Hi ! What is the focus range of LightCommander ? And the size of the projected image ? Thanks for any help !
Welcome to the TI DLP & MEMS E2E forum.
The LightCrafter light engine has a throw ratio of 1.66. That means that at any distance (d) from the lens, the ratio of the width (w) of the projected image will be
The focus range is from about 300 mm to infinity - though as the distance gets longer, and the image gets bigger, it also gets dimmer - as the square of the distance. The usable range depends on the ambient light, the nature of the surface (screen) and the brightness expectations of the user.
your answer was intended to be about the LightCommander and not the LightCrafter, as you referred, right?
The answer was for the DLP LightCrafter. Sorry for the confusion. I missed which kit was being asked about. My mistake. Also, my apologies for the delay answering. I was on travel, and then a national holiday in the US - Labor Day.
For the DLP LightCommander it is a different story. The LightCommander utilizes a standard Nikon SLR lens - F Mount. The kit as purchased comes with a Nikon 50mm f/1.8 lens. However, the user is free to attach any Nikon F-mount lens. For throw ratio, the same geometric rules apply as for field-of-view (FOV) with a camera. A shorter focal-length lens has a wider field of view, and a lower throw ratio (that is, the projected image is wider at the same distance) than a longer focal length lens. So, at a given distance from the DMD to the screen, a longer focal length lens produces a smaller projected image, and a shorter focal length lens produces a wider projected image.
Thank you for your answer!
Is there some test data about throw ratio and image offset of LightCommander with Nikon 50mm f/1.8 lens? It will be more helpful to us.
According to our optical expert the trow ratio depends on the focal length of the lens used, like, for a 50mm lens it is about 3.6 and a 20mm lens gives a throw ratio of 1.5.
so for the LightCommander with the Nikon 50mm f/1.8 lens we can say that its throw ratio is 3.6, right?
May I ask you how exactly is the throw ratio calculated. Should we take into considerations also the size of the DMD array?
In principle for DMD array you can apply same method of calculating lens specifications for a camera sensor. Only thing the light path is opposite to that of camera. Yes, the DMD array size is considered for calculating the throw ratio. I will request our optical expert to add more details to this thread.
A simple ray trace of the optics will show that the ratio of the lens focal length to the image width is congruent with the projected distance to projected image width (also known as the throw ratio).
Rather than using the DLP width for our calculations, we tend to use the DMD diagonal - DLP5500 diagonal is nominally 0.55 in. = 14mm.
For example: if the lens focal length is 50mm, and the DMD diagonal is 14mm, the throw ratio is 50/14=3.6. It will be seen that the projected image diagonal size will be the same ratio to the distance of the projected image.
For a 20mm projection lens, and 14mm DMD diagonal, the throw ratio is 20/14 = 1.4. Therefore a shorter focal length lens gives a wider projected image at a closer distance (and the inverse is also true - a longer focal length lens gives a longer projection distance for a given projected image diagonal.)
Thanks a lot to you both - Sanjeev and Pascal!
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