Making microscope filters with the Lee colour MAGIC complementary filter set.

 

By Ian Walker  UK.

 

Introduction.

 

For some time I have been using a simple colour quadrant filter for the microscope made from a cheap pair of red and blue 3D glasses, this has served me well giving good colour saturation when needed but I am always on the look out for new colours to test. On occasion I go 'down town' and look in the stationery shops for suitable material to make up new filters and although the shops seem to sell just about everything else good quality colour sheet doesn't seem to be on the menu. Having used SpeedGraphic [UK] for buying several camera accessories in the past I thought I would try the Lee Filters complementary pack designed specifically for photographic use, these high quality polyester sheets come in a variety of colours and conveniently are supplied all in one package. First impressions on arrival were very promising, the filters come in a well made plastic wallet and within this the stout cardboard folder has an excellent guide printed in colour with graphs showing transmitted light characteristics of each filter, some explanatory notes, plus a table showing the colour code and name together with common use of each filter.

Also available in the colour magic range by Lee as individual products are Studio Plus, Studio, Saturates, Tints, Original, Arc correction etc giving a wide choice of colours for different applications. In the past I have tried a number of different coloured plastic material normally coming as part of packaging for some product or other and always found that once high intensity light was shone through them from the microscope the colour became washed out or the plastic was too flimsy to support itself properly. Lee filters being designed for photographic purposes are made from good grade polyester and provide saturated colours under high luminance conditions, however using the less saturated colours supplied like [035] light pink or [007] pale yellow can give equally satisfying subtler shades.

The information on the complementary pack states it is "an educational pack of filters selected to be used as practical introduction to the theory of light filtration, colour addition and colour subtraction" so pretty well ideal for experimentation with a microscope! Each sheet is approximately 30cm by 25cm [12" by 10"] and protective paper comes with each colour to prevent scratching when packed together. I recommend cutting the sheets in two as soon as you get them to make them more manageable to work on.

 

Lee Filters, the complementary pack costs 13.60 inc VAT.

 All the colours shown.

 

 No.

     Name.

 

 

164

      Flame Red

124

      Dark green

119

      Dark Blue

176

      Loving Amber

174

      Dark Steel Blue

138

      Pale Green

101

      Yellow

115

      Peacock Blue

128

      Bright Pink

007

      Pale Yellow

117

      Steel Blue

035

      Light Pink

Part of the table from the Lee complementary pack showing the names.

 

Work in progress.

A cutting mat, circular cutter [compass cutter] and a few drawing tools and good results can be obtained. To allow accurate cutting of the segments with a sharp modelling knife I print out a 1:1 paper overlay with the correct number of sectors, this can be made from a CAD package or drawn manually with a compass or marked out with dividers, if you are making a colour wheel with just quadrants it is reasonably easy to judge the sectors by eye but I still prefer to use an overlay.

 

 Typical colour wheels.

 

Using the circular cutter to do most of the work you can make any number of combinations of colour filters for the microscope including Rheinberg although I haven't made any of these in the 'classic' centre and outer colours matched to each objective since I rarely like the effect without dark-field or polarizing combinations. I cut the disk first and then use the paper overlay with desired number of segments already printed out to accurately cut the disk making sure the pieces will fit together without gaps. I put the segments in the order I wish and then punch out with a paper punch from double sided Sellotape the centre spot. This is applied to both sides to provide good support to the centre point and after peeling off the upper protective layer of the double sided tape apply a black card spot also punched out from the paper punch as shown above. The outer card rims have already been cut by this time and carefully applied to the outer perimeter of the filter with a glue stick. Although I have made colour wheels here there is literally no end of combinations including a series of rainbow colours in the form of a strip of each colour side by side etc, anything goes!

Microscopes with slider systems.

The Zeiss Axiostar along with several other modern stands uses a slider for polarizing or dark-field applications; this is one of the main reasons I chose it since it allows many creative possibilities with a polarizer setup at any angle on the lamp housing I can use one of these filters with or without a dark-field stop [these are bigger than the centre fixing spot shown above] on a home made perspex slider specially designed to incorporate the colour filters. The filters are rarely used centrally I use them offset with part of the filter in the light path and of course with each objective different amounts of colour can be seen, the filter often interacts with the polarizer to give darker or lighter hues. Typically using the top right colour wheel I would have partially crossed polars, a little oblique from the dark-field stop beneath the filter [simple thin card stop] and slowly move the wheel in and out and around to get any combination of cross-over points of colours for example the transition from light- to-dark blue could  provide a graduated blue for a nice background for say a marine slide preparation. Subtlety can be the key here, not too much colour variation...however for crystal slides or similar almost anything goes so this is where the upper left colour wheel comes into play with primary and complementary red-green and blue-yellow giving rich colours.

Microscopes with swing-in circular filter tray.

Provided you accurately measure the diameter of your LOMO or other older microscopes that use a swing in circular filter tray beneath the condenser there is no reason you cannot get good creative results from these colour wheels. In this case I would place the colour segments on a clear glass or similar disk and just glue the outer edges leaving out the fixing spot in the centre, also consider off-setting the centre point of one of your colour wheels slightly so when you turn the wheel around different amounts of each colour may be active, of course you can also use the wheels with a card dark-field stop beneath if your tray is deep enough to take both without hitting the bottom of the condenser. If you make the filters a slightly loose fit in the filter tray a nudge with your finger tip on the bottom of the filter should be enough to move it around a little at a time for different effect. All in all then a great set of filters capable of providing top quality results on the microscope.

 

Conclusion.

High quality filter set at modest cost giving enough material to work with for a lifetime.

 

Click here for details of the Lee Filter range supplied by one of the UK distributors, SpeedGraphic, the information is in pdf format with prices. Provided items are in stock I have found SpeedGraphic to offer an excellent service with fast shipping, typically next day or day after delivery.

 

the end.

Comments to the author, Ian Walker, are welcomed.

 

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Published in the September 2005 edition of Micscape.

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