AO/Spencer series 4.

What equipment do you use? Post pictures and descriptions of your microscope(s) here!
Post Reply
Message
Author
apochronaut
Posts: 6272
Joined: Fri May 15, 2015 12:15 am

AO/Spencer series 4.

#1 Post by apochronaut » Fri Dec 16, 2022 12:24 am

Produced between 1955 and 1962, this microscope still shows up on ebay quite a bit and the optics are still quite common, although it can accept other 160mm optics as well. I thought it would be of some value to profile it here because it can be a very inexpensive entry level microscope, yet also can be built up into a fine instrument too, again quite cheaply. They are exceptionally well built and last for decades and decades. The entire base, frame and optical body is cast aluminum, with the bulk of the mechanical and optical metalworking chromed or enamelled brass with some steel or aluminum. No plastic.
There were basically 6 versions built on the same frame. The #2 had an optional illuminator between the legs. Variably one could choose a mirror or several illuminator choices, including a professional ortho illuminator. The #4 had a built in rear entry tungsten illuminator with Köhler. The #6 was identical to the #4 but with phase. Additionally there was a metallurgical model with a vertical illuminator and a polarizing version called the Polstar as well as a #4 with apochromats called an Apostar. There were a grand total of 27 different 160mm phase objectives that I know of available, over the 16 year run of AO/Spencer 160mm phase contrast production.
Two trinocular heads were made. One 0/100-100/0 with a sliding prism and another fixed at 20/80.
There were various stages, including a circular stage and a really nice fine micrometer large stage with a finely machined drop down coaxial control.. 6 condensers were available. Optics were achromat, fluorite or apochromat and the field could be as wide as 19mm. There was an optional removeable nosepiece.
A great number of these parts can still be found on the after market.
I have made 9 illustrative pictures.
Picture 1 and 2 show both sides of the stand. The one pictured has the 0/100-100/0 trinocular and large bakelite stage with drop down coaxial control. This one is set up as a phase microscope. In front of it are three spare 4 place nosepieces each with a different phase contrast system installed and centered. The 4 systems each have : 10X .25, 20X .50, 43X .66 and 97X 1.25 oil and are Bright M installed in the stand, Dark L center, Dark M left and B-Minus L right. There are 5 further phase objectives in Dark H, Bright H, B-Minus M(2) and Bright L. The Dark H is an uncatalogued objective which is difficult to use., requiring some manipulation to get a good image. I have found it best when used with obique illumination, which when carefully adjusted provides a kind of phase/DF hybrid image with some 3-D relief.
The removeable nosepiece was an option but a significant number of used 2/4/6s have that option. it is a feature worth looking for if you want to go beyond BF with the instrument.

Picture 3 shows several of the available condensers. On the left is a 1.3 N.A. achromat aplanat with an aux. wide angle lens., center a phase contrast universal condenser and an oil DF spherical type on the right.

Pictures 4 and 5 show the very well designed built in bertrand lens. out and in. It focuses by pushing and pulling the eyetube. Also visible is the push pull control for the trinocular prism.

Picture 6 shows a mounted Sony mirrorless camera with the screen positioned for easy viewing by the operator. Rigging up a camera mount on the trinocular tube is really easy. The tube threads into the head. Older eyepiece tube camera mounts such as the Asahi pictured, easily clamp to the tube and accept a photo eyepiece inside.A threaded coupling to a short helical focuser, then to the Sony bayonet allows for precise framing and parfocalization if wanted. The Sony sensor captures the maximum field coverage possible.

Picture 7 shows the fine craftsmanship of the micrometer XY coaxial stage control. A round stage is sometimes used on this stand and the changeover requires the loosening of one slot screw and takes about 2 minutes.

Picture 8 shows the 1 micrometer fine focus control. The coarse and fine were still separate on the stand but it is a hardly noticeable feature. Focusing is silky smooth and precise. This the only AO/Spencer that focused the stage.

