20-Inch-Telescope-Mirror

Perkin Elmer/Boller & Chivens 20" F5 primary telescope mirror

Per John Urciolo

Regarding the mirror... It came from a former NASA facility that excessed it along with the Unertyl mount. There are no specific numbers on any part of the mirror or its heavy circular housing. I was able to determine that it was made by Perkin Elmer/Boller & Chivens from the original government sheets. No additional information such as a model or serial number was provided by NASA. The Unertyl mount is intended to allow X-Y positioning of the mirror while holding it securely on an optical bench (for optical calibration??). I am assuming this mirror to be parabolic due to the fact it was intended to the best of my knowledge to ultimately be used in a telescope.

I see from your website that you sell Pyrex glass telescope primary mirrors. Please let me know if you can use one Perkin Elmer/Boller & Chivens 20" Pyrex F8 front coated telescope mirror I have for sale (turns out to be 4" thick rather than 7" as shown in the pictures). I also have available one optical bench mounted variable X-Y positioner for this mirror custom manufactured by John Unertl (Model YMM-C). Four pictures are attached.... Thanks.

My Deductions

The central hole appears to be about 4 inches in diameter. Boller and Chivens was a telescope company that was bought by Perkin Elmer is my conclusion and they made optical telescopes and some spectrographic instruments. The mirror figure is either suitable for a human viewing telescope or a schmidt camera. The curvature implies human use.

Notes

• www.clausing.com
• Clausing quotes at 500 USD + return shipping for re-coating
• John came back with a figure of 0.25 inches for the sagitta of this mirror
• Online Sagitta Calculator
  
  
• http://www.spectrum-coatings.com - 11 dollars per inch = 220 USD for entire mirror - This seems to be a better process that is more modern than Clausings.

Engineering Notes

• melockwo@uiuc.edu
• Mike Lockwood - Illinois He can check your mirror and fix anything that is wrong. He can also make the corrector or secondary. He is a mirror/optics god. Contact Mike, he is a good bud, great guy to work with. He wants to be our mirror guy so let him know you is the dude with the casting stuff.

Optics-Talk-With-MikeL

Spectrum Coatings

Address:

• 1165 Ring St.
• Deltona, FL 32725
• Phone: (386) 789-6662
• Contact Person: Paul Zacharias

Inputs Value

• Sagitta ==== 0.25 inches
• Diameter ==== 20 inches

Mirror Parameters

• ROC ==== 200 inches
• Focal Length (F) = R / 2 ==== 100 inches
• Focal Ratio (f) = F / D ==== 5X

Freight Costs

As quoted on the phone by Yellow Freight

• class 65 item # 86730-1
• general cost = ~ 380
• Quote number= 30217017
  
  

As quoted online by UPS

• UPS Ground Billable Weight: 150.0 lbs. === 120 USD*

Weight Calculation

• r=10*2.54 = 25.4 cm
• t=4*2.54 =10 cm
• vol=3.14 * r^2 * t
  
  
• mass= vol * 2.33g/cm^3 => 47 kg

weight(lbs)( assuming 4 inch thickness) = 2.2 * 47 = 105 lbs

Box Size Estimate

UPS uses a dimensional limit as follows:

L + Girth <= 165 inches

Assuming a box 36 X 36 X 16 inches:

36 + 2*(36 + 16)=140 inches.

This is well within the UPS limit

• UPS Dimensional Weight

Conclusions

• Since the mirror is an F/5 it probably requires a corrector plate
• Since it has a hole in the middle the tube length would be on the order of 50 inches or about 4 feet. This is very short for such a large aperture. Very desirable I would guess for this reason. Sub-Reflector will not be a flat.
• I will need to get access to a knife edge tester to test this mirror. Without figure data the mirror sell price will be much lower than otherwise possible.