Mystery lens and optics tube?

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  • #575139
    David Strange
    Participant

    While engaged in scrub clearance at NLO our team came across a black bin bag in some gorse which had we believed had only recently been abandoned there. It contained a large 7″ lens mounted in a brass tube with a slightly smaller lens ~ 6″ at the other end, the whole assembly must be about 18″ long. The optics were in good condition with no sign of damp ingress into the tube.

    There was also a smaller brass tube without lens (diameter 3″) with a curious adjustment engine at the other end. There was no eyepiece but just a small right angle prism with a tiny 5mm exit hole. Please see attached images. We are curious to know what these lens were used for, and from where they originated. Were they returned stolen property? Or was it just someone wishing to clear out their attic, if so why didn’t they leave it at the front door rather than toss it in the hedge? Please help us solve this mystery – any comments much appreciated!  David

    #585132
    Denis Buczynski
    Participant

    Hi David,

    The large lens (7 inch) may well be the original 7 inch  f/7 Zeiss astrograph lens that was missing from the Mond when Glyn Marsh and I rescued the instrument from NLO. The 7 inch lens was missing and was not amongst the other astrographic lenses we collected and are now back at NLO with the Cooke/Mond Astrographis mount. The 7 inch that you now have was one that Harold Ridley passed on to Glyn and did not come originally from the NLO.The lens design of the lens you ahve just found may be that of Petzval Doublet. The small 3 inch refractor looks like a guide telescope with a sliding plate that carries the eyepeice and diagaonal across the FOV to allow the observer to selected a guide star. I would guess that both instrument s were part of the original Mond Astrograph or from another of the large telescopes there at NLO. I have taken the liberty of posting your message and images on the Antique Telescope Forum to see if anyone ther can more positivley identify these instruments. Denis Buczynski

    #585134
    David Strange
    Participant

    Denis, that’s fantastic news if it’s true! Really opportune as well, as we are now starting to plan for the Mond’s installation.

    If it helps, here is a picture of the other end of the 7″ lens tube. Thanks very much for that information. David

    #585135
    Denis Buczynski
    Participant

    The main fact to find out is whether the optical design of the 7 inch you have found is a Petzval doublet or a Zeiss triplet(telephoto) . The original Zeiss triplet on the Mond was a triplet of f/7. Cooke mounted the Zeiss lenses onto the Mond astrograph for Robert Mond.I would look for some markings on the lens cell/housing which may show it to be a Zeiss.

    Denis

    #585136
    David Strange
    Participant

    I could find no manufacturer’s engraving or any stamp or symbol to say who made it. David

    #585138
    Denis Buczynski
    Participant

    It would be worthwhile measuring the focal length , the original Mond Zeiss 7 inch was f/7. Also have a look at the 7 inch Zeiss triplet lens that we sent back to NLO (the one Harold Ridley passed on to Glyn) and see if they are similar.

    #585163
    David Strange
    Participant

    Hi Denis, Do you know who was the author of this blog post? There is much useful information here and |I would like to credit him/her, but it seems anonymous as far as I can tell.

    https://srmmt.blogspot.com/2005/01/sir-robert-mond-and-history-of-norman.html   

    Thanks David

    #585164
    Denis Buczynski
    Participant

    Hi David, I do not know who wrote that article. I see from the end postscript that he/she had a private communication with Glyn who must have given him details after the removal of the Mond Astrograph from NLO. I will ask Glyn’s wife, Christine, if she knows who wrote it. I remember that there was a book about the history of Sir Robert Mond amongst the material I sent down to NLO with the Mond Astrograph and the measuring machines and some documents that Glyn had assembled. Did you manage to compare the  7 inch Zeiss lens that Gyln had on the Mond Astrograph and the mystery 7 inch you found? Was the focal length of the mystery 7 inch determined?

    #585165
    David Strange
    Participant

    Denis, we have a meeting on Friday to discuss and plan the re-instatement of the Mond telescope. We shall do a comparison of lenses then. We have been busy with a general refurbishment of the NLO entrance foyer, and the Mond is the next item on our to do list. I’ve just found this Jim Lockyer lantern slide of the Mond as new, taken at the Cooke works circa 1931. Interesting that Robert Mond paid £2171-5-9 for it which is £161,457 in today’s money.

    #585179
    David Strange
    Participant

    It’s looking increasingly likely that this is the missing Mond lens. It’s aperture is 17 cm and the focal  length seems to be around 120cm when bringing a ceiling light into focus on a screen, which agrees with the original specification in NLO Handbook 1935. We have also found some numbers inscribed into the rim of the lens carrier but cannot read them clearly enough yet. The lens also fits comfortably into the front of the telescope tube. It does look like a petzval lens as you suggest Dennis, so my only query is was the original lens a petzval? We also believe that the accompanying guidescope is also original to the Mond. We believe it is the bottom section of a longer instrument which you see in the above photograph. I thought it just had its lens missing but now believe another longer brass tube holding the objective lens was located over the end of this short one.

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