Trail cameras are a wonderful way to discover who you are sharing your block of land with – be it feral pests or some of Australia’s unique bird and animal species. However, they’re designed to look at large creatures and give disappointing results on small birds and animals. Moving the camera too close to the target (be it food, or a hole in a fence, or a water bowl) only results in a fuzzy picture as the cameras have a fixed focus that is set for objects a few metres away.
Fortunately, reading glasses work the same way on cameras as they do on people. So, taking one lens from a cheap (less than $10) pair of glasses and attaching it over the camera lens with Blu-Tack is all that’s needed to bring the focus in closer.
Reading glasses come in a range of “strengths”, denoted by the dipotre (D). This is usually printed on the frames or on a small removable sticker. Attached in front of a camera that was originally designed to focus on distant objects, the lens from the reading glasses will place the focal point of the camera at a distance from the camera (in metres) equal to 1/D. So, for commonly available glasses,
D New focus position
+1 1 metre
+2 0.5 metre
+3 33cm
+4 25cm
A few tips
* The cheapest glasses with plastic frames have the lenses glued in place. They are difficult to remove without some violence. For a few dollars more, metal-framed glasses come with lenses that will pop out under strong pressure from a thumb.
* It does not matter if the lens partially covers the infrared illumination LEDs of the camera.
* However, if the lens is too large it might prevent the camera door from opening. The plastic lens can be cut down to size with a small saw such as a Dremel.
* The “depth of field”, or range of distances over which focus is maintained, becomes smaller as the power of the lens increases. A +3 dipotre lens will create a depth of field of only a few cm, requiring careful placement of the camera relative to the subject.
All photos by the author. The small animal pictured above is a yellow-footed antechinus, or mardo (Antechinus flavipes), taken through a +3 lens attached to a Browning trail camera.
John Storey,
Gunning District Landcare
21 Feb 2022