What are the quality criteria for stereo microscopes?

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farnsy
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What are the quality criteria for stereo microscopes?

#1 Post by farnsy » Sat May 29, 2021 7:18 am

I would really like to purchase a stereo microscope, but I'm frustrated with the lack of availability of knowledge on the subject. In the same amount of research time, I learned so much about compound microscopes and I think I understand the main criteria distinguishing one from another, and which attributes are associated with quality (numerical apertures, degree of color correction, finite vs infinite, availability of special techniques like darkfield, polarization, fluorescence, phase, DIC) and I know what type of features to look for an expect from the body and peripherals. And of course, what doesn't matter (eyepiece magnification, etc.).

On the other hand, in stereo microscopes, I see some differences, but many vendors don't seem to list the features in a way that they can be distinguished and I'm not sure I'm really looking at the most important quality criteria anyway. For example:

CMO vs Greenough. CMO scopes seem to be more expensive on average, but there are very expensive current Greenough scopes from top manufacturers. This makes me wonder whether it's right to say that CMO scopes are really better, or what they are better for. Some sources say they are better for photography, but I see no reason why that should be the case based on their design, and have seen no explanation.

Zoom vs turret/galilean. Definitions are clear here and one can imagine why zoom turrets could be more convenient, but presumably there is a reason besides cost why fixed-style stereos persist. Better optics? I see conflicting views on the subject. It it just money-saving? If so, is the savings worth it?

I can find almost no information about color correction, although some high-end scopes say they are apochromatic. Is color correction not important in stereo microscopes? What kind of color correction should one want/expect? I can easily imagine that it's not critical as it doesn't seem to be as much of an issue at low magnifications in compound scopes within my experience.

How about finite and infinite optical systems? I see that both exist, though this information never seems to be obviously given in the descriptions. I understand this better in the context of compound microscopes, but it's not as obvious to me why an infinite system would be helpful in a stereo scope. I guess for polarization? How useful are infinite optics in stereo scopes?

I also have little idea how much technological innovation there has been in this field in recent decades. How does an AO cycloptic or stereo star compare with a current greenough or CMO from china or from a reputable current brand? I heard that issues like the perspective distortion in CMO scopes had been fixed in a certain generation, but to what degree do they persist in cheaper scopes?

I guess, help me understand what makes a good stereo microscope. I'm interested in the usual stuff: bugs, hangnails, daphnia, mold, objectives, circuits, etc. I don't have a budget, so anywhere hundreds to thousands of dollars is a reasonable range to discuss. I would say there would need to be a very good reason for me to spend multiple thousands on a stereo scope, though I have done that with my compound. I'm equally interested in used and new equipment. I'm interested in DIY but by no means an expert.

Anyway, I'd love to hear advice and opinions on this that may help guide me. Am I even looking at the right stats?

MichaelG.
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Re: What are the quality criteria for stereo microscopes?

#2 Post by MichaelG. » Sat May 29, 2021 9:05 am

The single most important feature of a stereo microscope must surely be the design of its binocular.
The suitability of a particular design, for your eyes and your type of work, is difficult to judge from descriptions, specifications, and the experience of other people ... You really need to find what style works best for you [and then consider the quality of construction available from various manufacturers].

When you know what what works best with your eyes ... then choosing the other optical and mechanical features is relatively straightforward [field of view, magnification, resolution, colour correction, focus stability, etc. etc.] and quantifiable.

MichaelG.

.
Edit: __ inserted the italicised words in the above, for the sake of clarity.
Last edited by MichaelG. on Sun May 30, 2021 9:09 am, edited 1 time in total.
Too many 'projects'

PeteM
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Re: What are the quality criteria for stereo microscopes?

#3 Post by PeteM » Sat May 29, 2021 5:44 pm

Perhaps the best way to look at this is to start with the intended purpose, rather than searching for the best specs attainable at any cost. The best specs for motorized transport might be something like zero to sixty miles per hour under 3 seconds and a payload capacity of many tons – but the first leads one to a sports car and the latter to a heavy truck.

