Lockwood Custom Optics - Frequently asked questions

Please read these before you place an order, send me an email, or post one of these question on my Yahoo group. Thanks.

What is your lead time?

-Currently it is about 6-12 months for new mirrors (depending on size, larger mirrors take longer), and approximately 1-3 months for a small-medium size mirror refigures.

-For new mirrors, I ask for 50%-60% of the price up front as a deposit to cover glass costs (which often include a large secondary mirror) and the first part of the labor cost, and to reserve your job's spot in my queue.
-The balance of the purchase price is due upon completion of the mirror, prior to shipment to the coater.
-For refigures, if the cost is relatively low I will ask for full payment upon completion of the refiguring, prior to shipment to the coater. If the cost is higher, such as for a large mirror, I may ask for a deposit based on the estimated cost of the work.

-Yes, BUT only after I have a buyer for the mirror that your ordered and have cancelled. Glass is not cheap, and I have to buy glass to make a mirror. Consider this carefully if you are ordering a custom mirror that may be unsuitable for other people's projects, and therefore hard to sell. I will not sell you a partially-finished mirror for a reduced price.

-For mirrors 20" in diameter and smaller, I recommend and use Nova Optical Systems for standard and enhanced coatings.
-For mirrors 22" to 46" in diameter, I recommend and use Optical Mechanics, Inc. for enhanced coatings. They are also only a few hours drive away from my shop, which reduces shipping costs for larger projects.
-The coaters listed above have done optical work, and understand how to strip old coatings safely and treat a polished surface without damaging it.
-It is the mirror owner's responsibility to have the mirror recoated in a timely manner by a good coater. Do not let your coating degrade to the point that they become unusable - this can result in chemicals etching the glass, and the degraded coating may be very difficult to strip, risking damage to the optical surface. If this occurs, the mirror may need to be refigured to polish away the remains of the coating and the possible damage to the glass, and this is generally done at additional cost.
-If there is an issue with stripping the coating, the coaters above will let me know, and I can perform the work necessary to restore the figure of the mirror. Again, this work is done at additional cost to the owner, so don't let the coating go too long.
-If you wish to have your mirror coated or re-coated by a company not listed above, please consult me first. If something goes wrong with the stripping of an old coating or a new coating, some coaters may take extreme measures to remove the residue before recoating. This can destroy the figure of the mirror. After the initial coating, I cannot and will not be held responsible for damage to the optical figure/surface caused by a coater, so if you wish to use a different one, choose carefully and do so at your own risk.
-I do not recommend silver or other metals for telescope mirror coatings. Some coaters may not be used to removing these metals before recoating, and they may damage the glass. While silver may initially offer higher reflectivity, I hear that if often fails earlier than an aluminum coating, especially in environments near the ocean or in high humidity.
-I do not recommend or specify chrome undercoats for aluminum coatings. Chrome is sometimes applied first, in the vacuum chanber. In this environment, with no air to react with the chrome, aluminum sticks very well to it. So, if the aluminum won't stick to the glass, chrome may used as a "band-aid" - but only once. While the aluminum can be stripped off of the chrome, aluminum will not stick to chrome that has been exposed to the environment, so it is useless afterward. To make it worse, the chrome is not easily strippable without risking damage to the glass surface through harsh chemical action.
-Bottom line, if aluminum won't stick to the glass, then the glass is not clean or it is damaged in some way. Choose your coater carefully.

-I have never had a bad experienced with the normal enhanced coatings offered by both coaters listed above. In theory, the extra layer in a properly applied, simple enhanced coating should make it a little more durable than a non-enhanced coating.
-Even if there is a coating issue, these coatings are easy to strip off without harming the optical surface (by a competent individual or coater), and are easily recoated after that. NO coater is perfect, but the ones I use stand behind their work.
-I recommend enhanced coatings for secondary mirrors, and for telescopes that have three or more mirrors to reduce light loss. Ideally for a Newtonian secondary mirror, the coating is designed for reflection at 45 degrees, and will be different than one used at normal incidence (0 degrees).
-I recommend standard coatings (overcoated aluminum) for Newtonian primary mirrors for one simple reason - lower cost. If you don't mind spending a little extra, then I can recommend enhanced coatings from the coaters listed above..

-Unless the mirror has massive problems, it does not usually make financial sense to destroy an optical surface just to make a new one.
-The client will probably come out ahead if he/she sells the mirror that they don't want and simply buy a new one from me.

-No, I'll work on mirrors of just about any focal ratio. I enjoy making or refiguring a slower mirror now and then.

-I can't give you an estimate until I test the mirror.
-My rates are by the hour, so cost depends on how much time I have to devote to the project. I believe this is fairest to both myself and the client.
-After testing, I will provide an upper and lower bound for the cost, and the client can either proceed or I can return the mirror, and the client will pay for the testing and shipping.

-For concave mirrors, I test most frequently with knife-edge/zonal testing, also known as Foucault testing. I have found that, even for fast mirrors, this testing method is extremely accurate when used properly, and provides results that agree with star testing to high accuracy.
-I use a proprietary, highly-sensitivity test to check the figure of revolution of each optic at multiple stages in the work.
-I have 12" and 38" flats, which are used for autocollimation.
-I have 10" f/12.5 and 10" f/6.4 reference spheres that can be used to test flats to high precision.
-I test all blanks for strain with a crossed-polarizer test.
-I have a Buccini MIC-1 spherical wavefront interferometer, a variety of divergers, and coated and uncoated reference mirrors. I can test uncoated or coated optics, and I can test Cassegrain systems in double-pass autocollimation with one mirror uncoated.
-Ultimately, I ask that you use my mirror under the sky, support it properly, collimate it well, cool it to equilibrium, and evaluate it with star testing and by observing the sharpness and clarity of the images. So far no one has been disappointed with what they see.
-I value customer feedback - this is a form of testing. Please let me know how my optic is performing.

