Filters and their challenges

A project log for A DIY Imaging Fluorometer

Is it possible to build a precise Fluorescence Imaging Device at home?

MaykeMayke 09/26/2020 at 12:050 Comments

As you can see above, the curves of the Longpass filters do not match, and that's what happens when you buy cheap filters :)

Ideally, the blue filter should have a steep curve down the 700nm, while the orange one should have a steep curve upwards the 700nm, meaning that the blue let's light below 700nm but blocks anything beyond it, while the orange blocks anything below 700nm while letting through anything above. 

The orange filter goes onto the camera lens, below a picture of a filter from MIdOpt, and the curve of the filter used in this project:

Usually, the steeper the curve the more expensive your filter is. I have added the red LED emission curve (in red) for you to see that the blue Longpass filter should cover it, which means that should allow most of it, which is not the case. 

I have requested some quotations from Chinese manufacturers as a filter 76X76mm in size would cost a fortune in the UK or the USA. It is not that the Chinese will give it for free, but we can expect a 50% reduction in price, probably at the expense of some quality.