The first thing you want to do is to flatten one side (it will become the back) by grinding it against a flat piece of glass (e.g. It will give your mirror its overall focal ratio. To achieve that, we will work from coarser to finer abrasive. F/D = 4) well suited for deep sky observations. If you were shooting for a high focal ratio telescope, you won’t have to grind for too long. It is possible to make a 12 inch (300 mm) mirror with ¾ inch, 19 mm ?? What size is best for someone’s first attempt at making a telescope mirror? A program like FigureXP does the job very well and provides you with a thorough surface error analysis. The courses to apply are pretty basic. Modern approaches to mirror making and telescope designs, In 1989, my then 13 year old daughter ground a 6″ F6 mirror that tested to better than 1/20 wave in white light. In that case, you end up with an hyperboloid and you will need to go back to the sphere before trying to parabolize again. In your opinion what is the biggest diameter that a have to attempt to make a Newtonian telescope mirror? Very organized. Our goal is to have the mirror concave and the tool convex. If you make the centre deep, you will end up with a fast telescope (e.g. I have followed Jean Texereau’s book (old but a great reference guide) for my first telescope and I’ve heard good things about the Richard Berry one. – Build Your Own Telescope – Richard Berry I have successfully made a 10″ mirror with 1″ thickness (1:10 ratio) and it performs very well. With book do you recommends to follow? July 19, 2006, By: The Editors of Sky & Telescope How can eyepieces offer a telescope's widest true field? Please let me know if you successfully glue glass together. During polishing we are trading the ceramic tile tool for a softer material capable of holding the cerium onto its surface. Thanks for the article. All rights reserved. The strokes stay the same but the difference happens at a microscopic scale. The most commonly used material is pitch. It will start to get its reflective surface after a couple of hours but you will need a few hours more to make sure you remove all the rough surfaces from fine grinding. I need to have a small piece of glass curved to a spherical curvature with radius of 2200mm (focal length of 1100mm). It will give your mirror its overall focal ratio. If you make the centre deep, you will end up with a fast telescope (e.g. Now you can start polishing the mirror. That’s why we need a tool. Even though some builders prefer to buy commercial mirrors and fit them in a DIY structure, I believe that making a telescope mirror is probably the most rewarding part of the whole built. (You can unsubscribe anytime). This is done by changing from chordal to normal stroke (1/3 centre over centre). Hi, this link is to a web page done by Mike Davis not David Davis. It is also supported by 9 floating points. Can you make custom mirrors? The shape of the mirror can easily be deduced from the curvature of the lines. A protective SiO2 layer is often applied on the aluminium to preserve it from oxidization. Mirrors larger than 1/6 their thickness are considered thin mirrors and will need more thoughts put into it (back of the mirror must be even and padded during polishing, used an appropriate mirror cell design, etc). What is perhaps an equally important consideration is the mirror’s focal ratio (focal length divided by diameter). Here are common defects as seen through a Ronchi screen. They consist of long chordal strokes with mirror on top. July 24, 2006, By: The Editors of Sky & Telescope F/D = 8) will be performing very well on planets and the moon. 0, Yes, I would like to receive emails from Sky & Telescope. More complex tools such as interferometers give a more precise reading but are less affordable. We will need to build special tools to control the shape of the mirror. Once the desired sagitta has been reached, it is time to make the surface more spherical (rough grinding usually creates a slightly conical surface). It is cheap and comes in various size (can range from #36 to #500). Once the back is flat, we can start to carve the front into its spherical shape. Basically, a paraboloid has a deeper centre and flatter edges than a spheroid. The surface is lit from the right. Telescope makers use silicon carbide powders (a.k.a. It is worth mentioning that pitch is very hard to remove from almost all surfaces. But what if you really want a big mirror? Once you reach the finer grains (at this point you might be using aluminium oxide instead of silicon carbide), the surface should start to shine a little when viewed from the side. Here is a ronchigram of a finished mirror. My name is Marcus Motta and I´m writing this e-mail from Brazil It was a real delight to see her pride in the project. July 19, 2006 The web based Ronchi simulator by Mel Bartels is also very useful. I purchase 5 of them…. Is possible to stick (to glue) two glasses to increase the thickness? [Fig 5]After you've ground the glass to the desired depth the mirrors surface will be opaque like this. To avoid doing the same mistake twice and learn from past errors, it is essential to keep a figuring log in a notebook.


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