Have you ever noticed how the out-of-focus highlights on a photo has the shape of the lens’ aperture? They are typically not perfectly round, but often septagonal or octagonal – exactly like the shape of the aperture of the lens. So it stands to reason that if you could change the shape of the aperture, then the out of focus highlights would get a new shape as well.
At a simple level, the aperture is just the narrowest point in the lens. To make a new aperture, you just need to make a new narrowest point that is more narrow than the real aperture (if you see what I mean). With that in mind, I set about to make a heart-shaped aperture to get heart-shaped out-of-focus highlights:
- Pick your longest and fastest (lowest f-number) lens that can focus close enough to what you want to photograph (the reason will become obvious soon). I chose my 105mm f/2.8 macro lens.
- Cut a cardboard disc with the same diameter as the filter thread on the front of the lens.
- Calculate the diameter of the lens’ aperture when the lens is at the aperture you intend to shoot at. The f-number is just the ratio between the lens’ focal length and the aperture diameter, so the aperture diameter can be calculated as focal-length divided by f-number. I intended to shoot my 105mm f/2.8 lens wide open, so my (real) aperture would be 105/2.8 = 37.5mm in diameter.
- Draw a circle in the centre of the disc with slightly smaller diameter than the calculated aperture. I chose to draw it at around 25mm, meaning that as long as I stay below f/4 (105/25 = f/4.2) everything will be fine.
- Draw a figure inside the circle. I drew a heart. Cut the figure out.
- Take the protective UV filter off the lens, place the cardboard against the lens’ front element, and screw the filter back on. If you don’t use a filter, you could gaffer-tape the disc to the lens (just don’t put the tape on the front element 😉 ), or you could make a little cardboard tube, tape the disc to the tube and slide the tube over the front of the lens.
That’s it. Now it’s just a matter of making sure you’ve got some bright highlights far enough behind the main subject to render them out of focus. Candles are good. Street lights are fine. Even the sun would work fine (bearing in mind that it’s not a very good idea to aim powerful optics towards the sun, and then look straight at it).
This technique is one where having a DSLR really helps. In theory it doesn’t matter, but imagine what result you’d get in step 3 with a point&shoot camera’s 10mm f/3.5 lens…it would take quite a stable hand to cut out the shape in the middle!
Now that I’ve seen it work, I quite look forward to make all the lights on the Christmas tree look like hearts. Or what about a road with the streetlights looking like cars or horsedrawn carriages. The possibilities are legio, although it probably starts to look a bit cheesy if used excessively.