Astronomy.CJDawson.com

Night Vision


Night vision is something that every astronomer must think about, there's some things that your telescope can do, you can add baffles to the equipment, but at the end of the night if you can't see a thing what's the point? In this section I'm going to explain some of the details of night vision, how to help your eye's adapt to the dark, how to see more in the dark.

Rough guide to your eye.
Every humans eye has been made to work at it's best during the day when vast amounts of light are comming from the sun. As night, your eye's cannot gather enough light in order to make anything out. To get over that problem your retina (the part at the if your eye that the light is focused on) is devided into two sections, called the Rods and the Cones.

The Cones are the part in your eye are are not very sensetive, you use they during the day, and they allow you to see colour. There's three types of Cone. Each type allows you to see a different primary colour (red, green and blue). These are concentrated in a spot in the middle of the retina. When your pupil is closed light only falls onto this area, so you don't notice that you're using the least sensetive part of the eye.

The Rods are a lot more sensetive than the cones, there's also a lot more of them. They're situated in a ring around the Cones. And they only come in one type, they're not sensetive to colour. This means that at night you see in black and white!

Turning your eye into night mode
So now that we know it's possible to make our eye's alot more sensetive, to be able to see fainter objects. How do you do it? It's quite easy to do, but it's important that you have the right conditions to do it. You need to make sure that there's no light around that could destroy your vision. By that I mean any artificial light (except for RED, I'll explain later)

Sitting in the dark your eye's with adjust from daytime mode to night mode. You don't need to do anything more than that, but you must be aware that it'll take about 30 minutes for this to happen. The process isn't just a case of allowing your pupils to open, also the Cones need to switch off, and the Rods switch on. It takes time to warm up those cells so that they work properly.

Artificial light should be avoided, as this will instantly tell your eyes that you should be working in daytime mode. Your sensetive Rods will be shut down, and the cones will take over. It doesn't even take a second of bright light to shutdown the Rods, so you should be careful about it.

Using a torch
We've said don't use artificaial light, you can use a torch provided that it emits only red light. This is because your rods are not sensetive to it, and will not shut down. You'll be able to see things with your torch, whilst see retaining your night vision. It might take a few seconds for your eyes to re-adjust after turning your torch off, but it beats the 30 mins that you'd have to wait if you used white light.