Reichert 181 eyepiece field curvature

[apochronaut]

double post.

[MichaelG.]

That's why I said murky. If CWD have prominent image flatness then some other prominence ( CFW) must be less flat. It's like Everest and Annapurna shrouded in cloud. There is an implication that CWD eyepieces provide better ca correction for the CF planapo objectives , which begs the question : if the objectives are supposed to be chroma free, then why do they need correction for chromatic aberration? When it comes to the CFW eyepieces , the information is very revealing. It seems the fact that they come with rubber eyeguards is their most important feature.

I suspect [but cannot find any corroborating statement] that they are talking about correction of the inherent CA in the eyepiece, not different levels of compensation for CA in the objective. ... The special feature of the CFD being that it is better corrected at the periphery.

If only we knew how these things were designed to work !
Perhaps Hans could be encouraged to broaden his investigations

I have found some interesting Nikon patents, but never seen a patent number declared on a piece of Nikon hardware ... so it’s all speculation !
Example: https://worldwide.espacenet.com/patent/ ... ?q=5546237

MichaelG.

[apochronaut]

Well, if two different eyepiece designs , each recommended for and grafted to an objective design , produce different levels of field flatness and perpheral correction, then of what particular intrinsic value is the level of correction those objective's have originally? They are either fully internally compensated or they aren't.
It is beginning to sound like a load of marketing hype. Nikon can call them what they like but if they still require correcting eyepieces, what makes them different from any other objective that is provided with complementary corrections in the downstream optical pathway and achieves a high image quality?

[Zuul]

For the sake of argument (not that anyone here enjoys debate...) let’s assume that the Nikon objectives do produce a perfectly corrected image. As soon as that image enters the tube/telan lens it develops aberrations. As it travels through the binocular beam splitter, it develops additional aberration. The prisms redirecting the beams to the eyepieces add still more aberration. That leaves plenty for the eyepieces to correct, none of which originated in the objective. If there is more than one binocular head design available, it may be that different eyepiece design is required to match each head.

And, just to add fuel to the fire... there is no such thing as a perfectly corrected image. Corrected beyond reasonable detection, maybe.

[MichaelG.]

For the sake of argument (not that anyone here enjoys debate...) let’s assume that the Nikon objectives do produce a perfectly corrected image. As soon as that image enters the tube/telan lens it develops aberrations. [...]

We were previously discussing CF [not CFI] objectives, which are for 160mm finite tube length ... and whether or not they could be used successfully in 'macro lens' mode. [ see Louise's DSLR thread for the origin ]
... This 'eyepiece field curvature' investigation that Hans is doing is interesting in its own right, but we now seem to have conflated the two discussions.

It may be time to separate them again.

MichaelG.

[MichaelG.]

Well, if two different eyepiece designs , each recommended for and grafted to an objective design , produce different levels of field flatness and perpheral correction, then of what particular intrinsic value is the level of correction those objective's have originally? They are either fully internally compensated or they aren't.

Sorry, but that is not what I said

My understanding is that [to the extent possible] Nikon's CF objectives are fully corrected ... and all the CF eyepieces are "fully corrected" ... the variations being necessary because they are working at different field sizes.

[ all claims to be taken with a pinch of cynical salt ... but I believe that to be the design principle ]

MichaelG.

[apochronaut]

Well, if two different eyepiece designs , each recommended for and grafted to an objective design , produce different levels of field flatness and perpheral correction, then of what particular intrinsic value is the level of correction those objective's have originally? They are either fully internally compensated or they aren't.

Sorry, but that is not what I said

My understanding is that [to the extent possible] Nikon's CF objectives are fully corrected ... and all the CF eyepieces are "fully corrected" ... the variations being necessary because they are working at different field sizes.

[ all claims to be taken with a pinch of cynical salt ... but I believe that to be the design principle ]

MichaelG.

I'm not sure what you mean, Michael. I wasn't quoting you.

[viktor j nilsson]

Nikon doesn't admit to that in any literature and I don't have the parts handy but I did note that they also make a CWD eyepiece that they vaguely recommrnd for low power CF planapo objectives. The translation is murky but it seems that they are different somehow. If there are is no ca compensation required, then the CFD must be correcting for something else differently, than the CFW. Field curvature? I was hoping Viktor could answer that question better.

I wish I could give a definitive answer but I can't. It is true, however that all the low-power CF PlanApo objectives are rather poor in the corners when used with direct projection on an APS-C sized sensor (~26mm.diagonal). This is well documented. See, for example, here:

https://www.closeuphotography.com/4x-te ... objectives

This is not fixed by stacking, so it is not only caused by field curvature.

[hans]

Perhaps Hans could be encouraged to broaden his investigations

The tin snips are oiled and ready if anyone wants to loan me one of these Nikon CWDs... but obviously, to avoid the expedient (to use MichaelG's word of the day) eyepiece modification, it would be better to do this by putting something like a reticle in the eyepiece, although I haven't yet seen one with features all the way to the edge of the FOV.

The main reason I did this was just to get a better intuitive/visual sense of the strength and general appearance of the correction, since I have very little experience looking microscopes, not because I doubted claims that the correction was present in the 181.

[MichaelG.]