The basics – often available in either Greenough or CMO versions – are:

- Appropriate magnification. 7x up to 30x or 40x is good for most uses. An even lower range (e.g. 3x) can be very useful for some tasks. A single magnification may be perfect from some repeated task - high quality 10x or so stereo microscopes really need to get more respect. People are delighted with single magnification wide view binoculars. Why not single magnification wide view stereo microscopes - perhaps fitted with a supplemental objective or eyepieces to make them perfect for some tasks.

Moving up to 50x to 80x adds cost if the image isn’t to degrade. 80x to 160x is possible, pricey, and useful for some research applications. Numerical aperture is the governing spec for quality at high magnificatons and usually not disclosed in low and mid-range stereo microscopes. At the high end of magnification, CMO designs predominate and may be available in plan achro and plan apo versions.

I'd add that beginners seem to think they want high magnification in a stereo microscope - and dealers oblige with unrealistic add-one eyepieces and claims. I'd much rather have a stereo microscope with a good low magnification (say 6 or 7x) that tops out around 30x than one that claims 10x to 80x and has empty magnification or just lousy images from about 30x on.

- Wide field of view, reasonably distortion free out to the edges. Cheaper imports won’t even describe the field number, which may be 18mm. Somewhat better new microscopes -- and many of the used classics -- will have 20mm. Getting up to the 22-24mm field range often makes a stereo microscope more productive and more comfortable (if of quality design) to use.

- Precisely converging optical paths (and built to stay in alignment). This is, I believe, one of MichaelG's points. No one tells you their microscopes are cheaply made or have such fiddly adjustments that if they either start poorly aligned (fairly common) or end up with a shifted or sticky lens or prism that they will be extremely difficult to put right. Money can – but doesn’t always – buy a better scope in these essential respects.

- Sufficient working distance to easily manipulate specimens and get illumination in from the sides. This generally gets smaller with higher magnifications; with better microscopes often offering greater working distance at any given magnification.

- Parfocal and parcentered images as the magnifications are changed. Cheap zoom microscopes are notorious for having the image go out of focus and wander around a bit as the magnification is zoomed. The wider the range and the cheaper the price the more this can be expected. Someone looking to get the best image quality at a reasonable price might well prefer fixed magnifications. These are also easier to calibrate should measurements be a factor. I generally don’t recommend buying cheap Chinese wide range zoom scopes. Good news is you might get one that’s reasonably parfocal and parcentered to begin. Bad news is that they don’t hold up all that well if seriously bumped or the lube dries and the plastic zoom gear splits.

- Added features such as coaxial illumination, photo tubes, and irises. As with regular microscopes, the world has moved to “infinite” designs to make it easier/cheaper to insert these in the optical path. A top end CMO infinity microscope might stack two or three intermediate pieces and still preserve the full wide field of view.

- Minimal geometric distortions and color aberrations. It’s the eye of the beholder here. “Doming” is a common distortion for stereo microscopes, especially at low magnifications. For biological specimens it might be seen as a neat 3D effect. For planar industrial specimens it might be seen as annoying pincushion distortion. The same plan versus not-plan and apochromatic verus achromatic (or worse) color corrections also apply – with more $$$ buying better lenses.

Stereo microscopes are commonly preferred over loupes and simple microscopes because they preserve 3D hand-eye coordination for manipulation, dissection, soldering, etc. And they may likely be used for hours at a time, rather than a quick glance to, say, make tiny print larger. So comfort over time is a huge factor – and not easily captured in specifications.

Just to give a comparison – the cheapest stereo microscopes we recommend for kids cost about $150 new and have two fixed magnifications (10x and 30x). They’re sold by AmScope and others. It would be nice if the low were more like 6x, but the high of 30x is about right for lots of stuff. The cheap 15x and 20x eyepieces to extend the range really aren’t much of a bonus. The cheap add-on supplemental objectives can be useful. A buyer should carefully inspect one of these $150 scopes for alignment upon arrival and send it back if far off.

