CELESTRON 1250mm f/10 Schmidt-Cassegrain reflex lens

Discussion in 'Classic Manual Cameras' started by jdm_von_weinberg, Mar 16, 2016.

  1. CELESTRON 1250mm f/10:
    Mania, Obsession, or Just having a Good Time?

    Well, I’m back, at least for the moment.

    When I left, some souls speculated that I was past my peak, so to speak. Actually I was only passing my pique. Others failed to notice that I was gone.

    Some had suggested that I should just take a sabbatical. This is one of the fruits of that view. We shall see how it turns out this time. Perhaps in my absence, my kinds of posts have become passé, or moderation more “strict”.



    When I had posted earlier* on various catadioptric (reflex) lenses, some of the more-or-less helpful commenters had suggested that I need still larger, longer mirror lenses to prove something or other. One lens suggested was a Celestron 1250mm f/10.
    ______________
    *e.g., http://www.photo.net/classic-cameras-forum/00RaKy - various Spiratone et al.
    http://www.photo.net/classic-cameras-forum/00d4Vf -Yashinon-DX 500mm f/8 Reflex
    http://www.photo.net/classic-cameras-forum/00XSrL -Sigma 600mm f/8 Reflex
    http://www.photo.net/nikon-camera-forum/00Pzdv - Reflex-Nikkor 500mm f/8
    http://www.photo.net/classic-cameras-forum/00c1nS - Quantaray 500mm f/8
    http://www.photo.net/classic-cameras-forum/00bVwA -Maksutov MTO
    00dp0S-561650484.jpg
     
  2. In the absence of participation on Photo.net since last year, however, I had plenty of time to browse the net. I found one of these lenses offered for a little more than I was eager to pay for it. After a cycle of not selling at the asking price, however the vendor and I were able to come to a midpoint—more than I wanted to pay, but less than what he wanted to sell for.

    What follows is the result of that transaction.

    As Celestron puts it:


    Celestron's C5 Spotting Scope is a 5" (127mm) aperture, 1250 mm f/10 Schmidt-Cassegrain optical system. Its optical excellence is the reason it was chosen by NASA for many space shuttle missions.

    The astronomical/spotting scope version of this lens is the Celestron C5, and the lens can easily be rigged with various additional adapters and so forth to the C5 entity.

    Here are some basic specifications from the lens manual:

    Celestron -1250mm, f/10
    Focal Length 50"
    f/value f/10
    Photographic Power 25X
    Photographic Near Focus 20'
    Resolution mm 200 lines/mm
    Linear Coverage at
    30' 5.78" x 8.67"
    100' 1.78’ x 2.67'
    1,000 yards 55.51’ x 83.84'
    Visual Power Range- 50X-310X
    Visual Near Focus 25'
    Construction Aluminum
    Tube Dimensions 5.5”x 11”
    Tube Weight 4 lbs. (The T-mount, etc. add little more mass to the object.)
    Case Dimensions 7"x9"x12"
    Case Weight 2.5 lbs.

    Here is a diagram of the lens construction:

