I have a few different fluorescent microscopes, the two that use Mercury lamps are older than 7 years. I notice on those that the thin film filters in the filter cubes (green, red, blue) have accumulated this haziness. Both the excitation and barrier filters seem to have this, more so on the ex filter and it's not present on the dichroic.

I've always referred to this as the filter being "burned" and my rational is that it's from the heat & intensity & low wavelengths from the Mercury lamp. But in all honesty I don't know what it is or if it's removable and if so how? I would like to see if removing it improves my image clarity.

I know a picture would help here and I'm having trouble showing it but will keep attempting and add it to an edit for this question. However I have seen this on many microscopes if you have one with a merc arc lamp and it's getting up there in age take a look at the filters on it. Let me know if you see this too.


In fact, filters can be damaged by heat. However, newer filter coatings are less prone to heat damage [details].

For the barrier filter, it's less likely to be heat damage. The older/less expensive filter coatings do degrade slowly over time and have to be replaced.

So I would guess that the haze represents permanent, non-removable damage to the coating. You should replace the filters with hard-coated filters, which are more durable if you do ever need to clean them for some reason.

Just to be safe, you may want to get a heat filter between the lamp and the excitation filter. One caveat with the heat filter: if you are using near-IR dyes (Cy5/AlexaFluor 647) check the transmittance of the heat filter to make sure it doesn't interfere with the ~640 nm excitation.


Its probably not from heat. Filters are basically a glass substrate with some ionic compound deposited in thin layers. These won't oxidize at reasonable temperatures, and furthermore since you have it on the emission filter as well, its even less likely to be from the source.

More likely its just accumulated organic material from the environment. 7 years is a long time, and microscopes are exposed to a lot of chemicals and other substances which can gradually build up on optical surfaces.

Most vendors have a recommended way of cleaning their optics, but usually it involves lens paper or lint free swabs and methanol (or sometimes acetone for more durable stains). You must be very careful though, as you do not want to scratch the filter.

Semrock for instance has a detailed guide here:


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    $\begingroup$ Thank you for this I haven't considered that strongly. However other glass on console is fine however. The excitation filters are considerably more burned than the barrier ones on the cubes. Your right about the time however. I have tried solvents but they don't remove it. I need/will get a pic up for this. $\endgroup$ – rhill45 May 9 '15 at 4:41
  • $\begingroup$ Thats interesting. I haven't seen something like that, but if even acetone won't clear it, then I think you'll have to replace it. Possibly its just a poorly made filter that degraded over time. $\endgroup$ – user1850479 May 10 '15 at 17:47

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