Need advice on mirror-making for a home-made amateur reflector [closed]

Question

For example, what would be some good references to read first? What sort of glass slab should I use? What size; diameter and thickness. Im a first-time builder trying to build one

Answer 1

I second the comment about Texereau -- originally written in French; it's the best, bar none. You won't need anything else.

Remember the old adage that is quicker to make a 4" mirror and then an 8" mirror than it is to make an 8" mirror first. Don't bother with borosilicate. You should be able to get mirror kits and all the abrasives that you need online. Join a club if you can find one.

How to Make a Telescope, 2nd edition by Jean Texereau:

• http://www.willbell.com/tm/tm3.htm
• https://www.amazon.com/Telescope-second-Texereau-published-Atlantic/dp/B00EKYQCQS

Answer 2

Here's what I've learned from making telescope mirrors.

Start with a mirror that's of a reasonable size and curvature. It is definitely possible to begin with a 12" f/5 mirror, but the problem is you have to handle not just the higher volume of work, but also the learning process in a field that's completely new to you.

Begin with making a 6" f/8 mirror. It's small enough, and the curvature is shallow enough, that you will be free to focus on the procedure itself. Complete that instrument, and play with it for a while. Later on just double the size, or go even bigger.

In terms of thickness, just make sure the glass thickness / diameter ratio is 1 / 6. That's pretty thick, but it will prevent it from being elastically deformed while sitting in a simple mirror cell. A little thinner than that is fine usually, but not a whole lot thinner; with thin mirrors you could simply use a mirror cell with more support points (6 or 9 instead of 3).

It is true that you don't have to use borosilicate glass. Unless you have a fully automated instrument that does astrometry, plain glass will work about the same, you'll only have to adjust focus a bit more often. But borosilicate is less liable to crack during certain stages of the manufacture process when the mirror suffers a thermal shock (when applying warm pitch to create the polishing tool). Also, borosilicate is cheap enough, so why not use it.

Here's a place where you could buy supplies:

http://firsthanddiscovery.com/astronomy/telescope-making.html

It's probably best to buy a whole kit instead of going the piecemeal route.

Keep in mind this will be a long term project. You will not finish it in one week-end. You will keep working on it for months (unless you make it a full time occupation). However, because you can keep working on it, you could obtain good results. The first mirror I ever made was parabolized to a precision of lambda/25, which is far above the average quality of commercial mirrors. It's simply a function of being able to work on the project until you're satisfied with the results.

OTOH, if it's taking too long, just accept the current results and move on. A lambda/6 mirror will work just fine, and if the scope is small it's probably not worth obsessing too much over quality.

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Books

Mirror making

'How To Make A Telescope' by Jean Texereau has been considered the foundational text of this field for a long time. Definitely read it, but keep in mind it's a little old.

http://www.willbell.com/tm/tm3.htm

'Build Your Own Telescope' by Richard Berry is a little closer to the present day. His choice of materials and procedures may seem a bit more familiar to you. I don't see it as an either/or choice - read both Texereau and Berry.

http://www.willbell.com/tm/tm2.htm

Another excellent source of info for mirror making is the Stellafane website. It's an even more modern approach than both of those books, and it's basically the playbook they use at Stellafane in Vermont to help dozens of newbies make their own mirrors every year (with supervision). Last time I checked they were missing the chapters on sphericization and parabolization, but you can get that stuff from Texereau and Berry.

https://stellafane.org/tm/atm/

I highly recommend you read all sources indicated above. Texereau is a classic, a bit old but full of wise advice. Berry is more modern, but it's his own method, it's what worked for him. Stellafane is a very practical approach that's still in use nowadays.

In practice, your own method will end up being a blend of all of the above, probably tracking the Stellafane process fairly closely, but with bits and pieces from the other authors too.

Telescope making

Both Texereau and Berry have some recommendations, but they're very old. Read them for informative purposes but don't follow them. Instead, use Stellafane's guide:

https://stellafane.org/tm/dob/

This is perfect for a 6" to 8" small dobsonian.

Later on, if you want to build a larger dobsonian, read the books by David Kriege and Albert Highe:

http://www.willbell.com/tm/dobtel.htm

http://www.willbell.com/tm/PortableNewtonianTelescopes.htm

The Kriege book is a bit older stuff, but he's very experienced (he's the owner of Obsession Telescopes). Highe is an engineer turned amateur telescope maker, and his book goes very deeply into the theory of engineering of such projects; you don't have to understand every single part of it, but it's very informative to just read it and see how he's doing it.

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Random useful links:

The Stellafane mirror and telescope calculator:

https://stellafane.org/tm/atm/general/scope-calc.html

Mel Bartels' diagonal calculator:

http://www.bbastrodesigns.com/diagonal.htm