# Do mirrors have a "resolution" quality to them?

I would like to know if mirrors have a quality of "resolution" to them like a regular photograph might, or like a JPEG does.

For example, if you looked to closely, or magnified a photograph, you would soon come to a point where the image blurs, or that which was too far away when photographed is not discernible.

If a high quality microscope was applied to a mirror, would it be possible to observe far-away objects reflected by the mirror, taking only the quality and scope of the microscope into account?

Are there different quality mirrors, all other things (e.g. shape) being the same?

Could you also talk about any loss of luminescence if possible?

Also, do all plane mirror have the same converging/diverging power i.e, the image size will be same on all plane mirrors ?

• Edited "ceteris paribus" to "all other things (like shape) being the same: it beclouds what you are trying to say, especially for those whose mother tongue is not english. Oct 7, 2013 at 1:11
• How do telescopes work? Oct 7, 2013 at 2:54
• Is that my question? Maybe...in a sense. "How do telescopes work, but forget the discussion about light traveling in a straight line and angles of reflections. I know that already, because I've taken enough photography art classes, and I've done High School Physics." Oct 7, 2013 at 3:10
• There are indeed different quality mirrors. They can be specified in terms of their flatness, for example (e.g. lambda/10 meaning they are flat to within 1/10 of the wavelength they are designed for). Also, they can have a specified scratch and dig rating, which specifies the maximum number and size of scratches and digs on the surface. By definition, a plane mirror does not have converging or diverging power. That, of course, assumes a perfectly manufactured mirror. In reality, this would be affected by the flatness of the surface. Flat mirrors are also diffraction limited(like any optic)
– Joe
Oct 7, 2013 at 17:35
• Are you asking about the possibility of using a microscope to examine, on the surface of a flat mirror, the virtual image of a distant object? Oct 7, 2013 at 18:18

The resolution of a regular photograph is limited by the size of the silver halide crystals in the emulsion, while the resolution of a computer image is limited by the number of pixels used to store it.

However, a typical telescope mirror has no structure bigger than the size of a grain boundary, and this is much smaller than the wavelength of optical light. In this respect there is no finite resolution comparable to a photograph or computer image.

The resolution of a telescope is limited by the size of the mirror rather than by any quality of the reflecting surface. The light reflected by the mirror is diffracted by the mirrors edges forming an Airy disk. This limits the angular resolution to approximately:

$$\sin \theta \approx 1.22 \frac{\lambda}{d}$$

where $\lambda$ is the wavelength of light and $d$ is the mirror diameter.

• That's for a perfect mirror. The rugosity of the mirror plays a role, and that's why astronomical mirrors are much better polished than a bathroom mirror ! Oct 7, 2013 at 17:33
• @FrédéricGrosshans: I'm not sure your bathroom mirror is that bad. The smoothness of float glass is typically excellent at optical length scales. It's the planarity at larger scales that means you can't use your bathroom mirror in a telescope. Oct 7, 2013 at 17:36

In response to your last question, all plane mirrors have the same converging/diverging power: zero. The size of the virtual image in a plane mirror is identical to the the size of the object. If you hold up a mirror and look at the reflection, in it, of the moon, for example, you are looking at a virtual image that is some 3500 km across, and is about 385000 km away, behind the mirror. If you use an auto focus camera to take a picture of this image, the camera will focus on infinity and create a in-focus photo of the moon. If you force the camera to focus on the surface of the mirror, you will get an in-focus picture of dust, scratches, pits, finger smudges, etc on the surface. There will be no image of the moon in the shot...