Parallax Laser Range Finder (#28044). Laser Distance Measurement Sensor Product Docu: Fill & Download for Free

I wouldn't suggest an ultrasonic sensor for this application. As you mentioned, the catch is that you are measuring a very long range. Sound waves would disperse over that distance and therefore most ultrasonic sensors are only designed to measure distances up to about 20 feet (and you're looking for 250 - 300 feet).Parallax makes a Laser Range Finder for Arduino, but it only detects objects up to 8 feet away and is considerably more expensive than an ultrasonic sensor that would detect objects up to the same distance. The advantage of the laser would the the ability to pinpoint and measure distance instead of accepting a reflection off the nearest object. Laser Range FinderThere are very expensive laser range finders that would give you the distance you need, but they may be way too expensive for your project, such as the sensors used in these instruments: TruPulse Laser RangefinderYou can also try these laser range sensors (OptoNCDT ILR series), although I am not sure what the pricing is: Compact and fast distance sensors (with reflector)One of the best articles I've found discussing your options for a rangefinder is here: phoenixgarage.org || crazy ideas, irrational projectsBasically it seems like your only/best options may be to try the OptoNCDT ILR series sensors or to make a homemade distance/range sensor based on using parallax method and processing images. The sensors in the articles described only measure distances up to a few feet away but if you build a large enough sensor perhaps you can measure the distances you want to with a reasonable amount of effort.

The easiest to imagine are the ones on capital ships because they are big. A range finder has two lenses that point at the target. The distance between the lenses is a known constant (forming the base of a long, isosceles triangle.) by having the base and the angles at each end of the base where the lenses are, you can calculate the other sides of the triangle. Strictly speaking, you would bisect the opposite angle to calculate the exact range (distance from where lines of sight from the lenses cross to base line between the two lenses.) the farther apart you can position the lenses ( usually the bigger the instrument) the more accurate the calculation. Difference in the angle from two different points to the same (distant) object is called parallax. Historical reference: when Galileo insisted the Sun was the center of the universe he had to renounce his position to avoid being burned as a heretic, and he did so reluctantly because real proof of his theory lay in showing parallax in the position of stars measured from earth six months apart when Earth was on opposite side of its orbit. The parallax was there but they had no concept of how far away the stars were and had no instruments precise enough to measure such infinitesimal angles.added: yes there was possibility of estimating range with lenses so that when the target was focused the lens setting will reveal range, but l am uncertain of accuracy here and if it was binocular, probably worked similar to above explanation. Not as accurate as the lenses were close together. Other contributor correct that radar replaced optical range finders and now thy use lasers. Interestingly, an item placed on the moon by our astronauts is a reflector for laser beams to track distance to the moon, which varies.

Ehmm. Can you make a photo from the Sun? If so your camera can zoom 150 million kilometer. Hence the zoom might not be the proof you are looking for.How do we know how far something is? Would you know? How for instance did battleships in the past figure out what angle to shoot some large gun?And the answer is to use a little bit of geometry and a lot of braverySee this poor dude has to look at some large tube. It has some mirrors in it that allow adjusting. Once the bottom of a ship lines up with the top of the ship as seen from this rangefinder than the tiny angle this mirror makes gives us a triangle with a known size (between the two mirrors) and two angles. This then gives us the exact distance to the enemy.Obvious this does not work with objects much further away. The difference in angle would be almost imperceptible from 90 degrees. But what you can do is the same using two cities. Say you watch the moon from both cities and you both take a measurement of the angle exactly at the same moment. Then you need to do a few corrections: the earth is bend between the two cities. There is also some stuff to calculate as to exactly what the angle is you looked at… but you get the point.With current astronomical parallax finders they can accurate measure distances up to about 100 light year.Already in 16th century did some very smart dudes figure out the distance to the moon, and that is currently constantly measured by a laser range finder.Of course you are free to live in your own reality, you are also free to ask why historic figures came to certain conclusions. You are however not free to your own facts. It is important to realize that your future depends very very strongly on how your boss perceives you. If you are into flat earth, Elvis is still alive, Bigfoot has been spotted, UFOs are from Mars… those things will keep you at McDonald's flipping burgers.