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Re: I Guess I Lucked Out

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  • John
    If you want to know how they went about designing optics most of it was rationalised by this person. http://en.wikipedia.org/wiki/Alexander_Eugen_Conrady His
    Message 1 of 64 , Apr 1, 2012
      If you want to know how they went about designing optics most of it was "rationalised" by this person.

      http://en.wikipedia.org/wiki/Alexander_Eugen_Conrady

      His book is cheap these days, unbelievably hard going and was required reading for optical designers to at least well past ww11.

      Modern software makes use of very similar techniques but having spent hours playing around with well regarded packages basically it isn't as simple as that. They will take things so far but the final stages seem to require skill and experience. There was some work by somebody like that on the web. The final result was perfect but even the range of variation that would be expected in the glasses would spoil that otherwise for obvious reasons the design wouldn't be on the web.

      Many old microscopes look to use a 10inch tube length plus a draw tube. I often see them at microscope meets. :-) Have also been tempted but they are still rather expensive even there.

      I don't know who did the 1st plan objective but do know that a lot of the break though related to corrections in the eyepiece and once some one had produced a design it spread like wild fire. I also think this happened well before computers were generally used. Much use was made of "simplified" approximation techniques followed by 6 or more figure logs and or mechanical calculating machines. There is a need to read Condrady's book to appreciate the quotes.

