4mm N.A. 0.85 vs. 4mm N.A. 0.66

Everything relating to microscopy hardware: Objectives, eyepieces, lamps and more.
Post Reply
Message
Author
J_WISC
Posts: 107
Joined: Sun Mar 06, 2022 7:28 pm
Location: Wisconsin, USA

4mm N.A. 0.85 vs. 4mm N.A. 0.66

#1 Post by J_WISC » Sat Feb 18, 2023 3:37 am

Hello.

Could someone explain what's meant by "high dry magnification" in this paragraph from a Spencer 1946 catalog? Are Spencer 4mm N.A. 0.85 objectives designed for use with or without a cover glass? While only the 4mm N.A. 0.66 actually requires a cover glass?

Screen Shot 2023-02-17 at 9.27.25 PM.png
Screen Shot 2023-02-17 at 9.27.25 PM.png (31.56 KiB) Viewed 2285 times

Thank you.

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

Re: 4mm N.A. 0.85 vs. 4mm N.A. 0.66

#2 Post by apochronaut » Sat Feb 18, 2023 5:09 am

The reason for the caution regarding the haemocytometer is because it's cover glass is thicker than the standard .18 mm thickness that was specified for the biological objectives. It is .40 and the higher N.A. objective of .85 has a shorter working distance than that, so would not be able to focus.

MichaelG.
Posts: 3976
Joined: Mon Apr 10, 2017 8:24 am
Location: North Wales

Re: 4mm N.A. 0.85 vs. 4mm N.A. 0.66

#3 Post by MichaelG. » Sat Feb 18, 2023 8:46 am

Further to apochronaut’s helpful note … I would just add that
what's meant by "high dry magnification"
is simply high magnification using a dry objective

… it’s just a jargon phrase which slips nicely off the tongue.

MichaelG.
Too many 'projects'

BramHuntingNematodes
Posts: 1538
Joined: Tue Jan 21, 2020 1:29 am
Location: Georgia, USA

Re: 4mm N.A. 0.85 vs. 4mm N.A. 0.66

#4 Post by BramHuntingNematodes » Sun Feb 19, 2023 1:01 am

It is important because after an NA of about .66, small differences in cover glass have comparatively larger effects in the quality of the image. It's highly nonlinear, such that to use a cover glass at all with a "high dry" objective, either very precise regulation of the thickness of glass or a correction collar or both are necessary for good imaging. If the glass is different from the range of the correction collar, it becomes impossible
1942 Bausch and Lomb Series T Dynoptic, Custom Illumination

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

Re: 4mm N.A. 0.85 vs. 4mm N.A. 0.66

#5 Post by apochronaut » Sun Feb 19, 2023 4:07 pm

From the practical point of view regarding the acquisition of high N.A. AO or Spencer 160mm finite tube achromatic objectives.
I have been monitoring the availability of Spencer and AO objectives quite frequently on ebay for as long as ebay has existed. Those objectives existed more or less in an optically unchanged form for about 65 years, from around 1896 to 1961 or 2. Any changes were minor and didn't result in very much in the way of large improvements. You can put an objective from 1897 in a 1961 series 4 microscope and it will work just fine and visa versa. The biggest improvement would have been by virtue of the adoption of optical coatings in the 40's and those objectives subsequently so treated were designated with a c prefixed serial #.
There were changes to the barrel styles and methodology of manufacture though and there was a steady modernization of the barrel design and simplification of assembly procedure but with skilled setting up of the illumination and precise control of the glass and sample continuum, the imageing quality of even the older objectives is outstanding.

Prior to 1896 and back to Spencer's first catalogue in 1838 I think it was, there were various designs, some of Spencer's, of Kellner and other employees but the first document that I can accurately determine to catalogue 34mm parfocal objectives to an R.M.S. standard is late 1890's , so I will start there.

During that 65 year period, considering the achromats only, there were 8 distinct barrel styles of cover slip corrected objectives not including styles associated with certain sub types such as POL, phase contrast, laser guiding or metallurgical types. Within those 8 forms I have seen only the following N.A.s. .55, .65, .70 .75, .80 and .85. Two of the forms only existed for specific objective types, for instance student or research level.

Lets say I have been looking out for them for 25 years. Here is an estimate of the number of each version I have seen over that period.

