Nikon small world

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.

Anything that can do a reasonable 200mm equivalent and can be manually focused to infinity can work well with an infinity objective, including my phone (Samsung Galaxy S21 Ultra). I've also used them with a Nikon 200mm f/4, and with an old 70-210mm f/4-5.6. You can get an RMS to 52mm or 62mm adapter for around $15. It's going to take more to couple to a finite objective.

I'm great at doing things cheap, but the cheapest one can get away with mounting a 210mm finite objective to a typical DSLR or EVIL is $63. That's $15 for an adapter from your camera to M42, $33 for three M42 extension tube sets (Acouto 3 piece set, 61mm total), and $15 for an M42 to RMS adapter. You probably want a tube clamp with an Arca foot, too.

As far as magnification, most modern infinity objectives have enough resolution to drive a 300mm or even a 400mm telephoto. Some won't vignette on a 135mm on FF, or a 100mm on APS. If you try running a 210mm tube-length finite objective down to 100mm or up to 300mm or 400mm it's going to get a bit squiffy. Been there, done that.

But wait, there's more!

They are designed for special microscopic techniques such as polarized light microscopy and differential interference contrast. They are designed so special optical components can be introduced into the optical pathway without additional compensating lenses.

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.

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?

• 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.