A Project is Born
In the latter half of 2016 Professor Paul Callanan, Department of Physics at University College Cork (UCC), approached the Cork Astronomy Club to explore the possibility of undertaking a joint project working with the 138 year old Grubb telescopes housed in the Crawford Observatory in UCC (pictured below).
Paul had a central role in the original 2006 restoration of the Crawford Observatory. The informal project brief was to undertake work to get the telescopes working with modern day visual and astrophotography equipment. Members of the club would provide design help and testing whilst UCC, led by the Professor would undertake changes and any required engineering. The project constraints would be that the observatory was now surrounded by buildings, trees and the observatory and its contents were Grade A listed. Any work carried out must respect the protected status.
Crawford Observatory 1880's (left) & 2015 (right) [Wikipedia]
Historical Background to the Observatory
Construction was between 1878 and 1880, the observatory was funded in part by local businessman William Horatio Crawford of Beamish and Crawford and by the Duke of Devonshire. The building was designed by Howard Grubb, one of the foremost scientific instrument makers of the nineteenth century. Grubb also designed and constructed all of the instruments and clocks for the observatory including an equatorial telescope, a transit circle and a siderostatic telescope. It is particularly due to the survival of the original equipment in situ that the building merits its national rating. Originally it was in its own field at the top of the hill, the nearest building being the County Jail but over the passage of time new buildings sprung up as the university expanded. It is the only telescope within a University grounds in Ireland. For the purposes of this type of project that is a distinct advantage.
The 8” scope and its clockwork design received a Gold Medal at the Paris exhibition of 1878 before it was installed. Clearly at the time it was at the cutting edge of astronomy. The 8" telescope was installed during the period 1878 - 1880 and the 13" astrographic tube assembly was added probably in 1890 or 91. Three years before, in 1887 the first international astronomy conference took place in Paris sponsored by the Paris Observatory at which the Carte Du Ciel project was launched. This project was to map the sky from various points in the world. In all 18 observatories agreed to take part in the project and all had to employ the same astrographic instrument originally proposed by the brothers Henry of the Paris Observatory. That is a 13 Inch Astrograph (Refractor) with a focal length of 343 Cm (Focal Ratio: 10.39). On a the photographic glass plates of the time used on all 18 scopes this would result in 1mm on the glass being equal to 1 minute of arc ensuring that all data was interchangeable. The Grubb Company supplied 7 observatories with either a complete instrument or, in one case, just the 13” lens. For Cork they supplied the complete tube assembly.
Over the years the telescopes fell into disuse and disrepair until 2006 when the observatory reopened after a €500,000 renovation project. If you look at the trees surrounding the observatory you can see that they were also pollarded at around that time to clear the view. Whilst the 8" with its original eyepiece was always operational to an extent the 13" probably was not used for many decades No information is available as to when the 13” astrograph was last used so, to our minds, the 13" seemed to be a green field awaiting the historic "first light" with a modern camera.
Grubb Telescope on the night of testing: From top right - Findescope, middle - 8” Refractor, bottom - 13” Refractor
Original eyepiece & photographic parts of the refractors. Left the original plate holder of the 13”, Centre – the eyepiece fitting and focus knob for the 8”, right – the original eyepiece in its screw fit 8”adaptor.
Design and Modernisation
Over the later months of 2016 the club met with Paul Callanan to review the telescopes and agree next steps. From the Club Jan Cap, a member since 1976, was the main contact with UCC. Out of their discussions the Department of Physics workshop at UCC rebuilt the eyepiece end of the 8” and replaced the glass plate holder of the 13”. This was done in such a fashion that new parts could be removed and replaced by original fittings. The originals are kept available for public viewing within the dome.
At one point the question was raised as to whether any other similar Grubb telescopes had been reinstated in a similar project to this. Paul Callanan didn’t think so and he added – “that’s what makes this a fun project”!
Both replacement features were designed for a 2” push fit to accommodate modern equipment and 1.25”adapters. For the 8” a new “visual back” was made which sat below the focus mechanism. For the 13” a new brass box rather like the original plate holder but now boasting a 2” lockable draw tube was fitted. Holding screws were placed so that the tube could be moved in or out for focussing. It was important for the tube to extend to the point below the scope where previously the glass plate would have been located as this is the focal point of the telescope for eyepiece and photographic purposes. The original focus mechanism in the 13” remained in situ and moved the focussing point forward and backwards by about a inch each way.
The 13”modifications ready to take images via a Planetary Camera
Proof of Concept
We wanted to test out the new features on the moon as a large bright target not impacted by the city and local light pollution. So whilst December and the festive period passed the next moon was awaited, and diaries aside, we marked in the 7th February at 20:30 hrs for a proof of concept test.
The telescope, not being “goto” nor having a working tracking mechanism and being rather large, needs several sets of hands to achieve results in situations like this. It can be moved easily with one hand but more hands in this situation seemed to be needed. The team from the club on that night was Garry O’Brien (myself), Jan Cap, Tony Jackson, John Cuthbert and Declan Foley. The plan was to achieve confirmed images via eyepieces and viewable images from both telescopes using a planetary camera and laptop.
