Overview of AO/Spencer 160mm tube objectives. 2-6X : 10X: 20X : 40x : 50- 60X.

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apochronaut
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Overview of AO/Spencer 160mm tube objectives. 2-6X : 10X: 20X : 40x : 50- 60X.

#1 Post by apochronaut » Thu Mar 02, 2023 8:27 pm

This thread is generated from J_WISC's thread https://www.microbehunter.com/microscop ... =5&t=17916. I had already posted a number of photos of Spencer objectives as info. for that thread but thought that as complete an overview as possible would be helpfull to those who either own an older Spencer microscope or who are considering buying one. AO/Spencer abandoned any further development of the 160mm finite system after 1961 or 2, so all Spencer 160mm objectives date from prior to that, going back to their beginning of the adoption of full R.M.S. standards, roughly around the mid. 1890's. Prior to and for about 10 years after additionally , a 250mm tube was offered , as well as custom lengths. Objectives made at a time when both tube lengths were available had the tube length marked on them. If the tube length is not marked, and the objective is cover slip corrected and says Spencer Lens Co. or AO , it is a 160mm tube objective. All the objectives in this survey are 160mm, except I think 1. Spencer and AO used a 34mm parfocal length, with the following exceptions. Very early apochromats are longer and come out to 1 1/2" parfocal or just over 38mm. Prior to W.W. II, Spencer also made objectives to the parfocal lengths of Bausch & Lomb and probably C.Zeiss too. This was particularly the case for research microscopists who would find that certain objectives suited their purpose from various makers and wanted them in the same stand, or chose to refit for instance a Bausch & Lomb stand with Spencer objectives or visa versa. Thus it is possible to encounter Spencer objectives with both 33 and 36.65mm parfocal lengths.
AO/Spencer made 3 objective categories. Achromat, Fluorite and Apochromat. Achromat is assumed, if unmarked otherwise . Only the Fluorite and Apochromats had the colour correction marked on them as FLUORITE, APOCHROMAT, very briefly APOCH. and on the very last production , APO. I have never seen any other designation.
The objective barrel designs went through about 6 eras for the cover slip corrected achromat objectives. In addition there were a couple of designs of educational grade objectives, POL ( strain free) objectives and later research oriented higher N.A. objectives.I haven't encountered them all for sure. With fluorites there were 3 designs and with apochromats there were 4.
I will post infrequently a magnification category covering the 6 eras that I can, plus whatever else from time to time, beginning with the group of photos already done for the other thread. If anyone else has other models or cat.#s to offer, please do.
The company used a cat.# for each part. These were not stamped on the part during the 160mm era. Details could be found from the cat.# ( model #) based pretty much on a description of function, through a dealer or if the manual was at hand. More complete objective specs. , for instance w.d., could be found by referencing the catalogue. Objectives carry serial #'s, which in addition to the barrel style can be used to date them. Later serial #'s had a letter prefix. If that prefix is a C, then the objective is coated.
When the infinity corrected era, denoted by an infinity sign on the barrel arrived, the serial #'s were quickly dropped , and replaced by the catalogue #. All infinity corrected objectives were coated.
Last edited by apochronaut on Mon Mar 20, 2023 11:57 pm, edited 7 times in total.

apochronaut
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Re: Overview of AO/Spencer 160mm tube objectives.

#2 Post by apochronaut » Thu Mar 02, 2023 8:49 pm

Spencer and AO low power achromats up to 6 X and N.A. .20.
For the earliest incarnation of a standard Spencer low power objective I have seen, look at this thread, down past the 4mm discussion. https://www.microbehunter.com/microscop ... =5&t=17916 .

That barrel design, with a separate threaded in aperture plate dates from, probably 1908 up to W.W. I. It was followed by a lacquered brass barrel with an integrated tapered nose, then the same as chrome on brass, then aluminum moved into the picture, initially as a brass conservation measure during W.W. II. It is a single doublet near to the objective base inside, and that was little changed up into the 50's, except for eventual coatings in the late 40's and the addition of engraved magnifications beginning after W.W. I. 2X, 2.2X, 2.6X, 2.8X, 3.5X and 4X are ones I have seen but there may have been others briefly catalogued and probably spanning a 28 to 48mm f.l. range. They were all simple achromatic doublets and aside from the marked focal length and magnification, were physically identical. They all have great working distances and are very useful as reflected light objectives, fitted into a conventional stand. I still use a similar 40mm in a monocular stand to view plant parts, bugs and the like with very small children who have difficulty managing the dual eyepieces of a stereo. Nice bright, well defined image. The objective range was used on simple inspection scopes a lot. Shop mics.
In the late 20's they began expanding the 2X-6.5X low power offerings into more complex more special purpose optical designs , with enhanced achromatism or flat fields or with a higher than expected N.A. One 5.1X , probably purpose designed during W.W. II sported an N.A. of .20
The simple doublets with the empty shroud and tapered short nose to an empty aperture, never carried an N.A.

