[DIYbio] Re: Possible filters for working with fluorescence

Not this specific brand, but I am familiar with things like them.  Gel filters and colored-glass filters typically transmit around 1% of the light at wavelengths that are "rejected."  Is that good enough?  It depends what you need them to do.  If you are doing fluorescence work, you have a bright illumination source, and much dimmer fluorescence of a different color.

Say you were working with a DNA - ethidium bromide gel, on a blue, violet or a near-UV transmission table.  A 540 nm long-pass piece of glass can improve the contrast for your eyes a bit.  If you are working with a black-and-white camera and want to take a picture of the gel, it can also help.  How much depends how sensitive the camera is to the excitation wavelength. 

If you are doing cellular fluorescence microscopy, you need much better sensitivity.  You usually use a laser excitation source and focus it with a lens.  The scattered light off the cell is strong, and the fluorescence is weak.  You hope to achieve quantitative results -- in other words, where there's no fluorescence, you want the pixel to be as close to background levels as possible.  To do this kind of work well, you typically want < 0.001 % transmission (10^-5)of the excitation light.  You can only achieve this with the fancy interference filters made of many layers of coatings.  They typically cost a few hundred dollars each, though some very popular wavelengths can go for less.