Today I have been making Rheinberg filters. Rheinberg fiters are a way of optically staining specimens, they were developed by Julius Rheinberg whose work was published in the Journal of the Royal Microscopical Society in August 1876. He was quite a clever chap. Inventing them was quite an achievement, making Rheinberg filters isn’t quite as tricky…..
Things you’ll need: Either some metal punches and a mallet to bash them with or some craft punches (the kind people use for card making) I prefer craft punches; a mat on which to bash things so you don’t ruin your floor or table; a pen that will write on plastic, an old filter, laminator pouches (gloss) and a laminating machine set on hot; scissors, black card or electrical tape, some coloured gel film – the kind they use for theatre lighting is good. I got a sample pack for a couple of quid. You can use other clear, brightly coloured plastics sheets. Use your imagination and poke around your “useful things” cupboard or drawer (I know you have one).
Stuff for making Rheinberg Filters
First, make some simple dark ground patch stops to help you determine what size your Rheinberg filter centre stops should be. Pop a laminator pouch through the laminating machine and you will have some nice sturdy plastic sheeting to start off with. Alternatively, just cut up some stiffish, clear plastic sheeting. You need to cut out circles of the clear plastic that will fit neatly into your condenser filter holder. My filter holder is 32mm diameter, I just draw around an old glass filter. You don’t need perfect circles, just make sure the disc won’t fall through the filter holder.
Now you have clear plastic discs on which you can put your dark ground patch stops. Use some black electrical insulation tape, or vinyl, or even a piece of black card. Punch out circles of various sizes using your punches and stick them in the centre of the clear disc. You centre them by eye. You should make a range of discs that look like this:
The sizes of the black central stops I made were:
A – 7.5 mm
B – 10 mm
C – 12 mm
D – 14 mm
E – 16 mm
F – 18 mm
G – 20mm
Now you need to decide which stops work best with each objective. Put a slide on your microscope. Something suitable for dark ground like diatoms, a stained section won’t work.
Open the condenser iris and the field iris and rack up the condenser as high as it will go. Place each of the patch stops in the filter holder in turn and record which patch stops produce the best dark ground with each objective. You’ll end up with a chart that looks something like mine:-
From this I can see that the best size patch stop to make will be E (16 mm). It should cover all bases, although I’d probably make one of 14 mm as well, just to be on the safe side.
Now I know what size patch stop to make it’s on to the fun part….
Making the Rheinberg filters:
The central stop will determine what colour background your image will have. The outer ring will determine what colour your specimen will be “stained”. A blue central stop with an orange ring around it will produce a blue back ground with orange specimens. The supergel samples I have tell you what transmittance the filters have. 10% transmittance or less works best for the stops (that’s very dark, so dark you can’t read text through the filter). Higher light transmittance is better for the outer rings.
Cut out some central stops of coloured film using your punches. I determined that 16 mm stops would work best with my Vickers objectives so that’s the size I punched out.
Cut out some coloured circles the size of your filter holder (32 mm for me) and then punch out the centres so that you will be able to place the coloured stops in the hole that’s left. The central stops and holes need to be cut out cleanly. There shouldn’t be any gap between the central stop and the outer ring/annulus when they are put together.
Annular rings and stops
Now carefully place your rings and stops into a laminator pouch and laminate them. Cut them out with a pair of scissors or a punch (do not use your spouse’s dressmaking scissors for this). You’re done. You have Rheinberg filters.
If you use a coloured stop with a clear outer ring you will get a coloured back ground and an unstained specimen. Sometimes it looks better than when you use a stop + ring. If you laminate the rings and stops separately you can try out lots of different colour combinations. A black centre stop with a coloured ring can also look very pretty.
Here are some images I took of Polycystina on my beloved old Vickers microsc0pe using my home made Rheinberg filters, all using a 20x objective. The photographs don’t do the images you see down the microscope justice. They look excellent viewed through the microscope . As I’ve mentioned before, I’m not really very good with cameras yet!
Pink central stop, orange annulus
Blue central stop, pink annular ring
Blue/green central stop, yellow annular ring
Dark ground – black centre stop
You can see that the resolution is somewhat better with the dark ground than with the coloured stops and some colour combinations work better than others but it’s great fun to experiment with. The choice of colour combinations is almost unlimited. I shall certainly be making more and trying them on some of my other microscopes.
Have fun with your Rheinberg filters!