Images below of most of the achromat objectives under 6X made during the 160mm production days.

Picture 1) Later than that early 32mm objective with the front taper carrying the aperture integrated into the barrel. These are post W.W.I with magnifications marked instead of just the f.l. . Left 40mm 2.6X, no N.A. marked. Right 32mm 4X, no N.A. marked.

Picture 2) Late 20's through the 30's. Left to right. 40mm 2.8X, no N.A. , 40mm 2.8X, no N.A., 30.2mm 3.5X, no N.A. marked but slightly later versions were marked .09, 25mm 5.1X N.A. 0.17.

Picture 3) Early mid. 40's. Left, 24mm 3.5X .08 N.A. An early flat field objective parfocal with the other achromats with a short working distance of 4.2mm. The field flattening lens alters the focal length from about 32mm to 24mm. Right, 25mm 5.3X 0.20 N.A.
Both have aluminum barrels due to wartime production.

Picture 4) Late 40's through to 1961. Left to right. 2X, no focal length or N.A., 4X, no focal length or N.A. These are modern versions of the older 48mm and 32mm objectives. The 4X is coated. Second from right is 3.5X .09 coated and on the right is 5X .14.
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Last edited by apochronaut on Thu Mar 02, 2023 9:45 pm, edited 1 time in total.

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Re: Overview of AO/Spencer 160mm tube objectives.

#3 Post by apochronaut » Thu Mar 02, 2023 9:22 pm

Spencer and AO 10X achromats.
These also were little changed from the early part of the 20th century up towards the second W.W. After the war the field was flattened some with perhaps some advancement in co!our correction. Early on Spencer made some .30 N.A. 16mm objectives but I haven't seen one made after the teens.

Picture 1) Probably 1908 or a little newer, with the thick Chinese hat front lens housing and the finely knurled grip ring and no magnification. 16mm 0.25 marked on the barrel.

Picture 2) Post W.W. I. with thin front lens housing and coarser knurling. Left, 16mm 10X .25 N.A. Middle 16mm .25 N.A. This was the 10X objective made for the # 60 portable folding microscope. R.M.S. threads and for a 160mm tube. Optically equivalent to the full size 34mm parfocal objectives. Right. Possibly a little older than the other two due to finer knurling and no magnification. 16mm .30 N.A.

Picture 3) Late 1920's. 16mm 10X .25 N.A.

Picture 4) Basically the same objective as above but after they abandoned lacquered brass and switched to chrome. From the very late 20's into the 40's.

Picture 5) The necessity for a scanning objective and the rarity of 4 objective nosepieces prompted a redesign of the 16mm achromat into a dual purpose objective, yielding 4 magnifications in a 3 objective nosepiece.. A "separable" objective. The mid. 1940's version was bright chrome and later they switched to brushed chrome. All versions were separable from a 16mm 10X .25 N.A. objective marked on the barrel by removal of the front element into a 32mm 4X .10 scanning objective, not marked on the barrel but available from published catalogue info. Bausch & Lomb also had a similar concept known as " divisible", noted on the barrel if it was one. Not all were.
A non-separable variant of the Spencer was produced as the first incarnation of Spencer phase contrast objectives.
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Re: Overview of AO/Spencer 160mm tube objectives.

#4 Post by apochronaut » Thu Mar 02, 2023 9:37 pm

Spencer and AO 10X achromats continued.
Picture 6)
Last production of 160mm 10X achromat objectives. No longer marked with the focal length.
Left. Standard 10X .25. 7 green colour code rings beginning in the late 40's. Also appeared as a phase contrast variant.
Right. The separable version with 4 green colour code rings This was a new design of the concept, a smaller objective than the above: 16 and 32mm( not marked on the barrel) 10X .25 marked on the barrel but 4.2X .10 as per the catalogue once separated.