Picture 9 shows extra objectives used for BF and DF. Back row. A 63X 1.0 oil achromat with a DF funnel stop on left and a 100X 1.25 oil fluorite with iris. These are Reichert 37mm parfocal objectives that work really well on the #4 stand as a DF pair with Reichert eyepieces. On the right are a pair of W.F. 15X cat.#147 eyepieces. These produce an excellent wide apparent field, giving 150X, 300X and 645X with excellent resolution. They are a little too much for the 97X objective.
The front row shows from left to right : a separable 10X .25 achromat giving 4.2X with the front section removed and 10X when threaded on, 20X .50 achromat, 43X .85 L.W.D. achromat, 50X .95 oil achromat, 97X 1.30 fluorite, 45X .85 achromat with iris and 95X 1.25 achromat with iris. The latter two work well as a DF pair, although the lack of oil immersion with the 45X introduces some limitations.

These microscopes can be very cheap and are well worth building a more enhanced W.F. system out of.
There were no plan optics made for the 160mm AO/Spencer line but appeared when they brought out the series 10 infinity corrected system in the early 60's. The 4 however does approach plan performance and with it's wider field for it's time, it isn't really missed, especially with such a good array of optics. If that was something that was really needed, older shorty Japanese optics made about 10 years after the series 4 was discontinued could be used. They would give a slightly reduced f.o.v. with 18mm compatible eyepieces but I am sure in all other ways would be good .
Attachments
1671143092478.jpg
1671143092478.jpg (61.56 KiB) Viewed 5129 times
1671140977793.jpg
1671140977793.jpg (61.77 KiB) Viewed 5129 times
1671143317075.jpg
1671143317075.jpg (95.28 KiB) Viewed 5129 times
1671143093236.jpg
1671143093236.jpg (76.04 KiB) Viewed 5129 times
1671143315956.jpg
1671143315956.jpg (80.55 KiB) Viewed 5129 times
Last edited by apochronaut on Thu Mar 16, 2023 10:29 am, edited 5 times in total.

apochronaut
Posts: 6272
Joined: Fri May 15, 2015 12:15 am

Re: AO/Spencer series 4.

#2 Post by apochronaut » Fri Dec 16, 2022 12:26 am

4 more.
Attachments
1671143092817.jpg
1671143092817.jpg (83.88 KiB) Viewed 5125 times
1671143317475.jpg
1671143317475.jpg (71.3 KiB) Viewed 5125 times
1671143444790.jpg
1671143444790.jpg (84.72 KiB) Viewed 5125 times
1671143445268.jpg
1671143445268.jpg (114.98 KiB) Viewed 5125 times

lorez2
Posts: 113
Joined: Wed Apr 21, 2021 2:06 am

Re: AO/Spencer series 4.

#3 Post by lorez2 » Fri Dec 16, 2022 2:12 am

Very nice presentation. I like to play (work) with the generations of scopes in the optical and mechanical realm. It's interesting to see the evolution of the mechanical aspects through the models as well as the development of the optics. I'd like to see a nicely compiled list of AO models as they evolved so nicely done that I wouldn't have to do any more than just read it. It would be nice to know how many primary models there were over the years so I could fill in the blank spots in my pile.

lorez
Nikon 80i

Hobbyst46
Posts: 4277
Joined: Mon Aug 21, 2017 9:02 pm

Re: AO/Spencer series 4.

#4 Post by Hobbyst46 » Fri Dec 16, 2022 9:10 pm

Apo, thanks for a very impressive presentation of the beautiful microscope.
May I ask questions.
1. I understand that the camera is afocally coupled ? would it be possible to fit and use it with direct projection, without eyepiece ? or are the correction of abberations in the eyepiece significant ?
2. What is the function of the thumb screw on the right side of the field aperture ?
3. How powerful is the original internal illumination ? would the aluminum base provide sufficient cooling ?