    00dp0T-561650584.jpg
     
  3. As a Schmidt-Cassegrain design, this is slightly different from the predominant form of catadioptric lenses that I have reported on before. The Wikipedia articles on the subjects are a good start for those who are interested ( https://en.wikipedia.org/wiki/Schmidt%E2%80%93Cassegrain_telescope vs. https://en.wikipedia.org/wiki/Cassegrain_reflector#Maksutov-Cassegrain ).
    The lens-
    <img src="data:image/jpeg;base64,/9j/4QAYRXhpZgAASUkqAAgAAAAAAAAAAAAAAP/sABFEdWNreQABAAQAAAAeAAD/7QAsUGhvdG9zaG9wIDMuMAA4QklNBCUAAAAAABAAAAAAAAAAAAAAAAAAAAAA/+4AIUFkb2JlAGTAAAAAAQMAEAMCAwYAABQeAAAvoAAAdVP/2wCEABALCwsMCxAMDBAXDw0PFxsUEBAUGx8XFxcXFx8eFxoaGhoXHh4jJSclIx4vLzMzLy9AQEBAQEBAQEBAQEBAQEABEQ8PERMRFRISFRQRFBEUGhQWFhQaJhoaHBoaJjAjHh4eHiMwKy4nJycuKzU1MDA1NUBAP0BAQEBAQEBAQEBAQP/CABEIArwBjgMBIgACEQEDEQH/xADaAAADAQEBAQEAAAAAAAAAAAAAAQIDBAUGBwEBAQEBAQEAAAAAAAAAAAAAAQACAwQFEAACAgEDBAEEAgICAwEAAAABAgARAyEEBRAgMRIGMEEiEzIHMxQjFUAWF0IRAAEDAgQDBAYHBgQFBAIDAAEAEQIhMUFREgNhcSIQgZEEIKGxwTITMPDR4UJSBfFicpIjFECCwjOistJDk1NzNDVQg+JjFRIAAQIDBgIIBQMFAQAAAAAAAQAhETECECAwQHGRQVFhgaGx0RIyklBw4SIDYMFi8PFCUnKC/9oADAMBAAIRAxEAAAD5FVBp5WVjFZuZA1CaIadNDZSGYCqR7fvct/DH6X0Zfyw/UuVPzc+z+e2eaBvIBSC6S6MNEjMqG6kvVuc2zqRhICgCgCvTho1KJqctM9ZkChNUDCEJgPe5aP0Ht3+L3pp+rIB0GBuEwvm/zr9n8/nfja1z+lxe6z2KQygBFS2KlU0BAFAFAFADdySzolzUyG8QNUACgKQBH6X+afr3yfR6WkX5Wgf0MJgw0+gDWqZuPJr8v+d+4+H9fMSfpwAUAUMGEykAQBQDpMGQFb1jRXIpmoveZnXGADGnLqo3r3Tfg/o/yfN5On3WHwuQfcY/E5d8fcx8RdfbbfB6L9/0fnnTP6H2fn2/Dp7f5x9fj0x8q/b8/wBHPkGWU7immmQBAFA+tsM9ckE0IBVjVAgjTPXpl4bwWfRXRz6aduffnppx9HYa8/j7+KMefu83Wc8tM9YjSHBpnqO3dxejnr2+x5Xs536PTh2uPN873/LNeJ4/0fJq8vxPo/F1z85dHO8wCBvt0Ti8GBGUAoAqxqBUpWsuncVnWnXydU9vf5voY6X1Yk8vm+nmnHweve8/PL6PTWPk39Y4+U0+nJ8Du9GsdNPU87sx09jt5et5xydvnD5OXV55rj8D6H53eCQs8p1Zax0YTlvLQZQAgCgCtAEGepPnjWdKn7zeL2fb+xPxv0ksfW23HGHJ5X5kX6ty/liT9Mx/OVX6IfnZX6Lp+bOv07o/KQv2Du/E+2f2o871Gx5fQkfl/nfsus6fmHnfpny2j5Z1JOLyDEDXMAoLbZjVABaAJXu+H7pvxvpfa8uvpvM+T99vJXucVXt5vtj9w07Hg/l36r+Y515k757zCpUhqgChgT6+ToH9R+i+K+0FxfNrP5H5ndy536v1HznpaPrflVOn5fn/AFT4XL88wuZctqrOUAMoNVqOU2+v+fzNZeh43sN6PkfTck+Lr7HzifVfR/nn2Q/XAjPjfl/6351r8sf6flo/Odfusq+MPsFXx0fbaV8Bn+k9I/lev6pc/O/d+f6OR+X6nix+a+T7Hkut/pvLmP1vD8h+ljbr+k/NzfB5X0Hz7lVLctNUgCCk20a5x0+nh1mvB9/zfr2+f7va8Gfouj4Bl98fAZZf0zl/OSfsPI8yk0wvTeeVdWescq6JHC9EJrEmvQ9H51519x6X5hmX69P5R01+m4/A6T9Z4XL6Wj5i/u+RPjPRz7cb8D0fP+gc/Jz08zzeuNs4ToBV15a5x6nq+VZr3fl+OY1jXrni6erWcuqbN3tOw456wmA89YUtay86VapGd9EOc612z3zrWarOsuP0Ybw+T6Hn1j52vX43Edfn89foV/Be0a8j3rxTl+f+j+csgDkBsAq7M9c06eJgveaHWpqejXLUdNsdDVuqqYGmee8azjnrOswrTUbRjcb4651trnpnWtTZoyqSz5ujFOHLSdYWeirhw9Tkc9nZ850p6fjep3T8wfQ8Eea7hyCddueuTnO50F1NmtaTHbbHedNcrNa1Dpwq0Tm1rM53GsgBavLTOp1zRrovPTOtaz3zqc9ues50yTn5ujFzMuarn6OavPYtcncDd/b4YP0vDj2WvCWuTj0ufpwc53FmjTOx3qAdtsN511y1HRAwxNnLNYianeYB0i5xrXTKs721y0zqry1NPHbIsZrnc5565JE6Kpw1yrz6Vb5E6Lecypxrf0fO7R8yQj0sejHRm0E6TNa3nVb65amtrw0nVzpQK0yVRvMKo1mSlTTjOr2yrG9NcNs60rMGhRUcu+aYRthDEUsN8K4Yc65dGc30ypqcvTvjedcIEerz9PPvMKLGmnnWzi602x0HbSNJsHIGaa5qd5FU7wpELQsup0zncaReN3MlaokcI6MEWFREsuc8d8S82KnfF1DapCupkDzNEerltz7zz6Y7C2qy66ZXO2uOo66Zazo5cuW9Zgc6ypqd4U0TFwZ1vtzb42i886oUjYkURabGKzhaZaysN8i8qNct8hpwFTXZjvyzAEerx9nHvMWnVVNZ1WuWg6bZaDrplrNipgYilveYnSdZgRSz0nLevPrjppeRnVNAkvKhBEZ3lS1ixmLzHzctcunEaca5srq5OnlkE49TDfj642x3wqqi+e6uLHovOx01x1m2UycDmwN5IZvMJgxGmYvXJY305UZ02jKpIpSKqyc07zsTPTMfOx2x6cRpwOXWmTKQFerlpy9MXm5qqi8b0vOh2259p00i61cuaz0nWWJ7wk1rMzUSCeUcPHSrzvOnDnK4cUKoqctFC0y0NPK8x4Mdsd8RpoCKAKAK9Tn6M955nFVVxedXc0V65aTvWewuopqA3mai9Zc1O8xNKpmjOs6Txu1OuNKHItyxiKyRqKEuGNZXmPFjtjviNCAFAFAFeoqNZ4XUs6ms61ALbTPSb1yudLzbW0bwJrRSRrMFRSTM6kRjbrN41oZsXBnQnnQ0iKizTx1zHiy1y3xBiICgCgCvUY9Z4kDOo0zrRzdVthoO9Y7y6itF1nesgq3mRyhFKkiRgFjbEsauGChSKHFKUE7izTkB4M9ct8WIQAoAoAr1WY6zgstBekVN3Dra5Y3cttLz0QpLRoBvLik5lOZmLQ50LGxMxqWQNSpIiipm85q87zpDkePLXLfFpiICgCgCvW5+nj1nC4saqamgdb3lpVa5a0aJs03rL0yveQRoUtVMOc6JZjUkVnTSjLSJkz0glFTNaJ50pqB5ctct8WIQAoAoAr2ODu4NZzqaGqjSaadabYaVo06vXKm0c1vKYazaDWZjSJhNZYpLOpVrGoTnOki6MLyJaZ3NTLzu4qR5stct8QBACgCgCvX870fN1lXnoJc1VVLnS4utaz1ouL0VSeihPeZYQS4RIWdSnGdOdMs6Sqc6hpkkMZTJmpeVoRrny1y3yGW5hMpAUAV6/mel5rlaZ6Wik6q4urvPWHrldaOa1VUveaYazTzeiU0MTeeXM0yzp0ljaCMtSoolzTSYsRnTQGuedF04jmUQ5IAoAr0+Dt4kKmpbTrSpqr0y2gqXWtRWy6itFVL1maQkqomZqcsy5zpNTlAWdRNUMJxQJiwDTTWdQqjrxMuiEyWuRCaIAru5OjmiqmlbVRdTVXpldbE6MUnoqpaVUveQEhF50k4NKKnGiHWdY2ZlpEGV5hLcMm5ZtpzlmKOvPYzWs7cdzmgAgCurHfnp1NM6lxemelVcVV3nbVc1obT1mrzrRQnrKzqaiajOpFONNCztBOWZqakSIoQjA00LOsxx05XCEARIHSArs5dMqq5pm1UVc3VNOLvO2uoeq2nrNOa1lOkikUqKzGFUZ0pc504qMrzaJBI0kxoA00w1FZ305Odlo5ltjmQggCqQVdTTOpqNBOLqNadRWq2qR1FaLcPWdUloU0qzmozpZsxqYqTUxRhSZMTpJDFI5ZqhPOspcb5adHLWiYpEgCAKYFXU0jqLq2nF3Fs7i2dKkbmtZYPQ3KQQpUVIxN551M0Y1KU5SSqgaEAkaedNpGs89c9cmAlQDIAgCm/XjD5xtj0HcuLuNIqppqbGdIS3L0NgjQtAnNLPSBnPSc6hOcaU1Aick0IRMpoDbHIrNzrnckoAEDVAFe08dPP14cdsfTypqoq4uNHNVpWdNbRoKTRuXoaT0IRSzuBmazzpxU41CciDkiWC05pNM1SA1Eta5pNQ0yhNUAV6zT4deCKn0cac3VWnFWqZ1NM6TSgNZVJsDjQK4qFcjnNxnWZSzqG88rmmUKsxqU6YBpgjURca5sqYqRNSFQAXqijh15ZqvRympuLqNIekaMqmkpglBWiWzQRSQm1U50Gs4vPLJU51MOcqAFIVDELaDTExiNI1ihNJAoTCQFepNZ8unFrJ159j4ka7s56zWN6Z6509dm5budYTZvLB6JltBNasys8sRc51CSxqUw0p01xrkXUh5ntEZ24ly9BwVTrBU0hLVCYSAr0stufGsmzrh1Li9I0RTs4wfVpPFr1aZ3xx14Kt8NemO31PG9brz8rk6OMnEzy665Ksa115qx06eZ89GNTrEqlZCSmJi7jTPTCbjXNMcSMYBEAV63N9B4AYOXs0cutnGmgpVF6RpVXFGpw2wZa5adOfV6vmen6ePkcvTzc9xFxjcoXPdaZaZ0ZbYjnNTUjRJMJAC6i89Mpc65sRDQ6E1QBX3vyP1XyXKhUermqZnVbZauRqq0ubqrijU464aneem+fX38Pf6OPlc+3PjaioxuRHPdXnpnay2xKJc0pckCCZILcEoCyDTABCaoAr6/5r0/OcQmu2chxz6b9XnEevfjpz7ung9A+rv41N1Z5S2+nLrvHf3eNp35LAnG1F541BE43sYznXRnih0mGTeYVyimgpoKaCgAgaYTRAFe3