30+inch+F4.6+Primary+Mirror+for+sale

A short video (2 file types) of Jupiter on the 9th March 2015. Note there is NO tracking and the image scale is small. Seeing was not great but you can see detail on the surface quite well. The moons are seen as different sized discs too. The disc is a little too small for Registax to get the best detail. Needed tracking and a barlow to get the best from it. Much more detail could be seen visually compared to the video clip. Colour QHY5 camera used and a rather slow PC. Note the mirror was un-coated for these video clips so brightness down a lot and exposure times up. WMV MP4



**30 inch (760mm diameter) F4.6 Parabolic Primary Mirror** This old mirror had been stored in its box for many years and On inspection the mirror’s coating had significantly degraded and moisture, of some description, had been on the surface and had possible etched into the glass.

Jupiter was a fuzzy blob with only the two equatorial belts visible, clearly it was not finished. The mirror was then tested using an interferometer to check for its surface form. Unfortunately the surface was significantly under corrected (2 Waves PV on the wave front). The coating was removed only to find that the surface had been etched.

Since then the mirror has been completely re-polished and re-figured. Testing has been done using the interferometer and star testing. Telescope test rig has a axial 18 point whiffle-tree and 3mm steel wire lateral support on the centre of gravity.

Jupiter shows great detail and the moons can be seen as different sized discs with colour (even though at the moment it is uncoated). This will make a fantastic telescope for deep sky viewing. A 30 inch blows away even a 20 inch as the TROK used to demonstrate. There are not many telescopes available this size around and you have to wait often years, and pay huge amounts, if you order one. A Paracorr coma corrector will reduce edge coma at low power at this F ratio, but it is not that objectionable without a corrector to be honest. That is personal choice. The small black edge around the mirror in the image is the bevel blacked out for testing.

Surface form is better that ¼ wave PV on the wave front Interferometry testing (OpenFringe):-
 * 0.897 Strehl, 1/19.1 rms wave front using a low pass 0.6 filter
 * Surface is 15.44 nm rms using a low pass 0.6 filter
 * 0.901 Strehl, 1/19.4 rms wave front using a low pass 0.4 filter
 * Surface is 14.17 nm rms using a low pass 0.4 filter

Open fringe calculates all final data at 550 nm. No matter what the laser wavelength is. Therefore surface is (1/19.4 * 550) / 2 = 14.17 nm rms on the surface

Image below is of the surface at 0 .901 Strehl, 1/19.4 rms wave front using a low pass 0.4 filter. Laser was calibrated and verified using an Ocean Optics spectrometer that I use in work and also against a Star Analyser and Rspec.

http://datscope.wikispaces.com/Bath+Interferometer

The mirror has now been coated and been on sky with the coated mirror on the 22nd September 2015. Stars look good and small and snap to focus.





The borosilicate primary is 45mm edge thickness and is uncoated at the moment as it has just been completed. The mirror price is supplied uncoated or coated (at additional cost) as stated below. A brand new secondary I have is available at cost if required.

The mirror will be delivered for additional cost (van hire and fuel), or the new owner can take the mirror away in its transportation box following on-sky inspection and payment clearing.

A new transportation box will be provided that is 900mm x 900mm x 250mm. Weight of this with the primary inside will be approximately 60Kg. This sized box will fit into a large estate car such as a Volvo V70 or a small trailer.

If you want to get the telescope about once you have built one then look at the 30 inch TROK telescope trailer that I built. It is possible to build a tube assembly that would fit inside a V70 Volvo or a small van with ramps and an electric winch (which would be best).

Prices:-

30 inch (760mm diameter) F4.6 Parabolic Primary Mirror uncoated = £5000

30 inch (760mm diameter) F4.6 Parabolic Primary Mirror coated = £5700

New 130mm minor axis Orion Optics secondary (HiLux coated) = £312

Note the telescope test rig is not included in the prices above. Optics only.

An image of the test rig with the mirror in is shown below. This gives some scale to the size of the telescope when it is built up. The test rig is not the completed telescope, just a rough wooden set up for testing 30 inch mirrors.





Below is the mirror after the coating was removed.

Below shows the error map at the start of figuring. You can see the high edge and centre in red and low 70% zone in blue/green showing spherical abberation

Below is the mirror prior to coating at GalvOptics August 2015.

Below is the mirror in teh test rig cell on the 22/09/2015 for 'coated' first light.

Below is Bren looking through the telescope on 22/09/2015 for coated first light and focus/balance check. Stars were good and snapped to focus. We managed to get it out of the garage, assemble it, collimate it, check on sky for a few objects, dis-assemble it and then get it in the garage in around 45 minutes before the clouds came in and some rain started!