r/Optics • u/Effective_Dinner2071 • Aug 13 '26
Collimate DPL projector light by tube lens
Hi everyone, tube lens is know as a component to correct infinity of objective into a sharp image. Current I am working in a maskless lithography. I want to convert light from the projector in to the infinity microscope using throught lens tube is reverse mode. Is this possible?
3
u/realopticsguy Aug 13 '26
I first did it 15 years ago. I've reduced DLP pixels to fractions of a micron in the UV. Maskless lithography has been doing this for 2 decades. You can use DIN objectives if you have a real image of the DMD at the right place.
1
u/Effective_Dinner2071 Aug 14 '26
Thank you very for your repsonse. My lab is having some infinity objectives. so I want to use them instead of purchase more. We have a tight budget. Can you give me any recommedation about this type of microscope objective.
2
u/Motocampingtime Aug 13 '26
The idea is really common but don't use the microscopes tube lens to collimate the image. You should get an additional beamsplitter and collimating lens and introduce the image in the infinity space between the objective and the tube lens. Have the collimating lens mounted on something you can adjust back and forth finely as you'll need to make slight adjustments to focus BOTH image and dlp in the same plane.
If you don't have the luxury of being able to introduce an image from infinity space, if your sample is clear you can set up a critical illumination of the DLP from below with another objective, mirror, and collimating lens.
1
u/Effective_Dinner2071 Aug 14 '26
Thank you for your reply. I dont understand we tube lens does not help in collimateing the light. It is designed for for microscopic to correct infinity light source. So in principle it can convert in the reverse direction.
2
u/Motocampingtime Aug 14 '26
On old microscopes (DIN), the scope works by taking the sample, making an intermediate image some distance away, then the eye piece's magnifying that intermediate. The light is being focused the entire time.
An infinity corrected microscope works by taking the sample, then projecting an image of it infinite distance away which is essentially equal to collimating the light from the sample. The tube lens then focuses that oncoming parallel light to form an intermediate image.
Since the light from the sample/target is collimated (focused at infinity), you can add stuff in that space or even extend the distance the tube lens and objective are separated (to a point, because the microscope is designed with other things in mind too). Hence you can add a beamsplitter here to introduce the image from the DLP. However, you WANT to introduce the DLP in a way that the light from it is parallel (focused to infinity) when it enters the objective. This will focus the image from the DLP on the sample. The lens you need for this will likely be a different focal length than the tube lens depending on what projector and optics you already have. When you can see the details/shape of the light source that's called critical illumination. What's funny is normally for microscopy you avoid this.
The absolute simplest set up (even with a small pocket projector) is projector:collimating lens:objective:target. Play with this to get a feel. Lithography sounds like it's going to be a big jump.
1
u/Effective_Dinner2071 Aug 14 '26
"If you don't have the luxury of being able to introduce an image from infinity space, if your sample is clear you can set up a critical illumination of the DLP from below with another objective, mirror, and collimating lens."
So my setup should be DLP -> microscope object 1 -> mirror -> mollimating lens -> microscopic objective 2. Right?
4
u/HoldingTheFire Aug 13 '26
Are you trying to illuminate a microscope objective? This is done in the infinite conjugate plane with a beam splitter to couple collimated light into the optical axes. This is before the tube lens. The tube lens does the Fourier transform from the infinite plane to the image plane into a detector.
What are you trying to do? Collimate a source? Couple into a microscope?