Since depth of field decreases at high magnification, a regular microscope with a 4x objective and 40x total magnification is a often a good choice once you go beyond 30x.

So, what does a $500 or so Meiji EMT microscope with the same 10x and 30x fixed magnifications as a $150 AmScope buy? It will have a 23mm field of view rather than something more like 18mm, a longer working distance, better construction, better collimation, a higher numerical aperture, better supplemental optics, etc.

Moving on to something like a Meiji EMZ (or the Nikon, Olympus, Leica, Zeiss etc. equivalents) and you get a properly constructed 7x to 45x zoom and better-made supplemental objectives to extend the range lower and higher if need be.

Moving on to a high end research microscope, typically CMO and infinite, may give extraordinary zoom ranges and allow many tasks to be done from start to end on the same microscope; rather than moving from a stereo microscope to a compound microscope as more detailed examination is needed. And still with usefully larger working distance under the objective. All for about the cost of a year or more of college tuition . . .

farnsy
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Re: What are the quality criteria for stereo microscopes?

#4 Post by farnsy » Sat May 29, 2021 6:52 pm

Thanks, Pete. The added features and converging optical paths you mention would seem to give the CMO microscopes an advantage. Are there any CMO scopes you might recommend (potentially on the used market...I'm assuming these are really pricey new)?

Is it your feeling that zoom microscopes are as good as the ones with a turret, optically? Is the only advantage of the latter a lower price?

lorez2
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Re: What are the quality criteria for stereo microscopes?

#5 Post by lorez2 » Sat May 29, 2021 7:35 pm

PeteM says it best:

"Perhaps the best way to look at this is to start with the intended purpose, rather than searching for the best specs attainable at any cost."

farnsy asks,
"Is it your feeling that zoom microscopes are as good as the ones with a turret, optically?"

I'm just a follower of this discussion, but I think equating optical quality and mechanical design may not be the right question. In my experience the microscopes that had the good optics also had the reliable mechanics and whether one chose the fixed magnification turret or slider or zoom was for the reason PeteM cited... what is the intended purpose.

lorez
Nikon 80i

PeteM
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Re: What are the quality criteria for stereo microscopes?

#6 Post by PeteM » Sat May 29, 2021 7:37 pm

Today's best and most expensive stereo microscopes are likely to be zooms.

It's a bit like manual and automatic transmissions (and now continuously variable transmissions) in the days before we learned how to make really good automatics. It's cheaper and easier to make an entirely satisfactory manual transmission with gears from low to high. And remember when all the really high performance cars had manual transmissions? With a microscope, if you don't mind "changing gears", you can do just fine with a high quality stepped optical design. And even easier to "drive." You'll likely have fewer issues to deal with if you're buying an older microscope as well, since dried grease in zoom mechanisms is a fairly common problem.

A good automatic and continuously variable mechanism will add cost and is more likely to have reliability problems over the long haul. But these days, with tens of millions of design and manufacturing experience behind us, things like continuously variable transmissions are beginning to predominate. Same thing in stereo microscopes.

The best deals in stereo microscopes are used - but you really want to be able to check out any particular example or easily return it if it isn't right. I wouldn't shy away from Greenough zoom designs. I really like my Nikon SMZ-1,1b, 2, and 445; my Olympus old SZ-III and newer SZ4045; and my Meiji EMZ scopes. Some of the old A.O. (570 & 580 high resolution models) and B&L stereo zooms (SZ4 etc.) are quite decent. Affordable supplemental objectives are also available for all of these. Note that a used Meiji EMZ with a trinocular head is likely to set you back around $1000 - and near as much for recent vintage Nikon, Olympus, and Leica models with a similar zoom range. I don't know the Zeiss line well enough to comment (but did once have a fine stepped-magnification Zeiss OPMI scope).