weh5/TnE6xvPOBx7AFFSIAZQBhMJDKTTpMGEOk06u8b64hVPLY0EAUxOgCgCgCgCmmmE0QBX/2gAIAQIAAQUA6L5+56CE9DuMQn+ykG4UwZUPYQB19YR3p56mZsqYsf8AtZdyyrQEAjCwu4bEQQRoo639BIR2cy3/ABbcUFXSoohWbhbGya9v9KuiR/PQmhutpj3Ix7DGk/Qk/Qk/UohTR9uGG1xfpTuAuGHsSORLhJn2g7D0HRSYDr0VbhIl9tmoYZWgFwIZ6GehnoYUMKkQQwQdBrC2naegUmEAQ+vSzdSpUqVDYg1lCALPWEQdaPYRZsWbM0Eaz0//AF2mL4g8UJqBQ6CoT2GATSCMG6AC7WWssS1nsstDAKh8UR0siMbgN9ldDK09gJ7NKaehgRYAs06EShCgnrKaBnE97mhjaHoDL6nQ1NJfUQdp6WYGMuUJqJdwH6Yg7DD1HW4B3HvHUw9D9Q94ghhh6HuXyQIRX0hBBDDDD9AGw3nqfHaIIBD0P0QahN9h7hBAYYYe494FxtO4QdTDD2noPHYpo5O4QdTD3HoPHYpqZDfcIOph7j0HjtbtEEEHQww9p6Dx2t57RB1MMPaeg8drdogg6mHuPQePpCCDqYYe09B4+kIIOphhEPYeg8fSEEHQ9DD2noPH0hBB1MMMPYeg8fSEEE+0MMPaei+PpCCDsMPaei+Kh7B3CAdTDD2noviHsHYOgg6mGHvXx9EdBB1MMPeviH6A6g9TDD2noPAP0RBBB2GHvHaXAg8dg6DqYYe8dw8dRB0HUww948dhrtHUdhhh7h2r5vXqOo6mEdCO4dqj8itz1Il5BFYmfsUQMpgPQdTDDCyiewlzWX0ENdcQ160JUKiBRFxqYMK0yAQ4zDjhxCfqWBAJXU+e3btawdoixfDQww9T1Pdtb9isrtEWL4byYYe6u7bIPQ/xbyGhIliaQVFqBhRNwwwyxLl/RwV6tVdBdfQUn1+gev8A/9oACAEDAAEFAOh7/wBbT9c/XCjfXbtRSzUE7SA0Ok8/Ubt28btEyD8vqNF6qllSVBYz2M9jAYBAsyIWJRh9RooMAgE8tGh6CLPsxgMYCmFggjoTXfXQQTW6MPSoIOjRbn2NVGFQDuA62BPdp7GfbtFQ6EMRP2GWD0bx3L48dR0+3aI41HlruoCRPI7h46ffp9qmk0lSpUYxfLXKlUV1jd326aT2QT3MLPCWn5TWC5+UDPPYz2WfhCDDEGigUfPZ9rgBMCiDoYT1HQdCBCiwrUsiAyqj+fpGHqIIOp6kT2mhhU9g6jsPUQdBD2HqCZdj7wdR2GGDoOgh7DGgJ6DqO8wwQQQdT1MPmqgg8dB3GGXBBBB3nz0+3QdxhhEEEHcOh89D46DuMPUQQdo6Hz0PRhcx9g6GHqIO4dG89hFxBXUdTD1EHcOjee0dxhh6CCDtHRvPavjtMPUQQdo6N57R3GHqIOg7B0bz9Mw9RB0HYOjefqHqIIIOwdG8/TMPQQdB2CDo3n6Z7BB3Do38uwd57BB2iDo3nsHeYewQdgg6N57B3mE9RBK6X0EHRvP0zD1EB7RB0bz9Q9R0HaOjefqHqOg7BB0bz9I9ogg7R0bz2BSe49ogg7R0bz9I9w7h0bz2a9x7hB2jo3nsPijR+iID3Do3nsY6BiD7qZ6YjGSp+rIQUYQg9o6hGM/W0qaQAmHtyHToZZnsYHaHI8OZ5/sPa5SQMsGUwZmhzZIXY9i+D57M3noeohjQ+V8CCDuXwfPZk8BpcPUQww+Vggg7vbuyn8h/IeCoM9Z6mUYbhBhU2BUEEB+plv2F39M1f0//2gAIAQEAAQUAMuHWZUgeEWxghJ7NKjHsqV9CpUrqmNnhUg/+A2kOsJqHWZVgaHoR1HQUB1UFjsPiPPb6bX+tWIxf13wiBfgfxwBvgPx1pm/rjiHm7/rbeoOQ+Pcxxvcie5JGNCe0LoAipSEkCVK7zqDDLj6gDToewCE9eA+KbzlzxPx3i+LUDvIBHNfCuL5IcrxG+4jc9FUkqvoruW7QQJcLWLP0rhOjQmOdPt3E9fivBDld3t8aogEH0DOa4jbcxsdzt8u13AFxAqx8hY9o+pUuA3DCYxh8fR+H7ZcPCoNB9Ewz55tBg53xCf8AwBD1Blwno08giu09QJw+EYNisEH0DDP7H2+h76lQEQ+e0Ke1WlwmExoscdhPXDtcuaLgfEeO+UcM+1yfM/juKP8A2FwKRv7J40Rv7MwQ/wBlMZ/9MyWP7Mif2VgMT+yOLMx/2BwGSYvmfxzLMXNcRuJ8+/Xl4XqBp0EMOncBcGIhSb7QYDLhhg8sLHUAmJjLzHss2U8XtMWTBtNsj71Nvtn267bM09McRBPTQ0QzZQVOMY3fIwXCjzBiVNrj43bHG3x/1b/1hDl3Xw4Ypk+J8mE3PF77akqyyiYMOUrBUPaBMGJVXcZv2t33Ceg0LDQjUKTMGNRkw7fG2Q7fGFdhi4/jf9jPi4jGcXJ7bCTs2CDJnOMHcNjbIdACBCRkn4mK7xGN7cOZxzh8fH4CuYbXb5ceXb3t8f8AtAb3b48rbjjMGeZuCUYtntlPHb1VXL2qpY49sMUz7g5Ol9l9D1Hk+SRQx/jgQe+BQ8wFSbfGu/z4W2exGIcXxjBuU2mRTx7gz1tnUqrOzKAFY0crhQ2LWKobHtT+zdbJsZy7RnObCQyY0YqzoJuMOY5SWyLu8gfjMdf9JmXG7PtmEOnVELnHiTCufcF/pmL5bySDEJIHvS4wqI5