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Diverging Optical Filters

  1. Apr 22, 2010 #1

    Is there a particular type of optical filter which is suited for use with diverging light? Most of the filters which I have encountered; dichroic, interference ... are suited to collimated light.

    I have an application where I would like to long pass filter a diverging beam of light between an objective and eyepiece.

  2. jcsd
  3. Apr 22, 2010 #2


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    Chemical filters (colored glass) are fine in diverging beams - it's only a problem for interference filters.
    Even then if you aren't too concerned about all the angles having exactly the same bandpass they will still work
  4. Apr 22, 2010 #3
    The problem I have is that I am trying to produce a low-cost fluorescence system and as such I am trying to filter the excitation wavelength (488nm +/-10nm) from the emission wavelength of 515nm.

    With such a tight band between exciatation and emission, the best filters, including the dichroic beam splitter, ideal for such a job rely on collimated light, but then that negates the low-cost aspect.

    Question is can I get enough information to do what I need with high background emission from the light which would not be fully attenuated by the long pass filter (chemical or otherwise).

    Last edited: Apr 22, 2010
  5. Apr 22, 2010 #4

    Andy Resnick

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    If you are willing to pay for a high-end filter set, I'm surprised you say it's too expensive to collimate the beam.

    Are you doing this using epi-illumination or trans-illumination?
  6. Apr 22, 2010 #5
    Did I?

    I am trying to make this low-cost.

    A DIN 60X objective (diverging) costs around £130, a 60X collimating objective costs around £1,300.

    Ideally I would like to create a epi-illumination set-up, but it looks like I will only be able to achieve trans-illumination because of the diverging beams and the lack of being able to use a beam splitter as required in the epi-illumination.

    Any suggestions greatly welcomed.

  7. Apr 22, 2010 #6

    Andy Resnick

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    I think so:

    Given the specs you posted, I estimate the three-filter set at around US$500, if you are using standard 25mm diameter filters and 'standard sets' (i.e. GFP, FITC). I regularly use Omega and Chroma- Chroma is a great company to work with.

    By contrast, a simple plano-convex lens will give sufficient collimation for $20, and add another $100 for the mount.

    But reading more of your post, I wonder if this is an imaging system or not- what is your application, exactly? There may indeed be a simple, inexpensive method.
  8. Aug 19, 2010 #7
    Actually, there are some filters with the function of with diverging light, it depens on your appliaction, and what effect do you wan to reach? could you tell details about your application?

    Last edited by a moderator: Apr 25, 2017
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