Intriguing objective design (Nikon CF 40x achro)

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jjtr1
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Intriguing objective design (Nikon CF 40x achro)

#1 Post by jjtr1 » Fri May 13, 2022 4:52 pm

Hello,

I'd like to share here an intriguing design of the first lens of my Nikon CF 40x achromatic finite objective (1990s). The tiny lens, instead of being mounted in a metal tube, seems to be mounted in an annulus of ground or frosted glass representing most of the objective's front end area.

Picture:
Image

Actually, the frosted annulus and the lens appear to be one piece of glass.

Through the ground glass annulus, I can see the second lens and its mounting quite well ! The frosting is mild.

It's beyond my understanding what the purpose of the frosted annulus is. It must be admitting tons of stray light in, why not make it opaque? The objective's 100x sibling is of usual design.

Do you have any ideas on why is the frosted annulus there?

LouiseScot
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Re: Intriguing objective design (Nikon CF 40x achro)

#2 Post by LouiseScot » Fri May 13, 2022 5:51 pm

jjtr1 wrote:
Fri May 13, 2022 4:52 pm
Hello,

I'd like to share here an intriguing design of the first lens of my Nikon CF 40x achromatic finite objective (1990s). The tiny lens, instead of being mounted in a metal tube, seems to be mounted in an annulus of ground or frosted glass representing most of the objective's front end area.


Actually, the frosted annulus and the lens appear to be one piece of glass.

Through the ground glass annulus, I can see the second lens and its mounting quite well ! The frosting is mild.

It's beyond my understanding what the purpose of the frosted annulus is. It must be admitting tons of stray light in, why not make it opaque? The objective's 100x sibling is of usual design.

Do you have any ideas on why is the frosted annulus there?
I'm afraid I don't know the answer to your question. It may be there's a metal annulus behind the front lens? Also, I'm not sure that it's strictly a CF lens. I've seen a number of lenses around (some very cheap) that are marked as Nikon and are finite 160mm RMS. Many are contemporary e.g. https://www.edmundoptics.co.uk/p/40x-ni ... ive/16599/
But I'm not certain if they have the same internal design as the original CF lenses. They could be a generic design, I'm not sure. I'm sure someone else on here will know more about it than me!

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

apochronaut
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Re: Intriguing objective design (Nikon CF 40x achro)

#3 Post by apochronaut » Fri May 13, 2022 7:01 pm

That looks to be a version of an emedded front lens, designed and patented by Arthur Shoemaker at American Optical in the early 70's.
USP 3700311 . Look up A Systematic Design of Microscope Objectives by Y. Zhang Pg. 62. Top of Table 6.2. I guess AO licensed the patent for a while. It is now a very common design for higher N.A. dry objectives.
Any I have seen where the surround cleared like that had a slightly foggy image.

jjtr1
Posts: 33
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Re: Intriguing objective design (Nikon CF 40x achro)

#4 Post by jjtr1 » Fri May 13, 2022 10:42 pm

LouiseScot wrote:
Fri May 13, 2022 5:51 pm
I'm afraid I don't know the answer to your question. It may be there's a metal annulus behind the front lens? Also, I'm not sure that it's strictly a CF lens. I've seen a number of lenses around (some very cheap) that are marked as Nikon and are finite 160mm RMS. Many are contemporary e.g. https://www.edmundoptics.co.uk/p/40x-ni ... ive/16599/
But I'm not certain if they have the same internal design as the original CF lenses. They could be a generic design, I'm not sure. I'm sure someone else on here will know more about it than me!

Louise
While my objectives are depicted in Nikon brochure on CF objectives at
https://krebsmicro.com/Nikon_CF.pdf
(With minor differences in stencilling) and listed as "E Achromats", they might not have the low-dispersion glasses since their paragraph doesn't mention "CF" and there are also "CF achromats". However, the 40x has no apparent lateral color with non-compensating eyepiece.

