Sky & Telescope October 1955 Cover

It was decided to bring the mirror back, and eventually it was left boxed in the basement of Dunsink Observatory.

Could that be where it is now, or in storage somewhere else? It could be a good project for an astronomy club to resurrect it and try to recoat it, get it 'working' again... Otherwise, its just lying idle, which, for its size, is a real shame. :x

Seanie.

It was decided to bring the mirror back, and eventually it was left boxed in the basement of Dunsink Observatory.

Could that be where it is now, or in storage somewhere else? It could be a good project for an astronomy club to resurrect it and try to recoat it, get it 'working' again... Otherwise, its just lying idle, which, for its size, is a real shame. :x

Seanie.

is not the ADH mirror ( armagh, dunsink, harvard) mirror from south africa not also stored in dunsink , or at least i think it was at one point.
stephen.

The 32/36 inch Baker-Schmidt telescope, jointly established by the Armagh, Dunsink and Harvard Observatories, ran out of funds back in the 1970s Because Harvard had a 90% share, while Dunsink and Armagh had 10%, Harvard pulled out. No other institutions offered funding. The main reason was that Ireland was signatory to the United Nations resolution forbidding, or at any rate strongly deprecating, cultural relationships being maintained with South African institutions that implemented apartheid, or racial discrimination.

In addition the ADH telescope presented severe technical problems which I can go into another time if you need to know. The other factor was that Schmidt telescopes at the time were been gradually eclipsed by other telescopes with CCD cameras during the late 1970s. Unfortunately the timing was bad technologically because no one had attempted to build the future Mosaic CCDs that we have now for example for the upgraded Palomar 48 inch Schmidt telescope. The ADH telescope was offered to Dunsink, but the cost of dismantling, transport and resurrection was prohibitive. The optics were the only items brought back to Dunsink. They have been stored in one of the out houses within the grounds of Dunsink.


The ADH telescope was a flat-field two mirror Schmidt system with a plate scale equivalent to the Palomar 48/72 inch Schmidt. Although the mirror was 36 inches in diameter, the correstor plate was a 32 inches and this was severely obstructed by a large secondary mirror of 18 inches in diameter; so the effective aperture was only equivalent to that of a clear 26 inch aperture, corresponding to 0.52 of the area of the main mirror. There was vignetting at the edge (12.5%)


I discussed with Patrick Wayman (Director of Dunsink) back in 1988 to resurrect the instrument. He showed me these optics if I was interested to build the mount and drive system at no expense to Dunsink. At the time I was interested in building another telescope. Because the Schmidt OTA would be double the size of a normal telescope, it would mean designing and building a massive mounting and drive system. I believe the optics are still there.

I did come up with another design that could have achieved a considerable reduction in cost and weight. In the end I thanked him for the offer. I eventually built a smaller 11/16 inch Schmidt telescope, that I was able to use for wide field photos successfully.

I think the 28 inch mirror would be more feasible to resurrect and
the mounting would have to be upgraded. The site location would have to be better. But all this is another possible project. Is anybody seriously interested?



Eamonn A

Seems such a shame to leave it out of service. Maybe it is something IFAS could do as a joint project pulling on resources from a number of clubs. There's a great deal of expertise out there if people were willing to donate time and raise some money. Could end up with a useful resource that could be shared amongst IFAS clubs.

I think the 28 inch mirror would be more feasible to resurrect and
the mounting would have to be upgraded. The site location would have to be better. But all this is another possible project. Is anybody seriously interested?

Not saying this in an official capacity, but, seeing as TAS is in the process of refurbishing its dome and mount, and with proper funding, it could take it on as a project. It would not have to be a TAS scope, in that anyone can get involved. I am only mentioning it because, as far as I am aware, apart from yourself Eamonn, there is not really another public accessable observatory around the whole midlands - and that includes the Birr Leviathan.

Seanie.

The restoration of the 32/36 inch would be a huge and complex project to suceed, besides aquiring the necessary funding. It would be sensible to resurrect the 28 inch telescope. It would be easier and far cheaper to resurrect again as compared with the ADH.

The 28 inch telescope was specifically fork mounted because of the space limitation on top of the small Dunsink dome in the main building.

The telescope has an effective focal length of 30 feet. Since the main mirror has no central hole, a rotational diagonal flat of 9 inches minor axis is in front of it and in the plane of the declination axis, serves to throw the image into different positions. The OTA is a solid tube.

My suggestion is that because it is a Cassegrain configuration, I would get rid of the convex spherical secondary which has been acting as an amplifier and use an appropriate small diagonal mirror and use it as a newtonian. Besides, the primary is parabolic. However, if it was only used as an imaging telescope (non visual), use a flat mirror at the top to send the cone of light to the imaging camera. It would allow wide field imaging with larger CCD cameras of the future. If there is coma, this can be easily overcome with a coma corrector to achieve for a flat field.

I think the 28 inch primary mirror can be stripped and cleaned. It then can be optically tested to find out the existing surface profile. Once that is interpreted, refigurring can be done and then aluminised. If one decides to go the newtonian route, an appropriate secondary mirror can be matched.

The mounting, drive and tube would need to be examined. I would suspect it is in good condition and could be refurbished.. I believe the mounting and OTA were originally lifted in by crane.

Once the drive mechnism is made working, the original motors could be replaced by stepper motors and interfaced with new microcontroller system
so that you have a GOTO system.

If their is serious interest in ressurecting the 28 inch I think it should be a major telescope for the IFAS community. I do realise that this is not an easy decision to make for everyone because of the scale of the project.

However, I think it would be worth a feasibility project at no cost, just some time needed to first, does everybody want a telescope that could be accessed by IFAS members on a scheduled basis. Because it is in education, I believe there are grants to support such a scheme if it fits the criteria. We could take the opportunity of time for discussion may be at the next Whirlpool, to see if there is a general agreement or not to pursue this further.

Eamonn A