Very early style. Brass with two knurled mid section grip rings, tapered and a THICK silver coloured Chinese hat shaped front lens housing threaded in. serial # 4 or 5 digits. About 1897 to about 1908. There was no magnification given. Prior to 1897, Spencer used focal lengths in inches : from 4" to 1/35th". I don't know when the switch to metric took place but in 1896, they were already using metric tube lengths.
.55.... 0
.66.... 0
.70.... 2
.75.... 2
.80.... 0
.85.... 4

Early style. Brass with two knurled mid section grip rings, tapered and a THIN silver coloured Chinese hat shaped front lens housing threaded in. serial # 5 digits. 1908 to about 1917. 44X.
.55.... 0
.66.... 4
.70.... 6
.75.... 5
.80.... 2
.85.... 10

Early Mid. style. Brass, tapered barrel with one middle and one base grip ring, with a thin silver coloured Chinese hat shaped front lens housing threaded in. serial # 5 to 6 digits. 1917 to about 1928. 44X
.55.... 0
.66.... 25+
.70.... 1
.75.... 0
.80.... 0
.85.... 3

Middle style. Few brass but usually brushed chrome plated on brass. Tapered barrel with a middle and base grip ring. Inserted front lens housing, split barrel. serial # 6 digits. 1928 to about 1944. 44 and 45X.
.55.... 0
.66.... 50+
.70.... 0
.75.... 0
.80.... 0
.85.... 1

Middle late style. Bright chrome or brushed chrome on brass, straight barrel with base grip ring. Inserted front lens housing, split barrel. serial # 6 digits. 1944 to about 1949. 44X
.55.... maybe. edit : yes colour coded anodized aluminum barrel.
.66.... 100+
.70.... 0
.75.... 0
.80.... 0
.85.... 2

Late style. Few bright but mostly brushed chrome with base grip ring and 7 colour coded rings at bottom.Inserted front lens housing. serial # alphanumeric with a letter prefix. A c always indicates coated.6 or 7 characters. 1949 to about 1962. 43X
.55....10+ different style tapered colour coded anodized aluminum barrel.
.66.... 100+
.70.... 0
.75.... 0
.80.... 0
.85.... 1 different style barrel. straight brushed chrome with no colour coded rings.

From an acquisition point of view, it will be very difficult to find more modern 4mm 43X .85 objectives. If one is looking, best to not discriminate as to type or age. Any of the higher N.A. objectives provide very high level dry imaging.
The POL objectives deserve special mention. Many of them were .85 and they work just as well in BF and DF. The POL objectives were black enamel and early ones were long and slender.

I will try to post pictures later.
Last edited by apochronaut on Tue Mar 14, 2023 4:55 pm, edited 4 times in total.

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

Re: 4mm N.A. 0.85 vs. 4mm N.A. 0.66

#6 Post by apochronaut » Mon Feb 20, 2023 3:43 am

Pictures of the 6 objective series.

1) Probably circa 1905. Marked 160mm tube 4mm 0.85 The front lens housing was originally plated silver. No magnification. The 1896 catalogue included a chart combining the objective focal length by the eyepiece focal length to arrive at a magnification. Up until at least 1914 the catalogues solicited custom fabrication at greater cost. Until about 1905 as well, they offered a choice of two tube lengths. An older length of 250mm or the R.M.S. adopted 160mm, thus the importance of the tube length engraving. A 4mm objective used with a 160mm tube yields approx. 40X, whereas a 4mm objective with a 250mm tube yields 62.5X. 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 44X 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 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. A 0.85 would look almost identical. Just a smaller front lens and engraved 0.85.
Attachments
1676862396462.jpg
1676862396462.jpg (92.68 KiB) Viewed 2113 times
1676862470320.jpg
1676862470320.jpg (110.46 KiB) Viewed 2113 times
1676862564504.jpg
1676862564504.jpg (56.09 KiB) Viewed 2113 times
1676863175470.jpg
1676863175470.jpg (97.86 KiB) Viewed 2113 times
1676863219549.jpg
1676863219549.jpg (91.15 KiB) Viewed 2113 times
Last edited by apochronaut on Tue Mar 14, 2023 4:57 pm, edited 4 times in total.

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

Re: 4mm N.A. 0.85 vs. 4mm N.A. 0.66

#7 Post by apochronaut » Mon Feb 20, 2023 3:50 am

6) Late 40's to early 60's . Left to right. 43X 0.66 N.A. 43X 0.85 N.A.
Attachments
1676863271088.jpg
1676863271088.jpg (73.6 KiB) Viewed 2111 times

J_WISC
Posts: 107
Joined: Sun Mar 06, 2022 7:28 pm
Location: Wisconsin, USA

Re: 4mm N.A. 0.85 vs. 4mm N.A. 0.66

#8 Post by J_WISC » Mon Feb 20, 2023 4:41 am

Wow. Thank you for this information, and especially the photos. I realize it requires a huge investment of time to do this. Grateful for the history and details.

