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Designing a digital eyepiece camera

  1. May 31, 2011 #1
    I have an optical design question - hopefully this is the right forum in which to ask. It is "engineer", but it's really optical engineering...

    I am wondering if someone can help me out here with a few questions. I do volunteer work at an eye hospital in India, and we would like to take photos of patient’s eyes, as viewed through a “slit lamp” (the device doctors use when you get an eye exam).

    The slit lamp is essentially a microscope. There are optics within the slit lamp, and then there is an eyepiece that you look through to view an enlarged image of the eye. Basically, I assume it is more or less “the same” as a microscope, a pair of binoculars, or a telescope, but with much less power.

    We have already developed a method of placing a small digital camera right behind the eyepiece, and we can capture excellent images this way. We have been doing this for years.

    In looking around for a better way to capture images, we found a device that is designed to drop into a microscope, replacing the eyepiece, record the image on a digital sensor, and display the image on a computer when connected to a USB port.

    Here is a link to one of those devices:

    The device works perfectly, but shows a greatly enlarged image of a small part of the eye. This is good for a microscope, but far too powerful for a slit lamp, where we want to see a lot more of the eye, not just a tiny part of it.

    We would like to make a device like this, optically designed for our needs. My problem is that while I do know and understand “camera lenses”, I don’t know where to even start on this project.

    (Either I need a device that shows more of the subject on the small sensor in the DinoEye, or perhaps the lens is fine, and I just need a larger sensor that covers more area?)

    Can someone please help me with the following:

    a) What is the difference between an “eyepiece lens” and a normal lens that one might use in front of film or a digital sensor? If there is no difference, can I just put my own lens into the microscope (slit lamp) and put a digital sensor behind it?

    b) Are there any good sources in the USA or India where I can purchase a lens for this purpose? I know about Edmund Scientific Company, but I wasn’t able to find anything that might work (possibly because I know so little about what I’m looking for).

    c) Are there any good sources for a sensor with USB electronics, that I can mount my own lens to?

    If I understood more about how an eyepiece works, I would have a better idea of what I need to find, but I think it is very different from a “camera lens”; a lens for a camera is fully self-contained, and the only thing between the subject and the film/sensor. With a microscope, there already are optics in the system ahead of the eyepiece. Maybe someone here can point me in the right direction to find the information I need? Thanks in advance!!

    (I have spent some time trying to understand what’s going on. The best resource I have found to date is http://www.birdwatching.com/optics/how_binoculars_work.html and I did take two Nikon camera lenses, as instructed, and sure enough, they did work exactly like a telescope/microscope, enlarging what I was looking at. I used a 200mm “objective” lens and a 50 mm “eyepiece lens”. What I need to do now, is replace the “eyepiece lens” with an appropriate lens and a digital sensor for capturing the image. That is the lens that I need to understand, and to pick one that has a large enough “field of view” to see everything that a doctor might see when looking through the eyepiece of a slit lamp.)

    Observations so far:
    1 - when using a 50mm lens as the Objective lens, and a 200mm lens as the eyepiece, the apparent size of things in the image are greatly reduced.

    2 - when using the 200mm lens as the objective lens, and a 50mm lens as the eyepiece, I end up with something that seems like "2x power binoculars"; everything seems to be twice as large as looking directly at the object.

    3 - when using a 200mm lens as the objective lens, and a 20mm lens as the eyepiece, I get something that seems like "6x power binoculars", with a much larger image size. (This is the opposite of what I expected!)
  2. jcsd
  3. Jun 3, 2011 #2
    Apparently this was not a good place to ask the above questions. Can anyone suggest a better place?
  4. Jun 8, 2011 #3


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    Science Advisor

    Welcome to PhysicsForums!

    The very basic information on an eyepiece:

    That said, how are you looking to improve the setup? Just with a camera that can connect to USB or without having to strap it on?

    Most (microscope) eyepieces have a magnification etched on it--any chance yours does as well? If so, you can probably find an eyepiece adapter with the same magnification. Barring that, perhaps a non-magnifying microscope coupler would suffice for your existing camera (or another one with USB output)?
    http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productid=2416 [Broken]

    EDIT: Oops, that's just the adapter rings! From Anchor Optics (a division of Edmund):
    http://www.anchoroptics.com/catalog/product.cfm?id=214&s=p&d=d [Broken]
    Last edited by a moderator: May 5, 2017
  5. Apr 2, 2012 #4
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