Backyard Aquaponics
A place to discuss aquaponics

When I point my laser pointer into my aquarium from the top down so that it lines up with a point... say... 1 cm inside the glass, that appears rational to my eye.

When I shift it a bit so that it points into the center of the aquarium (while still being held up against the top of the front pane of glass) it points further in than it looks like it should.

Refraction I guess.

Is there a way to calculate the error.

So for example if I wanted to shoot a non light based projectile into my fishtank (ignoring the physical deviation from glass and water - and just thinking in terms of light and diffraction from the laser sight) is there a way to calculate the deviation error I see from my laser sight?

LOL

Never read your own questions

But it is a real question.

Anyone?

I'm sure someones figured it out BW. I think probably it starts here for figuring out where the light ends up - https://www.britannica.com/science/refractive-index

The speed of your physical projectile apparently matters just like the speed of light affects the refraction in that link.

Truthfully though if you ignored all the physical deviation from glass and water, I think it would go right where you aimed it .

If the light beam is perpendicular to a glass or water surface it should go straight through unless there are changes within the objects. If you put it on and angle the light will travel faster though the air than the object thereby changing the direction, intensity and distorting the image. As for calculating the change it would be quite complex.

I suggest using a net, rather than trying to shoot your fish!

I think he wants to blind them so he can actually catch them with the net Gordon

stick your face and gun inside the tank, stop being a wimp, its only a little water.....

Refraction. If you want to calculate the angle, use Snells Law
https://en.m.wikipedia.org/wiki/Snell's_law

I meant ignoring the deviation a projectile would see if it hit glass on an angle. ie if the exit point of the projectile was under water.

But it occurs to me I can just put the laser underwater as well, solving everything.

Doh!

I think that's the solution

There's some dence reading in those links.

Thanks people.

BW,

The simple rule of thumb to hit an object below the water from above is simply to aim 1/3rd deeper than any object appears. Great for shooting fish in a barrel!

just make sure you hit the fish and your bullet doesn't go through it or you might break the glass and have to catch all of the fish on the floor =) maybe use a small spear, like a toothpick instead of a gun and practice throwing 1/3 lower than it looks like you need to instead of shooting it out of a gun...

The reason for all this (from ages ago) is here...

https://youtu.be/6EnbhZ_NXcY?t=41

I made a little cannon that shot the darts as well, and mentioned in my blog that they were being launched all over the neighbourhood, but the reality is they went about 15 feet. I try to never let facts get in the way.


The question about going through water was purely academic. I was shining the laser through my fish tank, and it got me wondering how I could spear fish from a canoe as a kid in Papua New Guinea, when I have no idea now.

Kids are smarter than grownups.

You make me look up crazy things..

Chuckle chuckle Rininger85,

You have reminded me of my early teens, when one of my classmates was shooting trout with a .22 in a rocky mountain stream. He copped a ricochet through the fleshy part of the base of his thumb. Apparently he used to aim along the submerged part of the rifle barrel to hit the fish, but after this incident decided maybe there were better ways to catch trout. The outcome could have been considerably more drastic LOL.