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Wednesday, 10 April 2013

Close Focusing with the Acorn 5210A Trail Camera

Fig 1:  Great Tit and Blue Tit trying out the feeder I'm 
using for the close focus tests with the Acorn 5210A
Click image to view full size
There have been a number of close focus experiments with trail cameras recently carried out by users of these cameras.

Adrian Jevons using an Acorn 6210

Kate MacRae using Bushnells

Both have achieved good results applying external close up lenses of various diopters.

Kate has produced her own piece of
commercial kit as an add on to the Bushnell cameras.

While effective this method does however involve hanging bits and pieces on the outside of the camera and to my mind this is impractical in many field environments. 

Fig 2:    Bench test at 10cm

I particularly want to use the Acorn cameras for small mammals and in such applications the camera can often be in a vulnerable situation close to the ground where animals such as badgers and pine marten will almost always show too close an interest.
Fig 3:    Bench test at 20cm

Another issue with using an externally mounted lense is fogging and rain falling on the lens.

Fig 4:     Bench test at 30cm
I decided that the only practical answer would be to adjust the lens inside the camera if this proved to be possible. I had already asked Acorn if they could supply the camera set up for closer focus and they said they could so I assumed the lens assembly would be adjustable.

Upon investigation I found that the lens is a single element in a plastic mounting which is located directly over the image sensor. It has a screw thread which can be adjusted to change the position of the element relative to the sensor.

During manufacture the lens is adjusted and the threads are locked into position using something similar to plumbers tape. With gentle persuasion this will unlock to allow repositioning of the lens element but with enough friction remaining between the threads to prevent the lens self adjusting during use.

Fig 5:      Bench test at 40cm
Depth of Field is a problem when adjusting a simple single element lens for close focus but I hoped that I could get a workable range below a metre and close enough to fill a good part of the image with mouse/vole sized creatures.

Bench test results using a 5210A are shown left in figures 2 (10cm) to 8 (70cm) and proved a perfectly acceptable result through 20 to 60 cm.

My assistants for the first field trial were small birds and a badger. The distance from the camera lens to the wire mesh on the feeder is 45cm.

Fig 6:      Bench test at 50cm
Fig 7:      Bench test at 60cm
Close focus at night results in over exposed IR images as shown in figure 9.

The perfect solution for reducing the level of IR lighting at distances of around a metre or less is a single thickness of PVC adhesive backed camo tape which produces the result shown in figure 10.
Fig 8:      Bench test at 70cm
Fig 9:    Normal IR at 45cm

In the next day or two I will try and post results using a 6210MC and I will also illustrate how to carry out the modification.

Click on any image to view a slideshow.
Fig 10:     Reduced IR at 45cm
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This web site is about the wildlife, particularly the mammals, of the Glen Affric National Nature Reserve area in the north west Highlands of Scotland, UK; and the equipment I use to search for them, which is chiefly trail cameras.

I provide a technical support and parts service for the Ltl Acorn range of cameras and the income from this provides for the upkeep of this site and the purchase of cameras for my own surveying.

I hope you find the site useful and informative; and please contact me if you have any questions that I haven't already covered.