gets more challenging. A more complex description is on the excellent Handprint site.

February 17, 2017

How to Cheat at Perspective pt1

Filed under: Drawing,How to do,Perspective,Uncategorized — Tags: , , — Rob Adams @ 3:43 pm

This post and the forthcoming ones are for anyone who has had perspective explained to them, but found that their brain started to close down causing them to feel an irresistible urge to get as far away from the person explaining as possible and have a quiet coffee and read OK magazine because it is certain there will be no article on perspective in it. Every now and again I am in the position of the abandoned explainee when I have to explain some of the finer points of perspective to a fellow painter. It starts off fine when I say, “Hold up your brush as close as you can and as level as you can, right in front of your eyes.” They do this and I pronounce. “You see where it cuts across your vision, that is always the Horizon line.” Over the years I have mastered the skill of saying horizon with a capital ‘H’.

They mostly just accept this, but some say, “What about if you are up a mountain, won’t it be lower?”

Fixing an irritatingly patronising smirk on my features I reply,”No, if you hold up your brush when you are on the very top of mount Everest it will still mark the horizon.”

“What about in space?” The smart-arses come back.

My smirk slightly morphs into a pout at this point…”When exactly are you going to paint in space…?” I enquire.

“So it doesn’t always work! What is the use of that then?”

So there we are, the rules of perspective are rules that don’t always look right on the page when you follow them. In actuality, as I have written in other posts, the whole business of linear perspective is a crude approximation of what and how we actually see. It is convenient I suppose that one point perspective is fairly easy to explain, with railway tracks meeting at the horizon etc. However once you are in the territory of 2 and 3 point perspective and quite wide angles of view your explanations gain an ever increasing degree of complexity which are going to glaze over most painter’s eyes. Also linear perspective assumes you only have one eye and a flat retina. Also it is taken for granted that neither your head or your peepers can swivel. I don’t know about you, but when I paint something I do a fair amount of swivelling and general rubbernecking!

Many artists avoid the whole thing by never doing town or cityscapes at all, or if they do they look way off into the distance which is where linear flattens out into cardboard cutouts. Most of us who don’t avoid such subjects stick to the safe territory of one point perspective and a tight view. Where it all falls apart though is when we take that slightly wider view.

Time for one of those diagrams, but don’t click away, there will be no equations or hyperbolic geometry.

Perspective drawing

Here we are in a town with mostly one point perspective, there are only a few bits of sticky-out shop and rooflines that don’t recede from us. The rest tapers off to meet at the point on the horizon in the middle of the street. I’ve gone quite wide too and all seems well. I have cheated a bit though. If I had stuck to the constructed rules of perspective the shop on the far right would be sort of stretched out; indeed in a photo that is just what happens. So a skinny man standing in the middle of a photograph will look like a fat man if he goes to the far side of the frame. We are so used to this effect in photos we no longer notice the distortion. Just for fun below is an image where those perspective rules that you have never quite understood start falling apart.

perspective drawing

The wide-angleness of this image is not far off a point and click camera or your phone. As you see we have a straight row of perfectly identical computer generated men. Well call me picky, but to my eye the chap on the far right has had a few more iced buns in the last month than his friend in the middle… but they are identical models just duplicated, the distortion is purely caused by using the rules of linear perspective. To make it worse the chap on the right is about twice as far away from you the as chap in the middle… now I always thought the “rules” said things got smaller as they got further away. The blimps in the sky, by the way,  are all perfect spheres… it is a property of spheres that they always have a circular outline wherever they are in your field of view. These appear to break that rule with enthusiasm. To recap, if you got a set of bald grey elevenplets (rarer that triplets I hear) and stood them in a line in front of your point and snap this is how they would look in your photo.

perspective drawing

Here we are back in our city. We have stepped back a bit and widened the view. This is version one. At first glance this looks sort of OK. However the building on the far left has a corner that should be closer to you than the point at which it leaves the picture on the left of the frame. Yet following the rules of linear perspective it causes that face of the building to get taller as it gets more distant. The very opposite of what our eyes see in reality. Below is my guestimate fix.

perspective drawing

Take a moment to compare versions one and two. I have made two simple adjustments one quite obvious, one less so. Firstly can you see that this looks more likely than the first version? If not can I suggest a quick coffee and a copy of OK? Ahem… the big change is on the left. The vanishing point has flipped from right to left so the building goes away from you as it should, you might also notice that the chimney stacks and the zebra crossing make more sense and the corner feels properly square. The other change is to the shop corner to the right of the picture. I have slightly curved and flattened the angle of the perspective as the lines reach the square corner. This helps the building on the left fit in better, though beware if you over do it things start to look bendy!

Linear perspective is fine as a starting point, but you do have to make subtle corrections to make up for its considerable deficiencies. Essentially you need to make some straight lines a bit bendy in order to get things to make better sense. My own take is to not over do it and get into fisheye territory, but to do the least possible to reduce any inconsistencies. I do get asked, “How can straight lines be bendy?” they will often hold their ruler against the offending roofline and go, “See it’s straight.” Instead of telling them the unwelcome fact that they are seeing their ruler bendy too, I usually suggest a coffee…

I am doing these little tutorials in small bites to make them a bit more digestible. If people have perspective questions post them below and I will try and cover them in future posts.

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