A Theory on Automatic Focus for Lasers

[IsaacT]

I have had ideas in the past on how to make an automatic focusing mechanism to go on some of the bulkier handhelds or laser guns. The idea would be to have a range finding laser which activates when you prime the laser....lets say a secondary button similar to a safety switch on a rifle. This range finder would send the data to a chip in the laser host or gun style host, which would compute the necessary focal distance for the lens based on data input by the user. So you would find out how far the lens is from the laser for a variety of distances, and then based on the trend line the chip/device could make a prediction for how far from the laser the lens would need to be to achieve focus for the distance input by the range finding laser.

Then the chip/device could send that information to a motor connected to a gear designed to turn the focus ring. The motor would be given the precise amount of turns needed to get the focus ring to the necessary length from the diode.

Here is a picture of what I mean:

What is more, if the range finding laser was left on while using the laser device, the computer could provide real time focus. So while you moved your laser back and forth it keeps the laser focused.

This is just an idea I have had for a while, but have nowhere near the expertise or skills to implement it so I figured I would share it and see what yall thought about it. I may draw a diagram later but I have work shortly and don't have time to do it now. but if this works and we can figure out an easy way to implement it into our hobbyist systems, then we could eliminate the need for manual focus, the finger burns would basically be unnecessary, and we would use less of our diode's life trying to get it "to the damn focal point".

Lemme know if you have any critiques about this idea or ideas about it.
Cheers,
Isaac

EDIT: an idea for the motors would be a similar program used inside DVD readers. They have motors that turn precise amounts so that the data can be read. Just a thought.

 

[RA_pierce]

Re: Possible AutoFocusing Mechanism?

Digital camera AF systems would be a good place to start.

Some potential problems:
1. Focus can only be achieved up to a limited distance.
2. It may actually take longer for the computer to calculate the focal point and for the motors to move the optics than it would take to manually focus.
3. Manual focus may be more accurate.

This is based on my experience with DSLRs and SLR lens AF.
Sometimes, especially when light is low, even my fastest lens will "hunt" for focus.
Manual focus is superior in some situations.

 

[IsaacT]

Edited my first post to show a diagram I made of it. Hopefully it should be easy for people to understand, I tried to spread everything out well enough. In response to RA pierce, I think Camera's go off of definition in the photo to Autofocus, whereas my method would be a result of inputting the concrete distance data from the ranging laser into an equation we figure out from collecting data about our lasers.

 

[Soulstorm]

Pangolin tried this, without feedback from the termination point, they shelved it from what I have heard, moving that focus lens is too slow. From memory they tried moving coils, like a loudspeaker. A top of the range 21" 500g paper cone sub, can do about 60Hz before crossover starts to kick in. Smaller speakers will go higher but with less displacement and less mass. Some diode display lasers modulate out to 50-100kHz in some cases, go figure. Only audio device I'm aware of that can touch that frequency is the diamond tweeter on a B&W nautilus, certainly not with enough movement to change a focus lens..

Perhaps useful for slower focusing, I'll be keeping an eye on this for an upcoming build, probably using GM20/VRAD to adjust divergence more simply, 3mm or 6mm. Nice idea!

 

[sinner]

Very nice wbs.. I like your theory!! Any chances you are going to do such thing in real time..

 

[Bionic-Badger]

One problem with relying on the rotation is that you're relying on the screws and such being perfectly calibrated with respect to focal length. Usually with auto-focus mechanisms there is some sort of feedback in a PID-type loop to converge on the focused state. In terms of camera auto-focus, this corresponds to maximizing the derivative of edges. For a laser, this might mean reducing the spot size to a minimum. You'd need to be able to zoom in on the spot for that to work.

Another thing you can do is just pass the calculations through a lens matrix calculation. This site had the clearest example that I could find. This document also covers how to apply this to camera lenses; check out the zoom lens calculations if you want to do variable focusing. Note that the online calculator on the first site isn't labeled correctly; it wants the angle in radians, not degrees. Then you just adjust for certain parameters to get the correct focal length at the correct distance.

