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Thursday, 9 May 2013

Ltl Acorn 5210 and 6210 Close Focus Adjustments

Fig 1:   Lens assembly sitting over the image
sensor on the main camera board.
Following on from last month's posts about close focusing, the following shows how to make the adjustments to the lens to achieve various ranges of closer focus with the Ltl Acorn 5210 and 6210 cameras.

Please be aware that if you mark or damage the camera when carrying out the following procedure it may affect or negate your right to claim under warranty; so you do this at your own risk.

To access the lens assembly you will need to remove the six screws from the back of the camera. This will release the camera front which can then be lifted away to expose the lens and IR filter assemblies.

Warning: There is a small sealing washer located internally in the pillar at the back of each case screw. They may become dislodged when the camera case front is removed. Do not lose them and make certain they are relocated before the case front is refitted otherwise water may gain entry past the case screws.

The IR filter assembly is actuated by a servo and can be manually moved back and forth across the lense to position it out of the way; but be careful not to knock or damage it while using the pliers to shift the lens.

Both camera models are basically the same except for the focal length of the lens. The 5210 models
have a lens focal length of 6mm and the 6210 models are 3mm. This makes the 6210 more suitable for close focus adjustment because of its greater depth of field (DOF).

Fig 2:
Mark the original position of the lens before you do anything else, otherwise you will lose track of how much adjustment you have made, making it impossible to return the lens to its original position should you wish.

I dip a very thin miniature screwdriver in white correcting fluid and then carefully place it between the case and the lens so that a small amount of fluid is deposited on both (see figure 2).

The crucial issue is can the lense be adjusted without causing damage. The answer is yes, providing great care is taken with the initial shifting of the lens.

The lens is locked in position during manufacture using something that looks very much like PTFE (plumbers) tape (see figure 5) and to loosen it you need to grip the edges of the lens front very firmly with a pair of bent long nose pliers, and then gently rock back and forth until it starts to move (see figure 3). Because you are only making a very small amount of adjustment there is still sufficient friction to stop the lens from self adjusting during future normal use.

Fig 3:
Once the lens is moving turn it anti-clockwise approximately 10 degrees to the position shown in figure 4. If you are lucky this will give a DOF of about 0.5 to 5 metres with the 6210. It is impossible for me to give accurate positioning figures for either camera model because all cameras vary slightly in their closest focusing position from new.

You will need to experiment and test to find the optimum lens position for your purpose but I have found that with the 6210 it is possible to get a workable DOF for small to medium sized subjects starting at less than 50 cm.

I use a lens test chart to carry out these settings as shown in Close Focusing with the Acorn 6210MC Trail Camerabut if this is not possible a series of clearly defined objects or distance cards set at regular intervals away from the camera will work just as effectively.

Good luck and I hope you find this useful.

Fig 4:
Fig 5:  
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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.