UbdMhbl8WMcZtceBOP2ef9e/wbjGMOfKiTLlw+5cBUB9acxfdSNXbKLxOXm3yJ+nbf8uHjyz7fj9rkxzEjhs2Mlc/vhG4Qqm1ZGbFi9uPe1LXRxjKGRkIBJxImNc+cufpVCIiyoAYp9YgJXDSHCwJxZmyDPxfKb5F+Mbpi/xvaJk3HFI+X/oN64T4rzzEfBvkLlf6+5+f/OucMP8AXPNz/wCd86Cf6/55Y3wnnVn/AKvzKnFxfI7ccbsv0rtsWXFjRM6xsmT13KIdzvgGfdZ8W2XjHw7rb5WJc+Y6q6hGxnJlNfUCFoYysOg1iY8rDFsnZdhwe5ytsuA3YicXgDDZbUR8OxwjLz3AbaZfm/xnFH/sT46sf+y+FEb+z+OEP9obSf8A1Dawf2hsov8AZ3GRP7K4Jon9hfG2mL5p8ayzDzHD7mDHhYfpx2+3DTLx7EcjxmZRyGInBgybrZpnCqt3BD4yPa/SHTzN7s12+AyomNmnGfEOY3w4/wCB7HDDj4Dh03fzzgNtOG+W/wDb7zp86x+3G5U9WuDtHSzPuGJmyY/t4B/2cYOhap/7dwaZgOF5bHv/AIVx+4HJ/DuY2ky4mxv4h8Oe1ELnJgfGR2iDzzQYD1Ynh/hO+3ww7H438bxch/Yu1xne/JvlHJKnxncryPHcLwp3Hw7EMXNDp8wT34nKmrCj9DUQHXbNeT4luPbaDplNJzT3vP2Pjycf80+Q7Gcb/ZmzyF8Hxr5Lh5j4Bu9vMuHLhfMpU9ALISWAcmQEdyfz3uHLyXJcfxPD/HdvyXznf7tsvEb99xtNhxfHbjLl2WHiuV3+y2XI8Zzw2h+K7He7Xlunyk1xe6RPZ1BYiHu06ATbMonw/MGyr4nIZBi2nIhsmbPtMuMbTbYjsuG+Icdu+S3/APX3K7HJsPm/N8VmzYfj3yzbc98d3nFZCCDAYDcI7jBNtifNmXd7P41sd/yG75DNwW4y49lv9/x+Dcchyh3T4eI5vkMPC7favxPG7hVG1GROS6fKzXF7k25RiRsd5ki8LyzwfHOcM/8AV/kBn/q3yGH4zz4jfH+bWNxPJqX2e5QgOswIS/xFK3a9Of3rbPYclvxlLAzFyG4xbX4Z8kwYN/g3O33WPf8AG7HkcXMfC9/scvF/IcHL7L5DxGTi990UCAFie1h04Rse3Yrn5HdTZcHmy7PDxe34/J8Y3Gx2XGZflXH4MWx3+42WPZ8bz+8PxbgOX2e7jOiDebnhs2Mbn4htwflfx3BH+fcUkb+xdmI39k4RD/ZIn/0kwf2SsX+xsJif2FsmKfNuJyQc98d3E/V8W3E2mz4TA6+pE+S8bu9/suU4Tldo7qRFfidzxmThcIyZcu94vk+I/sfc45x/LcdymL5Gv/K3InmOE6A6kkmjXShVxp99szHFvduvG7KovIccnDtyvLchl2PwDmNycHwf49x6Y+W+IcbH+YZHmPmuS3DDP7Lud/x2Kbv5Bxqzcc7sTMvLbdo/I4iTvMRg3Hu/+yl/7Kw7qDehVHIoHx8vjBw85tFm2+Scep23yjjmG15jY5od6VDczlQD5KinNn+I8lN1/X3C7td78K+R8fM+TcYMuX/V5HksZ3ex3XInPm4zYD0J4Ta5MTo2N+mP1yTKiKQB0qMJ9+CxB8vyDXFx/F77ks2x+FcbsMWb5lwfGY958z53enJnDuOT2+KHn86hua5TIxHKbgLx26eJw2UxeIFjjsYB2GAQ7LEsOzSv9JCW2LkPssnsnGs0PFuWPF5KbjMon/T7oh+N3iQ7bdJE3vJbeY/knLYynyfI0XmtrmOHcZA20+Zc1tInyv45y6b/AOAcdvE3Gx5biN3ywB4zaX+jGrCcivrvugyECDpcbWGcI64px/F5OUbe/L9tsMW83+63uU51E/Zmcrs87xONxiY9ltlKLjBVVJ9VolfbKGEdRAFAcAz1BmlF8hVwWGE+r5g3ouZ2ZABt8TgIMYxsuLHH2uKsvGbPIuXhsBmbiM2Ofqz4Mi73KCm9wtNlv93scvHfNMG6x87wKbritsGXCrfjzXC/r4/tIqWKMYa8Jt8e4fl+Yy75nygFUyZTj2yAoqgDWUtK0BIKN+CBCHwuY4xhXuz7hywo3CWJRSX9qxGi2LSBS2RAQMagsCQzCmsmN6zNiUtoY4V2bb48hzbErKy4mxb6cXzO649uZXZ8jtVv9XJb4/8AU95jTDn/AFbB3LFMdTGCOinQEiKBSGiuS0tlUZ2ANAkj1bGPcrUoT0AgIE9Wv10KEqtAr7UABj9PU48akPfqWEZvUsxEypo90DYyV7nGCmbakHHkyYX2G9UhSfTe7D/bXPtdxtm7aNsIYzH1xCy38k0ESDULRClifXX8njYUyBsLYz+yw9EEghgI/kqpCiUXCkCWLUCscQAKTDQNhYXAByCsmQFcy+pVzMg9jkChiNN1iBVHZZg5HPiGLk8DzHuG9Muw4zcTPwe5SNhZOt6GMIwFYhS/cRbIWKPYLRCgGA+w/IRR+ORqFALQM0ENz/8ALGxpeM1HUgBABYvE0BKhA0s1k9vWldy7EnGPbMor8VFj1uyZm1U6EdMebLiOLlMgmLfYMobLjzJm4fb5AVINGMIfJiCgPK+RoCDeM6DQKjywJ7e0/YwVgWJB9RrD7GE2T5FQBjFICLkjKSRbQKSFCqcOJUipYZEjMqx1bIHdKyWCSVb+SjybmawMg/Mdux3DOqvR3R9txHGjeSNF8CXB4XUWAE1xqUJQJ6k6DUk
     