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

Re: 4mm N.A. 0.85 vs. 4mm N.A. 0.66

#9 Post by apochronaut » Mon Feb 20, 2023 9:04 am

A few further bits of info., all based on what I have handled, seen or seen in catalogues.
I have never seen a Spencer or 160mm tube AO objective with the word achromat on it. There was an assumption that unless a higher colour correction was stamped on the objective, then it was an achromat.They did catalogue several fluorites off and on over the 65 years and marked the objectives with the word Fluorite. I know of only the following fluorites.
4mm 44X .85 N.A.
3mm 60X .85 N.A.
1.8mm 95 X 1.25 N.A. and 1.30 N.A. which were catalogued both individually and concurrently in certain catalogues.
1.8mm 97X 1.30 N.A.
The fluorites can be distinguished by black enamel upper barrel sections and nickel on brass lower lens sections. The last incarnation of a fluorite objective was during the last 1949-1962 160mm era, a lone 1.8mm 97X 1.30 N.A. It had a chrome barrel with 3 black colour code rings near the bottom. It was engraved Fluorite.

Apochromats for the 160mm system can be distinguished by the word apoch. or apochromat on the barrel. Apochromats made up until W.W. I were a deep orange lacquer on brass. Some of the earlier versions had only the focal length marked, no magnification. Between W.W.I and about 1955, they were gold plated. The last production were brushed chrome on brass with colour code rings.

16mm 10X .30 N.A.
8mm 20X .58, .60 or .65 N.A.depending on the year manufactured.
4mm 43 or 44X .95 N.A. depending on the year manufactured, with a correction collar.
4mm .85 N.A. Made around W.W. I only. No magnification . marked apoch.
3mm 60X .95 N.A. with a correction collar.
3mm 60X 1.4 N.A. oil immersion.
2mm 80, 82,85,86X up to about 1920 depending on the year manufactured. After 1920 , 90X.
2mm 90X 1.3 N.A. with iris diaphragm. Not catalogued in that many years. Usually a funnel stop was employed for DF.
2mm 90X 1.4 N.A. oil immersion.
1.5mm 120X 1.3 N.A. oil immersion.

J_WISC
Posts: 107
Joined: Sun Mar 06, 2022 7:28 pm
Location: Wisconsin, USA

Re: 4mm N.A. 0.85 vs. 4mm N.A. 0.66

#10 Post by J_WISC » Mon Feb 27, 2023 3:01 am

Hello.

Is the "hat" on this 32mm objective indicative of year, or simply a design requirement for a Spencer 32mm vs. other objectives?


image_6483441.JPG
image_6483441.JPG (174.76 KiB) Viewed 1953 times

Thank you.

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

Re: 4mm N.A. 0.85 vs. 4mm N.A. 0.66

#11 Post by apochronaut » Mon Feb 27, 2023 5:52 am

Yes, for sure.. Even by the early 20's they had dispensed with that nickel plated, tapered, front aperture plate on their group of low power objectives and integrated it into the barrel. That objective was made in the teens sometime, maybe as early as 1908.
That barrel design was followed by lacquered brass with an integrated tapered nose, then the same as chrome on brass, then aluminum. The doublet inside 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
Your objective is probably around .10 N.A. and in the 3.8 to 4.2X range , variable some due to the differing chemistries of the sand batches sourced for the two glasses in the doublet.

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

Re: 4mm N.A. 0.85 vs. 4mm N.A. 0.66

#12 Post by apochronaut » Mon Feb 27, 2023 6:04 pm

The 1917 catalogue gives the cat. # as 104 , the N.A. as .10 and the w.d. as 15mm. In 1924, they add that the initial magnification is 4X but in 1930 when they were still using the same illustrations since 1917 for the objectives, the w.d. has been changed to 21mm. The specifications stayed the same until at least 1955. The last reference I have for 160mm objectives, 1961 only lists two multi-element sub. 10X objectives, a 3.5X .09 , w.d. 11mm , and a 5X .20 with a w.d. of 20mm!

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

Re: 4mm N.A. 0.85 vs. 4mm N.A. 0.66

#13 Post by apochronaut » Wed Mar 01, 2023 9:43 pm

Images of most of the achromat objectives under 6X made during the 160mm production days.
Picture 1) Later than your early 32mm objective with the front taper carrying the aperture integrated into the barrel. These are post W.W.I with magnifications marked. 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.
Attachments
1677705362268.jpg
1677705362268.jpg (93.55 KiB) Viewed 1798 times
1677705405442.jpg
1677705405442.jpg (74.68 KiB) Viewed 1798 times
1677705459041.jpg
1677705459041.jpg (81.1 KiB) Viewed 1798 times
1677705501416.jpg
1677705501416.jpg (99.21 KiB) Viewed 1798 times

Chas
Posts: 422
Joined: Tue Jan 19, 2021 3:11 pm

Re: 4mm N.A. 0.85 vs. 4mm N.A. 0.66

#14 Post by Chas » Sun Mar 12, 2023 8:29 pm

Thank you for all this information :-)
So.. if I would like a low power (~4x) objective that was approximately parfocal with a 44x that seems to be the "Early Mid. style. Brass, tapered barrel with one middle and one base grip ring, with a thin silver coloured Chinese hat shaped front lens housing threaded in. serial # 5 to 6 digits. 1917 to about 1928. 44X"
I would need to go for an objective like those in your picture 3.
i.e the ones in picture 4 would not be ? As these are 'moderm versions of the older 48mm and 32mm objectives' ...Or have I got the wrong end of the stick?
Many thanks.