Would be great to see slide images taken with it.

apochronaut
Posts: 6272
Joined: Fri May 15, 2015 12:15 am

Re: AO/Spencer series 4.

#5 Post by apochronaut » Sat Dec 17, 2022 3:07 am

Hobbyst46 wrote:
Fri Dec 16, 2022 9:10 pm
Apo, thanks for a very impressive presentation of the beautiful microscope.
May I ask questions.
1. I understand that the camera is afocally coupled ? would it be possible to fit and use it with direct projection, without eyepiece ? or are the correction of abberations in the eyepiece significant ?
2. What is the function of the thumb screw on the right side of the field aperture ?
3. How powerful is the original internal illumination ? would the aluminum base provide sufficient cooling ?

Would be great to see slide images taken with it.
Here are some phase images at low magnification I posted about 5 years ago. https://www.microbehunter.com/microscop ... f=6&t=4289

It isn't afocally coupled. There is no lens on the camera. It has a photo relay or tube lens in the trinocular tube. I have used a few. Native eyepieces, an AO photo lens from the 50's and a Wild 6X. The Wild possibly is the better but they are pretty close. The images in the MH link were done with the AO #146 eyepiece, if I recall. Perhsps I mention which in the link. Direct projection without a tube lens would not likely work due to corrective qualities required of the eyepiece as you surmise. With apochromats, a different eyepiece would be needed as well. The diagonal of the frames in the link covers the 19mm f.o.v.

The thumbscrews on either side if the field lens are adjustors for the mirror.

The illuminator is only 18 watts. I have adapted an external illuminator that fits in the rear port, so the 970X DF is bright enough.

Dennis
Posts: 674
Joined: Wed May 13, 2015 3:19 pm
Location: New Jersey, USA

Re: AO/Spencer series 4.

#6 Post by Dennis » Sat Dec 17, 2022 11:04 pm

Book on the American Optical Company-

https://www.ebay.com/itm/265924280865?h ... Swn9RjGgt1

From the Ebay seller-

Definitely a "Must Have" book for anyone who appreciates and/or collects the magnificent microscopes and associated equipment produced by the Spencer Lens and American Optical Companies!

A very nice copy of the famous American Optical (AO/Spencer) "Blue Book," a comprehensive guide to the scientific instrument offerings of the American Optical/Spencer Lens Companies. American Optical acquired the Spencer Lens Company in 1935, and in 1945 began trademarking their various instruments with the AO/Spencer logo.

The exact title of the book is "SPENCER Scientific Instruments," and the book was published by the American Optical Company, Scientific Instrument Division (Buffalo, NY). 

There is no publication date in the book, but various sources put its date of publication at about 1950. The book is 207 pages long, with an index.

The book begins with a history of the Spencer Lens Company and provides an overview of the American Optical Company, describing the manufacturing facilities for the various instrument offerings of AO/Spencer.

The comprehensive Table of Contents describes everything from Microscopes and Microscope Accessories to Microtomes, Refractometers, Opthalmic Instruments, etc etc.  

Dennis
Posts: 674
Joined: Wed May 13, 2015 3:19 pm
Location: New Jersey, USA

Re: AO/Spencer series 4.

#7 Post by Dennis » Sat Dec 17, 2022 11:51 pm


lorez2
Posts: 113
Joined: Wed Apr 21, 2021 2:06 am

Re: AO/Spencer series 4.

#8 Post by lorez2 » Sun Dec 18, 2022 12:06 am

The "Blue Book" is a wealth of information for the microscope enthusiast and historian. I have the digital copy and if I were not trying to consolidate I would grab this offer. I have looked through the resources at my disposal to help me establish a "time line- model" chronology, but seem to have some instruments that don't seem to fit... I would appreciate anyone who may be able to share ideas or links to comprehensive lists of the AO models and, while we're at it, why not B&L as well. I am familiar with the psneeley site.

loerz2
Nikon 80i

apochronaut
Posts: 6272
Joined: Fri May 15, 2015 12:15 am

Re: AO/Spencer series 4.