  4. The lens was described as having ‘slight haze’, but when I received it, this fortunately does not seem to be a fungus infestation nor was it ‘obvious’. When I got an adapter (EOS T-mount) on the lens, I dragged out my heavy-duty “iron boy” tripod, and my Manfrotto 393 head. The pictures show no strong effect from clouding and the results were as good as many of my mirror lenses that look nicer.

    Understandably, a 1250mm lens requires even more stability to avoid tremors at the user end, than do 500-600mm lenses. For the images that follow, I used mirror lockup, wired trigger, and high ISOs. I also focus-bracketed — an f/10 lens can be fairly dim for precision focus.

    My subject is the same as I have used in my other mirror lens reviews — the world-reknown (seriously: http://omeka1.artstor.org/items/show/308316 , http://dome.mit.edu/handle/1721.3/30746 ) Carbondale Polyspheroid Water Tower.

    Here is the 55mm lens view of the water tower.
    00dp0W-561650784.jpg
     
  5. Here is the view with the lens mounted on a Canon 5D mark ii “full-frame” body.

    00dp0Y-561650884.jpg
     
  6. Here is a 100% crop of a section of the above image:
    00dp0Z-561650984.jpg
     
  7. I also shot the lens on a Canon EOS 50D. First, the full view with the 1.6X “crop factor”, the equivalent of a 2000mm lens on that body.

