Non-Uniform Intensity in Projected Images

Hi Veronica,

If you have captured and attached the picture in the discription it would have been easy to understand.

Couple of things you need to try -

1) Check the aperture settings on the projection lense. Refer to user guide on adjusting the projection lense.

2) We found that the curved mirror setup in the optical module is mis aligned while shipment. There are two curved mirrors in the optical path which will bend the light from LEDs to the DMD mirror array. The mis-alignment could result in showing pinkish color tinge in the displayed white images. If this is what you are seeing then you can try contacting distrubutor where you purchased the kit. If not then i will send you the instructions.

Regards,

Sanjeev

Hi Sanjeev,

Here is one image showing the behavior described before. For this image, the projector was placed perpendicular to the projection plane.

Regarding the options,

1) The aperture lens we are using is 2.8 as suggested on page 11 of the user guide.

2) I think the curved mirror is OK since it is not showing a pinkish image. We had this problem with the first unit and it was replaced by Logic.

Regards,

Veronica

Sorry... I forgot to attach the image.

Thanks,

Veronica

Hi Veronica,

It looks like the light beam is out of focus when falling on the DMD. Two things could be possible suspects,  a) problem with one of the element in the optical path is misaligned b) it could be DMD seating on the adapter board is moved. Let me check with optical expert here to find what optical element has to be adjusted.

Regards,

Sanjeev

Hi Veronica,

I got some more details for you.

Even if the optics and DMD is aligned perfectly there will be 'some' roll-off. A little tweaking in the DMD position can move the brightes spot to the center but will not 100% get rid of the vignetting.

Couple of suggestion to mitigate this effect.

1) Reduce the LED current intensity a bit

2) Adjust the camera iris and/or projection lense until the roll-off effect is diminished.

Let me know if this is helpful to you.

Regards,

Sanjeev

Hi Sanjeev,

I made what you suggested and the problem is still there. The DMD array is smaller compare to the sensor for which the lens was built for. Then, I wonder why are we going to have vignetting? and how is this related to the deviation of the brightest area? If we need to project the same intensity on different pixels, how are we going to do this if the intensity levels have a spatial pattern?

Regards,

Veronica

Hi Veronica,

I received your further query. I will check  with our optical expert and ask about any recommendations if they have.

Regards,

Sanjeev

Hello Veronica,

You are correct that the projection lens is designed for a sensor (DX) that is larger than the DMD array.  There is no vignetting from the lens in the final image. 

The issue is not on the projection side, but on the illumination side.  The illumination is approximately shaped like the DMD with some overfill, but there is still 'some' rolloff (you could call this "illumination vignetting"). 

Regarding the image that you attached in your message above: 

It is difficult to tell from the image alone what the actual difference in measured intensity is from the center to the edge of your image.  If the illumination shows gross rolloff then one of the optical elements between the illumination module and the DMD are out of alignment.  However, it is very difficlut to elimate all rolloff.   

The effect of rolloff and how you can mitigate the effect depends greatly on the particluar application that you are targeting.

Fizix