#9 Post by apochronaut » Sun Dec 18, 2022 3:04 pm

Spencer and then later AO/Spencer published a comprehensive catalogue that covered every item they made. I have the 1917 and 1946 versions. I don't know if they put out a full scale catalogue every year or just every few years followed by yearly catalogues covering the various product categories. I have seen several 1917 catalogues but only a few others. The 1924 is on Neeley's site but there have been numerous product brochures and smaller catelogues of product categories. I have never seen a comprehensive catalogue from the 30's, just individual category catalogues, " Spencer Research Microscopes" for instance. I'm pretty sure the first comprehensive one designated as a "Blue Book" was 1946 but I am not 100% sure on that.
The Blue Book seems to have ended in 1954, by which time they had pretty much dismantled the horseshoe based product line. The big catalogues after that for a while became the Red Book, then probably about the time they converted over to infinity correction the catalogue went to binder format with individual removeable brochures for each model.
All of these were sales literature. Operating, reference or technical information was usually in other booklets.

One of the problems in establishing a timeline covering model production periods is that gaps exist in the availability of catalogues. I note that in the early years the year was clearly noted but I have never seen 1925 for instance or many other years. It is possible that publishing was intermittent ; needed only when the product line changed sufficiently. Then by the 30's , you have to determine the date from a code on the back and there is a month too, indicating that the catalogues came out as needed, irregardless of the year.
Bausch & Lomb catalogues seem to follow a similar pattern.

Dennis
Posts: 674
Joined: Wed May 13, 2015 3:19 pm
Location: New Jersey, USA

Re: AO/Spencer series 4.

#10 Post by Dennis » Sun Dec 18, 2022 4:53 pm

Besides publications and catalogs from them,
You could get a free month's trial (quit before the end of the month)
of newspaper.com
and search them.
Look in their localest newspaper that newspapers.com carries. Someone said Buffalo, NY

News like new president, models, etc...
company sold to the new companies
Well in fact when you get names like owners/president you can look them up everything down to an obituary and find company history.

apochronaut
Posts: 6272
Joined: Fri May 15, 2015 12:15 am

Re: AO/Spencer series 4.

#11 Post by apochronaut » Sun Dec 18, 2022 6:55 pm

Yes. I'm sure the newspapers in Buffalo would have been full of news about Spencer and then AO. Big employer and taxpayer. The company actually had 4 premises at least. Originating in Canastota New York with Charles Spencer's first catalogue published in 1838, he moved to Geneva N.Y. briefly in a partnership with Geneva Optical Works after a fire in 1875. Then to Buffalo in 1895 under the ownership of his son Herbert Spencer. There was a move later in Buffalo with the current premises occupied by the spinoff company, Reichert Technologies which specializes in Opthalmic and Refractometric technology. AO invented the hand held temperature compensated refractometer.
The company went through about 4 name changes. Charles Spencer or C.H. Spencer , then Spencer Lens Co., then after many years of ownership by the American Optical Co., or simply became AO. Various mergers and owners showed up between 1967 and 1990. In 1967 Warner Lambert with 19,000 employees merged with American Optical's 14,000 employees. This meant that Chiclets, Listerine and the AO Spencer 20 could now be mfg. with the benefits of cost sharing. I suspect that the AO labs never quite developed a perfect optical cement from Chicle but the company cafeteria was always stocked with gum, O.Henry bars and cough drops.
In 1980, Warner Lambert( later Pfizer) sold off the AO Scientific Instruments Division to Cambridge Instruments. Bausch and Lomb's Scientific Optical Products Division went there too, as well as C.Reichert which AO had owned since 1962. The caché associated with Europeanness and quality, caused Cambridge to adopt the name Reichert for their combined microscope empire in 1985. During a short period in from the late 80's to early 90's the AO factory in Buffalo gave birth to miroscopes or microscope parts associated with 5 companies.
Cambridge later merged with Wild-Leitz in 1991 forming the wholly new company, Leica Microsystems. This means that despite being the newest of the big 4 microscope companies, Leica can claim as well to being the oldest.
The AO factory over a short span of time was the manufacturing center for 5 brands of microscopes or parts. AO, Reichert, Cambridge, Bausch & Lomb, Leica. In one case at least, a part exists that carries 4 brand names. Many with 3.

