Step by step

STEP 1

The lens aperture size is determined by its f-number setting. The lower value will vary between lenses but it typically rises to a high value around f/32. For good quality Venus spikes, a setting around f/11 to f/16 works well. A useful tip is to ensure your sensor is clean, as high f-numbers bring any specks present into sharp relief.

STEP 2

For camera setups, a tripod can be used as long as the exposure time is kept short enough to prevent trailing. With a stopped down lens, a high ISO will be required and this will introduce noise, unwanted grainy artefacts that will affect the quality of the spikes. A tracking mount is a more rewarding option, allowing for a longer exposure at lower ISOs.

STEP 3

Different lenses use different types of aperture blades. Some are suitable for creating sharp diffraction spikes while others are not. If you have an unsuitable lens you might find the spikes less well defined. The only options are to try a different lens, or fully open the lens aperture and stretch cotton across the lens front (Step 4).

STEP 4

Using a lens or an unobstructed aperture instrument like a refractor, diffraction spikes can be introduced using cotton. The easiest method is to create a card tube to slide over the front of the lens or scope. With the tube in place, cotton can be stretched across the diameter and fixed with tape.

STEP 5

Two threads of cotton at 90˚ orientation will give two overlapping sets of four spikes. More creativity can be achieved by changing the thread numbers. An arrangement of three threads at 120˚-intervals will give six spikes (two per thread), while two sets of 90˚-threads rotated by 45˚ will produce two overlapping sets of eight spikes.

STEP 6

Venus produces the best spikes because it’s a bright point source. However, for a really dramatic effect, it’s also possible to generate spikes from a larger, non-point source such as the Moon. The Moon will be close to Venus on 25, 26 and 27 April providing an opportunity to achieve this.