John,
Here are a few thoughts. First, try mounting a moving polarizer above your condenser and use your condenser in the transmitted light position. You would be able to use your fixed analyzer and then spin the polarizer to parallel or crossed position. This would be the simplest answer. Fashion some type of a holder for the polarizer and simply sit it on top of the condenser, knowing which direction the polarizer is oriented, you could quickly manually orient the filter for either position. Some microscopes come with empty, spare filter holders that fit between the light source and the condenser. Check to see if you have one, and then adapt your filter to the holder.
If you need to mount analyzers in your filter cubes, try the following: Do you have access to a light box? If so, put a polarizing filter on top of the box. Adhere it to the box with some tape by the edges so it will not shift. Put your filter cube with polarizer in it above the first polarizer, and orient it either to parallel or crossed position. Use a small drop of nail polish on a toothpick at an edge of the polarizer to “glue” it in place in the filter cube, then carefully screw the retaining ring into place once the glue has hardened. This is a trick I’ve seen with some older optics when someone needed to orient a filter or lens in an exact position. I don’t know how reasonable it is to expect 1 degree accuracy, but I’m willing to bet that if the filters stay put when you screw in the retaining rings, you’ll have your solution. The key, obviously, is to be careful with the glue so it doesn’t ruin the filters. Superglue would be too low in viscosity, and hot melt glue from a glue gun might not hold securely, and is flexible. If you have glass polarizers, the nail polish can be removed from the filters with acetone or non-toxic polish remover if necessary for repositioning. The nail polish dries slowly enough that you would have time to turn the polarizer in the holder if you don’t align it perfectly to start with.
Another possibility would be to go to a camera store and to purchase a polarizing filter mounted to fit on a 35mm camera lens. These can’t be too expensive. You could use this lens above your condenser in place of a rotatable analyzer. Whether these suggestions solve your problem or not, please post your answer so the rest of us can benefit. Thank you, John.
Ed Haller
Edward Haller, Lab Manager
Microscopy Core Labs
University of South Florida
College of Medicine
Tampa, FL 33612
813-974-0569
From: Confocal Microscopy List [[hidden email]] On Behalf Of John Oreopoulos
Sent: Thursday, June 05, 2008 2:51 PM
To: [hidden email]
Subject: How to align polarization filters in two filter cubes
Hello confocal listserver,
I have an unusual situation that I'm hoping someone out there might be able to advise me on. I would like to modify my lab's inverted Olympus IX70 microscope to have the ability to look at polarized light when illuminated in the transmission pathway. I want to polarize the white light that illuminates the sample, and then analyze the polarization of the image by examining the light that comes through the sample with another polarizer that can be oriented parallel and perpendicular to the direction of the polarizer in front of the light source.
We have DIC optics for the microscope - this means that I have a polarizer that can be fitted on top of the light source condenser, and I also have a fixed position analyzer that can slide in below the fluorescence filter cube turret. My problem is that the polarizer in the analyzer slider is fixed in a direction that is crossed to the polarizer in front of the light source. What I really want to do is to be able to rotate the the polarizer in the slider to the parallel direction as well. I know that Olympus and Leeds sells rotating analyzers that can slot into these positions on the microscope, but my supervisor does not have the funds to afford these right now. So I've come up with a slightly cheaper alternative solution.
We bought two 1" round film polarizers from Edmund optics (~20$ each). These are the exact same size as interference filters that normally get fitted into the fluorescence filter cubes which go in the rotating turret below the objective nosepiece on the inverted microscope. My plan was to take two empty fluorescence filter cubes and insert a polarizer in each - one oriented in the parallel direction and one in the perpendicular direction. Here is my problem: how can I orient and lock the position of the the two polarizers in the filter cubes such that they are aligned with their polarization axis directions correctly? Ideally, since I'm trying to be quantitative with the imaging, I'd like their alignment from their relative crossed position to be within 1 degree or less. When I screw them down with the retaining ring of the filter cube, they rotate slightly in the cube before they become locked. Also, I can't tell if I'm dropping them into the filter holder in the right position since their reference axis position is marked on the edge of the filters. Can anyone out there suggest a good method to overcome this problem? How do the microscope manufacturers align their polarizers in the sliders they sell for DIC imaging, etc?
Thank you in advance for any help!
John Oreopoulos, BSc,
PhD Candidate
University of Toronto
Institute For Biomaterials and Biomedical Engineering
Centre For Studies in Molecular Imaging
Tel: W:416-946-5022