Are Nikon OEM 20x 0.75 objectives really UV enhanced?

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Lou Jost
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Are Nikon OEM 20x 0.75 objectives really UV enhanced?

Post by Lou Jost »

Image

Recently Nikon OEM 20x 0.75 apo objectives have flooded the used lens market, because the DNA sequencers in which they were used had become obsolete. These very high end objectives now sell from $100-$150, making them one of the best values in microscopy if you can deal with the 1mm working distance. There are several long threads on this forum about these objectives, which are excellent. However, the eBay listings for them make some claims that have never been checked. One claim is that these are OEM versions of the "VC" (violet-corrected) Nikon 20x 0.75. The other frequent claim is that these are "UV enhanced", presumably meaning that they transmit more UV light than the Nikon VC version.

I'll save the first claim for later, but I've now tested the claim that they are "UV enhanced". I tested the OEM 0500-0087 and 1501-9398 models against a true Nikon fully-labeled 20x 0.75 Apo VC. I used epi UV 365nm excitation lighting with Schott UG1 filter. I did not use an emission blocking filter. I focused each objective on a piece of white paper that fluoresces, refocusing between objectives. I found no difference in brightness (as measured by the camera meter) between the true Nikon VC objective and the "UV enhanced" OEM objectives. So it seems to me that the eBay sellers' claims are unfounded. Nevertheless, these are still fantastic objectives!

jmc
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Post by jmc »

If anyone in the UK has any of these, I can measure the transmission spectra between 280nm and 420nm using the system I use for measuring UV transmission of my lenses for photography.

Transmission is only one part of the story though - by 'enhanced' do they perhaps means that they are more chromatically corrected in certain parts of the UV?
Jonathan Crowther

physicsmajor
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Post by physicsmajor »

I didn't think these were enhanced above and beyond the 'official' VC objective. However, because of the guy who used one at the core of a DIY step and repeat photolithography setup, I did expect them to be VC.

If it matches the VC objective, and it sounds like it does, these are certainly bargains - even if they do need a double cover slip to reach potential, cutting the working distance further. For those unaware, in a separate thread digging into patents around this gene sequencing machine it was realized these are optimized not for a 0.17 coverslip but they were designed to peer through a flow cell closer to 0.3-0.4 in thickness. Two coverslips (or one carefully affixed to the objective) was found to bring the OEM objective's performance up fairly significantly.

Here is Nikon's page for the Plan Apo VC objectives, and I've embedded a snap of the stated transmittance of the 20x Plan APO VC - which shows 365 nm probably is near the edge of its usable range (around or a bit less than 20%).

https://www.microscope.healthcare.nikon ... -vc-series

Image

Ichthyophthirius
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Post by Ichthyophthirius »

physicsmajor wrote:Two coverslips (or one carefully affixed to the objective) was found to bring the OEM objective's performance up fairly significantly.
Hi,

Has someone actually tested two coverslips vs. just one?

Regards, Ichty

Lou Jost
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Post by Lou Jost »

Has someone actually tested two coverslips vs. just one?
Yes, I did that on an OEM version and posted the results in this forum.

https://www.photomacrography.net/forum/ ... x+0.75+oem

The right thickness was between two and three coverslips. This result more or less coincides with what we now know about what the gene sequencers that these OEM objectives were designed for.
Transmission is only one part of the story though - by 'enhanced' do they perhaps means that they are more chromatically corrected in certain parts of the UV?
There would be no reason for them to do that, since they are detecting only visible emission light in the gene sequencers. We know a lot about the sequencers; see the threads on this forum and elsewhere.

Scarodactyl
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Post by Scarodactyl »

Did you ever determine if the cover glass correction was different from one model of oem objective to the other?

Lou Jost
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Post by Lou Jost »

No I didn't bother. I'll do that some day. No time now. But the information in the threads about these objectives is very detailed and I think we can make good guesses.

Scarodactyl
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Post by Scarodactyl »

I'm still thinking about getting a 1501 to complete the set, just haven't found one as cheap yet. It'd be nice to have three different correction levels on the same nosepiece for looking at gem inclusions at different depths.

Duke
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Post by Duke »

As far as I'm aware, VC stands for Violet Corrected, which means that it features super-apochromat correction of 4 wavelengths (405nm, 475nm, 555nm, 635nm), instead of ordinary apo 3 (475nm, 555nm, 635nm). It may also have some extra coating, to further improve image, but it's unconfirmed.
UV is typically considered as region of wavelengths shorter than 400nm, and usually is stated on the objectives in different ways - like 'UV', 'Quartz', '340nm', '246-330nm'.
In other words, there's never was a clue that this series would perform any better in UV than other similar objectives. Why would they? It would be very untypical for highly corrected refractive objective to have great transmission in UV, because to reach this you would require different sorts of glass, some of it would be heavy flints, which has high dispersion meaning unavoidably having high absorption in UV region.
“Thoroughly conscious ignorance is the prelude to every real advance in science.” - JCM

abednego1995
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Post by abednego1995 »

Yup, Duke's comments pretty much nails it.
UV transmission isn't the point with VC, axial chromatic abberation correction is.
We use Fluors for better UV transmission, and if Nikon had "UV enhanced" Plan Apochromats in the first place that should have entered the market as the "dream objective"

P.S. I doubt those OEM objectives are even VC. Their original use in the sequencers don't use UV or even 405nm illumination negating the requirement. At least they should be normal Plan Apo.

Cheers,
John

Lou Jost
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Post by Lou Jost »

As far as I'm aware, VC stands for Violet Corrected
Of course, That's what I said.
there's never was a clue that this series would perform any better in UV than other similar objectives. Why would they?
That's right, for the original Nikon versions. That's why I wanted to test the OEM versions. The eBay sellers claimed these were "UV-enhanced". It would have been great if they were. Sadly, they weren't.

They could well have been UV enhanced though. For the OEM versions, Nikon could have sacrificed some overall color correction, knowing that the application only uses a few discrete wavelengths.

Boron
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Re: Are Nikon OEM 20x 0.75 objectives really UV enhanced?

Post by Boron »

Nikon Plan Apo objectives are not designed to work in UV region (neither 'normal', VC or lambda) and you can pick much better objectives for that.
Already mentioned Plan Fluor give some improvement in that matter but what gives you wow factor and also great performance in fluorescence microscopy is S Fluor series.
I have a full set of them and compared to Plan Apo they give much, much brighter image at every magnification.
They also go much lower in terms of excitatation wavelenght.

Macro_Cosmos
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Re: Are Nikon OEM 20x 0.75 objectives really UV enhanced?

Post by Macro_Cosmos »

Yeah, VC stands for violet corrected, corrected for 405nm ie axial CA up to the violet range has been accounted for.
If Apo refers to correction in 3 wavelengths, then 4 would make it sApo.
Doesn't necessarily mean it's "UV enhanced", however looking at the transmittance graph, it's adequate for NUV applications and good for IR.

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