The Edmund-sold objective looks 100% the same as mine incl. details of stencilling! Very surprising given that mine are >25 years old.
apochronaut wrote:
Fri May 13, 2022 7:01 pm
That looks to be a version of an emedded front lens, designed and patented by Arthur Shoemaker at American Optical in the early 70's.
USP 3700311 . Look up A Systematic Design of Microscope Objectives by Y. Zhang Pg. 62. Top of Table 6.2. I guess AO licensed the patent for a while. It is now a very common design for higher N.A. dry objectives.
Any I have seen where the surround cleared like that had a slightly foggy image.
Thank you, you are very knowledgeable! The copy of Zhang article I found is three-part with no pg 62 and no table 6.2. Do you mean the table labeled "Comparison of the front lenses ..."? (Part ii, pg 21, table 4)
I think that's it! What I thought was a glass annulus is actually a large hemispherical/meniscus lens. My impression of looking through a flat piece of glass is probably erroneous.

The lens is not fully clean, and finger oil can easily make frosted glass look very mildly frosted, while also fogging the central (working) concave region, as you mention.

I didn't mention before the center is concave, so it's a meniscus, not an embedded lens, I think.

abednego1995
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Re: Intriguing objective design (Nikon CF 40x achro)

#5 Post by abednego1995 » Sat May 14, 2022 11:51 pm

Nice observation. That 40x objective at NA0.65 wouldn't require a embedded first element as used in high NA objectives (i.e. NA1.40), so it is made to be concave at the first surface and isn't missing anything. The surrounding donut of frosted glass should have been initially blacked out with a thick application of paint, but over the years it has come off. The objective will work fine without the paint, but with reduced contrast from light entering from the frosted area. Repainting it will improve contrast. Hope this helps.

Cheers,
John

MichaelG.
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Re: Intriguing objective design (Nikon CF 40x achro)

#6 Post by MichaelG. » Sun May 15, 2022 6:51 am

abednego1995 wrote:
Sat May 14, 2022 11:51 pm
Nice observation. That 40x objective at NA0.65 wouldn't require a embedded first element as used in high NA objectives (i.e. NA1.40), so it is made to be concave at the first surface and isn't missing anything. The surrounding donut of frosted glass should have been initially blacked out with a thick application of paint, but over the years it has come off. The objective will work fine without the paint, but with reduced contrast from light entering from the frosted area. Repainting it will improve contrast. Hope this helps.

Cheers,
John
That looks like a perfect analysis, John
… and a 40x 0.65 objective will surely have a relatively uncomplicated design.

I would love to find the formulation.

MichaelG.

.

Edit: __ This one looks too complex: https://worldwide.espacenet.com/patent/ ... S61275812A

… or does it ? :?
Too many 'projects'

jjtr1
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Re: Intriguing objective design (Nikon CF 40x achro)

#7 Post by jjtr1 » Sun May 15, 2022 9:08 am

abednego1995 wrote:
Sat May 14, 2022 11:51 pm
Nice observation. That 40x objective at NA0.65 wouldn't require a embedded first element as used in high NA objectives (i.e. NA1.40), so it is made to be concave at the first surface and isn't missing anything. The surrounding donut of frosted glass should have been initially blacked out with a thick application of paint, but over the years it has come off. The objective will work fine without the paint, but with reduced contrast from light entering from the frosted area. Repainting it will improve contrast. Hope this helps.

Cheers,
John
There seems to have been no paint originally on the tip - see the photo here:
https://www.edmundoptics.co.uk/p/40x-ni ... ive/16599/
These look 100% the same as my objectives from 1990s, including the stencilling. No paint, just frosting.

I think too that lack of paint or other way of blocking stray light would lead to loss of contrast.

MichaelG.
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Re: Intriguing objective design (Nikon CF 40x achro)

#8 Post by MichaelG. » Sun May 15, 2022 9:25 am

jjtr1 wrote:
Sun May 15, 2022 9:08 am
There seems to have been no paint originally on the tip - see the photo here:
https://www.edmundoptics.co.uk/p/40x-ni ... ive/16599/
These look 100% the same as my objectives from 1990s, including the stencilling. No paint, just frosting.
Now … Returning my previous Edit

Is it even conceivable that such an objective could be marketed at £138 ?

MichaelG.
Too many 'projects'

abednego1995
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Re: Intriguing objective design (Nikon CF 40x achro)

#9 Post by abednego1995 » Sun May 15, 2022 10:01 am

Jeez, you're right. I see no paint there! I assumed it was the same with the CF PlanApo 40x, which has a painted over frosted donut much alike your objective. And that paint rubs/flakes off over time. Thanks for the input! I can only guess it's a cost cutting move. It's for the entry market afterall.

