Do you find it hard to assess dimensions and sizes for a drawing or a painting? Or find that judging dimensions from a photo references is frustrating? Enlarging or reducing size methods too complicated or time consuming? Fret no more because I have a solution for you, and its called a Proportional Divider. I guarantee once you start using it you will not look back!
The Proportional Divider- we’ll call it PD for short- is a very simple tool: it is made from two pieces of equal length- let’s call them legs- with holes in both starting from their centres. A locking nut which can be moved from one hole to the next which can then be used to lock the two legs together at that position. The legs can then move relative to each other from that point.
One end of the PD is used to measure the size you want to transfer from, and the other end will give you the size you want on your drawing (see photos one & 1a below).
Some PDs might have markings on the side to help with placing the locking nut. Always check the tips of the legs are the same before using the PD; if one end is longer than the other your measurements will be out.
To help make things easy to follow, I suggest you mark the ends as A and B. It doesn’t matter which end is A or B as long as you stick with your designation. I chose to use the locking nut end as A, the other as B, because A is what you do first and B is next! If you follow the same designation it will be easier for you to follow the instructions. See photo two, below.
How it works
A) From photo to drawing
The A end measures the size you want to enlarge. If the locking nut is in the centre, then leg B would transfer the exact size to your drawing (see photo three, above). If the locking nut is moved, say a couple of slots down towards the A end, the size at the B end is made larger (Photo 3). This is very useful if you have a small photo but want to transfer the dimensions to say an A4 drawing sheet.
You can also work from a computer or tablet screen in the same way. However, once you have zoomed onto the photo you must not change the zoom setting until you have finished transferring the information to the drawing support.
B) Working from life
I used an artist’s manikin to demonstrate the use of the Proportional Divider in a life drawing situation. It works in exactly the same way when doing a portrait, figure, or still life drawing. There are two ways to do this: decide on an arbitrary unit of measurement, such as the head; or just measure each part and put the measurements relative to each other on the drawing.
By using the head of the manikin as the arbitrary unit of measurement (see above), I measured the rest of the body by how many head sizes. Of course I could have just measured each part individually and marked the positions on the drawing see below.
In a still life situation you can either transfer each individual measurement, or use relative size approach: measure one item against the other(s).
C) Plein Air
In plein air situations the PD is immensely useful when it is not so easy to judge sizes relative to each other. Again you must use the PD at full arm stretch to ensure accuracy of measurements.
To demonstrate this I stood outside the studio and measured the sizes of the trees in the background (see photos 9-11, below). As you can see, the bottom bush is virtually as high as the trees in the background. In reality they are not, but what you are seeing are the effects of perspective: the trees are much further away than the small bush.
Spend a few minutes following the instructions above and before long you will not do without the Proportional Divider, it will become a permanent part of your toolkit.