Attempting Rheinberg-- first steps

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gekko
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Attempting Rheinberg-- first steps

#1 Post by gekko » Tue Mar 03, 2015 1:18 am

At last I decided to venture into Rheinberg territory. My Nikon condenser does not allow easy access to its iris diaphragm to allow use of contrast enhancing filters, such as Rheinberg. I finally obtained a generic condenser that I modified to fit my microscope that now allows me to insert a filter through a slot below the iris diaphragm. This afternoon I made up a very rough and ready Rheinberg disk with a dark green center stop and a red outer ring. I also placed a piece of polarizing material over the center stop that, together with a 2nd polarizing filter allowed me to adjust the "darkness" of the center stop. Some time ago, Tony ('microgreen') posted a design of filter that used a polarizing filter for the center stop, but I no longer remember the name (of the originator) of the filter nor the exact construction. I hope Tony would read this and repost the information he had provided on the old forum. My initial attempt at Rheinberg was rather encouraging (at least to me), so I will probably try to construct a better-made filter with different colors and play around with that. For the initial test, I used the 8-form diatom test slide made by K.D. Kemp. I used the 10x objective. I'd be grateful for any comments and suggestions.

1. My first Rheinberg filter (very crudely made, I'm afraid)
Image

2. Test slide, brightfield
Image

3. Test slide, Rheinberg filter
Image
 

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Crater Eddie
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Re: Attempting Rheinberg-- first steps

#2 Post by Crater Eddie » Tue Mar 03, 2015 2:25 am

That is a very encouraging first result, I would say.
I would be thrilled to get something that good on my (yet to be made) first attempt.
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75RR
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Re: Attempting Rheinberg-- first steps

#3 Post by 75RR » Tue Mar 03, 2015 9:58 am

I would say that that is spot on. A successful condenser adaptation + filter.
You are right about swopping condensers, unfair to expect just one to do everything.
Do not forget to play around with oblique!
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Re: Attempting Rheinberg-- first steps

#4 Post by JimT » Tue Mar 03, 2015 1:32 pm

I think you just opened up a whole new area of observation and photography. Filters are lots of fun and if you don't like the result you just throw it away and do a different one. Good first results.

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Re: Attempting Rheinberg-- first steps

#5 Post by gekko » Tue Mar 03, 2015 1:33 pm

Many thanks to all for the encouraging comments.

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Re: Attempting Rheinberg-- first steps

#6 Post by gekko » Tue Mar 03, 2015 2:57 pm

Yes, the "new" modified condenser makes access to its front focal plane very easy through a slot on the side, so I can manually move any filter I put there to center it or off-center it, making experimentation with oblique and other filters easy.
I have found the post of Tony that I mentioned above on the "Arthur Strange VAC 2 variable contrast method" in a thread started by MicroMan2
[ viewtopic.php?f=5&t=57 ]
with excellent information contributed by several people. I'll see if I can successfully print the filters as discussed in that thread with my inkjet printer.

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Re: Attempting Rheinberg-- first steps

#7 Post by mrsonchus » Tue Mar 03, 2015 4:25 pm

Wow - what a great start! Really good result - you've gone and made me want to have another go at it too...
Thanks for the super post. :D
John B

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gekko
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Re: Attempting Rheinberg-- first steps

#8 Post by gekko » Tue Mar 03, 2015 9:32 pm

mrsonchus wrote:Wow - what a great start! Really good result ... Thanks for the super post. :D
Many thanks for your kind comments!
you've gone and made me want to have another go at it too..
That was the idea :D

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Re: Attempting Rheinberg-- first steps

#9 Post by carlh6902 » Wed Mar 04, 2015 2:31 am

Gekko-

What type of microscope/condenser did you use? I have a similar problem with my Olympus BH2, so I'm curious how you did this.

