Nikon gene sequencer objectives

[abednego1995]

Hmmmmm. Never thought about that since PSFs are obtained for each channel, shift and rotation corrected in software. That applies even for the best objectives. Would be more than nice to have one "perfect lens" though:-)

But I would guess, yes. If the objective were perfect, and the imaging train is perfect also, I would agree with your criteria. I just don't have the background to give confirmation.

[apochronaut]

The point spread function of the tube lens is just a part of the point spread function of the entire optical system. The ideal would be that required by the requirements of the objective. Tube lenses can be neutral, correcting or compensating depending on where the engineers have decided to load the system.

[Scarodactyl]

The earliest Nikon tube lens I know of (in the head of an infinity Optiphot) can easily cover ultra widefield eyepieces or aps-c given the right objective. Nikon's ITL200 also covers full frame with a Mitutoyo m plan apo fairly well. I don't think the tube lens is a limiting factor. Some modern Nikon objectives can cover more than a 25mm image circle, some less.

Unfortunately I don't think I'll be able to do more tests of my own any time soon, but if I get the chance I'll do some more.

Practically speaking, Nikon objectives work well enough without specific compensating optics to meet the standards of very picky photomacro/micrographers, which probably qualifies the CF claim as at least 'close enough.' Why eyepieces would be a limiting factor is a bit headache-inducing, especially with cheap modern ones doing better (to the camera and the eye). I can only say that's what my own limited testing seemed to indicate.

[abednego1995]

Yeah, I’ve seen your comparisons on the Nikon Users Group on fb. Those oculars are impressive considering their price.

[apochronaut]

How can you have a chromatic aberration free achromat?

[DonSchaeffer]

Why is it calleda Gene Sequencer objective?

[PeteM]

Why is it calleda Gene Sequencer objective?

As I understand it, TIRF microscopes (a type of high resolution fluorescence microscope) are used to figure out things like gene cut and splice points. And the 20x Nikon Plan Apo objective was once incorporated in one of these TIRF microscopes - bought in large numbers to facilitate gene sequencing - but replaced by somethng better:

https://blogs.swarthmore.edu/Illumina+G ... own/?cat=4

End result, a whole bunch of $3000 objectives suddenly became available. An enterprising Ebayer or two picked them up. And the market ended up deciding they were worth $100-250. Had they not been Nikon's somewhat unusual 25mm thread and even more unusual 60mm parfocal spec, they might now cost more like $500? Just buying a high quality Nikon scope to host this objective is more than most hobbyists can afford - and researchers who wanted both a Nikon infinity scope and a 20x objective probably got it when they spent tens of thousands for a new Nikon infinity setup.

[hans]

How can you have a chromatic aberration free achromat?

I always assumed "chrome-free" referred specifically to lateral CA, since as far as I understand axial correction has always been handled primarily in the objective?

[apochronaut]

Axial must be the axis, where there is no ca. Where is lateral? Is it 10 degrees off axis, 20 degrees? It is actually, zero plus any degrees. The wider the field the more extreme it is. Lens systems have varying degrees of controlling off axis ca. One is to use low dispersion glass, another is to use various critically chosen glass types to cancel or re-converge dispersion. Another is to use larger lenses. It is all complicated by the fact that the effort to control lateral ca can create spherical aberration and not necessarily do anything about astigmatism. This has created some really complicated lens formulas and resulted in an increasing expansion of lens dimensions. By the 1980's, everyone was expanding their barrel diameters and lengths in order to fit wider and more lenses into them so the could control ca over a wider field and as well keep the other aberrations and distortions within bounds. So everybodies achromats got better but they were still achromats. Why call them achromats if they are better colour corrected than achromats. Is it so they could still sell apochromats?

In an infinity system the tube lens is actually the back lens of the objective. All of the objectives are corrected to utilize , or rather corrected as much as possible to utilize the tube lens as their final convergent lens. I say " as much as possible" because with many systems one or more objectives are idealized , whereas others are imperfect . Sometimes different eyepieces will resolve those imperfections. Depending on the design objectives, the tube lens in any given system will be made to certain requirements that the objectives require to make them as perfect as possible. There is no reason why a final lateral ca correction cannot be a part of the tube lens' equations. The ultimate result out of the eyepiece can be the same.

The B & L system has always intrigued me because they split the objectives, lengthening them considerably and widened them considerably when compared to their 160mm stuff. The actual objective body appears to be responsible for the field flattening aspect of the design and the negative common back lens of the entire system completes the corrections, while also modifying the focal point. The interspace between them is convergent. From that common fairly complicated lens system downstream, the system must have a high degree of corrections because most of the work has been done by the time the image gets to the tube lens. The tube lens itself buried in the head, is quite simple, a doublet that primarily appears to be a convergent focusing lens. It may be slightly compensating, since it would itself create some lateral ca and the objective system might be slightly overcorrected. One of the hallmarks of the system is the diameters. The tube lens is quite wide. It seems they utilized diameter as a simple but useful tool to limit dispersion.

