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Why purchase your mirrors from Lockwood Custom Optics?

Quality Glass

It's common to see online questions about mirror quality and the price of that quality.  Mass-market, imported telescopes are so tempting at their bargain-basement prices, and for some, these are the right choice.  However, for those who want the best substrate, figure, coating, and support, it makes sense to spend a bit more.

Let's start with the glass.  To use an analogy, you wouldn't put a substandard, poorly-constructed foundation beneath an expensive, top-quality house.  So, when I make a mirror, I start with a quality piece of well-annealed glass.  A properly annealed blank, properly machined so that it has very little wedge, will allow a high-precision shape to be polished into the glass, and it will hold that shape virtually forever if undamaged mechanically and chemically.

A poorly annealed blank may change shape over time, thus undoing the precision optical work that was done.  A mirror made from such glass can also show a significant amount of astigmatism or other upredictable distortion while the mirror is cooling.  Differences in temperature within the glass due to cooling cause temporary changes in the shape of the glass.  This is perfectly normal, but it puts temporary internal stress in the glass, which interacts unpredictably with the internal stress left by a poor or non-existent anneal.  This results in a time-varying amount distortion (often astigmatism) that is worst early in the night, but which often never completely goes away.  There is no cure for this behavior unless you completely re-anneal the glass and regrind, repolish, and refigure.

Most of the mirrors produced by LCO are made from borosilicate glass, such as Pyrex or Supremax, which are fairly hard.  Thus, it is more difficult to polish roughness into the optical surface, as often happens in large-volume production of inexpensive mirrors using softer, less expensive glass.

Borosilicate will change shape temporarily as it cools.  Softer, less expensive glasses such as plate or BK7 have a coefficient of thermal expansion that is several times higher than borosilicate, and they will change their shape by several times more than borosilicate.  Quartz is of similar hardness to borosilicate, and is far more stable in its shape under cooling, having a coefficient of expansion that is roughly six times less than Pyrex.  Naturally, it is significantly more expensive than borosilicate.

When it comes to glass, you do get what you pay for.  However, this means that the cost of a high-quality, well-annealed, and nicely machined borosilicate mirror blank (just the raw machined and annealed glass) is comparable to the cost of a finished mass-produced mirror.  Thus, the quality of the glass is one obvious reason for the difference in price between "premium" and mass-produced mirrors.  Any glass might have some internal bubbles (which are of no concern for reflecting optics), but with a good anneal it will not change shape in strange ways as it cools, or more importantly, the figure will not be at risk of changing over time.

The Process

With a good foundation to start on, I first grind the back of the mirror for several hours at least.  This ensures that it has a regular shape, that it will get uniform support while on the turntable of a machine, and thus that strange distortions will not be ground and polished into the front of the mirror due to the shape on the back.  A fine-ground mirror back also ensures that it will slide easily and with little friction on a properly made mirror cell, and this means the cell can work properly and support the mirror with little distortion.

Next, I grind the front and thoroughly polish the front surface that will become the optical surface.  I check the figure of revolution of the mirror and eliminate any significant astigmatism, trefoil, or other distortions.  Many opticians skip this step or use tests that have poor sensitivity to these issues, and it is one reason why I have to take many mirrors that I am refiguring back to a near-sphere.  In that process, I can make the mirror a good figure of revolution, a point from which it can be figured.

After a good figure of revolution is achieved, I can then do the figuring work that puts a precision parabolic shape on the mirror.  This work must be done patiently so that the surface is kept smooth.  Many fast-working opticians leave surface roughness, and this will scatter light and degrade images.

Also, the figuring must go right up to the edge of the mirror without turning it.  For many cheap mirrors, the time available to produce them is limted, so the outer zones are very nearly spherical, and the figuring work never makes its way to those very important areas of the mirror.  This will degrade images later on when conditions are superb.  In contrast, I spend most of my time working on getting the shape of the outer part of the mirror right, because this is critical to obtain the best performance and images.