Dennis
Posts: 674
Joined: Wed May 13, 2015 3:19 pm
Location: New Jersey, USA

Re: AO/Spencer series 4.

#12 Post by Dennis » Sun Dec 18, 2022 8:32 pm

apochronaut,

So you are saying... AO owned the same Reichert of Austria company?

I have a nice Reichert Microstar 4 microscope with tag in back says Cambridge Instruments, Made in USA.

Well then I have a second one not fully working.

I wish would have continued and kept their directions etc...

All those innovations on the Microstar (Reichert microstar)
but then they make the base neck so bulky. That is usually a good handle place to pick it up but...

apochronaut
Posts: 6272
Joined: Fri May 15, 2015 12:15 am

Re: AO/Spencer series 4.

#13 Post by apochronaut » Mon Dec 19, 2022 11:35 am

Yes. AO bought Reichert in 1962. Austria had a very depressed economy, having only escaped the clutches of the Soviet Union in 1955. The Reichert product line was masterfully made but ageing and quickly becoming obsolete. AO injected some capital and Reichert quickly followed up AO's introduction of infinity corrected optics with their own infinity corrected models. Both AO and Reichert designed and manufactured with each factory shipping finished product to the other. Due to the much lower labour costs in Austria, many labour intensive components were made there.

The Microstar IV was built in the Buffalo plant. There was a similar microscope built in Vienna called the Diavar 2 which was sold in Europe only.

The pillar and arm of the Microstar IV are larger than older models true but that is also true of many microscope models built after about 1975. Most modern full size microscopes have gone way beyond the carry by the arm stage. It's one hand under the arm and one hand under the base. Move as little as possible.
In the case of the infinity models made by AO, those castings are used to house the focusing mechanism and and in the case if the Microstar IV the transformer as well, so some space is needed. This works out well because the extended diameter up to the head is just oversize for the dovetail. The B & L Balplan, an eatly 70's design has a very large dovetail and it similarly has a large box frame casting for an arm.
Older microscopes often used cast iron for the pillar and arm and in some cases brass. With aluminum castings plus housing components, the casting needs to have a larger diameter for structural rigidity.

Dennis
Posts: 674
Joined: Wed May 13, 2015 3:19 pm
Location: New Jersey, USA

Re: AO/Spencer series 4.

#14 Post by Dennis » Mon Dec 19, 2022 12:52 pm

apochronaut,

If you or anyone ever decide to make a book, maybe you should.

I have authored about 6 books on local history of my town.

POD books are Print on Demand so there is no big cost.

Note- You will never make any money on a color printed book from POD publishers such as Lulu.com (What I have used)
The cost they say you need to charge is probably higher than what many would want to pay so when you sell only small profit.

But if like me you are not doing it for self profit.
I could give advise if anyone needs it.

Also you can make a book which isn't for sale but you just order. Could be anything from wedding photos to vacation photos to whatever.
What I marvel at about microscopes or I guess many items is the comparison to guitars. Guitars must be so important.
You can buy a guitar which is a reissue of some past famous production year. You can buy switchable upgrade parts.
I don't know exactly what microscopes would be reissued.

apochronaut
Posts: 6272
Joined: Fri May 15, 2015 12:15 am

Re: AO/Spencer series 4.

#15 Post by apochronaut » Mon Dec 19, 2022 4:15 pm

No time Dennis. If I did though, it would be about animals I have known. I have had enough strange experiences with animals to fill two books.

