20x Microscope Objectives

[rsb]

Thanks to this forum I'm good with 4x and 10x objectives. Now I'm looking for 20X objective. A favorite on the forum seems to be the Nikon M Plan 20x/0.40 ELWD. I was wondering if there were other (and hopefully less expensive) options. From what I can see in new Nikon objectives the only 20x with sufficient working distance are outrageously expensive (like thousands). I've also seen reference to 20x BD objectives but working distance was not specified and the ones I found were quite short. If there are no other viable options then I would need some help sorting out the used ELWD options. A quick internet search found the following offerings.
• M Plan 20x/0.40 ELWD 210/0 EPI - $600 eBay China
• Nikon CF Plan 20x/0.40 ELWD ∞/0 EPI - $530-600 eBay China
• Nikon CF Plan 20x/0.40 EPI ELWD ∞/0 - $950 eBay USA
• Nikon M Plan 20x/0.4na ELDW 210/0 - $850 Spectra Services
• Nikon CF Plan 20x/0.40na ELWD ∞/0 - $906 Spectra Services
1. Assume the CF would be suitable since the cover glass is 0 like the M?
2. Are All the M's also CF?
3. Do we have experience dealing with China eBay vendors? I have real qualms about sending that much money to a place that can make exact copies of anything.
4. Apparently these objectives were made in both are finite and infinite models. Is either one ok?
5. Some are EPI. Does it matter?
6. Any experience with Spectra Services. Are there other used equipment suppliers that you would recommend?

[ChrisR]

This is mostly from personal experience, but a couple of things are remembered from others' anecdotes:
• M Plan 20x/0.40 ELWD 210/0 EPI
"Epi" doesn't mean too much afaik. The lens is designed for light to be sent through it from the back. Perhaps zero difference in normal use, I don't know.

The Nikon Mplan 20x Elwd is good, though you do get some purple fringes as a type of CA. Those are often quite easy to deal with in post processing though I find.
The LWD and normal WD have less of the purple, but WD does get short.
I'll look them up and edit them in later.

The BD, non LWD types are some folks' favourite. If you remove the lighting collar, you get a very slim nosed thing which does allow you to light the subject.

All CF designated finite objectives were designed to be used with cover slips, but it doesn't seem to be too influential at this NA. The 20x NA 0.5 does well too and iirc has a slightly longer WD.
The finite CF 20x NA 0.4 has a short WD and is quite fat, so not really practical for "us" using incident light.
I have a CF Plan 20x/0.35 SLWD ∞/0 WD 20.5mm EPI objective which is OK, though the NA is a bit lower than either the 0.4 Nikons or the Mitutoyo at 0.42. When I first wrote a reply I'd forgotten I had it .
The Nikon CF Plan 20x/0.4 ELWD ∞/0 WD11mm objective is one I know nothing about - the spec looks OK, but they aren't cheap, . A Mitutoyo has a longer WD and is apochromatic, so probably a better choice.
There are some later Nikon LU and other 20x objectives, but they're expensive. and it's uncommon to find a LWD version.

MPlans are "CF" (=chroma free) but are designed for no cover slip.

Other than Mitutoyo, there are things like UMSCO. Central performance similar to Mitutoyo, edges going off a bit, but after PP, little difference.

There is/was/has been a JML 20x which sometimes surfaces, which is no the best NA (0.3?) but does well, with a reasobale WD.
You'll find others LWD by eg Unitron, which have some CA but, again, can produce a decent image.

Finite/Infinite is very important. See the FAQ on how to hook up a microscope objective to your camera. You have to use the objective the correct way.

Chinese, indeed any Ebay vendors - I've had some absolute junk arrive for $250, and had trouble with vendors. It's a lottery. Often it's OK. Do you feel, lucky?

Edit - Thanks to a pm from another member I'm remiinded that there ARE CF designated objectives which are for use without coverslips - these are all infinites I believe, which came after the finites. Apart from the one I now remember I have, I don't know about the others, at NA 0.4. I'd be hesitant to recommend you "have a go" at those prices - I do remember results form some of their near-brothers.

I have too many objectives. Sometime I may do a website testing them all.
First choice would probably be the Mitutoyo for most people, though others are happy to use very short WD with a slightly higher NA. Many are happy using less expensive glass, which may have disavantages, but none I have are so bad that the resulting image would be much different without pixel-peeping.

Sorry this is such a rambling reply!

[enricosavazzi]

I assume you are already set up to use both finite and infinite objectives, since you list both. You don't mention sensor size either. With APS-C or smaller sensors, you can use infinity-corrected objectives with tube lenses of focal lengths as low as 100-135 mm and significantly lower the magnification. Some finite objectives let you do this by shortening the tube length, but usually not to the same extent, so you have a bigger gap between the magnifications possible with finite 10x and 20x objectives.

I would second Chris on the M Plan 20x/0.40 ELWD 210/0 (I have the type without the epi-illumination sleeve). Second-hand prices seem to have gone up quite a lot since I bought it.

The Mitutoyo M Plan Apo 20x 0.42 is my go-to choice - not only because of good IQ and long working distance, but because I keep it mounted with other M Plan Apos on an FS-60 Mitutoyo scope. It might be a good choice for you if you already use other Mitutoyo M Plan Apos or if you find a very long working distance useful.

[Chris S.]

