Designing a digital eyepiece camera

In summary, someone is looking for a way to improve the image quality when taking photos of patient's eyes using a slit lamp, and is wondering if there are any good sources for a lens and sensor in the USA or India.
  • #1
mikemyers
3
0
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...
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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:
http://www.aunet.com.au/dinoeye_am423.htm

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!)
 
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  • #2
Apparently this was not a good place to ask the above questions. Can anyone suggest a better place?
 
  • #3
Welcome to PhysicsForums!

The very basic information on an eyepiece:
http://en.wikipedia.org/wiki/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

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
 
Last edited by a moderator:
  • #4
Thanks for the help - I've been working on this for a long time, and the discussions, with a short movie of what we built, can be found here:

http://www.sgrid.com/forum/forumdisplay.php?37-Slit-Lamp-Camera-Design

Maybe that's a better place to continue this discussion. If anyone is interested, please join us there.
 
  • #5



Thank you for bringing this optical design question to the forum. As an optical engineer, I may be able to provide some insight and guidance on your project.

Firstly, the eyepiece lens in a microscope is designed to magnify the image formed by the objective lens. It typically has a shorter focal length than a standard camera lens, as it is meant to be used with a shorter distance between the lens and the image plane (the eyepiece). This is known as the eyepiece distance, and it is typically around 10-12mm for microscopes. In contrast, camera lenses are typically designed to work with a larger distance between the lens and image plane (known as the focal length), which can range from a few millimeters to several centimeters.

In order to design a digital eyepiece camera for your slit lamp, you will need to consider the eyepiece distance and the magnification of the existing eyepiece. You can achieve a larger field of view by using a shorter focal length lens for your eyepiece, but this may also decrease the magnification. Alternatively, you can use a larger sensor to capture more of the image, but this may require a custom sensor or cropping the image.

As for sources for lenses and sensors, there are many companies that specialize in optical components and systems, such as Thorlabs, Edmund Optics, and Newport. You may also want to consult with an optical design expert or company to help you with the design and sourcing of components.

In terms of your observations, it is important to note that the magnification of a lens is determined by the ratio of the focal lengths of the objective and eyepiece lenses. So, using a 200mm lens as the objective and a 20mm lens as the eyepiece will result in a higher magnification than using a 200mm lens as the objective and a 50mm lens as the eyepiece. This is why you observed a larger image with the 20mm eyepiece.

I hope this information helps guide you in your project. Optical design can be complex, so don't hesitate to seek out additional resources or consult with an expert if needed. Good luck with your digital eyepiece camera!
 

Related to Designing a digital eyepiece camera

1. What is a digital eyepiece camera?

A digital eyepiece camera is a device that can be attached to a microscope or telescope to capture digital images or videos of the magnified view. It is an alternative to traditional eyepieces, allowing for easier sharing and analysis of images.

2. What are the benefits of using a digital eyepiece camera?

Using a digital eyepiece camera eliminates the need for manual observation and sketching of images. It also allows for easier sharing and storage of images and videos, as well as the ability to enhance and edit the captured content.

3. How do I choose the right digital eyepiece camera for my needs?

When choosing a digital eyepiece camera, consider the type of microscope or telescope it will be attached to, the resolution and magnification capabilities, and any additional features such as image editing software. It is also important to read reviews and compare different models to find the best fit for your specific needs.

4. Is it possible to connect a digital eyepiece camera to a smartphone or computer?

Yes, many digital eyepiece cameras come with adapters or software that allow for connection to smartphones or computers. This allows for easier sharing and storage of images and videos.

5. Can a digital eyepiece camera be used for professional purposes?

Yes, digital eyepiece cameras can be used for professional purposes such as research, education, and medical imaging. However, it is important to choose a high-quality camera with the necessary resolution and features for your specific needs.

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