# How to test a parabolic mirror?

• sergeant_pv
In summary, the conversation is about aligning a newly purchased 10" primary mirror from Coulter Optics. The speaker is looking for advice on testing and checking the parameters of the mirror, and another person recommends using a Ronchi test or simply observing any problems during first light. Coulter Optics is known for producing quality products. The speaker expresses gratitude for the advice and mentions the knife edge test as another helpful method.

#### sergeant_pv

Hi,

I just ordered my first primary mirror (10") for DOB from Coulter Optics.
I want to test it after it arrives. Does anyone has expirience with testing/checking params for parabolic mirrors?

Clear skies!

If you feel so inclined to do so, then a http://www.telescopemaking.org/ronchi.html" [Broken] will do the trick.

Or, at first light any problems will become evident.

However, Coulter Optics I have found produces quality products.

Last edited by a moderator:
Thanks a lot, Waveform - this is exactly what I need!

The knife edge test is also good - http://www.fvas.net/victor/testing.htm

Hi

How to align parabolic mirror for optical beam?

## 1. How do I determine the focal length of a parabolic mirror?

To determine the focal length of a parabolic mirror, you can use the mirror equation: 1/f = 1/do + 1/di, where f is the focal length, do is the distance between the object and the mirror, and di is the distance between the image and the mirror. Measure the distances and plug them into the equation to calculate the focal length.

## 2. How do I test the accuracy of a parabolic mirror?

To test the accuracy of a parabolic mirror, you can use a laser or a light source to reflect off the mirror onto a flat surface. The reflected beam should form a straight line if the mirror is accurate. You can also use a piece of graph paper placed at the focal point to see if the reflected light forms a perfect point.

## 3. How can I check for any imperfections on a parabolic mirror?

To check for imperfections on a parabolic mirror, you can perform a Ronchi test. This involves placing a Ronchi ruling (a series of parallel lines) in front of the mirror and observing the reflected image. Any distortions or imperfections on the mirror will be visible in the reflected lines.

## 4. What is the best way to clean a parabolic mirror?

The best way to clean a parabolic mirror is to use a soft, lint-free cloth or tissue. Avoid using rough or abrasive materials that can scratch the surface of the mirror. You can also use a mild cleaning solution made specifically for mirrors. Gently wipe the surface in a circular motion to remove any dirt or debris.

## 5. How do I prevent a parabolic mirror from fogging up?

To prevent a parabolic mirror from fogging up, make sure to store it in a dry place. If you are using the mirror in a humid environment, you can use a dehumidifier or silica gel packets to absorb excess moisture. You can also warm up the mirror before use to prevent condensation from forming on the surface.