Cheers,
John

LouiseScot
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Re: Intriguing objective design (Nikon CF 40x achro)

#10 Post by LouiseScot » Sun May 15, 2022 11:10 am

The Edmunds objective isn't being marketed as CF - just as a basic achromat with 'Nikon' on it. Overpriced for what it is, to be sure! I couldn't find a definitive reference for the MSB50400 model number. Would be interesting to know. The original E series CF achromat were marketed as suitable for 'student' microscopes and clearly had an 'E' on them. There must have been a difference between them and the highly regarded silver CF/N Plan achromats. Maybe just the plan, else the contrast you get in use - or both!

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

Chas
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Re: Intriguing objective design (Nikon CF 40x achro)

#11 Post by Chas » Sun May 15, 2022 11:33 am

LouiseScot wrote:
Sun May 15, 2022 11:10 am
The Edmunds objective isn't being marketed as CF
Doesn't it say in the specification "Finite Conjugate" ?

MichaelG.
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Re: Intriguing objective design (Nikon CF 40x achro)

#12 Post by MichaelG. » Sun May 15, 2022 11:38 am

Chas wrote:
Sun May 15, 2022 11:33 am

Doesn't it say in the specification "Finite Conjugate" ?
That's not what Nikon means by CF

MichaelG.
Too many 'projects'

LouiseScot
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Re: Intriguing objective design (Nikon CF 40x achro)

#13 Post by LouiseScot » Sun May 15, 2022 12:09 pm

Apparently 'E' stands for 'Economical' viewtopic.php?t=9586

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

abednego1995
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Re: Intriguing objective design (Nikon CF 40x achro)

#14 Post by abednego1995 » Sun May 15, 2022 1:32 pm

>Michael

That patent seems to be for their NCF PlanApo 40x (Nikon announced NCF in 1985, and the patent was granted in 1986.)
I couldn't find a patent for the "frosted donut" objective, but looking for close ones I found diagrams for their CF Achromat, CF Plan Achromat, NCF PlanAchromat.

CF_achro_40x copy.jpg
CF_achro_40x copy.jpg (72.96 KiB) Viewed 6323 times

The CF Achromat would be a good starting point to guess. Typical high mag achromat lacking the rear groups that provide plan correction (the rearmost group is there to provide CF correction).
It also lacks the "monolithic" 1st lens that shows up in the CF PlanAchromat. That monolithic 1st lens design is repeated in their NCF PlanAchromat. I couldn't find a diagram for their
NCF E-Achromat and NCF Achromat. However looking in their brochures, it is evident that they took that lens and implemented it widely.

NCF_E-Achro copy.jpg
NCF_E-Achro copy.jpg (87.83 KiB) Viewed 6323 times

Not sure exactly why the design propagated even to their entry line of objectives, but it sure should have performance/economical reasons behind.
I wouldn't be surprised if the aforementioned objective had the basic design of the CF Achro with the monolithic first lens from the CF Plan Achromat.

*just to be clear. Nikon had used the monolithic first element from around their Plan 20x, 40x of their model-S short barreled objectives, so it's not something novel.

Cheers,
John

LouiseScot
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Re: Intriguing objective design (Nikon CF 40x achro)

#15 Post by LouiseScot » Sun May 15, 2022 1:54 pm

Interesting that the Edmunds objective has a wd of 0.6 which seems to be the same as the CF Achromat and CF E Achromat. I've seen "MSB50400 CF Achromat 40X N.A. 0.65, W.D. 0.6 mm (F.O.V. 18)" mentioned elsewhere. Probably doesn't help. Quiet afternoon...
Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

Chas
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Re: Intriguing objective design (Nikon CF 40x achro)

#16 Post by Chas » Sun May 15, 2022 9:09 pm

jjtr1, does the rear element of your objective appear to have a concave surface (and appear to be made out of a thick slug of glass) ? ....a bit like the PlanAchro's in abednego's illustration.

