So, what should you look out for when purchasing a new compound microscope? What are the key variables? There are several quality criteria that need to be taken into consideration.
When purchasing instruments, look out for the following:
- Stability: Make sure that the construction of the decive makes a solid impression. A solid device minimizes vibrations. Do not forget that even vibrations are amplified by the magnification.
- Mechanics: The focus knobs and X/Y knobs should turn easily and without friction. Is there any play when turning the knobs? Does the stage stay in place or does it shift? If the stage changes position due to gravity, then a readjustment is necessary. Does the revolving nosepiece center the objecitves properly? Is there any play in the nose-piece?
- Optics: Is the resolution and the contrast of the objecitves sufficient? Also make sure that the objectives are of the same series so that parfocality is guaranteed. Is the field-of-view of the eye piece large enough?
- Lighting system: Does the light intensity correspond to the objecitves? A higher light intensity is required for higher magnifications. A halogen lamp delivers a brighter image. This is an advantage if students are required to work much with the 100x objecitve.
- Student Proofing: A student proofed microscope requires special tools for the removal of eyepieces and other components. There are no finger-screws to turn, everything must be adjusted using the tools.
Notice that I did not include maximum magnification as one criterion. This is the least important aspect. In most circumstances a total maximum magnification of 400x is absolutely sufficient.
If your school decides to purchase used microscopes – hospitals and research institutions occasionally replace their equipment – then take care of the following points as well:
- Are the knobs difficult to turn? This is an indication that the lubrication oil has started to solidify and must be replaced. Do not turn the knobs with force, as this may damage the gearing.
- Check if the mechanics demonstrate excessive play. Over time there is a natural wear of the gearing.
- If dust is visible then the optics must be cleaned with pressurized air.
- Microscopes that were used in a humid environment may start to grow fungi on the optical surfaces. Some optics are sprecially treated with anti-fungal substances to prevent this from happening.