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

Re: 4mm N.A. 0.85 vs. 4mm N.A. 0.66

#15 Post by apochronaut » Sun Mar 12, 2023 10:01 pm

I don't think parfocality would be a slam dunk with the 6X and under. That short 48mm to 32mm group that all looked alike ; in lacquered brass prior to 1929 and chrome on brass after, were simple good quality achromats with working distances dependent on the focal length. One of them might be close.
In order to introduce parfocality into a long focal length design, the lens formula needs to include parfocalizing elements, for instance like that long barrelled 3.5X .08, which appears to be specifically made as a flatter field, parfocal low power objective. It has the basic magnifying achromat doublet situated at about the shoulder level like all the others but in addition has 2 other lens groups. That's why it can be 24mm and 3.5 X.
If I recall correctly, that little 3.5X .09 button objective in the 2nd picture is close to parfocal with higher powered objectives too.
It is easy for me to test them all against a couple of 4mm objectives from that W.W. I to stock market crash era and report back.

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

Re: 4mm N.A. 0.85 vs. 4mm N.A. 0.66

#16 Post by apochronaut » Mon Mar 13, 2023 6:34 pm

I did a few tests on 5 of those low power objectives against several examples of the cat. # 115 4mm 44X .66 N.A. objective made between 1918 and 1928, all lacquered brass. There was a decent span of representation with serial#'s ranging from the low 100,000's to low 300,000's. One with 305,xxx was chrome, so the last brass one with 302,xxx was close to the very latest production of the 1920's for lacquered brass objectives and the one with the low 100,xxx serial # close to the earliest. That objective was not catalogued in 1917 but was in 1924. When it was first catalogued, I don't know but not too long after 1917 I would guess.
In general, the two left hand low power objectives in picture 2 have enormous working distances of about an inch and inch and a half, and when switching to either a 10X .25 or 44X .66 a great deal of focusing towards the subject is required. The two right hand objectives in picture 2, the little 3.5X button objective and the 25mm 5.1X are more or less parfocal with a 4mm 44X, requiring a small amount of focusing away from the specimen. The 4mm are more or less parfocal amongst themselves as well. This was caused by glass batch discrepancies but also slight design changes. No doubt when a microscope was assembled for delivery, some attention would have been given to the selection of objectives that were within an acceptable parfocal specification. When someone is dealing with a case of having only 1 set of objectives a hundred years later, which may not be in quantum entanglement, then shims can be used. Shimming the low power objectives slightly, would parfocalize them with the 44X. You always shim the objective(s) that focus closer than needed in order to parfocalize.

Chas
Posts: 422
Joined: Tue Jan 19, 2021 3:11 pm

Re: 4mm N.A. 0.85 vs. 4mm N.A. 0.66

#17 Post by Chas » Tue Mar 14, 2023 10:07 am

Thank you for checking these out; am I right in thinking that the extra parfocal-correcting elements in those two right hand objectives are cemented to the 'main' lens?
I have a black 1960s(?) Watson 40mm x4 that is nearly parfocal with the Spencer objectives but I cannot detect any air space inside it.
I find it very frustrating that I cannot guess if a low power objective is going to have an over-long working distance,or not, from its outer appearance :-(

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

Re: 4mm N.A. 0.85 vs. 4mm N.A. 0.66

#18 Post by apochronaut » Tue Mar 14, 2023 12:46 pm

I am almost certain each of those low power objectives that are close to being parfocal with higher powered objectives are air spaced. The 3.5X button type objective first appeared in a brass housing, so it was probably a late 20's introduction of a Lister type II objective with two air spaced doublets : the front doublet is a double convex and the rear is a plano convex or possibly double convex too. When the forward plano surface, such as was the design from the 1830's by Lister is modified to convex, the control of various aberrations becomes possible.
The 5.1X objective I think too is air spaced doublets but the front lens is plano. I should disassemble that one and see how it is constructed. Might have a third element.
The long 3.5X objective in the 3rd photo is interesting too, since it is not only parfocal but also contains field flattening elements. The front element can be unscrewed and it becomes a 24mm roughly 5X single doublet objective but with certain unwanted distortions. With the front element installed, it is a reasonably planar, parfocal 3.5X. It works out to be a good complement to the apochromats.

I have a 2X Beck apochromat. Very fine objective with stellar colour correction but with a huge working distance. It turns out to be a really good macro photo lens.

Post Reply