Not enough light for Rheinberg filters

[janvangastel]

I have bought Rheinberg filters from ebay. Problem is, that the image stays dark because there's not enough light going through the filters. I use a 50W halogen lamp in my orthoplan. I could use a 100W lamp, but that will create too much heat I think, because even with 50W I can feel that the filters get warm. Is there a kind of heat absorbing filter I could use to prevent the heat from reaching the filters?

[Gasman]

I'm not familiar with the Orthoplan as I have a Laborlux S but I had to convert my scope to LED to save my desk from the mini supernova Halogen lamp!. Heat no longer a problem now. Not sure how you could use any heat absorbing filter without jeopardizing the scope
Steve

[MicroBob]

Hi Jan,
I think that 50W halogen should be more than enough for Rheinberg illumination which is basically bright field with medium intensity color filtering. Are you sure you have set up your microscope correctly and use all the available power?

IR filtering is possible but the filter would become hot quickly.

Bob

[Hobbyst46]

Is there a kind of heat absorbing filter I could use to prevent the heat from reaching the filters?

Yes, there are such filters. From Schott, for example, KG filters (KG1, KG2...KG5) that block IR. They are absorption filters, so must be thick to be effective. I would try a KG3 filter by guess; better yet, consult with Schott customer service, they are helpful.
They come in 1" circles or 1"x1" square (possibly other dimensions, don't know).

Yet, as Bob mentioned, they become very hot, so for best cooling, should not be in direct contact with other glass (or plastic) parts.

[janvangastel]

Are you sure you have set up your microscope correctly and use all the available power?

Yes, I am sure, I tried at least 10 times, with different colors and different objectives/magnifcations. Black field is no problem, but when I try Rheinberg the whole field becomes black. Or, when I don't close the iris far enough, not only the specimen but the whole field gets the color of the colored ring. I matched the center of the Rheinberg filter, where the light is blocked, with a black field filter of the same size. Maybe these filters are too thick and block too much light.

[janvangastel]

I just did a quick experiment and cut a round piece of the right size from a red sheet of thin plastic. I used it with a dark filter on top of it, to block the block the light of the background field and it worked very well: the background stayed black and the specimen became nicely red. So I suppose that proofs that the plastic filter I bought are too thick and block too much light.

[Gasman]

For Rheinberg filters I read that you have both field lens iris and condenser iris fully open or you can cut off the part that colours the specimen. Is the centre disc (the part that colours the background) too big or off centre?
Steve

[janvangastel]

No, the center disk in well centered and not too big.