Picture 7) I almost forgot about this one. It doesn't even show up in any of the catalogue listings of objectives I have looked at. No magnification and no N.A. it was supplied on monobjective student scopes between at least 1917 and the early 30's.
The barrel is engraved 32mm & 14mm so it is another separable objective of about 4 X and 10 to 12X. It is always on the Spencer # 74.
Picture 8) Separated.

20X overview coming soon.
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J_WISC
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Re: Overview of AO/Spencer 160mm tube objectives.

#5 Post by J_WISC » Mon Mar 06, 2023 2:56 am

Thank you for providing this overview ... and all of the other knowledge you share here!

apochronaut
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Re: Overview of AO/Spencer 160mm tube objectives. 2-6X : 10X: 20X.

#6 Post by apochronaut » Tue Mar 07, 2023 6:03 pm

I hope it is generally useful.
On to the 20X , now. Until the 1950's, 20X achromat objectives were not that common. There were several reasons for this. One was that since 4 objective nosepieces were not common and usually found mostly on research stands, there were few stands that could easily accept a 20X. Some microscopists were willing to swap objectives and some preferred a 20X for specific applications but the market was small. In the research sector, where a 4 place nosepiece was standard after about 1925, 20X objectives were part of the 4 objective standard complement, so there were probably more 20X apochromats made prior to the second W.W. than achromats. Another was that due to the low volume, 20X objectives were much more expensive than a 10X and since it was still common for users to have a 20X eyepiece, a 10X objective/20X eyepiece combination was considered as usefull.
Pictures below. All Spencer or AO or in fact Reichert Buffalo 20X achromat objectives were .50 N.A. I have not seen any other. I suspect the reason for this is again that 20 and 25X eyepieces could be employed in order to achieve 4 or 500X magnification if a 4mm (40-44X) objective was supplanted in a 3 place nosepiece with a 20X. As time wears on, newer objective designs are derived from older ones, so .50 continued to be the standard AO 20X N.A.

1) This is a very old objective going back to about the teens. Has an excellent image.

2) The optics are the same on this one but oddly it has an iris diaphragm? It dates from the early 30's, possibly into the W.W. II years. The iris isn't for DF because the N.A. is too low. It is probably an early transmitted fluorescence objective. Would therefore be strain free.

3) Mid to late 40's. Basically the same optics but with some field flattening. This was the 20X used for the early phase contrast objectives.

4) Late 40's until 1962. Again used as the basis for the phase contrast objectives, slightly improved in contrast and flatness of field. Those designated with a c in advance of the serial# were coated.
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apochronaut
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Re: Overview of AO/Spencer 160mm tube objectives. 2-6X : 10X: 20X : 40x.

#7 Post by apochronaut » Tue Mar 14, 2023 1:41 pm

On to the 4mm or 40 to 45X. This was originally posted for the thread referenced at the beginning of this one but it has been edited here with some extra inclusions.
Pictures.
1) Probably circa 1905. Marked 160mm tube 4mm 0.85. The front lens housing was originally plated silver. No magnification. The 1896 and 1914 catalogues included a chart combining the objective focal length by the eyepiece focal length to arrive at a magnification. Up until the 1914 catalogue Spencer solicited custom fabrication at greater cost. Until at least 1905 they as well offered a choice of two tube lengths . An older length of 250mm or the R.M.S. adopted 160mm were standard , thus the importance of the tube length engraving on the barrel. A 4mm objective used with a 160mm tube yields approx. 40X, whereas a 4mm objective with a 250mm tube yields 62X. 250mm tube objectives are uncommon and some earlier focal lengths may have been in inches too.
2) Group picture of objectives made between 1908 and about 1917. Left to right. 4mm 44X 0.70 N.A., 4mm 44X 0.75 N.A., 4mm 0.80 N.A. ( possibly closer to 1908 production), 4mm 44X 0.85 N.A. There were 4mm objectives from this era marked 62X and in all ways are the same as the 44X version and when used in a 160mm stand give the expected magnification of 44X. It appears that although they should be for a 250mm tube that they were in fact used with a multiplying head, equipped with a negative achromatizing lens.
3) 1920's. 4mm 44X 0.66 N.A. A 0.85 N.A. would look almost identical, just a smaller front lens and 0.85 N.A. engraved.
4) Left to right. 4mm 44X 0.66 N.A. aluminum barrel from W.W. II. , 4mm 45X 0.85 N.A. with iris.
5) Late 40's Left to right.. 4mm 44X 0.66 N.A. polished barrel. 4mm 44X 0.66 N.A. brushed barrel. On the right is a 4mm 43X 0.85, probably from a very late production just prior to the advent of the colour coding rings.
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apochronaut
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Re: Overview of AO/Spencer 160mm tube objectives. 2-6X : 10X: 20X : 40x.