Dennis
Posts: 674
Joined: Wed May 13, 2015 3:19 pm
Location: New Jersey, USA

Re: AO/Spencer series 4.

#16 Post by Dennis » Mon Dec 19, 2022 4:31 pm

I had a domestic swan goose friend a few years ago.
It must have been a pet once cause when I called it, it would come over and stand next to me and stay there while I talked to it.

On the flip side I was walking down the railroad tracks and saw a male turkey down in the field with a bunch of females.
The male came up and walked me out of the territory!

apochronaut
Posts: 6272
Joined: Fri May 15, 2015 12:15 am

Re: AO/Spencer series 4.

#17 Post by apochronaut » Mon Dec 19, 2022 7:50 pm

Generally speaking we make assumptions about animal behaviour based on their response in our presence or in an artificial environment. A disproportionate amount of that behaviour is fear and anxiety driven. When individuals, pairs or groups can be observed unnoticed in their native environment, some surprising behaviour often results. Surprising communication skills too, as well as tool use.
Even in domestic situations, animal behaviour is often heavily informed by fear and distrust. Once trust has been attained, the behaviour and communication can astound. Telepathy has often been ascribed to certain animals . I have experienced it in a circumstance that cannot be explained in any other way, except that the individual feline in question, understood a complex English discussion used to describe potential future events.

The microscope slide is an artificial environment. Bright, frequently hot and confined, with imminent dehydration that the residents seem to be able to sense. These conditions are not favourable for observing a typical behaviour. Not even a typical morphology often, due to a fight or flight or dormancy response. Shapechanging occurs as well as frantic motility.

Dennis
Posts: 674
Joined: Wed May 13, 2015 3:19 pm
Location: New Jersey, USA

Re: AO/Spencer series 4.

#18 Post by Dennis » Mon Dec 19, 2022 9:18 pm

Well,
I think many of the microbes carry on natural behavior. It is just when they get too big
like water fleas, mid to adult coped cyclops, larvae, bigger worms-
they get pinned down and can just twitch a leg or something or make moves which are in a circle or short as they are squeezed.

You got me thinking about spring but I do know of one place I can go to see deer. Palmyra Cove Nature Park.

apochronaut
Posts: 6272
Joined: Fri May 15, 2015 12:15 am

Re: AO/Spencer series 4.

#19 Post by apochronaut » Wed Dec 21, 2022 1:16 am

After close to 60 years of microscopy, I disagree.

Dennis
Posts: 674
Joined: Wed May 13, 2015 3:19 pm
Location: New Jersey, USA

Re: AO/Spencer series 4.

#20 Post by Dennis » Wed Dec 21, 2022 1:00 pm

I just said I think. Isn't a concrete statement of fact.
Plus there is always to an extent or whatever.

Reminds me of someone I knew had a Koi pond in their yard.
We mentioned fish tank aquariums and he said "They know exactly what they are in."

User avatar
rnabholz
Posts: 3086
Joined: Thu Jan 08, 2015 10:11 pm
Location: Iowa USA
Contact:

Re: AO/Spencer series 4.

#21 Post by rnabholz » Wed Dec 21, 2022 10:55 pm

Great as usual Apo.

Here are a few more pics of one I am fond of...

https://www.homebuiltastronomy.com/AO4/index.htm

User avatar
zzffnn
Posts: 3200
Joined: Sat Jun 20, 2015 3:57 am
Location: Houston, Texas, USA
Contact:

Re: AO/Spencer series 4.

#22 Post by zzffnn » Wed Dec 21, 2022 11:44 pm

Only Apochronaut can call back Rod the elusive man :o happy holidays, gents!

Apo; that 45x 0.85 iris objective is an air objective of around 34 mm parfocal height, correct? It sounds very convenient to use.

apochronaut
Posts: 6272
Joined: Fri May 15, 2015 12:15 am

Re: AO/Spencer series 4.

#23 Post by apochronaut » Thu Dec 22, 2022 9:43 am

rnabholz wrote:
Wed Dec 21, 2022 10:55 pm
Great as usual Apo.1.