We started with the eyepieces on both scopes and they worked with no problems. Next we placed the camera within a 1.25 adapter where it stayed with no problems on the 13”. The laptop was at the opposite side of the dome on an upturned crate as the interior of the dome is not gifted with tables or benches. Jan targeted Copernicus for all imaging tests and attempted to keep the scope on target and in focus – not an easy task in the event but achieved with suitable encouragement from the other team members. As a precaution I had fitted a safety strap to catch the camera if it or the 2” adapter fell out. The camera settings were originally Bin 1 and auto for exposure adjustment, and the largest frame size to capture focus. For a good 10 minutes it was impossible to get any focus by moving the tube in or out. Clearly there was some form of image there on 640 x 480 frames and larger but eventually I selected bin 4 which made the task easier. Each time the target was in focus the call would go out to hold it there and the video run started. It was expected that the target would move from the lower left of the frame to the top right and to capture around 200 – 300 frames at 52 FPS. On the night the direction proved roughly correct and it captured between 53 and 599 frames.
Out of 11 runs I rejected 7 as too blurry and did a quick on-site process of the other 4 in Registax where we all could see that we had fairly decent images of the moon and, as such, this part was a success.
Clearly we needed a finer focussing mechanism and more about that later. At home I took my time to process the four good videos putting one, which juddered all over the place, through PIPP (Planetary Image Pre-Processor) first. As the images all cantered around Copernicus I found they would fit together as a mosaic which gave a better presentation – see image below –
The result of testing the planetary camera on the 13” Refractor.
Jan placing a 1.25” eyepiece into the newly provided 2” holder on the end of the focuser
Turning the attention to the 8” the target was changed to Mare Imbrium but focus could not be found. Experimentation proved that the new visual back pushed the focus point out too far. With this removed Jan held the camera in place with his hands inside the telescope tube which achieved three videos runs that all processed smoothly.
One of the images of Mare Imbrium from the 8” refractor – note the blue/green tinge at the top
Results of Proof of Concept
Clearly visual and photographic use of both telescopes was achieved. In some ways this was “First Light” for the 13” refractor in terms of digital imaging after 139 years since it was built. We met with Professor Callanan the following week and made recommendations for adjustment to the tube, its holder and creation of a form of Crawford focussing mechanism on the 13”. The tube also needed a coat of matt black inside to prevent light reflection problems. The new eyepiece holder on the 8” holder needed shortening to allow the point of focus to move inwards.
So far I have omitted to describe other aspects of the telescope which we hope to build upon or investigate. The clockwork tracking mechanism is still in place but for various reasons not operational. At a further date I hope we will be able to update you on progress with this. The intention is to connect an electric driving mechanism to replace the winding handle of the upper portion of the original drive. The lower part of the clockwork mechanism which included the driving force of the mechanism is located inside the rectangular pillar of the mount and was originally connected to the upper part (shown here).
The upper portion of the clockwork drive from left and right hand viewpoints
The current upper mechanism can be driven via the winding handle rotated at one revolution every two minutes to give the correct counter rotation for tracking. We are looking forward to seeing how this will work with a variable drive electric motor instead of the handle. The handle would need to be rotated at the speed that would corrrespond to one rotation of the worm drive mechanism every 2 minutes. The sector drive was able to guide the telescope for 2 – 3 hours before it had to be reset . The exposure of Carte du Ciel negatives were 40 minutes long. Research by Jan indicated that other Grubb telescope mounts were incredibly precise and had an accuracy of 0.20”.
The optics for the scopes are unlike modern telescope designs. The 13” optical design of the time had to take into account that the emulsions used on glass plates then in use were most sensitive to the blue part of the spectrum. Therefore it is not suitable for visual work unlike the 8” which is, as are all visual achromatic instruments to this day, corrected for the yellow/ green part of the spectrum to which the human eye is most sensitive. Some colour cast was detected in our first images and it will be interesting to see how various filters might affect images in our future experiments. We hope that the new drive will soon be installed and the workshop can, despite its considerable workload, complete the manufacture of essential adaptors so that we can resume our efforts over the spring and early summer when the moon, at first quarter is high and therefore unobstructed by the nearby buildings. We can then look forward to providing the next installment of our adventures with this unique Victorian instrument.
The author using the Grubb 8”fitted with 2” modern eyepiece
Grubb 8” Equitorial Refractor, FL 300 cm (not measured) Focal Ratio F15 , Installed 1878
Grubb 13” Equitorial Refractor (previously titled astrograph), FL 343cm, Focal Ratio F10, Installed c1890 or 91. Built for imaging onto glass plate.
Grubb 1878 clockwork modified at various points over initial 30 years. Manually set and showing setting circles.
Imaging Telescopes: as above
Imaging Camera: Neximage 5 –
Software: iCAP, PIPP 2.5.9, Registax 6.1, Adobe Photoshop Creative Cloud 2015.5, DStation 0.5
All images are by the author except the 2 views of the observatory copied from Wikipedia.
The Cork Astronomy Club would like to thank Professor Paul Callanan for including us in this exciting project and to Christy Roche in the Dept of Physics Workshop for his work in making the adaptors, and, especially in making them in a style in keeping with the original design of the telescope. I am indebted to Jan Cap for his encyclopaedic knowledge of the Grubb telescope into which I dip at frequent occasions and for his tireless design work with UCC. To my colleagues on this team who supported us during design and testing and proof read this article for me.
For complete list of Grubb Telescopes: http://www.saao.ac.za/~isg/g.html
To see the exact position of the observatory relative to buildings in 1888 go to OSI.ie and review the map of Cork with that date.
Garry O’Brien, February 2017