Rsb,

Now that ChrisR has done all the hard work (very well, by the way). It's safe for the rest of us to fill in a little bit around the edges.

3. Do we have experience dealing with China eBay vendors? I have real qualms about sending that much money to a place that can make exact copies of anything.

Regarding eBay vendors in China—I’d rather not paint all vendors from any nation with a single brush. I've had quite a few excellent buying experiences with vendors in China. On the other hand, there is one Hong Kong-based eBay vendor (diyaudio.hk) with whom I and several other forum members have had issues. PM me if you want more information about those.

I see a fair number of second-hand objectives, as the acquisitions of a number of forum members pass through my hands, and I test most of these. My sense is that there is currently no serious problem with fake copies of high-end microscope objectives. The real problem one faces with a second-hand objective--from any vendor, even a highly upstanding, professional one--is that it may deliver notably subpar results. I presume this is because some objectives are sensitive to being dropped or bumped too hard. Repairing this sort of thing is--so far as we know at this time--either unreasonably expensive or impossible.

Notably, the cosmetic condition of the lens tends not to tell you very much about its optical quality; I've seen rough-looking specimens that delivered excellent results, and like-new specimens that delivered poor results. One bad objective looked brand new, and came from a vendor whom I believe to be highly responsible. The vendor replaced it with an objective that did fare well in a test. And expressed what I think was sincere surprise that the first objective was subpar, as he had personally stuck it on a microscope and looked through before sending it out. Such a quick visual test is, in my opinion, generally not rigorous enough. It's much better to photograph a stack of a test subject with two lenses, one of known quality and the other, the lens in question. This should be done with a single subject, on the same rig, by the same photographer, under identical lighting. Then flash between the resultant images, viewing at 100 percent or higher in Photoshop.

All that said, purchasing a used objective has a lot better odds than the lottery. In my experience, only about 10 percent of second-hand objectives have needed to be returned. And most have cost between 1/3 and 1/2 of the new price. So if you purchase with a return privilege, and carefully test your new acquisition (or ask another forum member, who has the same lens, to do a comparison for you), you stand a good chance of landing a quality optic at a fair price.

4. Apparently these objectives were made in both are finite and infinite models. Is either one ok?

Either a finite or infinite objective--properly set up and used--can deliver fine results. Based on your other post, in which you were going to order a Nikon 10x CFI (an infinite lens) and were discussing the matter of converging lenses, it sounds as if your setup will be based around infinite optics. That being the case, it's probably better for you to go with an infinite 20x optic. You can use it on the same converging lens that you use for the 10x CFI. If you get a finite 20x lens, you will need to switch to either a bellows or extension tubes when you go from 10x to 20x.

I have sets of both finite (mostly Nikon) and infinite (Mitutoyo apochromat) objectives, the former for use on a bellows, the latter for use on a converging lens (in my case, an official Mitutoyo MT-1 "tube lens"). Both the finite set of objectives and the infinite set of objectives work well, but I find it convenient to stay with one set or the other for a given photo session.

I would second Chris on the M Plan 20x/0.40 ELWD 210/0 (I have the type without the epi-illumination sleeve). Second-hand prices seem to have gone up quite a lot since I bought it.

I have two specimens of this lens. One, I recall paying $500 for a few years ago. The other’s price I don’t recall. If the $600 specimen is very good, I don’t think the price is unfair. I also concur with ChrisR’s evaluation. And I also use my Mitutoyo 20x/0.42 more often—as in your case, Enrico, partly because of the lack of chromatic aberration and long working distance, and partly because I more often work on my Mitutoyo tube lens than on the bellows.

There is/was/has been a JML 20x which sometimes surfaces, which is no the best NA (0.3?) but does well, with a reasobale WD.

The JML 20x that ChrisR mentions was the subject of this thread, which is a bit of a tangent for this discussion, because the lens in question is likely unavailable now (unless some forum member wants to sell his copy). But it's a cool thread and a fun read: An obscure but interesting lens, available in quantity, is discovered by a forum member. Other forum members add information, eventually including test results. It is determined that the lens offers good value at the price offered (though not as good as the best optics available for 10-20 times the price). Shipping to non USA addresses is prohibitive, but a forum member volunteers to do a group buy--a lot of work--which makes these lenses available at low cost to forum members in Europe. Voila! Decent, inexpensive 20x capability appears in the hands of many.

It was a great example of the way we work together here at PMN.

Cheers,

--Chris S.

[jazzper]

rsb:

No one have mentioned this, so I'll do it:
Nikon CF Plan 20x/0.46 ∞/0 WD 3.1

An excellent objective. The only downside is the WD of 3.1 mm, but it's not that much of a problem really.

You can see an example shot in this thread:
http://www.photomacrography.net/forum/v ... hp?t=23055

[g4lab]

I should like to post a plug for SpectraServices. They are extremely nice people.

We got a new professor at our university. He had bought a used Olympus scope from Spectra. It took quite a while for it to get unpacked and used. Like two years. At which time it was discovered that the scope had a booboo in one of the oculars. They replaced it without asking very many questions.

That is not the only good experience I have had with them but possibly the most noteworthy. I have done lots of business with them.

[rsb]

Once again, I thanks to all for your kind and helpful advice. I am watching eBay for Nikon 20x infinity objective and will begin working with my 10x shortly.

Robert