18.5 inch (470mm) 3.5 inch thick ZERODUR High Precision Spherical Mirror
An 18.5 inch diameter ZERODUR mirror in a metal cell. The actual mirrored surface diameter is slightly over 18 inch (~460mm), since the edge of the mirror blank is chamfered. The mirror is thick - (edge) thickness is 3.5 inch (88.9 mm).
This is a concave spherical mirror, the radius of curvature (NOT the focal length - that is half of this radius for paraxial rays) is 24.5 inch (622.3 mm) (I verified it with a laser retroflection test, checks to within ~1mm).
This mirror is made of zero-thermal-expansion glass-ceramic (Schott ZERODUR), and was made by Perkin-Elmer (the company which made the Hubble Space Telescope mirror).
According to the previous owner, it was made for a very expensive photolithography system for making VLSI chips, and was fabricated as a vey high grade optic (for “Offner relay”-like arrangement) to attain maximum contrast and resolution in projecting the IC mask onto silicon wafer, with typically better than lambda/40 accurate mirror surface figure and also very smooth, ripple free polish to get the best attainable contrast of projected IC features. While I can not confirm those claims, the material and thickness of the mirror and the overall high quality look of the mounting hardware, and seemingly vertical intended mounting position seem to support that purpose and quality claim (but again, it is merely an observation and speculation on my part, not a guarantee).
I guess one could build, for example, a great Baker-Nunn - like or a Baker Super-Schmidt - like super-fast wide-field astro camera based on this mirror - check e.g. https://www.slideshare.net/operacrazy/dennis-gabors-catadioptric-design-and-some-new-variations for inspirations, and e.g. http://articles.adsabs.harvard.edu//full/1992PASAu..10...74C/0000074.000.html concept for redesigning a Baker-Nunn camera for CCD imaging (make it a flat-field camera). Perhaps, when paired with a right software, such a camera based on this mirror could make an ultimate amateur automated comet hunter.
The mirror is, to the naked eye, in excellent condition. The mirror surface has no visible stains, chips nor scratches. It is also reasonably clean, with some dust particles visible under strong light - I did not attempt to remove any dust particles or clean the mirror in any way - I shall leave this to the buyer if he/she is compelled to do so..
The cell seems to be in a good condition, with some rust-colored spots (which look superficial, not deep rust - I did not attempt to clean them, but I suspect a little rubbing with fine steel wool would do the trick.)
Item Condition: Used
California buyers: please add CA sales tax.
Shipping: will only ship to an address in the USA. Please contact me with the destination information, we should discuss the options and costs of shipping/insurance. Due to the weight of the item (needs a shipping pallet) it will have to be shipped freight or picked up locally (San Jose, California, ZIP 95125). Freight cost depends on distance, and should be paid by the buyer (added to the item price) before shipping. UPS or FedEx preferred. Will only ship to the buyer's confirmed shipping address; the shipping addresses cannot be changed after an item is shipped. On delivery a confirmation signature will be required.
Return Policy: No returns.
Contact me: Please feel free to ask any questions.
Filed under: Eyepieces & Accessories