The old A.O. Cycloptics are the first widely available CMO design -but with a choice of fixed magnifications. They're still pretty good if the prisms haven't detached, but not as bright as more modern CMO stereo scopes.

The only pretty decent CMO designs I have as "keepers" are a Nikon SMZ-10 zoom with most every accessory, a Wild M8 with plan optics, and a Wild M3c with the movable plan objectives for photography. I like them all fine, and the plan achromats and the supplemental objectives are pretty good, but they all edge into empty magnification around 80x. You might like either the newer Nikon SMZ-10a or a Wild M8 or its Leica equivalents -- and plan on switching specimens to a regular compound microscope once you're past 60-80x or so.

After lusting after a CMO scope with something like a 10x zoom range, plan apo objectives, and a 24mm FN for myself - I've realized (at least for now) the money would be better spent (for me) elsewhere. "Scarodactyl," who posts regularly here has a greater need and more experience at the high end of these scopes.
Last edited by PeteM on Sat May 29, 2021 8:08 pm, edited 1 time in total.

PeteM
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Re: What are the quality criteria for stereo microscopes?

#7 Post by PeteM » Sat May 29, 2021 7:56 pm

Just to add on the Wild M8, once I added a plan objective my main complaint was that the OEM eyepieces are limited to 21mm. It turns out that 10x/23mm FN Nikon stereo eyepieces work just fine once you machine them to fit about 6mm further into the Wild eyetube. Despite the wider field, I'm not seeing vignetting with a photo/iris and even another ergo intermediate attached. The iris will vignette when nearly fully closed.

I might have been lucky to have optics well enough centered to allow moving from a 21 to 23mm field - but this was a welcome upgrade. Since my vision is not 20-20 and different in each eye, I machined in the diopter corrections by having a slightly greater entry depth in one of the Nikon eyepieces. I've also done this with generic 10x/22 eyepieces and those also turned out better to my eye than the OEM 10x/21 Wild/Leica eyepieces.

This is a pretty decent, somewhat affordable, edging towards "higher end" option. I generally use it with the 6+x to 50x range with a normal 1x plan objective; but it holds up just fine with a 1.6x supplemental objective to zoom from 10x to 80x.

dtsh
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Re: What are the quality criteria for stereo microscopes?

#8 Post by dtsh » Sat May 29, 2021 9:07 pm

If I can add anything here, when I was looking for a stereo microscope (wow, just over a year ago) I wasn't really sure what I needed. I was looking for something to help me with insect identification, mostly smaller insects such as flies and mosquitoes. Some of the papers I'd read suggested I'd need something capable of 100x so that's what I was looking for. Here a year later and many thousands of insects sorted I find it's pretty rare that I go over 40x and most typically I'm at 10x for the bulk of my efforts and commonly flip to higher mags upto about 40x. My scope goes upto 80x with a barlow, but it's very rare that it gets used.

I'm a happy AO Cycloptic user and can't see upgrading it without a significant investment. I'm not trying to plug the Ctcloptic, it has the aforementioned issue with the prisms (there are solutions as well), but it's what I am most familiar with and what I use so it's my reference which is why I'm mentioning it.
Here are some images I took from it a few months ago to help someone get a rough idea of what to expect at various magnifications, I hope it helps.
stereo_mag_s.jpg
stereo_mag_s.jpg (102.2 KiB) Viewed 723 times

farnsy
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Re: What are the quality criteria for stereo microscopes?

#9 Post by farnsy » Sat May 29, 2021 10:17 pm

Thanks, dtsh. I was actually just reading your 2020 thread as you were writing this. Seems like a good thread for me to read as you and I have a lot of questions and desires in common. I was just reading that you had bought that cycloptic and gotten a new head for it (since the optics were not, initially, aligned properly). I'm glad to hear you still like it.