      John


      --- In Microscope@yahoogroups.com, "Randall Buck" <rbuck@...> wrote:
      >
      >
      > There are some images of a.P. using an objective made Tolles, in the late
      > 1800's I believe. It is in Merv's photos. I am not sure but I think some
      > of the really old objectives may not be designed for 160mm TL?
      >
      > As you have observed, the pioneers seemed to get the aberrations in hand
      > while field flatness had to wait a bit longer (until better computation
      > methods, perhaps?)
      >
      > The real contemporary contributions are better and better antireflection
      > coatings, which increase sharpness (contrast) by reducing the amount of
      > scattered light inside the objective. Also, new glass formulations that
      > have the same index as real fluorite but without its fragility.
      >
      > Perhaps someone can clarify or add to this ?
      >
      > Randall
      >
      >
      > -----Original Message-----
      > From: Microscope@yahoogroups.com [mailto:Microscope@yahoogroups.com]On
      > Behalf Of Rick
      > Sent: Saturday, March 31, 2012 8:16 AM
      > To: Microscope@yahoogroups.com
      > Subject: [Microscope] Re: I Guess I Lucked Out
      >
      >
      > Hi Randall,
      >
      > I'm using it on a AO 4 series stand. That was their first 'modern' stand and
      > the last to use 160 mm tube length objectives. My 'good' system is an AO 10
      > series, but it sits upstairs in my bedroom where space to work is somewhat
      > limited. I bought a 4 series stand to use in the garage for making slides,
      > and that led to the purchase of several more for parts and upgrades.
      >
      > One of the sidelines of my hobby is to mount antique objectives on the 4
      > series stand to see what kind of images I get. Surprisingly, most of these
      > old objectives work very well except at the edges of the field, where modern
      > objectives would no doubt perform better. I have some old B&L objectives
      > dating from the late 1890s to about 1940, three Leitz objectives from the
      > early 1930s, some brass and plated Spencer and AO objectives from around
      > 1920 to the late 1950s, and a very old Gundlach 1/6" from probably the
      > 1890s.
      >
      > After testing these, it looks to me like most of the improvements in viewing
      > comfort over the old monocular stands comes from binocular viewing with
      > eyepiece tubes inclined at a comfortable angle, wide field eyepieces with
      > good eye relief, and bright even light from an in-base illuminator. The
      > increase in performance of newer achromats over the old uncoated ones in
      > good condition is more subtle than I would have guessed.
      >
      > --- In Microscope@yahoogroups.com, "Randall Buck" <rbuck@> wrote:
      > >
      > > Hi Rick,
      > >
      > > Interesting, I just bought a very old Leitz 1/12 Fluorite for much the
      > same
      > > reason.
      > > What microscope are you using it on?
      > >
      > > Randall
      > >
      > >
      > > -----Original Message-----
      > > From: Microscope@yahoogroups.com [mailto:Microscope@yahoogroups.com]On
      > > Behalf Of Rick
      > > Sent: Friday, March 30, 2012 8:25 PM
      > > To: Microscope@yahoogroups.com
      > > Subject: [Microscope] I Guess I Lucked Out
      > >
      > >
      > > About a week ago, I saw an auction for an old Spencer 95X oil immersion
      > > fluorite objective. I collect old Spencer stuff, but my better judgment
      > told
      > > me not to bid on it because the fluorite element had most likely gone bad.
      > > But the starting bid was so low, I couldn't resist the temptation. I bid
      > > just a couple of dollars above the starting amount with my bidding service
      > > and went about my business.
      > >
      > > That evening I discovered I had won the the auction, no one else had bid
      > on
      > > it. I guess they were thinking the same thing I was. Yesterday it came in
      > > and I started checking it out. There were a few tiny specks and some
      > > haziness on the accessible elements, and after a little cleaning it looked
      > > pretty clear. I couldn't see any signs of cement separation, but did see
      > > what looked like a few tiny bubbles and a faint diagonal line. The
      > objective
      > > also looked a little long. Some careful measuring determined it was about
      > > 1.5 millimeters longer than any of my old Spencer 95X or 97X oil
      > achromats,
      > > so I couldn't just swing it in place after using the 43X.
      > >
      > > Got it focused on a stained slide of hay infusion bacteria, and was
      > > pleasantly surprised. The image quality was good, at least near the center
      > > of the field, and the field wasn't as strongly curved as with my old
      > > achromats. But I noticed I could get objects near the edge of the field
      > > focused with the achromats by adjusting the fine focus, while when I tried
      > > refocusing with the fluorite, there seemed to be other aberrations present
      > > at the edge of the field, so performance was really good only fairly close
      > > to the center of the field. However, sharpness was at least as good with
      > the
      > > fluorite, maybe a little better, and I think contrast was a little better
      > > with the fluorite, also.
      > >
      > > I tried my 10X wide field eyepieces, a pair of old 10X huygenian
      > eyepieces,
      > > and a pair of 10X compensating eyepieces from the AO 4 series ApoStar
      > system
      > > I bought last year. It seemed to work best with the compensating
      > eyepieces.
      > > The 90X oil Apo that came with the ApoStar was toast, massive cement
      > > separation in the upper lens group. I think I have found a replacement.
      > The
      > > objective looks a little out of place, being almost 30 years older than
      > the
      > > rest, but that doesn't bother me any. I will have to do some considerable
      > > shimming to get my other objectives parfocal.
      > >
      > > I measured the parfocal length of several of my Spencer and AO objectives,
      > > using a dial caliper with tape on the anvil to prevent scratching the
      > front
      > > element to get overall length and a depth micrometer to get the distance
      > > between the top of the objective and the shoulder. After subtracting the
      > > depth micrometer measurement from the overall length, the working distance
      > > was added to get the parfocal length. The old brass Spencer objectives are
      > > right around the nominal 34 mm parfocal length. My later 160mm TL AO
      > > achromats are a bit shorter, around 33.5 mm, and the Apos are about the
      > > same. The parfocal length for the 95X fluorite is about 34.7 mm.
      > >
      > > I checked the serial number of the fluorite against my old brass
      > objectives
      > > and two stands that I could date by the serial numbers, the it looks like
      > > the fluorite was made around 1930, maybe a little earlier. It performs
      > > surprisingly well for an uncoated antique.
      > >
      > >
      > >
      > > ------------------------------------
      > >
      > > Yahoo! Groups Links
      > >
      >
      >
      >
      >
      > ------------------------------------
      >
      > Yahoo! Groups Links
      >
    • rdj999
      D oh! What I meant to say was -- I was blessed with three Wide-FIeld Tubes , not Microscope[s] AA . These tubes are designed to be used in a simple tripod
      Message 64 of 64 , Jun 25, 2012
        D'oh! What I meant to say was -- I was blessed with three "Wide-FIeld Tubes", not "Microscope[s] AA". These tubes are designed to be used in a simple tripod stand or inserted in place of an ocular in a standard microscope body with the objective removed. (All of that is explained in the B&L catalog!)

        I've posted pictures of the relevant catalog pages and a picture of one of my wide-field tubes in the "Photos" section if anyone's interested in taking a look.

        -^-rdj-^-

        --- In Microscope@yahoogroups.com, "rdj999" <rdj999@...> wrote:
        > ... it turns out that I was blessed with one 10X and two 20X "Microscope[s] AA for Elementary Work" as describe and pictured on pp. 83-84 of this amazing resource!
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