Here are a few more pics of one I am fond of...

https://www.homebuiltastronomy.com/AO4/index.htm
Thanks for those really crafted photos, Rod. They really portrsy the instrument well, almost sumptuous.
I guess that came intact as an Apostar? I have never seen a 20X apochromat in the chrome barrels with colour coded rings. It looks like they had sold a certain number of 3 objective apochromat systems as Spencer model 3s or 5s up until the discontinuation of the 5 , so relatively fewer 20X objectives were sold from the last gold plated production run and they were using them up. .60 N.A. is an odd one. 65 is the norm.
When the series 10 arrived around 1963, just a year or so after your microscope was made, there was a brief period when they made some infinity corrected apochromats that physically look very much like those on your series 4. I have 10X .30 and 43X .85 with a correction collar. I have also seen an 80X 1.30 oil. Then there was a huge gap of about 20 years when they ceased making apochromats and focused on improved planachros. Their later 34mm parfocal production were more like planfluors in performance but were called " advanced planachro". I suspect that they did not actually use fluorite glass in the objectives but another modern low dispersion glass instead, plus the embedded front element concept, which revolutionized the design possibilities for highly corrected wide field objectives.
In 1985 they returned to making apochromats with a 10X .30 planapo and a 40X .80 planapo without correction collar Space limitations of the 34mm barrel precluded the development of a more highly corrected 100X, somrthing they returned to with the 45mm parfocal objectives for the series 400.
Last edited by apochronaut on Thu Dec 22, 2022 10:56 am, edited 1 time in total.

apochronaut
Posts: 6272
Joined: Fri May 15, 2015 12:15 am

Re: AO/Spencer series 4.

#24 Post by apochronaut » Thu Dec 22, 2022 10:34 am

:twisted:
zzffnn wrote:
Wed Dec 21, 2022 11:44 pm
Only Apochronaut can call back Rod the elusive man :o happy holidays, gents!

Apo; that 45x 0.85 iris objective is an air objective of around 34 mm parfocal height, correct? It sounds very convenient to use.
I don't know. I'll bet Rod has been keeping an eye on us.

I suspect that objective was a mid war period production or shortly thereafter. Maybe custom or a prototype. It almost looks homemade, the way the collar is just set into the barrel, cutting off some engraved letters on the barrel. It is Spencer for sure and 34mm parfocal. Up until 1939, Spencer had a specific barrel design which was tapered with a further tapered tip. The finish was in a dull lightly polished chrome, then as of the mid-40's the barrel design went to a straight sided drum shape in polished chrome. It is hard to tell when the transition in barrel style occured but it was probably in the early 40's. That objective has elements of both barrel styles but seems based on the earlier style barrel. It is a very useful objective particularly with DF, providing 450 and 675X with surprisingly good resolution. Too bad it isn't oil, which would blend it seamlessly with the 95X objective.

There is another oddfity from the same era, this time in the later barrel style. A 60X 1.25 oil objective. Straight side polished chrome barrel.
50 - 60X oil objectives are quite common but usually, either as mid level around .85 achromats or very high N.A. apochromats,, usually 1.4. Obviously there was a market for the 60X 1.4 design in the days when a 20X eyepiece with their notorious low eye relief was acceptable. With a 10X eyepiece would a 60X 1.0 oil apochromat objective give an inferior image?
It is hard to know where a 60X 1.25 achromat fits in. It seems like there was some special purpose for that, although still a 20X eyepiece must fit into the mix. There is no advantage in terms of working distance with these lower power oil objectives as there is for instance using a 10 or 20X objective and a 20X eyepiece.....There is the ability to obtain 300X, 600X, 900X and 1200X magnifications and dead center registration of the object with a monobjective microscope and 4 eyepieces. Without entering empty magnification too. Or maybe just stretching the capability of a 3 objective microscope.

Post Reply