 

[dogdrag]

Hi everyone. I didn't really know we're to put this so I decided to put it here I just want to give back to the community because I have learned a lot from the site it is a auto zero for a cnc laser here is a video of it being used and I will also post a code that goes in mach3
here is the code just copy and paste

If GetOemLed (825)=0 Then 'Check to see if the probe is already grounded or faulty
DoOEMButton (1010) 'zero the Z axis so the probe move will start from here
Code "G4 P5" ' this delay gives me time to get from computer to hold probe in place
code "G31 Z-2 F5"
While IsMoving()
Wend
Call SetDRO( 2, .001 )
code "G0 Z0.3 F40"
code "G31 Z0.0 F4"
While IsMoving()
Wend
Code "(Laser is now zeroed)" 'puts this message in the status bar
Else
Code "(Z-Plate is grounded, check connection and try again)" 'this goes in the status bar if aplicable
Exit Sub
End If

http://www.youtube.com/watch?v=y4EP9xnah2A

 

[chipdouglas]

I gave dave a while ago a camera mechanism with motors and stuff I got from a job site. You guys should ask him for pix and maybe you might be able to buy it from him.

 

[laserdog]

I have had ideas in the past on how to make an automatic focusing mechanism to go on some of the bulkier handhelds or laser guns. The idea would be to have a range finding laser which activates when you prime the laser....lets say a secondary button similar to a safety switch on a rifle. This range finder would send the data to a chip in the laser host or gun style host, which would compute the necessary focal distance for the lens based on data input by the user. So you would find out how far the lens is from the laser for a variety of distances, and then based on the trend line the chip/device could make a prediction for how far from the laser the lens would need to be to achieve focus for the distance input by the range finding laser.

Then the chip/device could send that information to a motor connected to a gear designed to turn the focus ring. The motor would be given the precise amount of turns needed to get the focus ring to the necessary length from the diode.

Here is a picture of what I mean:

What is more, if the range finding laser was left on while using the laser device, the computer could provide real time focus. So while you moved your laser back and forth it keeps the laser focused.

This is just an idea I have had for a while, but have nowhere near the expertise or skills to implement it so I figured I would share it and see what yall thought about it. I may draw a diagram later but I have work shortly and don't have time to do it now. but if this works and we can figure out an easy way to implement it into our hobbyist systems, then we could eliminate the need for manual focus, the finger burns would basically be unnecessary, and we would use less of our diode's life trying to get it "to the damn focal point".

Lemme know if you have any critiques about this idea or ideas about it.
Cheers,
Isaac

EDIT: an idea for the motors would be a similar program used inside DVD readers. They have motors that turn precise amounts so that the data can be read. Just a thought.

I have one idea. But please say, in what range of distances you plan use AF?.

 

[sinner]

I think just the clockwise and anti clockwise movement would be awesome to begin with.. so you can semi-automatically adjust the focus instead of sinking your heads into servo's and whatnot, start with the simplest ideas and go forward ..

 

[IsaacT]

@Laserdog: I was thinking the AutoFocus would be good to use for up to 10, maybe 15 feet. The program receiving the output from the range finding laser would have a clause in the programming so that if the distance was longer than 10 or 15 feet, or if the reading failed, that the gears would move the lens to a predetermined Infinity, which would be a fixed data point in the program.

@sinner: Yea, keeping it simple has begun to sink in, since I don't have the money to sink in to gears, Arduino boards, and range finding lasers. I thought about creating a manual focus mechanism that would be scaled up. It would be similar in appearance to the bolt action on a gun. By moving the bolt action back and forth(on a relatively larger scale than the focus), the lens would be moved small amounts. There would be marked points on the side of the bolt action similar to a ruler with known distance values. So if you placed the bolt part on that distance, the lens would be moved so that the focal length was that distance. Then, of course, the only expensive thing would be the range finding laser.

 

[laserdog]

My idea:
Instead laser distance detector use ultrasound HC SR04 Ultrasound Wave Detector Range Ultrasonic Sensor Distance Module | eBay. Its cheaper and:
•Voltage: DC5V;
•Static current: Less than 2mA;
•Output signal: Electric frequency signal, high level 5V, low level 0V;
•Sensor angle: Not more than 15 degrees;
•Detection distance: 2cm-450cm
•High precision: Up to 0.3cm
Take output and convert it to the standard signal, used in the models proportional systems, and use a servo for lens moving.
But how to do this signal converter???