MichaelG.
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Re: Intriguing objective design (Nikon CF 40x achro)

#17 Post by MichaelG. » Sun May 15, 2022 11:09 pm

abednego1995 wrote:
Sun May 15, 2022 1:32 pm
>Michael

That patent seems to be for their NCF PlanApo 40x (Nikon announced NCF in 1985, and the patent was granted in 1986.)
I couldn't find a patent for the "frosted donut" objective, but
[…]


The CF Achromat would be a good starting point to guess. Typical high mag achromat lacking the rear groups that provide plan correction (the rearmost group is there to provide CF correction).
[…]

*just to be clear. Nikon had used the monolithic first element from around their Plan 20x, 40x of their model-S short barreled objectives, so it's not something novel.

Cheers,
John
Thanks, John … very useful ‘leads’ there

MichaelG.
Too many 'projects'

apochronaut
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Re: Intriguing objective design (Nikon CF 40x achro)

#18 Post by apochronaut » Mon May 16, 2022 12:30 pm

jjtr1 wrote:
Fri May 13, 2022 10:42 pm
LouiseScot wrote:
Fri May 13, 2022 5:51 pm
I'm afraid I don't know the answer to your question. It may be there's a metal annulus behind the front lens? Also, I'm not sure that it's strictly a CF lens. I've seen a number of lenses around (some very cheap) that are marked as Nikon and are finite 160mm RMS. Many are contemporary e.g. https://www.edmundoptics.co.uk/p/40x-ni ... ive/16599/
But I'm not certain if they have the same internal design as the original CF lenses. They could be a generic design, I'm not sure. I'm sure someone else on here will know more about it than me!

Louise
While my objectives are depicted in Nikon brochure on CF objectives at
https://krebsmicro.com/Nikon_CF.pdf
(With minor differences in stencilling) and listed as "E Achromats", they might not have the low-dispersion glasses since their paragraph doesn't mention "CF" and there are also "CF achromats". However, the 40x has no apparent lateral color with non-compensating eyepiece.

The Edmund-sold objective looks 100% the same as mine incl. details of stencilling! Very surprising given that mine are >25 years old.
apochronaut wrote:
Fri May 13, 2022 7:01 pm
That looks to be a version of an emedded front lens, designed and patented by Arthur Shoemaker at American Optical in the early 70's.
USP 3700311 . Look up A Systematic Design of Microscope Objectives by Y. Zhang Pg. 62. Top of Table 6.2. I guess AO licensed the patent for a while. It is now a very common design for higher N.A. dry objectives.
Any I have seen where the surround cleared like that had a slightly foggy image.
Thank you, you are very knowledgeable! The copy of Zhang article I found is three-part with no pg 62 and no table 6.2. Do you mean the table labeled "Comparison of the front lenses ..."? (Part ii, pg 21, table 4)
I think that's it! What I thought was a glass annulus is actually a large hemispherical/meniscus lens. My impression of looking through a flat piece of glass is probably erroneous.

The lens is not fully clean, and finger oil can easily make frosted glass look very mildly frosted, while also fogging the central (working) concave region, as you mention.

I didn't mention before the center is concave, so it's a meniscus, not an embedded lens, I think.
More of a thick meniscus lens. The design's first iteration was probably this Zeiss patent from 1938 invented by Hans Boegehold. It shows up as a scattered design feature until the 70's, afterwhich it was widely used by at least 5 mfg. I can think of during that decade.
https://patents.google.com/patent/US2206155

The Zhang thesis also exists as a 172 pg. single volume. Pg. 62 of that for the Shoemaker embedded front lens.

jjtr1
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Re: Intriguing objective design (Nikon CF 40x achro)

#19 Post by jjtr1 » Mon May 16, 2022 7:54 pm

Chas wrote:
Sun May 15, 2022 9:09 pm
jjtr1, does the rear element of your objective appear to have a concave surface (and appear to be made out of a thick slug of glass) ? ....a bit like the PlanAchro's in abednego's illustration.
The rear lens of my 40x is concave and lies right at the end of the barrel, as in NCF PlanAchro. Hard to say anything about thickness.

jjtr1
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Re: Intriguing objective design (Nikon CF 40x achro)

#20 Post by jjtr1 » Mon May 16, 2022 8:04 pm

apochronaut wrote:
Mon May 16, 2022 12:30 pm
More of a thick meniscus lens. The design's first iteration was probably this Zeiss patent from 1938 invented by Hans Boegehold. It shows up as a scattered design feature until the 70's, afterwhich it was widely used by at least 5 mfg. I can think of during that decade.
https://patents.google.com/patent/US2206155
Apochronaut, in the objectives with a thick meniscus first lens that you have seen, was the annular surface just frosted as on mine, or was it made opaque by paint or other means? I'd tend to agree with abednego1995's opinion that leaving the annulus bare is just cost-cutting.

