blueeyedpop wrote: Hi Mike,
You gave me every bit of the information that I needed. Now to see if I an make the phototransistors sensitive enough to do any thing useful with it! I have LOTS of polaroid adjustable lens setups lying around from hacking the SONARs out of them, now I've got a good use for them.
have fun, DLC
: Hi Dennis,
: Let's cover some abbreviations first. ( I use these at work, though optics : texts use different. )
: EFL=effictive focal length : FOV=field of view : DOF=depth of field : f#
: The formula to determine the FOV is 2*ATAN(1/2 sensor surface length/EFL)
: So imagine you have a 35mm EFL single element ( no need for anything more : complicated ) : SQRT(1.5^2+2.5^)=2.9=29 mm ( the diagonal of the sensor array)
: 2*ATAN((29/2)/53)=45 degree field of view.
: ---- : f# is used to determine DOF
: Since your sensing elements are so large, we can almost ignore this, except : to say that
: f#=EFL/diameter. : Let us assume a 25mm diameter lens element. It will have an f# of 35/25 or : 1.4 : The larger the f#, the more depth of field we will have, and the less light : gathering power we will have.
: The typical progression of f# is : 1.4 : 2 : 2.8 : 4 : 5.6 : 8 : 11 : 16 : 22 : 32 : 45 : 64
: This is what you will see on the side of an SLR camera.
: Every step is halfing the intensity of the light, but increasing your depth : of field. : A 10 mm diameter lens will give you a value of f3.5, or less than 1/4 the : light gathering capability : (this would also apply to pinhole lenses)
: ----
: A lens will focus at infinity when it is 1 focal length from the imager's : surface. Moving it further out will focus on closer objects. Take 5 leds : into a darkened room, arrange them in a recognizable pattern. make a frame : with scotch tape(frosted) and hold the lens at some distance away from the : scotch tape. At some point, you will be able to observe the leds' image on : the scotch tape. I would even sugest making a mask that looked like your : sensor. print clear dots on frosted laser transparency film, and observe.
: If you have a digital camera, you can take pictures of this image to : simulate what is going on with your sensors.
: --- : I would use the cheapest optics you can get your hands on. depending on the : sensitivity, I would even consider a pinhole lens. Take some brass shim : stock, and drill a 1/16th inch diameter hole in it. You can use the above : calculations to determine the EFL of the lens based on its distance from the : subject, and its diameter.
: Mike
: > I've built up a "vision" system that is pretty low cost. A series of : > opto-transistors in a 5x6 array that I'm trying to get to work as a : > cheap vision board. I've run up hard against trying to match a lens : > to the thing. The array is about 2.5cm by 1.5cm. Not small nor is it : > of great resolution, but I'm hoping that it'll work as a motion sensor : > when all is said and done. : > Now my problem. I need to put a lens on it to give me a reasonable : > field of view, but I've no idea how to figure out the proper lens : > type or focal length to mount a lens. Heck, I'm not even sure what : > diameter or strength to make the lens. : >
: > If anyone has any ideas, suggestions or solutions I'd love to hear : > them. : >
: > thanks, : > DLC : >
: > -- : >
: ============================================================================ : > * Dennis Clark snipped-for-privacy@frii.com
formatting link
: * : > * "Programming and Customizing the OOPic Microcontroller" Mcgraw-Hill 2003 : * : >
: ============================================================================