For fluorescence filters fitted into an Olympus cube should the arrows on the filter sides reflect the light direction through the cube, i.e. Ex arrow pointing into the cube and Em arrow pointing out, or should both arrows point into the cube? I have a Semrock guide which states the former while someone else I have just spoken to says that both filters should be fitted with arrows pointing in. Interestingly, the emitter filter I recently removed from a cube had the arrow pointing in. Which is correct?
It depends on who made the filter, Chroma and Semrock have different recommendations for orientation.
Chroma filter orientation
Semrock filter orientation
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OK, thanks. Without taking the filters out to look is it easy to distinguish between Chroma and Semrock filters? I think my cubes were built with filters from both.
I don’t think it would be easy to tell the filters apart without taking them out of the cubes. I can only tell them apart by seeing the label.
Without taking the filters out to look is it easy to distinguish between Chroma and Semrock filters?
Its not a foolproof method but filters (and dichroic but it’ll be harder to see in a cube) are made of a glass substrate coated on one face (sometimes they are coated on both faces and then you need to see the arrow). The coated face of the filter gets a different appearance when viewed at blazing angles. It looks almost like a mirror and one can only see the surface one is looking at. On the other hand, the other surface behaves more like regular glass. When looking through the other surface, one can see the coated surface beneath by looking at the edges. I know it doesn’t sound clear (and I’m sorry about it), so I’m attaching picture of a BrightLine filter from Semrock (447/60) below (see link from @Hazen_Babcock for correct orientation of Semrock filters).
This is the face that the arrow points at ( → | ). In the picture, I used an orange arrow to show the bottom edge of the back face of the filter. Also, notice how my upper finger (in the picture) is reflected twice on the surface. This is not the surface that has been coated. Therefore, light should not enter through this surface.
Below is the other face ( | → ). Notice how the double edge that I indicated with an orange arrow is not present here. I tried to take the picture under the same lighting conditions. Also, you can see there’s only a single reflection of my finger on the mirror surface. This is the face that should be oriented towards the light source.
Depending on your cube, you might be able to identify the filter orientation in this way. As I said, its not foolproof, but maybe it can help you.
Take care,
Omni