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Step 10Testing
Despite it being December 22nd, winter solstice, the shortest day of the year, I proceeded to test out the completed lens system. But even with the least possible sunlight to work with (several hours before noon, at 37o latitude, we got a very satisfactory spot of blinding energy at the focus. When the device was aimed so that this spot fell on the secondary lens....nothing happened.
Failure Analysis
Despite moving the lens tube back and forth through the focal point, no beam of light formed beyond the lens mount. To find out why the light wasn't cooperating, we decided to do a beam visualization by blowing dust to reflect the light. We first used flour, but then switched to water mist (from a sprayer) since it's not as messy.
The light funnels into a highly concentrated point, as expected, but then basically fizzes out. If your Fresnel deathray is doing this, most likely the Fresnel lens is backwards and flat side is facing the sun, rather than the ridged side. Getting this right is essential to getting a good beam profile (which we'll see in the next step).
Since the secondary lens is convex, i.e. it bends light inward, the incoming light has to be diverging in order to form a straight beam. Since the light from the Fresnel seems to disperse randomly past the focal point, almost no light even entered the secondary lens. Other Fresnel lens devices on the internet demonstrate good beam shapes, such as in this picture.
Failure Analysis
Despite moving the lens tube back and forth through the focal point, no beam of light formed beyond the lens mount. To find out why the light wasn't cooperating, we decided to do a beam visualization by blowing dust to reflect the light. We first used flour, but then switched to water mist (from a sprayer) since it's not as messy.
The light funnels into a highly concentrated point, as expected, but then basically fizzes out. If your Fresnel deathray is doing this, most likely the Fresnel lens is backwards and flat side is facing the sun, rather than the ridged side. Getting this right is essential to getting a good beam profile (which we'll see in the next step).
Since the secondary lens is convex, i.e. it bends light inward, the incoming light has to be diverging in order to form a straight beam. Since the light from the Fresnel seems to disperse randomly past the focal point, almost no light even entered the secondary lens. Other Fresnel lens devices on the internet demonstrate good beam shapes, such as in this picture.
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One of the best instructables.Congrats.