Chas
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Re: Intriguing objective design (Nikon CF 40x achro)

#21 Post by Chas » Mon May 16, 2022 9:53 pm

Slightly off at a tangent, but it may be relevent ...I have a Baker 40x 0.7 with a similar but more viciously ground-out front element, the surrounding glass of this front element doesn't appear to be (even) frosted:
Baker 40x front element.jpg
Baker 40x front element.jpg (25.37 KiB) Viewed 6174 times
I think it is a design by C.G.Wynne ( DOI:10.1088/0950-7671/38/3/307 )

apochronaut
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Re: Intriguing objective design (Nikon CF 40x achro)

#22 Post by apochronaut » Mon May 16, 2022 10:54 pm

There seem to be a bunch of different strategies to solve the problem of stray light entering as a corona around the concave front element. Since the function of the design is to remove the thick plano convex/thin meniscus air spaced duo found in conventional plane faced objectives and substitute one lens, the back of the lens has to be considerably wider than the back hemisphere of a conventional front lens : similar in diameter to the earlier style second meniscus lens in order to create the same field, yet with a design goal of better planarity.
This means that the the large circumference of the front glass represents the diameter of the back convex surface and the lens is more or less cone shaped. Some of the surface modifications I gave come across are 1) grinding the lens block to a conical shape with sides extending from the front circumference to the back circumference.The side is then covered by a metal conical surround ( as on the Baker objective above), coated in a black coating or both. 2) Leaving the surface as a broad cone. This is left exposed but coated in paint or blackened but transluscent. I have seen the same objective treated either way. I think the full black coating was a later idea. 3) Leaving the surface flat and coating the surround with a rough textured metallic looking coating.4) Leaving the surface flat and stippling the surface of the surround similar to a frosted surface.5) No coating at all as in your case. I can't say I remember seeing that before. It almost looks like there is a discontinuity of the n at the lens - surround interface , as if embedded. Expensive , though.
Presumably, in each case there has been quite a bit of mathematical modeling and or ray tracing to determine the efficacy of the design. All of the ones I have looked through seemed to work nicely up to their intended sepecification and the f.o.v. and planarity goals met.

apochronaut
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Re: Intriguing objective design (Nikon CF 40x achro)

#23 Post by apochronaut » Tue May 17, 2022 10:34 pm

I did a little further digging on the derivation of this design because collectively, along with the Arthur Shoemaker-AO patent for an embedded tiny crown glass plano convex lens embedded in a large flint glass substrate plano convex front lens , the patent of Hans Boergeholder- Zeiss Jena, using a meniscus lens as a front lens are probably the two major milestones in the development of the modern microscope objective. The earlier Zeiss 1938 patent provided the backbone upon which further development of plan objectives could be built and the later AO 70's patent provided for complete corrections within the objective as well as full planarity across a broader field as early as 1967. Later AO/Reichert/Leica designs moved away from full correction in the objective . They must have known something but no one I know , knows what. Do you perhaps?

With regards to the concave front lens. I long ago sent most Zeiss and Leitz objectives that I had gathered packing and at that time was not paying attention to that front lens detail, so if anyone has any older Zeiss objectives that display that feature, I would love to hear about them. Sometimes a patent shows up but is too expensive under the current economic conditions to implement. Patents take time to be fully realized.

The earliest volume manufactured objective I could find that utilized that form of front lens was an AO 43X .85 collar corrected apochromat . It was a very low production objective, uncatalogued, infinity corrected. In the 40's and 50's AO offered coating as an option and designated the application of that option with a C prefix in front of the serial #. This was for the 160mm tube objectives, which ceased production around 1961 in favour of the infinity designs. Infinity objectives have a cat. # but no serial #. This one is infinity but has a C serial # and no catalogue #, so it must have been made right around 1961 or so. A Bausch & Lomb Flat Field 40X has a similar front lens as does the first issue cat.# 1078 45X .66 achromat from AO. The B & L , 1963 or 4 and the 1078, 1962 or 3.

