Nikon small world

ThrillaMozilla wrote:

Joseph S Wisniewski wrote:

ThrillaMozilla wrote:

Joseph S Wisniewski wrote:

Infinity objectives are the "new darlings" of microscopy.

I don't know if they offer any advantages for ordinary macro photography, though.

• They couple well to cheap, easily obtainable things.
• You can change your magnification, within reason.

Interesting. Yes, I see. A finite objective would require too much extension to change the magnification by much.

Technically, they were simply optimized for one magnification. It's hard to make a lens perform well at multiple focusing distances/magnifications. You can optimize a design for multiple focusing distances, at the expense of overall resolution.

For camera lenses, this was addressed with "floating elements", like the system that let a Nikon 55mm f/2.8 Micro-Nikkor be bitingly sharp all the way from infinity to 1:2.

But for microscope objectives, there's not much reason to make it adjustable. It would help those of us who repurpose them as macro lenses, but it wouldn't have helped the microscope users they were created for. (I have a "zoom head" for my Nikon Optiphot 88 scope. It's a contraption that replaces the standard head of a high-end modular microscope and lets you crank the magnification up by and additional 2x. You can also change the eyepieces themselves).

So you end up with an objective that has one tube length where it's optimized for the highest resolution, the lowest distortion, curvature of field, etc. That's especially important in scopes like mine that was originally built for IC wafer inspection. And thus scope objectives get "mushy" when you try to use them at other tube lengths. I've cataloged which of mine work well for changing tube lengths, because it's used for a focus stacking technique called "bellows draw focusing".

The classic RMS thread macro lenses like Leitz Photars, Zeiss Luminars, and Nikon Macro Nikkors have wider "tuning", generally being pretty consistent over a 4:1 range.

Enlarger lenses (typically M39 thread) are generally optimized over a 10:1 range.

The biggest advantage infinity objectives offer is what my optical engineering prof back at Oakland called "the three-year rule".

More optical design calculations have been performed in the last three years than in the preceding 200 years of optical design.

Very interesting.

I always thought it was. It's why modern lenses are so amazing.

This is thanks to advances in computers, optical design software, and the growing demands of industry. Optical manufacturing also continues to improve: more glasses of various capabilities are available, more advanced grinding techniques led to simple parabolic aspherical lenses, complex formula aspherical lenses, double sided aspherical lenses, and the abilities to grind aspherical lenses with ever-increasing deviations from the norm.

Infinity kinda' came along for the ride, or the three-year rule enabled it. But whichever side you take in that "the chicken and the egg" discussion, the results are pure win.

At the same time, three other trends converged.

Scope manufacturers increased their parfocal lengths (the length from the base of the objective to the subject) allowing for more complex, faster, higher resolution, and better corrected objectives, as well as increased working distances. I have some old Zeiss objectives with a 35mm parfocal length. Most of my flock of CF and CFI Nikons have a 45mm parfocal length, which is how the 40x ELWD has 33mm for optics and still pulls off a 12mm working distance.

I assume those long working distances come at the expense of NA as before?

Sometimes, but sometimes the optical engineers surprise you.

The bulk of my objective collection is Nikon CF objectives introduced for the Optiphot 66 and 88 series scopes. I have about twenty-five of that series, most of which are mounted on four turrets.

• 4 objective BD loaded with a 5, 10, 20, 40x series with the 20 and 40 being ELWD. I have an ELD 100x that can get swapped into one position when I want more magnification. Technique at 100x is basically standard microscopy. For that matter, 40x is more like microscopy than "macro". I also have a 150x standard distance CF PLAN APO (fractional mm,
• 4 objective BD DIC head loaded with a 5, 10, 20, 40x series of DIC objectives. Nikon DIC objectives are only standard types, no LWD/ELDW.
• 5 objective brightfield head loaded with a 2.5, 5 DIC, 10 D(C, 20 ELWX, 40x ELWD series. This can also mount on my bellows. I don't have a way of mounting BD turrets.
• 4 objective BD head loaded with whatever redundant objectives I'm OK to loan out.

Back to ELWD vs NA

• 20x BD "standard" has a WD of 2.5mm and an NA 0.4
• 20x BD ELWD has a WD of 8.5mm but that same NA 0.4
• 40x BD "standard" has a WD 1mm, NA 0.65
• 40x BD ELWD has a WD 9.8mm, NA 0.50

I find the 20x ELWD to be a generally superior objective to the standard working distance. However, I have to have standard working distance 20x and 40x DIC (strain-free glass and adhesives for use with polarized light) in the DIC head, because Nikon didn't make DIC ELWD objectives in the CF or CFI series. Not sure about CFI60.

Oh, two other changes that came with infinity.

The CFI scopes like Optiphot 100 and 200 have 5 objectives in their BD turrets, 6 in their brightfield turrets.

I believe they pushed that to an insane 6 and 7 for CFI60. With 7 of those massive objectives, the turret looks like an alien cow.

I only have 3 CFI objectives:

• 5x BD
• 10x BD DIC
• 20x brightfield ELWD

And one CFI60

• 20x brightfield PLAN APO. The working distance is a miniscule 1mm, but the NA is 0.75.

• The latest Nikon objectives are their CFI60 series, named after the 60mm parfocal length. I have a CFI60 biological objective, and like most biological objectives it has a very short working distance. In this case, 1mm. That leaves 59mm for a heavy, unusually wide objective just packed solid with lens elements.
• The Mitutoyo 5x that's the darling of the macro field these days has a 95mm parfocal distance, which lets it have an insane 34mm working distance and still leave you 61mm for lens elements.

Scope manufacturers placed nearly all the aberration correction in the objectives. My old CF Nikons had to be matched to Nikon CF eyepieces or a CF "projection eyepiece" for photography. Directly projecting on a camera sensor showed off the high field curvature and chromatic aberrations. (Nikon says CF stands for "color free", but that's only when the objective is matched to a Nikon eyepiece). Now, it's 2022 and focus stacking fixes curvature of field, while software chromatic aberration correction is routine, but still...

The CFI objectives are better corrected on a generic 200mm telephoto than the old finite CF objectives were with matching projection eyepieces.

The fields just keep getting wider. Last week, Allan Walls and I were discussing objectives and their field sizes, and he politely cast doubt on my outdated ideas of field sizes. I tested what he claimed, and yes, the Nikon CF objectives cover a 43mm FF field surprisingly well.

They are designed so special optical components can be introduced into the optical pathway without additional compensating lenses

There's a lot to be said for that ability. I'm about to publish my open-source BD/epi illuminator.

Thanks for all that information. I have not shopped for microscope equipment for quite a long time.

It's pretty complex when you get up to high end biological, metallurgical, or inspection scopes. Heck, the fact that we now have "inspection" as a separate category from "metallurgical" is a big deal. That, and Nikon still has 45mm and 60mm parfocal instruments in their catalog.