I have a NRC 910 Spatial Filter and sometimes find it difficult to align. It was cheaper than the more typical 3-axis models which I was used to working with at NY Holographic Labs (many, many moons ago). I have an Edmunds 20/0.40 objective and a 15 micron Melles Griot pinhole in it now. I have a 25 micron MG pinhole and a few home made ones as well as a variety of objective lenses.
What would be the best combination? Oh, I'm using a SP 10mw HeNe But not sure about the beam diameter.
Newport 910 Spatial Filter
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Dinesh
Newport 910 Spatial Filter
Your 15u should be fine. One thing that's important is to make sure the beam is going right down the axis of the objective. Sometimes it seems to be so, but may be slightly off. To check this, have an almost all-the-way closed iris (or a piece of black paper with a tiny hole to allow the beam through) behind the objective - the end where the beam goes in. Now look at the back reflection from the objective. It should surround the hole in the iris (or the black piece of paper). If it's off, the objective is not properly centred.
If the beam is properly centred, place a mirror in front of the objective while you're pinholing so that you can see the reflection of the front of the pinhole in the mirror. This way, as the pinhole comes in, the light from the objective will become more and more visible.
If the beam is properly centred, place a mirror in front of the objective while you're pinholing so that you can see the reflection of the front of the pinhole in the mirror. This way, as the pinhole comes in, the light from the objective will become more and more visible.
Newport 910 Spatial Filter
I can see the bumper sticker .... "I'd rather be pinholing!" 