I need to calculate the halo value for a tube but don‘t know if I‘m doing it right. I took a picture of a lit L.E.D. using an L.I.F. and having the camera fully zoomed in (it goes to 6X). In the picture the L.E.D. measured to about 9 mm and the halo was about 51mm. I tried using the formula in an earlier post but its too confusing and there is no example. Also do the units (mm) cancel out or does do they stay? How and Why? Thanks in advance.
The tube is about 18mm and it‘s variable (same one used on PVS 14, the MX 11769 I believe). Also which is better to do the test in, full gain or just enough that the halo shows up? Does this even matter? Again thanks in advance.
The easiest way I can think of is to look at a bright point-source of light. A bright star is a good one - just find one that produces a halo. Otherwise a light in the distance will suffice.
Then take a picture through the ocular with a digital camera.
Put the image on your computer screen. Now measure it... With a ruler on your computer screen.
Then the diameter of the picture of the halo divided by the diameter of the picture of the tube multiplied by 18 - and you have your halo size.
So does this mean I have to retake the pictures? I only took pictures showing the halo circle (51mm) and the lit L.E.D. (9mm) while in full zoom. I never included the entire green circle (the tube I guess?). I‘m still a bit confused but I think I understand. Parts I‘m confused on is the units (mm). Do they stay or is the number dimensionless? Also if it is dimensionless why do companies add mm? As I said earlier an example would greatly help. Thanks for replying and thanks in advance.
Here‘s a comparison I did of an ESI and FOI Gen2 tube. One has a 1.2mm halo and the other doesn‘t really have a halo at all, although the "bright spot" is about 0.5mm and I‘ve seen it down to around 0.1mm
Not a lot of people realise that ESI ( ElectroStatic Inversion) tubes don‘t have a halo. In that respect, they are quite useful in urban environments.
FOI means Fiber Optic Inversion - ie, most tubes.
Anyway, I won‘t bore you with the technical details - You can see the halo size relative to the "circle" of the screen, which allows you to calculate the actual size in MM. Theoretically, you could reduce by the size of the light, but it‘s less than 0.1mm so don‘t worry about it -
Just so I know I‘m doing this right I‘ll try to calculate the "halo value" of the ESI gen 2. I know its not a halo and its a bright spot but for the sake of an example let‘s just assume this is a halo. Also I did measuring without clicking zoom on the computer.
So I measured the "Halo" to be about 5mm and the green screen on the pic to be about 160mm. 5mm/160mm is 0.03125. Then 0.03125x25mm= a halo value of 0.78125mm. Am I correct?
That would be correct, though you can zoom the image on the screen to make sure you have the halo... Especially when it‘s only a small size - eg, 3 to 6mm. Don‘t forget that if the image is small enough, the camera will make a bright spot. What you‘re looking for is the "circular" glow around a bright spot.
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