If the Nikon objectives do provide ca free performance or in the case of the achromats...almost : how does the system compensate for the ca created in the tube lens? Presumably, that is the job of the eyepieces?

[Scarodactyl]

If the Nikon objectives do provide ca free performance or in the case of the achromats...almost : how does the system compensate for the ca created in the tube lens? Presumably, that is the job of the eyepieces?

In the higher end Nikon heads the tube lens is not really a single lens. It's hard to get direct data but they sell an industrial standalone through Thorlabs (the itl200) which is described as apochromatic in its specs and looks very similar to what I've seen in their higher end heads.

[apochronaut]

I understand that Nikon has some pretty good optical solutions and sells a lot of pretty high end and expensive systems but whatever refined convoluted optics are applied there, don't really relate to the tube lens of an Eclipse 100.

[Scarodactyl]

Sure, the eclipse 100 is made in China and uses a simplified tube lens as well as lower FoV eyepieces, and it's also equipped with lower end objectives with smaller image circles. It has lower end optics made to lower overall standards, which is kind of the point. I'm not sure what relevance that has to the system as a whole, since the answer to 'how do we deal with inherent aberrations in a cheap system meant for students' is pretty much always just 'we don't.'

[apochronaut]

Sure, the eclipse 100 is made in China and uses a simplified tube lens as well as lower FoV eyepieces, and it's also equipped with lower end objectives with smaller image circles. It has lower end optics made to lower overall standards, which is kind of the point. I'm not sure what relevance that has to the system as a whole, since the answer to 'how do we deal with inherent aberrations in a cheap system meant for students' is pretty much always just 'we don't.'

Yes but Nikon says they are CFI., just like the rest of their scopes. Are they or are they not? What then about the Eclipse 200 or 400. Are they more chroma free than chroma free? I'm not drinking the kool aid.

[hans]

Axial must be the axis, where there is no ca. Where is lateral? Is it 10 degrees off axis, 20 degrees? It is actually, zero plus any degrees.

I think we are talking about different things. As far as I know normal use of those terms is describing the direction the focal point is shifted in relative to ideal, not where in the field the aberration is present:

• Lateral/transverse: perpendicular to the optical axis, chromatic difference of magnification, for example.
• Longitudinal/axial: parallel to the optical axis, can be present on axis in the center of the image, what achromatic, apochromatic, etc. refer to.

So I assume "chrome-free" refers specifically to lateral CA to differentiate from systems which intentionally leave a large amount of lateral CA coming from the objective to be corrected later. I don't think it makes sense to interpret "chrome-free" as referring to axial CA unless you have in mind some earlier systems that intentionally left a relatively large amount of axial CA coming from the objective then corrected it later?

[hans]

Yes but Nikon says they are CFI., just like the rest of their scopes. Are they or are they not?

If you interpret CFI as meaning "objectives are not designed to have some standardized, non-zero chromatic difference of magnification" then I would say yes, nothing wrong with calling the cheaper less-corrected objectives CFI. Maybe makes more sense to think of CFI as a common specification objectives are designed to for interchangeability rather than a grand claim that CFI objectives have no chromatic aberration of any kind. Has Nikon ever claimed that?

[viktor j nilsson]

Sure, the eclipse 100 is made in China and uses a simplified tube lens as well as lower FoV eyepieces, and it's also equipped with lower end objectives with smaller image circles. It has lower end optics made to lower overall standards, which is kind of the point. I'm not sure what relevance that has to the system as a whole, since the answer to 'how do we deal with inherent aberrations in a cheap system meant for students' is pretty much always just 'we don't.'

Yes but Nikon says they are CFI., just like the rest of their scopes. Are they or are they not? What then about the Eclipse 200 or 400. Are they more chroma free than chroma free? I'm not drinking the kool aid.

Of course Nikon's lens designers never meant that all their CF and CFI series objectives were completely free of chromatic aberrations. Why would there be achromats in their lineup in that case? What it means, and I think you know this, is that the design principle was to let all the intended corrections take place in the objective, and let the eyepieces act as neutral relayers of the intermediate image. But an achromat will still have been designed to produce an intermediate image that is corrected at the level of an achromat.

I think what you are trying to say is that the Nikon CF (chromatic aberration free) name is misleading. I can agree with that. But that's marketing, not optical design.

I don't think anyone is drinking any Kool-Aid here. It's just pretty neat to have apochromatic objectives that perform like apochromatic objectives even when used with direct projection. The final image isn't better than any other top brand from the same era, it just allows using the objectives in some ways that simply isn't possible with other brands.

[Scarodactyl]

Yes but Nikon says they are CFI., just like the rest of their scopes. Are they or are they not? What then about the Eclipse 200 or 400. Are they more chroma free than chroma free? I'm not drinking the kool aid.

Ooooooook then. I thought we were discussing the corrective/noncorrective nature of nikon eyepieces and tube lenses, but I guess I misread the thread. This feels weirdly personal so I'm out.

[apochronaut]

Incorrect. I'm just saying I'm not buying what Nikon is advertising that's all.