Mirror Diameter - 508 mm (20 inch)
Mirror Thickness - 35 mm (1.375 inch)
Focal Length - around 2250 mm (88 inch)
Focal Ratio - F/4.5
Material - Supremax33 low expansion glass, fine annealed, made in Schott AG factory in Germany
Coating - Aluminum coating 91% reflectivity
Mirror Weight - 12 Kg
Circle in the center for easy and minute collimation
Strehl > 0.8
Interferometer test report included
Price - 3,250 CAD
Availability - Yes
Telescope Specifications - Sky Observing 20 (Complete Telescope with 20-inch mirror)
Primary mirror - 508 mm diameter (20 inch) - see above mentioned mirror specifications. The 1.375" thin mirror cools fast in about 1 hour and after follows the air temperature drop during the night. Compare this with thicker mirrors which are not capable to follow the temperature drop during the night. Primary mirror which is 2 inch thick will need forever to cool down, and even if we suppose is cooled down, it is not capable to follow the fast temperature drop of the air after the sunset. And also the slow temperature drop of the air after midnight. In every astronomy forum people report how they need to use several additional side fans at full speed to blow away the hot air from above the ever cooling thick mirror surface in order to do observing.
Focal Ratio - F/4.5
Focal Length - around 2250 mm
3.5 inch minor diagonal secondary mirror from well-known supplier, 1/10 wavefront error, enhanced aluminum coatings 95-96% reflectivity, interferometer test included
Heavy duty spider and secondary mirror holder with requred off-set from well-known supplier
Top of the line Feathertouch dual focuser 10:1, low-profile, the newest model FTF2015BCR, 1.5 inch travel. Feathertouch focusers from Starlight Instruments are the best focusers in the world
Secondary mirror dew heater with RCA jack ready to connect to 12 V DC power
Cooling fan ready to connect to 12 V DC power
1 inch diameter aluminum trusses, very strong and lightweight, they are connected in pairs at their top ends for faster and easier installation
Aluminum handles, lightweight with 6" wheels
Wooden box for storing and protecting the mirror when not in use
Light shroud made from quality stretchable material
Baltic birch cabinet grade hardwood used - stained and varnished several times
The telescope is optically and mechanically excellent. You can apply up to 500 magnification in a night when the seeing is excellent (no atmospheric turbulences). The scope holds its collimation without any problems all night - once you collimate the scope - it is collimated till the end of observing. Very easy to collimate. It takes maximum 5 minutes total time.
Mirror cell is with 18 points supporting without problem the mirror. No fancy things placed bellow the mirror to act like a mirror cell reinforced with some scientific theories to make you think that the mirror is supported properly. Mirror cell is all steel in order to be strong and not deformed under the weight of the mirror.
Mirror is held by steel cable with adjustable length (again no fancy mirror holders coupled with some scientific theories) - very easy to place the cable around the mirror and also very easy to center the mirror inside the mirror box simply with adjusting the length of the cable sling - you just tighten the cable sling and the mirror is centered in the mirror box. Adjusting the cable length is very easy. Also cable sling can be adjusted very easy in height to match the height of the mirror which you can change if you lift or lower the mirror cell.
Fine 24 TPI (threads per inch) collimation rods and big 2.25" diameter collimation knobs make the colimation very easy.
All work in the mirror box: positioning and centering the mirror, attaching and adjusting the sling around the mirror, tightening the mirror pins and clips and whatever else can be done by hand and very easy without effort and frustration, no tools required. Everything is with knobs. Once you collimate the scope there is no need to check and do it again, it is collimated till the end of the observing.
The telescope is designed to perfection - it is classic, lightweight and portable at the same time - making it easy to load, transport, unload, move around and set up. Also the bearings are detachable which allows the whole scope when disassembled to fit even in a small car to transport it to dark location for observing. Excellent design allowed the mirror box to be only 7 inches tall and rocker box to be only 4 inches tall too. See pictures - rocker box is almost lost in the grass. Top of the mirror box is only 12 inches above the ground level!
Moving the scope in altitude and azimuth is very smooth and precise and requires very little force from one finger. Big bearings make the movement even smoother and easier and allow very precise positioning on the target.
The telescope have perfect balance. Excellent design of the whole telescope allows the telescope to perform perfectly regarding its balance. Furthermore you can load the telescope on its top side with heavy Paracorr2 and heavy Nagler31 eyepiece and 4-channel dew controller with three dew heaters and 9x50 finderscope and it will still hold its balance with no counterweights needed to be attached at the bottom. Or you can go in another extreme situation - use on top side only small light eyepiece and 9x50 finderscope and on bottom side even hang a heavy battery 12 V 12 AH on the back side of the mirror box and still the telescope will hold its balance with no counterweights needed to be attached at the top. No, I do not use fantastic and patented friction control systems, knobs and nuts to tighten the scope every time you move the scope to the targets up or down. My telescopes are perfectly balanced by itself, and you can move them up-down and left-right with one finger.
Please take in mind again what you will get when you buy Sky Observing telescope. Quality optical and mechanical components (quality primary mirror, quality secondary mirror with 1/10 wavefront error, Feathertouch focuser, 27 point mirror cell, 24 TPI fine threaded collimation rods and big collimation knobs for easy collimation) and so many free extras: focal ratio of the primary mirror F/4, secondary dew heater which is already installed with wires pulled out with RCA jack ready to be connected to the controller, heavy duty spider and heavy duty holder, off-set of the holder already done, thin primary mirror for fast cooling, lightweight primary mirror to lower the total weight of the scope and also for easy manipulating with the mirror, cooling fan with jack ready to be connected to power, interferometer test for primary mirror, interferometer test for secondary mirror, primary mirror center spot for easy collimation, super low profile focuser, detachable bearings, lightweight and low profile mirror box and lightweight and low profile rocker box you can hold them even with one finger, light shroud, wooden box for storing the mirror when not in use, scale with altitude and azimuth. Check whether you will get the same when buy 20-inch telescope from other seller or manufacturer. And how much extra money they will ask to give you the same.
Every my telescope is custom made one each at a time, and after finishing is tested three or four evenings real observing to ensure that it performs perfectly optically and mechanically and to check that every single component functions properly, and to adjust the optical alignment of the components. No need to disassemble the secondary holder in order to install secondary heater and to attach or glue its wires, no need to drill holes to install the dew controller holder, no need to install new bigger and better collimation knobs and new and finer collimation bolts, no need to install fan, no need to cut and adjust the trusses, no need again to assemble and align the secondary holder and so on. The telescope is ready to start observing.
The complete telescope is lightweight, and very easy to load and unload inside a minivan using ramps and push to the observing place. I can hold the rocker box together with the base of the telescope and aluminum handles attached with wheels with one finger! And also the mirror box together with bearings! See last two pictures at the bottom of this page.
Weight of the components when telescope is in operation:
Rocker box together with the base of the telescope - 9.1 Kg
Mirror box - 18.3 Kg
Bearings - 3.9 Kg
Trusses - 5.3 Kg
Secondary Cage - 5.2 Kg
Nylon Shroud - 0.5 Kg
Mirror - 12 Kg
Total weight - only 55 Kg (121 Lb)
Add to this the dust cover over the mirror which is 1.7 Kg and aluminum handles with wheels which are 4.5 Kg when the telescope is not in operation for a total weight of 61 Kg (134 Lb).
Price - 5,250 CAD
Availability - Yes