Common defects of old microscopes

During the past couple of years I’ve seen numerous microscopes that required maintenance due to heavy use. Here are some of the problems that I observed. It may pay off to also consider these problems when shopping for a used microscope.

Problems with the optics

• Dirty lens: This is due to immersion oil on the optical surfaces, which have collected dust and have hardened.
• Lens kit dissolving: Some lenses are glued together. Flower-like bubbles forming in the lens are an indication that the lens kit is coming loose.
• Fungi on the optical surfaces: This is a problem with microscopes which have been in use in areas of high humidity (such as the tropics). An anti-fungal coating of the lenses may prevent this.
• Scratches or cracks: These can occur if the objective is rotated into the specimen. You can see an extreme example of this in the following post: Dirty microscope objective: Its effect on image quality
• Loss of coating: Excessive rubbing or a wrong cleaning solution may remove the anti-reflective coating of the lenses.

Problems with the mechanics

• Stage drift: In this case, the stage slowly lowers due to its own weight. This can be fixed by tightening some screws.
  Focus difficult to turn: In this case the oil in the gears has solidified due to age and accumulated dust. Do not use force, it may increase the wear on the gears. It’s better to get the device cleaned.
• Mechanical stage difficult to move: Like with the focus knobs a solidified oil makes the stage difficult to move.
• Too much slack: Sometimes there is too much tolerance and turning the focus knobs. There may be too much slack in the gears, possibly due to too much wear.

Problems with electricity

• Old lamp: An old lamp will have a spectrum shifted towards the red. This is a disadvantage for digital photography. The sensors of the camera are very red-sensitive. Use a blue filter.
• Brittle insulation: Old power cables may become brittle and be a hazard.