The diffusers provide an overhead light source on a sunny day, when the sun is not directly overhead.... They would also provide overhead light sources indoors from a single light IF the area between them is blocked, so that is the strongest light source instead of the straight lines between the single lamp and the sensors.... You don't need the diffusers on a cloudy day, because the light is coming from "all" directions.... The Chrony uses the brightest source (generally overhead, but in all cases parallel), and detects the dimming of that source as the pellet travels over the sensor.... If it can't do that, you usually get an ERR message....It is a tribute to current Chrony designs that they work as consistently as they do in varying light sources.... Still, I have found that I get the best results outdoors by using the diffusers with quite bright lights mounted above them.... just like I do indoors.... I have the sides of my Chrony, between the diffuser support rods, covered with plastic sheets, painted flat black on the inside, to eliminate side illumination, which I found increased the number or ERR messages.... As long as my shots are more or less centered above the sensors, the velocities I measure are consistent, and therefore I take that to mean accurate.... I have two Chrony's which measure within 3 fps of each other at 900 fps....Light does travel in straight lines, other than a couple of special effects, such as diffusion, diffraction, or bending by intense gravity.... We don't see the latter here on earth (unless observing a distant star, where the light is passing a black hole)…. We do see the former, because of dust and water vapour in the air, which causes the light to "diffuse" or spread out, but even that is mostly due to it reflecting off the dust or water particles (or the plastic of your diffuser).... In space, in a vacuum, your shadow would cast a sharp line, bright around it, completely black inside it.... The reason that is not the case in a room with a single light source is that the light is reflecting off the walls, other objects, even dust particles, and "filling in" your shadow to some degree.... Diffraction is a different effect, that happens when light passes the edge of a solid object, or through a pinhole.... Within a few wavelengths of light, it interferes with itself, and creates bright and dim areas on a microscopic scale.... but this is not something you can see without magnification, with a few exceptions, such as the "moire" patterns on a window screen.... Again, this does not concern us with the operation of a Chrony…. where light essentially travels in straight lines from the source to the sensor, interrupted by the passage of the pellet....If the brightest light source indoors is a single light source, relative low down and between the sensors.... you can get the effect I drew in the diagram in the OP.... If you don't believe it, test it for yourself.... I did, and I was able to "fool" the Chrony into getting a velocity of 1180 fps instead of 720 fps.... This is the reason for some of the ridiculous velocity claims you sometimes see.... THAT is the reason for this thread, to educate you to that possibility....Bo
After somebody expounding on another Forum about how the slots in the top of the sensor housings on a Chrony prevent light entering on an angle, so can't cause a velocity error, I ran a quicky experiment to prove this diagram has merit....If you use a single indoor light source above the Chrony, instead of two, you shorten the pellet path, and the velocity reading will be artificially high.... How much difference can that make?I set up my well proven, undamaged Chrony and checked the velocity of my Grouse Gun at 1500 psi with 18.1 gr. pellets.... 720 fps, as expected.... I then set up a single light source, centered (by eyeball) between the diffusers, and 27" above the sensors.... I shot about 9" above the sensors and got (drum roll, please)….1180 fps.... Pretty much proves that using a single light source is the cheapest way to double the FPE of your gun (or more)…. Bob
I find this hard to understand.The pellet passes over front sensor and it reads object, then passes over rear sensor and calculates distance and time.How does the light placement have any effect? The sensors do the calculating. I dont see how the placement of light source matters, if anything the error message would show.Case in point: In the illustration looks to me like if the front sensor did read the object, it would be read as it passed the rear sensor, not when it broke the plane of light indicated on the drawing.Just my thoughts on this.
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