    00dp0a-561651084.jpg
     
  8. and a 100% crop from that same image:

    00dp0c-561651284.jpg
     
  9. I think the results do suggest that American specialized lens production was pretty well competitive with what was coming from Japan in optical terms, if not in terms of convenience of use. To date (ominous tones from above), I do not have any of the Zeiss Jena mirror lenses to compare.

    As seen in the images above, the little focus knob is more a micrometer device than one practical for rapid focus in sports or birds on the wing. I can confidently assert, however, that it does not take more than 1000 twists of the knob to go from closest to farthest focus. When I first mounted the lens, I wasn’t sure just when I would reach a given in-focus position.

    I’ve also fooled around with various brands of tele extenders, and during my ‘sabbatical’ I found a supposedly ‘perfect’ 2X teleconverter made by Nikon (TC-1). To anticipate what will be a longer comparison of various makes of converters, here is the Celestron 1250mm f/10 mounted on the Canon 50D with the Nikon TC-1 and a 2X Vivitar MC Tele Converter . This translates to a 4000mm telephoto with camera body crop and extender.
    00dp0d-561651384.jpg
     
  10. The Nikon TC-1 ( intended for use with Reflex-Nikkor 500mm as well as other Nikkor lenses ) does a fine job with the Celestron, but seems no better to me than the Vivitar.


    So now’s the moment of truth. Those who took the trouble to attack my mental health when I left (in posts deleted by the moderator), can now tell me that this is nothing new, of little interest. Do I dare to eat a peach? Perhaps so. However, at 4000mm equivalent, my lens hood is bigger than their lens hood when all is lined up. ;)
     
  11. SCL

    SCL

    Welcome back! Fascinating report....I can't imagine even lugging that monster around, much less shooting with it. Seriously though, do you attribute the any of the image softness to atmospheric temperature differentials, or is most of it from the lens itself?
     
  12. I think that the "softness" is simply what is to be expected from so long a lens, especially when viewed at 100%, nose-to-the-screen distances. You will note in the specs above that Celestron only claimed 200 lines per mm definition.
    Remember also that the focal zone of "sharpness" is extremely thin on these really long lenses. You have to look at the sharpest part of the image, not the full frame or even whole crop.
     
  13. Welcome Jon! Interesting post. I have not used any mirror lens. My knowledge of them is restricted to college physiscs. Hope to see a post or two from your workshop experiences in India, soon. Thanks. sp.
     
  14. Welcome back JDM. Now to get my Pentacon 6 out again!
     
  15. First, welcome back! Wow, that is a serious piece of kit, scary even.The only mirror lrns that I ever used was a Minolta one, 250mm I think, just a baby compared to that.
    Also great to see that water tower again, seriously missed it.
     
  16. I'm glad you're back. I was at the Second Sunday camera show in Wayne, NJ on the 13th. A fellow photo.netter recognized me and also mentioned your name. So far I haven't been tempted by any mirror lenses but I enjoy reading your posts about them. The closest I came to getting a mirror lens was years ago at 47th Street Photo in NY. The lens was a Sigma 600mm f/8. At that long focal length I wouldn't ask how sharp the lens is. I would ask how sharp it is compared to enlarging from anything shorter which I have. Somewhere I have a Vivitar focusing 2X which was made for the 450mm Series 1 mirror lens. It's in T mount and comes with an Allen wrench for adjusting the orientation of the lens.
     
  17. Welcome back JDM. A sharp reflex lens no doubt. The thin correcting plate allows large SCT optics to reach thermal
    equilibrium with the outdoor air somewhat faster than Maksutovs of same aperture. An interesting accessory available for
    Celestron SCTs is an f 6.3 adapter. It would allow your lens to operate as 787.5 mm f 6.3. Thanks for sharing.
     
  18. An amazing piece of glass described by an equally amazing gent!
    Willkommen zuruck.
    Jim
     
  19. JDM, great to see you back, and hope you stay and continue to contribute. I never tried one of the mirror lenses, but sometime I'd like to. Best regards.
     
  20. JDM,
    Glad you are back. You have been gone so long I almost forgot your interest in mirror lenses. Not really. Great to see the familiar water tower.
    Nice report.
     
  21. Welcome back, JDM! I'm so glad to see your posts again, as I enjoy them immensely. This one is no exception; that's a most impressive lens! Thanks for the detailed and informative narrative; I learn from posts like these.
     
  22. Hi JDM, do you use a focusing magnifier with this monster?
     
  23. I'm not a great fan of mirror lenses, or of long lenses in general, to be honest. But perhaps I'll regret selling my Sigma 600mm if, for example, a pressing need arises to photograph a water tower from a significant distance.
     
  24. With the Schmidt Cassegrain (SCT) the secondary mirror can require collamination by means of thread small screws at the front of the secondary mirror.
     