Looking at Nikon catalogues for the various S models, the 1968 catalogue lists a 40X plan objective. I have one of those and it indeed does have a concave front lens ground out of a lens block, so likely Nikon used that design for many years subsequently as a plan facilitating design.

Many of the early designs( Nikon included) had a kind of smokey quality to the glass around the actual lens. It may have been enabled by a kind of stipple textured surface. Looking right down through the front lens , the surround is very weakly illuminated, almost as though under a dark veil. From an angle , the surface looks rough and opaque but there must be some controlled reflection going on because so does the lens surface. From the back, there is no evidence of light entering from outside the lens aperrture.

Others ( AO primarily but they also used the above design) used a painted surround, completely blocking out any peripheral possibility of scatter. The earliest one I can identify, the old AO infinity apichromat used paint but a 20X .50 planachro from only 4 or 5 years later had a smoked glass surround.
If you can identify any others from way back, maybe post them.
Last edited by apochronaut on Wed May 18, 2022 12:49 am, edited 1 time in total.

MichaelG.
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Re: Intriguing objective design (Nikon CF 40x achro)

#24 Post by MichaelG. » Tue May 17, 2022 10:58 pm

This may be a clue … Objective is stated to be for the YS100
https://www.ebay.co.uk/itm/273759467572

MichaelG.

.
https://www.nikonusa.com/fileuploads/pdfs/YS100.pdf
Too many 'projects'

apochronaut
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Re: Intriguing objective design (Nikon CF 40x achro)

#25 Post by apochronaut » Wed May 18, 2022 12:42 am

Clue for what?

MichaelG.
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Re: Intriguing objective design (Nikon CF 40x achro)

#26 Post by MichaelG. » Wed May 18, 2022 4:36 am

apochronaut wrote:
Wed May 18, 2022 12:42 am
Clue for what?
Probably nothing much … it was just that it shows the box
labelled MSB50400
which supports Louise’s recollection

Feel free to ignore

MichaelG.
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Adam Long
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Re: Intriguing objective design (Nikon CF 40x achro)

#27 Post by Adam Long » Wed May 18, 2022 11:13 am

I have a Zeiss West F 40x 0.65NA 160/0.17 which shows the same feature of a clear element at the centre of frosted glass. No sign of any paint.

From the logos etc I guess it is late 70's/ early 80s vintage. I can photograph if anyone's interested.

MichaelG.
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Re: Intriguing objective design (Nikon CF 40x achro)

#28 Post by MichaelG. » Wed May 18, 2022 1:01 pm

Adam Long wrote:
Wed May 18, 2022 11:13 am
I have a Zeiss West F 40x 0.65NA 160/0.17 which shows the same feature […] I can photograph if anyone's interested.
Yes, please

MichaelG.
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Adam Long
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Re: Intriguing objective design (Nikon CF 40x achro)

#29 Post by Adam Long » Thu May 19, 2022 9:16 am

Here you go. It is obviously just frosted to the eye - no paint or blackening - but that is less clear to the camera.
AL-6244.jpg
AL-6244.jpg (87.83 KiB) Viewed 5987 times
AL-6235.jpg
AL-6235.jpg (76.22 KiB) Viewed 5987 times
AL-6236.jpg
AL-6236.jpg (65.05 KiB) Viewed 5987 times
AL-6237.jpg
AL-6237.jpg (64.21 KiB) Viewed 5987 times
My Planapo 25x appears to be the same design but the glass is blackened. The Plan 25x also looks similar.
AL-6242.jpg
AL-6242.jpg (55.13 KiB) Viewed 5987 times
Last edited by Adam Long on Thu May 19, 2022 12:20 pm, edited 1 time in total.

MichaelG.
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Re: Intriguing objective design (Nikon CF 40x achro)

#30 Post by MichaelG. » Thu May 19, 2022 10:02 am

Thanks, Adam … Much appreciated.

MichaelG.
.
.
Listed here as F-Achromat : http://www.the-ultraphot-shop.org.uk/obj1.htm
… does that identify a particular optical design, or just a ‘price-point’ I wonder.
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Update: __ There’s a brief but useful comment about F here:
viewtopic.php?t=488
Too many 'projects'

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