In fact, many mirrors that I have refigured have been fairly far along in figuring, but were left undercorrected in the outer zones, sometimes to save time, and sometimes in a futile attempt to compensate for the change in mirror shape that happens as a mirror cools off.  This means that I have several days of work to do to fully correct the outer parts of the mirror and finish off the rest of it to my standards.  This extra time and labor is partly why my prices are higher than other vendors, but it is vital to get the best performance out of the optic.

Center mark, courtesy of KentNear the end of figuring I take many very careful readings as I tweak the figure to the best precision that I can achieve without spending obsessive amounts of time removing tiny defects that will never have an effect on an image, even on the best of nights.  Such obsession would drive prices even higher and not produce any gain at the eyepiece.  Still, the final tweaking can take days, and this is another reason my prices are higher.  With figuring complete, I do a last check of the figure of revolution to make sure nothing abnormal has popped up during the figuring process.

With the optical work complete, I clean the back and sides of the mirror, touch up the bevel if necessary to eliminate any sharp edges and reduce the risk of chipping if it were banged into part of a mirror cell or something else.  The last step for the glass (if it is not a perforated Cassegrain primary) is for me to carefully center it on my turntable to high precision and scribe in three small circles that are exactly centered on the mirror.  See the photo from one of my clients at right.  These permanent, precision markings make it possible to apply a center spot very, very accurately marking the center of the mirror.  This allows very precise collimation to be achieved with a good quality laser even for very fast optical systems.  In the image below at left the adhesive center mark is very, very precisely centered.

An adhesive center spot placed using my center markOne might think that my job is done now, but it isn't.  The final step for the optic itself is to receive a good quality coating, and I recommend those based on much experience.  I provide a clean mirror to the coater so that their work is as simple as possible.

Going Beyond the Process

Finally, the last step in my process is to help the client get the most out of their optic.

This is what most people don't consider - the service after the sale.  I want your mirror to perform as well as it can, because if it does not, it reflects poorly on me.  I also want to share my experience.  So, in buying a mirror from me, you get my support in bringing your fan setup and mirror cell up to modern standards if possible.  This often happens while a telescope is being built.

I can often recommend changes or vendors that can help a client maximize the performance of their instrument, and these can make a significant difference in the performance of the mirror, the stability of collimation, and the equilibration of the mirror, all of which will add up to the best images that you can achieve with your instrument.

Additionally, I've advised many clients on their observatories, telescope storage, telescope equilibration, and other practical issues that need to be addressed in order to achieve maximum performance and enjoyment with a large telescope.  This information comes from my experience using large instruments and from things that I have learned traveling domestically and internationally and visiting clients and other amateur astronomers.


To summarize, the above mentioned steps are what make my optics, I believe, the best performing optic you can get for your money.  You can pay less and get much poorer performance, or you can pay more and not achieve better performance.  I am an engineer by training, and after over 20 years of building telescopes I understand the factors involved in obtaining superb performance and I share my knowledge with my clients.

So, if you want the best performance from your large telescope, I believe that you should have a mirror from me, and with your purchase you will also have support from me and have my experience at your disposal.


Important events and firsts

Note:  Many of the first/events described below are listed on my Projects Page.

LCO was founded in 2006.

In 2007, I began making thin monolithic primary mirrors for Dream Telescopes.  These were Pyrex, 16.5" in diameter, 1.25" thick, and at that time no one was making such thin mirrors commercially.

In early 2008, Dream switched to cast cellular blanks, so I bought the blanks and began making these mirrors for Starmaster Portable Telescopes.  They proved to be a sensation in the visual telescope market.  It was the first production visual instrument to combine high-quality, fast, and thin optics.  This telescope allowed seated (comfortable!) observing all over the sky.  More on these mirrors can be seen on this page.  This was called the FX Series of Starmaster Telescopes.

Later in 2008, I made the first 20" f/3 mirror for visual use, an unheard-of 1.25"-thick, made from Pyrex.  Five years later, I am still the only optician making such a mirror.   Starmaster Portable Telescopes built the structure, and it is still my main visual instrument.  I called it the 20" f/3 MX telescope, MX standing for "Mike's eXperiment".  
Three articles have been written about this instrument: First look at the Starmaster 20" f/3 MX, Observing with the 20" f/3 in Missouri, The 20" f/3 goes to Florida and WSP 2009, and it has been featured in columns in Astronomy Magazine and Sky and Telescope.  In 2013, JPAstrocraft built a highly customized 20" f/3 for a client using my optics.  (Update:  In recent years, others have copied it, but I did it first and with the thinnest, fastest-cooling glass.)