-For a small mirror and matching flat (diagonal, secondary, etc) mirror, cost will be around $100 plus shipping. Larger primary mirrors and flats over 10" in diameter will require more time, and are closer to $200. Again, this is done by the hour, so more complicated tests will cost more. Please clean your mirrors before sending them to me so that I will not have to.

-First, charging a testing fee shows that both the owner and the optician are serious about doing the testing. Second, others don't have a backlog of work - I do - and time spent testing is time not spent polishing. In my opinion, you get what you pay for.

-To see how I pack mirrors, read this installment of In the Shop. If you have more questions about how to ship your mirror, please email me at the address found on my information page.
-To see how I don't recommend packing mirrors, read this installment of In the Shop. (I'll probably add more bad examples.)

-Because inevitably they end up on the internet, where "experts" will "debate" them without consulting me.
-For telescope mirrors made by me to my highest standards, I guarantee performance to 50 power per inch of aperture on nights when the atmosphere is steady enough to allow this, so long as the mirror is properly supported, equilibrated, collimated, and reasonably clean. When you experience a night that allows this type of use of my optics, you will forget all about the numbers.
-Mirrors ordered with a less stringent specification (which is often appropriate for non-astronomical uses) are guaranteed to that specification.
-If you have a question about a mirror that I have made, such as in the case that you are buying a used mirror, please contact me so that I can consult my records to see the specification. You will need to provide the serial number and the size and focal ratio of the mirror.

-I'm not set up for it, and others are properly equipped and will do a good job. I am set up for ~14.5" mirrors through 60" primary mirrors, and I make smaller custom Cassegrain secondaries. I also supply tested elliptical flats to go with my primary mirrors so that the client can be sure that the entire optical system is up to my standards.
-I will refigure mirrors of just about any size, though I prefer to work from 10" and up with my current machines.

-For new mirrors, I grind the back of the blank smooth with very fine abrasives before optical work is begun. This makes them look better, allows them to be cleaned more easily, and the mirror will then "slide" nicely on mirror cell supports without binding.
-I also scribe, permanently with a diamond-tipped scribe, a small circle in the glass, exactly centered on the mirror after carefully centering it on a turntable. This helps you locate your centering triangle, ring, square, or other shaped sticker on the mirror for collimation.

-Supremax is basically the same as Pyrex in terms of chemical composition, coefficient of thermal expansion, and how it reacts during optical work, polish quality, etc. It is made by Schott.
-Supremax is a higher-quality product than some sheet Pyrex was, though the Pyrex I have used was always very good in quality. Benefits (compared to poor quality Pyrex, which I never used) include fewer striae, inclusions (stuff in the glass), and bubbles.
-Supremax is available up to ~2.5" thickness, which is more than the ~2.25" maximum of Pyrex. That's good for me, because I make big mirrors. The largest mirror that can be cut from a sheet of Supremax is ~44" in diameter.
-Supremax is readily available - Pyrex is no longer available in large sheets.
-The end user will notice no difference in most mirrors, except somewhat higher prices for mirrors because the material costs more.

I can't answer that question unless I know the measurements of the instrument, the required fully illuminated field, etc. In general, the telescope builder is the one that determines this.

-For new telescope mirrors 32" and under I usually achieve a scratch-dig rating of approximately 20-10.
-Also, almost all new mirrors that I make in these sizes have no scratches or sleeks.
-However, it is impossible to completely avoid the occasional cosmetic blemish in the form of a few small residual pits, bubbles, or sleeks, so for normal telescope mirrors, I do not promise a perfect, blemish-free surface. However, any blemishes that are present are merely cosmetic, and while they may be visible on the surface of the mirror, they will not affect the images formed by the telescope, so there is no reason to be overly concerned about them. They have less effect on the image than a few minutes of dustfall!
-On larger mirrors, more factors come into play. It is far easier to miss blemishes, and since the polishing time is longer and the area of the mirror larger, the chance of getting a sleek increases. Sometimes the glass itself may have more defects that I cannot control. So, for these larger mirrors, I do my best and typically achieve better than a 60-40 scratch dig.
-It pays greater dividends, in terms of image quality, to spend time tweaking the figure of the mirror, which will affect image quality, than it does to worry about some cosmetic blemishes that will not affect image quality.
-In certain glass, especially surplus quartz blanks, bubbles are common, and I cannot guarantee a bubble-free optical surface because I cannot reject an expensive and difficult-to-get blank just because it has bubbles.
-For refigured mirrors, I generally improve the polish quality of the mirror, but don't any pre-existing scratches to go away. If there are sleeks or scratches that you wish to have removed, then this generally requires many, many hours of polishing or regrinding, which will greatly increase the price of the work compared to the price of simple refiguring.
-If you have a scratch/dig requirement for a particular application, then please specify it when requesting a quote and I will quote appropriately.
-If no value is specified, then I will assume a value appropriate for the use of the mirror. For mirrors that are simply collecting light, a perfect polish is not necessary, and will unnecessarily raise the price of the optic. For telescope optics, the mirror will be thoroughly polished.

Frequently Asked Questions