#8 Post by apochronaut » Tue Mar 14, 2023 2:17 pm

The rest of the 4mm objectives.

Picture 6) Late 40's through until the infinity corrected era around 1962 or 3. They had stopped engraving the focal length, providing just the magnification. Left, 43X .66 N.A. Right 43X .85 N.A. S.F. L.W.D. Probably a Pol objective. There is a similarly shaped 50X oil immersion objective that will be in the next installment. The cone shaped design is unusual for post W.W. II AO. Perhaps they were from a special products division or something akin.

Picture 7) The black objectives. Beginning very early, Spencer enamelled certain objectives black instead of lacquering them, then when chrome was used they continued the practice with certain classes of objectives. It appears that most were Pol objectives and therefore strain free. Others are fluorite.
Left . Unmarked but figured out. Based on the magnfication in a 160mm tube, it is a 4mm and 44X. The image is achromatic and based on the diameter of the front lens of average N.A., likely .66. The black would indicate that it is for Pol use. Probably 1920's. The shape is a bit odd because it has been turned down, removing the engraved data.
Left middle. 4mm 62X .75 N.A. Pol and based on the image quality and front lens diameter fluorite too. This is one of those 4mm objectives that is for either a 250mm tube or to be used with a 1.4X magnifying head. It is likely the latter, since the tube length is not marked on the barrel. With a 160mm tube it gives 44X. Before 1918.
Right middle. 4mm 44X .85 N.A. fluorite. 1920's.
Right. 4mm .85. 160mm tube. Likely an early Pol objective giving about 44X in a 160mm tube.
Back. 4mm .66. 114mm tube. Likely for a specialized Pol microscope with a short tube. The objective barrel makes up the difference, so the magnification is probably still about 44X.
.
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Re: Overview of AO/Spencer 160mm tube objectives. 2-6X : 10X: 20X : 40x : 50-60X

#9 Post by apochronaut » Mon Mar 20, 2023 10:34 pm

Spencer and AO made relatively few achromat objectives between 4 and 2mm. Prior to the early 60's, when the dissolution of the 160mm sytem came about it was still quite common at most companies to achieve 500 or 600X magnification by mating a 4mm or 40-45X objective with 12.5 or 15X eyepieces.
There was a 3.5mm or roughly 50X .85 objective made around W.W. I and prior by Spencer. It was earlier marked, 1/6 inch. I have only seen one. Pictured here are the most common 50 to 60X objectives around.
Left. 3mm 60X 1.15 water immersion. This objective spanned quite a few decades, showing up in various barrels from at least 1914 until 1935, where it is an N.A. 1.0. The example here is from the 1920's and is slightly longer than 34mm parfocal, fitting the Bausch & Lomb parfocal format.

Second from left. The standard dry 3mm 60X .85 achromat, catalogued originally as just a 3mm and made almost unchanged for over 40 years. It went through 5 barrel design changes, disappearing from the catalogue sometime after 1950 and replaced with a 3mm 57X achromat but essentially the same objective. It also exists as a coated version if the serial # begins with a C.

Second from right. This objective replaced the 60X 1.0 water immersion as a 3mm 60X 1.25 oil immersion. They were catalogued together in 1935 but the water immersion was then retired and the oil immersion retained for at least 10 years when it became a 60X 1.30 oil immersion briefly. . By 1949 it had disappeared to be replaced by the one below.. This particular one is from the early 1940's sometime.

Right. This became the heir to the middle magnification immersion achromat throne : a 3.6mm 50X .95 oil immersion, catalogued intil the end of the 160mm era beginning about 1955. Middle magnification oil immersion objectives became popular due to the cumbersomeness of going back and forth between an oil immersion high magnification objective and a high dry objective. When mounted specimens are used, it isn't such a big deal but can be a pain with temporary mounts. I don't see any evidence that this objective ever existed as an iris equipped version, which would have made sense for DF , since the N.A. of .95 is a little high for their DF condensers. Perhaps there was a funnel stop for it.
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