So, I'm still working on the aspheric from hell, SST-90 with the big aspheric lens. I am finally getting around to setting the final lens to led distance. I thought, at the beginning, I would just set it so the lens showed the square die, focused to where you can see the definition of the die, (lines), but I am finding that doesn't give the highest lux. If I set the assembly in a vise and use a lux meter, (at one meter), I find that the highest lux measurement is when the die is just defocused a little. I also find that the highest lux at 5 meters is a different lens to die distance than at one meter. I didn't think aspherics worked that way, but now I am concerned that to go for 2 or 3 miles, I would have to focus that lens at that distance! Is that true, or am I missing something here? Is there a set distance that I should set it up at?
The lens is this one:
Edmund AX32345 Grade 1 LENS PCX 95MM DIA X 166MM FL
Any thoughts from the guys who know, would be a help here.
What you’re doing is trying to converge the beam to get the highest lux at a given distance.
To get the highest reading at 2-3 miles you’d have to focus the lens to that distance. If you want a truly collimated beam you can try point the light in the sky at night and use the particulates to judge the convergence.
What you want to achieve is a Collimated beam (in other words, converging at infinity or close to that) for maximum throw at very long range. The aim is to get as much light downrange as far as possible, checking this at close range is not useful.
Getting the highest lux reading at 1 meter is irrelevant when that setup results in a massively reduced lux (and as a result throw/candela) at long range.
This also applies for maximizing throw with reflector based lights, I’ve seen people obsess about getting the absolute maximum lux readings at 3 or less meters and actually completely disregard the longer range results where proper focus really matters.
Ideally yes, putting a lux meter at a large distance like that and tweaking the lens would be the way to absolutely maximize the throw of any light. Hardly practical though
I would suggest getting a focused die image at a point at least 10 meters away and using that as your working distance, then once that is roughed in do some extra tweaking at even larger distances to fine tune the final focal length.
That said I’m not sure you’ll see massive differences is total throw figures as long as you get the focus more or less in the right zone.
It’s very similar to focusing a manual camera lens. Close up focus is very critical and a lens will have very accurate distance markings to get the target exactly in focus at ranges below 1 meter. After a certain distance the markings become very vague and ultimately result in a single setting called infinity, where basically everything a certain distance away from the camera will be deemed more or less in focus. The only difference is most camera lenses won’t let you focus the lens past infinity!
Mind that -in case the luxmeter sensor is smaller than the die image- the luxreading is not the same over the die image, there is an area out of the middle in the direction of the bond wires where the brightness is a bit higher.
I would think you could point it skyward and focus the beam culmination point at the beam cut-off (limit where the light ends). On a dark clear night, you can see all the details of the beam and any flaws that might hinder throw. This method works well for my dedomed throwers and remote focusable searchlight.
I disagree. The convergance point (depending on focus and lens etc…) can range from a few feet to a few metres in front of the lens. At that point the image is inverted, upside down and left to right. From there the light image gets larger until it is ‘focused’. That is why the die image is much larger than the lens emitting it. You will not get true colimation (the closest to that is a laser), and the convergance point is not the ‘focal’ point (or the image would be smaller than the lens).
why not focusing it with the help of a colleague? give him the luxmeter and let him tell you via radio the readings, standing in front of each other in those huge industrial units you seem to work in (of course, if you have some spare time)
I don’t know the accuracy of those meters at those distances, I’m probably writing nonsense
Yep you’re absolutely right, that sentence doesn’t make a lot of sense.
I just wanted to point out that that the important metric of whether the lens is in “focus” has everything to do with what goes on at long range. Measuring anything up close is useless precisely because of beam crossover and all that stuff which can throw you off.
Stick the lux meter far enough away to begin with (>10meters), and dial in the rough focal length until the die is in sharp focus and the numbers stop getting bigger.
Then repeat if possible at a much longer range to get it just right, dialing in focus to get a sharp die image at the shortish range like 10 meters I suspect will limit the maximum throw somewhat. I haven’t measured the actual variation yet but you mentioned your Deft-x for example was not showing a focused die image at those kind of short ranges so they seem to have optimized the focus for the longer distances on a light like that. Makes sense.
Aiming the light up into the sky is a decent way to rough it in but I wouldn’t use that to try and maximize throw, a meter placed far away is going to be the way to go if absolute numbers are important.
Nah, that actually sounds like the ideal way to do this. Although having a way of smoothly and very finely adjusting the positioning of the lens will probably be the trickiest hurdle. Unless you have a host with a decent threaded section that allows fine adjustment.
As far as adjusting the lens for focus at different distances, there will be more adjustment needed to change from 5 to 50 metres. There will be less adjustment needed from 50 to 500 metres ( iirc it is very minor ) .
Thanks everyone for all the help. I just tried it out and I was really surprised how much I had to change the distance between the lens and the led, to focus it. From focusing at 5 yards, to focusing at 100 yards, I had to move the led about 25mm. Basically, the farther out the object, the closer the led has to be, to the back of the lens. I do have concerns that I will find I cannot accurately focus out to 2 miles or more. I will be taking the light to work tomorrow night and I will try to focus the beam on the bank building that is 2 miles away. If I can achieve that, I think I will be satisfied. I sort of wish I had done this before the anodizing, becasue I will have to cut the tube much shorter, but such is life. Live and learn as they say.