With the availability of TeleVue Ethos eyepieces and later the Paracorr Type 2, telescopes at f/3.6 and faster could be enjoyed by all telescope buyers.  (When the 20" f/3 was built, the eyepieces and correctors had not quite caught up to the drop in f/#.)  With the Ethos and Paracorr Type 2, the 20" f/3 performed beyond my expectations.  I quite literally forget that it is f/3.0 when I am using it.

So, in early 2009, I made the first f/3.3 primary mirror for a commercial visual telescope, a 22" f/3.3.  It was made from 1.4"-thick Pyrex.  The telescope was built by Starmaster Portable Telescopes, and the f/3.3 telescopes were called the Super-FX series.  Later in 2009, I produced a 30" f/3.3 for Starmaster, and the owner raved about its performance.  Soon, other opticians were offering mirrors at f/3.3, but I did it first.  24" f/3.3 and 28" f/3.3 mirrors were also offered to fill in the range of sizes.

Also in 2009, I made a 14.5" f/2.55 mirror for an experimental visual instrument that I built.  Visually it was a success, and is my favorite instrument for scanning the Milky Way that I have ever used.  An article about it can be seen here.

In 2010, I moved to a new, larger shop.  I chose to do this to allow work on larger, heavier mirrors, to reduce my lead time, and to increase my production and testing capability, all while maintaining the same high standards.  In the middle of 2010, I produced the first 20" f/3.3 mirror from 1.25"-thick quartz.  It was offered exclusively in a Starmaster telescope with a 4.5" quartz secondary mirror.  This Starmaster model is called the Super-FX-Q.

Also in 2010, in my shop, under controlled conditions, John Pratte (of JPAstrocraft) and I tested a multitude of mirror edge support schemes for John's 25" f/4 telescopes.  We discovered that adding a roller to a whiffletree edge support prevented the support from pulling on the mirror, causing astigmatism.  We have freely shared this discovery (see this article on mirror cells), and this type of edge support has since been implemented by several other manufacturers, at my urging.  This has improved telescope performance markedly when the telescope is not pointed high in the sky.  At LCO, we believe in helping manufacturers to support our mirrors in the best manner possible, and we support them in that endeavor whenever possible.

In 2011, I made a 28" f/2.75 mirror, another first.  The telescope was built by Webster Telescopes, and the owner reported superb performance from an instrument that only needed one step at zenith!

From 2011 through 2013, I completed three 50" mirrors, two 42" mirrors, a 43.4" mirror, and two 40" f/3 mirrors.  

At the beginning of 2014, LCO was incorporated and became Lockwood Custom Optics, Inc.  I purchased a second Buccini MIC-1 interferometer and upgraded it to phase shifting capability (PSI), with analysis done by Durango from Diffraction International.  PSI is the current industry standard, is a great improvement over static-fringe analysis, and allows very powerful analysis to be done on optics and optical systems.  The other MIC-1 will be dedicated to high-precision flat testing in the future using the same software package.  Additionally in 2014, an order was placed for a 32" f/2.8 to be built by Equatorial Platforms, and an article can be seen here.

A 45" f/3.75 mirror was completed in 2015, and a 40" f/3.75 Cervit primary was completed in late 2016 and had first light in a StarStructure in early 2017.

A shop expansion is planned for mid-2017 in order to allow dedicated test setups to be constructed in a space where they can sit semi-permanently.  This will also allow more space for generating and other optical work and general construction of equipment.

The future will see completion of a 40" R-C system, and another 40" f/3.75 optic for a StarStructure.  Other large mirrors are on order, and research continues in optical testing methodology.


Links

I answer Frequently Asked Questions here (FAQ).
I describe Recent or Notable Projects here.
I list my Talks and Presentations here.
A link to my other Company Information Page is here.
My old (and not up to date!) amateur telescope making (ATM) site

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