The most typical demonstration of oil migration (in relation to optical lens systems) is seen on the iris blades of a lens. This is often visible as the blades have a shiny appearance and can appear wet when looking through the lens. This can cause damaging results, especially if it is left untreated and the lens continues to get used.

If oil migration is left to build up on the iris blades, it will cause them to stick to each other, rather than sliding freely over one-another. Over time this will put serious stresses onto both the blades and the pins that drive the movement. Once it reaches a fatigue point, it can either cause the blades to buckle or, it will rip the pin out of the blade. Oil migration can also be seen on elements as well, causing a haze or film that degrades the final image produced by the optical system you can read more about haze here - My lens has fungus and/or haze, what can you do?.

Oil migration usually happens over time. It can be caused by the grease degrading or environmental conditions. It will also depend on the specifications of the grease used. Oil migration is when the oil within the grease begins to separate from the other substances. An easy example to understand is during exposure to heat, above the recommended specification of the grease. If the grease becomes too hot, the oil will begin to separate (or evaporate) from the other substances. As the grease is being used internally within the lens, it will migrate within the mechanics of the lens.

Oil migration will typically show up first on the iris blades. This is because it is the easiest route in for the grease. Generally, optical systems are well sealed, and it is difficult for grease to migrate within the optical cells. However, the iris must be driven from a drive pin from the external sleeve. This external sleeve will have some form of grease on it to keep the movement smooth and free for years of service. However, this does leave an open area (even if small) that grease can migrate through. Therefore, it is important that high grades of grease are used (designed for this purpose too) and only small amounts are used in close proximity to the iris assembly.

If the oil does separate from the grease, it can also be deposited or migrate onto the glass elements within the lens. This can either show up as a haze/thin film or sometimes small white/silver specs across the area of the element. Fortunately, oil migration is easily rectified. The best course of action is to disassemble the lens, including all contaminated components, and thoroughly clean them. It is best to use a chemical such as acetone (where possible) to make sure as much oil/grease is removed. Once all the components are cleaned, use a small amount of specific grease to lubricate the moving parts of the lens.

How to prevent oil migration

Most users of lenses will want to prevent oil migration from happening. The best way to prevent this is to have the equipment regularly serviced and cleaned. This means a full service that disassembles to the point of the iris blades for optimum longevity. Furthermore, using the manufacturers recommended grease will also increase the lifespan of the lens as well as reducing the risk of oil migration. Another consideration is the environment you’re planning on using the lens. If the lens is to be used in harsh climates (either extreme cold or heat) then it is best to talk to a professional servicing centre. Specialist grease exists that are designed for use with either extreme cold or heat. Therefore, the lens can be prepared before the shoot to work at optimum performance. These temperatures are usually below -20 or above +40 degrees Celsius (-4/104 Fahrenheit) but will depend on the manufacturer’s specifications.

If you’d like a quote or more information on oil migration, please get in touch with us at sales@truelens.co.uk or calling our office on +44 (0)1455 848411.