Why a wide view can defeat a sketch

Stand on a path across the North York Moors, or on the seawall at Burnham Overy Staithe, and the difficulty isn't finding something to draw. It's the opposite. There is simply too much: sky, water, mudflats, a line of pines, a couple of walkers, three distinct weather systems moving in from the west. Faced with all of it, most of us do one of two things. We attempt to fit everything onto the page and end up with a thin, busy smudge, or we freeze, unsure quite where the drawing begins and ends.

A viewfinder solves that problem in the simplest possible way. It is a small window cut in a piece of card, and it turns an overwhelming panorama into a manageable rectangle. You hold it up, move it about, and suddenly you have a composition rather than a view. It costs nothing, weighs nothing, and it will change your outdoor sketching more than any new pencil or paint.

Making a viewfinder in ten minutes

You don't need anything specialist. A piece of mount board, the back of a hardback sketchbook, or a cereal packet will do. Cut a rectangle of card roughly 10cm by 15cm, then cut a window out of the middle. Aim for a window about 6cm by 9cm, which is close to the proportions of a typical A5 sketchbook page and roughly a 3:2 landscape shape.

Two refinements are worth the extra effort:

• Draw a faint cross through the window with a fine marker, dividing it into quarters, or mark thirds along each edge. This is a rule-of-thirds guide, and it helps you place a horizon or a lone oak tree deliberately rather than accidentally.
• Make an adjustable version from two L-shaped pieces of card held together with a paperclip or a small bulldog clip. Sliding them lets you try square, portrait and panoramic crops from the same spot without moving your feet.

Laminating the card, or drawing the whole thing on the back of an old bank card, will keep it alive through a damp afternoon in the Peak District. Tie a loop of string through one corner and wear it round your neck so it doesn't vanish into the grass.

Scanning the scene before you commit

The trick is to use the viewfinder as a browsing tool, not a final decision. Stand still, shut one eye, and hold the card at arm's length. Then move it slowly across the whole scene, left to right, high to low, like a torch beam. Give each frame two or three seconds. You are looking for the moment your eye stops moving, when a particular rectangle suddenly looks like a picture.

Then make a small thumbnail sketch, no bigger than a large postage stamp, inside your sketchbook. It takes sixty seconds and it tells you whether the composition holds up. If the thumbnail is dull, no amount of careful drawing will rescue it. Try sliding the frame a few paces left, or tipping it down to cut out the sky entirely, and thumbnail again.

Matching the window to your paper

Nothing causes more grief in outdoor sketching than framing one shape and drawing on another. If your window is 3:2 and your page is square, the drawing will sprawl or shrink to fit, and the careful composition you chose outdoors will quietly fall apart.

Measure your usual sketchbook first. An A5 landscape page is roughly 21cm by 15cm, so cut your window to the same ratio, scaled down. A square sketchbook needs a square window. Keep the viewfinder at a fixed distance from your eye, arm's length is fine, and note that distance. When you start to draw, hold the sketchbook at the same distance. The proportions will then translate honestly, and you can mark the main shapes straight onto the page with light pencil strokes before any detail goes in.

What to look for inside the frame

A viewfinder teaches you to see like a designer rather than a tourist. A few things worth hunting for:

• A clear focal point. One gate, one windswept hawthorn, one boat on its side at low tide. The frame should have a centre of gravity.
• A strong shape in the foreground. A tussock of marram grass, a stone wall corner, a puddle. It anchors the eye and gives a sense of scale.
• Layers. Foreground, middle distance, distance. Three tonal bands do more for a landscape than any amount of fiddly detail.
• Avoidable clutter. The car park, the litter bin, the waymark post. Slide the window until they fall outside it. This is half the value of the tool.

Squinting as you look through the window is another old habit worth borrowing. It flattens colour and reveals the big light and dark masses, which is what your sketch is really made of.

Building the habit

Use the viewfinder for a fortnight and it becomes second nature. You will find yourself framing scenes while walking the dog, without the card in your hand at all. Start with one ten-minute thumbnail a day in the garden or a local park, then take it somewhere with real weather and real distance: a coastal path, a canal towpath, a view down a Welsh valley.

Keep the framed sketches loose and quick. The viewfinder has done its job the moment you have chosen what to leave out. Everything after that is simply drawing.