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RE: Mirror Deformation

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Posted by Steve Fejes on August 14, 2000 21:41:28 UTC

My information here is based on an article that was published in Sky & Telescope magazine, which had the results of a computer program by Toshimi Taki. According to his information, your mirror would work well with a 9 point support system.

Mounted this way, your mirror should have less than 1/32 wave peak-valley error. This is 1/16 wavefront error when aimed at the zenith - straight up, this is the maximum error. The mirror will have even less distortion when the telescope is aimed at objects lower than this.

I would say that your mirror should give excellent performance. The one thing to make sure of is that all of the support points are properly contacting the mirror. This includes the supports on the sides of the mirror also.

If you want to get an idea of the wavefront error, the best thing for you to do is to star test your telescope. Willman Bell has a book about how to do this and how to interpret the results. A star test will work well. It will show if the secondary mirror is accurately flat, and is mounted well.

The star test should show a good image at focus. The image outside of focus should look similar to the image inside of focus. The problem you will have with a telescope this big is the turbulence in the air. The image will not be steady enough to see all the detail that the mirror should be able to show you.

The mirror should not be distorted at any temperature while you are observing. What I mean is that the mirror will work well at -10 degrees to +40 degrees. The mirror will be distorted when it is not at the same temperature as the air around it. This will happen a lot, especially in the early evening when the temperature is not steady. The earth`s atmosphere will be the biggest cause of distortions with a telescope this size. You will probably never or very rarely be able to see all that this telescope is capable of showing you because of our unsteady atmosphere.

Good luck with your big beautiful telescope.

Steve

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