Carl
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Re: Attempting Rheinberg-- first steps

#10 Post by gekko » Wed Mar 04, 2015 11:48 am

Hi Carl,
I use a Nikon Optiphot microscope with Nikon condenser. The Nikon condensers of that era had the iris diaphragm well inside the condenser body, so using darkfield, Rheinberg, etc. filters effectively was not possible. At one time, someone was selling on Ebay an adapter that was supposed to plug into the bottom of a "regular" condenser (by "regular" I mean one that fits into a sleeve in the microscope substage) and that had the round dovetail at the bottom that slides into the Nikon substage. I bought one, and had an old Abbe generic "regular" condenser, but the adapter did not fit the condenser (which, I now realize was fortunate). So what I did was glue the adapter to the filter ring of the condenser; the space/gap between the filter ring and the body of the condenser formed a slot through which I could insert the Rheinberg filter. I did have to unscrew the top lens of the condenser slightly in order to get it to focus properly (in retrospect I think should have instead used a spacer ring between condenser and adapter to get the right focus). I will take a picture of the adapted condenser and post it here. I have checked on ebay, and I couldn't find the adapter offered anymore, but one can be made if one had a small lathe or access to one.

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Re: Attempting Rheinberg-- first steps

#11 Post by carlh6902 » Wed Mar 04, 2015 2:25 pm

Gekko-

This is good to hear, and please do post photos of the finished assembly. As it turns out, I bought one of these adapters when they were offered, hoping to do something similar one day. The BH2 uses the same condenser mounting, and can even use the Nikon condensers. FYI - that adapter seems to be designed to allow an Alphaphot condenser to mount onto the models that use the circular dovetail.

Carl
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Re: Attempting Rheinberg-- first steps

#12 Post by microgreen » Wed Mar 04, 2015 11:29 pm

Arthur Strange published his method in the 1980's

The stops are made from polarising material.

1/ A disc ,the diam of your filter holder is cut and a quadrant is cut out.
2/ A smaller disc is cut from the polar material then centred(accurately)on the disc and accurately crossed and fixed in place.(see photo)
You will need to make the centre stop a different size for each of your objectives. Only the centre stop should be seen in the back focal plane of the objective.

The stop is placed in the filter holder below the condenser and a second polariser is placed on the light source.
When either polariser is rotated contrast is increased until darkfield.

It also increases resolution with higher powers
http://i1289.photobucket.com/albums/b51 ... 6371ca.jpg
You can also achieve colour by placing a piece of hard clear plastic in the lightpathImage

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gekko
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Re: Attempting Rheinberg-- first steps

#13 Post by gekko » Wed Mar 04, 2015 11:35 pm

Tony. thank you very much for kindly repeating the details of your original post. With my generic condenser adapted to my microscope, now I can actually try it, and I hope others will also give it a try.

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Re: Attempting Rheinberg-- first steps

#14 Post by gekko » Thu Mar 05, 2015 12:09 am

carlh6902 wrote:Gekko-
This is good to hear, and please do post photos of the finished assembly. As it turns out, I bought one of these adapters when they were offered, hoping to do something similar one day. The BH2 uses the same condenser mounting, and can even use the Nikon condensers. FYI - that adapter seems to be designed to allow an Alphaphot condenser to mount onto the models that use the circular dovetail.
Carl
Carl, thank you for identifying the condenser for which the adapter was intended (I didn't know that). Here are the pictures I promised:

Image
Top view: condenser with the filter ring swung partially open. The adapter is glued to the underside of the filter ring.

Image
Side view. C, condenser body; F, filter tray; A, adapter with dovetail glued to bottom side of filter tray. I used a sliver felt pen to "paint" the edge of the filter ring and the lower edge of the condenser body proper in order to make it easy to see the slot between condenser and filter tray to allow easy insertion of darkfield stops, Rheinberg filters, etc.

Image
Filter tray swung open below the condenser. Adapter was glued to the filter tray using Elmer's Glue-All which has sufficient strength yet will allow removing the adapter without damage should the need arise.

Anyone duplicating this may want to first rest the condenser over the adapter and check that the condenser can be focused properly. Mine would have needed a thin spacer/shim/washer between the adapter the filter tray in order to raise the condenser a bit for proper focus. I had not done this, so I had to unscrew the top lens of the condenser slightly to obtain proper focus.
 

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