All telescopes, whether they are the one that you use in your backyard to the Hubble telescope, have one thing in common: they depend on mirrors to make sure that they work. When it's a small telescope, like the one that you would use at home, then it isn't as important that the mirror be set in such way that there is very little to no distortion or error, but when you get to the large, professional, or research telescopes, the mirrors must be perfect; they must not add any jiggle, and they must not add in any noticeable distortion. One way to do that is to use something called fast steering mirrors. 

Fast Steering Mirrors

These are mirrors that have been made to exacting standards. Not only are they very carefully made in clean rooms and highly polished, they are also set within a special kind of framework. That framework has tiny motors in it which can move the mirror around on the XY axes. But the way that the mirror is set in the framework also means that the framework is going to absorb wiggles and jiggles that might happen when the motors kick on and move the mirror around. There are a lot of other benefits to using fast steering mirrors in telescopes. 

No Pincushion Distortion

One of the benefits to using FSMs is that they get rid of the pincushion distortion. There are all kinds of distortions that can show up in optics, like telescopes. One of them is the pincushion distortion. With this distortion, the image ends up pinched in the center. Think of what it looks like when you push a pin into a pincushion or a finger into a pillow. Where the tip of your finger or the pin goes into the cushion, everything moves toward the center and down, and ends up pinched under that area. Generally, the further an object is from the telescope, the more distortion will show up, and it will make that area look more magnified, which will distort results, and cause measurements and such to be wrong. Fast steering mirrors can help to eliminate that distortion. 

When it comes to research into the space in our local neighborhood and out further into the universe, researchers and scientists need to know that they have the most accurate measurements and pictures of what's going on out there. A fast steering mirror can help with that.