I'm not sure what you mean, Michael. I wasn't quoting you.

My mistake ... I thought it was conversation

MichaelG.

[Zuul]

Perhaps Hans could be encouraged to broaden his investigations

The tin snips are oiled and ready if anyone wants to loan me one of these Nikon CWDs... but obviously, to avoid the expedient (to use MichaelG's word of the day) eyepiece modification, it would be better to do this by putting something like a reticle in the eyepiece, although I haven't yet seen one with features all the way to the edge of the FOV.

The main reason I did this was just to get a better intuitive/visual sense of the strength and general appearance of the correction, since I have very little experience looking microscopes, not because I doubted claims that the correction was present in the 181.

It would be easy enough to cut a disk of graph paper ... perhaps adhered to a thin transparent plastic to keep it flat.

[hans]

Regarding the more general discussion about these systems where the components are intended to be used together in relatively small number of officially-supported configurations: I think the default assumption that components have been optimized jointly across the complete optical path (as seems to be apochronaut's?) is a good one. Taking advantage of any available opportunities to arrange for error cancellation across components should allow the best possible correction within any given budget. For example, in the simple case of a finite objective and eyepiece, there will be some level correction possible when considering the final image alone and making no attempt to correct the intermediate image in any particular way. If it were desired to also correct the intermediate image in some intentional way, that would almost certainly involve compromises in the final image unless the budget (number of optical surfaces) were increased.

As far as the motivation for these experiments with the trinocular head and eyepieces: I view the goal as finding an acceptable substitute for the official Photostar components since those appear to be rare and undocumented. It would of course be nice to discover that some subset of the complete optical path produced a fully-corrected image, but I think that is unlikely by the reasoning in the previous paragraph.

[wabutter]

We have a subject of this thread related to the 181 eyepiece as it relates to curvature of field. However most of the discussion is related to CA and correction on CF systems such as Nikon. Two factors come into play,
1. Manufacturers develop “ optical systems”. It is not relevant to discuss Leica 181 eyepieces unless you take into consideration the tube lens and the objective for SYSTEM.
2. Discussions on CA relative to the optical system are not relevant to field curvature.

To clarify, the 181 is an uncompensated eyepiece, as was the 176, 180. . Interestingly, the CF optical system from Nikon essentially copied what AO had been doing since the 60’s.

It is shameful to speculated on the design intentions, systems integrations of an optical system while interjecting competitive prejudice the discussion.

[MichaelG.]

It is shameful to speculated on the design intentions, systems integrations of an optical system while interjecting competitive prejudice the discussion.

Shameful ?

interjecting competitive prejudice ?

Speaking for myself: The reason for discussing Nikon is to better understand their approach to field curvature compensation [the CA side of things is generally understood and agreed]

I am interested in optics not ‘brand loyalty’

MichaelG.

[hans]

1. Manufacturers develop “ optical systems”. It is not relevant to discuss Leica 181 eyepieces unless you take into consideration the tube lens and the objective for SYSTEM.

Not sure if any of the post was directed at me, but I think you and I are in agreement on this point, at least.

[MichaelG.]

Interestingly, the CF optical system from Nikon essentially copied what AO had been doing since the 60’s.

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It may be time for a ‘Fact Check’

Nikon’s CF optical system is for finite tube length
Nikon’s CFI optical system is for infinite tube length

MichaelG.

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P.S. __ This may be of interest [but feel free to contradict it]
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BDD22DE5-D9EB-4637-B3F8-DEE6FBAF6B4F.jpeg (247.4 KiB) Viewed 5177 times

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[apochronaut]

That is from Yuequien Zhang's masters/doctoral dissertation. He did make a seemingly thorough analysis of patents in order to systematize microscope objective design, so it would be likely that he is correct in that statement. I don't know exactly when the CF objectives came out but the principal of design was there for some time I'm sure. What he makes clear though, is that this is a design choice, not a discovery. Olympus, sometimes later made that choice.
Of course using the term CF or CFI , is a marketing ploy nonetheless because technically it refers to to laterally induced ca. An achromate objective can in theory be ca entirely free but if the same manufacturer continues to produce fluorite or semi-apochromats and apochromats then that implies that their achromats are not fully corrected for ca.

This is apart from the discussion that arose regarding field curvature above, which I would assume has been laid to rest on the side of the CF objectives requiring what might be called loosely, plan compensating eyepieces.

Yuequien Zhang, despite his authoratative and fairly complete approach. completely ignores Bausch &. Lomb patents. He apparently investigated something like 450 patents and has a category of others, outside of the developmental work of the biggies : AO, Leitz, Leica, Mitutoyo, Nikon, Olympus and Zeiss. His intent is systematic. He acknowledges that various specifically purposeful microscope objectives are outside of his systems approach. Since his purpose is to categorize existing design trends and develop a system of advanced nomenclature to further the nomenclature beyond the limits imposed by apochromatic( some have super apochromatic), I suspect he didn't know what to do with Bausch & Lomb's approach. It doesn't fit into his systems theory. The fact that they sought to solve the field flattening dilemma early on with a unique design and had a very early success at it , I would have thought should have warranted a bit of special attention. I suspect his focus must have been mostly on ca.