  25. ...but why a "Schmidt-Cassegrain" system?
    The special thing about Schmidt systems is that they use spherical mirrors instead of a parabolic one. The spherical abbereation is avoided by setting the entry pupil in the center of the sphere of the mirror. Theoretically, all light beams are reflected exactly to this point. Practically, with an opening greater than zero, the light beam has a certain diameter and so minor aberrations will occur. These can be corrected by the "Schmidt plate", actually a very thin lens with an aspherical curvature on one side. This lens will have only small chromatic aberrations.
    The Cassegrain design (with the secondary mirror reflecting the light beams to an opening in the primary mirror) was known earlier and was combined with Schmidts design. The secondary mirror can be attached to the Schmidt plate, thus avoiding diffraktion from a mirror holder.
    And ... welcome back, JDM!! It will be a pleasure not only for me but for everyone (I think) to read your contributions from time to time.
     
  26. JDM, by all means eat a peach.
    This is what Modern Photography reported in the 2/77 issue:

    Lens Date Resolution Contrast
    Ctr Edge Ctr Edge

    Celestron 1250/10 2/77 64 56 44 40
    I think Celestron's resolution claims are for an aerial image. Resolution on film will be lower. I hope you can match up the headings with the columns under them. I can't manage to format the table so that the headings are properly aligned.
    In MP's tests, the 1250/10 Celestron and its 750/6 variant (also sold as Honewell Lumetar, that's what MP tested) are in the same class as the 700/8 Questar. If you're back to accumulating and trying out mirror lenses you really ought to get a 750/6 Celestron/Lumetar or a Q 700. These two, and also the 1250/10 you now have, stand out from the other mirror lenses MP has reported on.
     
  27. Ceci n'est pas une peche:

    Thanks Dan. I don't have that issue in my accumulation of old magazines.
    Here's a formatted version of the table above:
    Lens Date Resolution Contrast
    Ctr Edge Ctr Edge
    Celestron 1250/10 2/77 64 56 44 40
     
  28. Those are good numbers, especially for a long focal length. With any long lens, the stability of the air between the lens and the subject can have a major effect on image quality. On those days where the air is especially calm, the C 1250 and other long optics can deliver incredible images. An excellent job of showing this lens capabilities, JDM.
     
  29. Whoopee! He's back! Good to see another typical well-researched, informative and comprehensive post. All good stuff, JDM, and the water tower is just a bonus...
     
  30. Right. It isn't a sin, it is a pear.
     
  31. Sandy Vongries

    Sandy Vongries Administrator Staff Member

    Interesting article, thanks. I have always thought that my Nikon 500 reflex was a useful lens that got less respect than it deserved. The birds are returning, I'll have to give it a workout.
     
  32. You say pêche,
    I say peche....
    Let's call the whole thing off.
     
  33. BTW:
    Calculating depth-of-field for a generic 1250mm f/10 lens
    from the Canon calculator at http://cpn.canon-europe.com/content/education/technical/depth_of_field_calculator.do

    Canon 5Dii ("full-frame")
    The depth of field of this lens at 10m focus is only ~0.03m.
    At 100 m, DoF is less than 4m
    At 1000m distance, DoF at 398m

    Canon 50D (1.6X "crop")
    The depth of field of this lens at 10m focus is only ~0.02m.
    At 100 m, DoF is less than 2.4m
    At 1000m distance, DoF at 246m



    Thus, getting both the eyes and nose of a nearby squirrel in apparent focus can be tough with any long lens.
    Also see the excellent discussion of DoF by our own Atkins : http://www.bobatkins.com/photography/technical/depth_of_field.html (where there is another DoF calculator)
     
  34. Here is the Modern Photography test of the Celestron from February 1977.
    00dpCh-561676084.jpg
     
  35. Here is the Modern Photography test of the Questar 700mm lens from January 1977.
    00dpCl-561676184.jpg
     
  36. Thanks very much, Marc.
     
  37. Hi JDM
    Herzlich Wilkommen. So nice to see a post and right on target too! Please stick around! I too have a 500mm mrror lens.....I've yet to use it..
     
  38. What a wonderful surprise. Welcome back JDM. You've been missed. I've run a few rolls through my two Praktinas and just love them. Whenever I take them out, you come to mind. I hope you're well.
     
  39. Hey Jon, way back in a former life as a camera dealer, I owned a copy of a lens very similar to yours. It was a C6. I'm sure I took some test shots with it, but I'd have to dig back through about 26 years of photos to find them. I do have one photo of the lens, though.
    [​IMG]
    I've owned a few of these smaller format Celestron and Meade scopes/lenses -- even a Meade LX-3, which was a 10" f/10. That scope worked out to be a 2540mm f/10 optic, and was actually quite sharp. Kinda wish I still had it. I found the smaller ones all to be excellent long telephoto lenses. But you really had to know how to use lenses with such long focal lengths. A cable release or self-timer and mirror lock up was a must.
     
  40. I've always liked Mirror lenses, they are especially useful for IR work. Modern multi-coated optics tend to attenuate
    Infrared, my Meade 97 replaced an expensive Nikon spotting scope for some IR work- and was about 5% of the cost.
     

Share This Page