I have quite a bit of AO stuff in various states of repair, so I feel somewhat comfortable with AO, even if it's not 100% working. But since that is the very first CMO widely available, I did question whether there had been significant technological steps forward since that time that made a difference.

What I might do is buy an inexpensive, but still good, stereo. If I end up wanting something better/more, I might pass it along to my kids and get something more expensive for myself. Stereo microscopes, when not too expensive, seem to be perfect for children.

linuxusr
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Re: What are the quality criteria for stereo microscopes?

#10 Post by linuxusr » Sun May 30, 2021 1:25 am

@ ET AL:

I need to find out if a stereomicroscope fits my use case. I know very little about them. A quick scan from Wikipedia tells me a few basics: a. the oculars are asymmetric enabling 3D, b. long WD,

I am blind in one eye, NLP, "no light perception," so the stereo aspect will not work for me. I thought that I could use an inexpensive Amscope in this way: When I am checking my specimen jars for microbes, which I do on a daily basis, it'd be much easier to take a quick look via a stereoscope for a quick yes or no and type, then proceed to my compound scope if a "yes." If a "no," no problem. Easier than dragging out all my equipment . . .


Will a stereoscope me useful for this purpose? And, if so, any opinion on AmScope SE305-P (WF10x oculars; 1x and 3x objectives; upper and lower halogen). About $128.00 on Amazon. This model seemed good for simple uses such as the above.

BTW, I'm a little ambivalent and disheartened by AmScope's sales of compound scopes with "empty magnification" to young children who are just becoming interested in science. This is fraudulent.
Nikon AlphaPhot 2 < Zeiss Primostar 3, Full Koehler

PeteM
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Re: What are the quality criteria for stereo microscopes?

#11 Post by PeteM » Sun May 30, 2021 1:50 am

Something like a "macroscope" or an inspection microscope -- possibly connected via a camera to a large 4K monitor -- might be more useful for you. With "NLP" in one eye, half the optics in a stereo microscope are lost to you and also just take up a bit more pace on a bench.

These might have a similar range to a stereo microscope. Edmund Scientific made some affordable ones that sometimes show up at low prices used. More expensive ones were once made by Wild Heerbrugg and now by many makers. Scopes meant for inspection in manufacturing applications are another possibility.

PeteM
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Re: What are the quality criteria for stereo microscopes?

#12 Post by PeteM » Sun May 30, 2021 1:52 am

To add, the AmScope 1x & 3x (10x and a30x) stereo microscope model you (linuxuser) linked is one we recommend as one of the least expensive usable new microscopes for kids. I don't recommend getting one with the 15x and 20x eyepieces or any model that doesn't go down to at least 10x.

In your case, the same $150+ might buy a used inspection / macroscope with better optics, perhaps a zoom, a wider field of view, and easier connection to a camera.

Scarodactyl
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Re: What are the quality criteria for stereo microscopes?

#13 Post by Scarodactyl » Sun May 30, 2021 2:09 am

I might have a stereo that's clear but misaligned, which could be ideal for your usecase. I'll dig around.

farnsy
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Re: What are the quality criteria for stereo microscopes?

#14 Post by farnsy » Sun May 30, 2021 6:33 am

Here's an example of confusing marketing. I have seen each of these microscopes mentioned in various places as both CMO and Greenough. They are very common microscopes so there's a lot of info about them, but not the basic info that one wants to know. Probably it's made worse by the fact that Nikon doesn't use the "CMO" terminology. Are the following three microscopes all CMO?

Nikon SMZ-1 (and 1B)
Nikon SMZ-2 (and 2B and 2T)
Nikon SMZ-10

Pete, you talked about the 1 and 2 in such a way that one understands that they are Greenough and the 10 as a CMO. I've seen the opposite claims elsewhere on the internet. Can you double confirm?

I've seen people confidently mentioning the SMZ-10A, SMZ-U, and SMZ-800 as CMO, so all my sources seem to agree on that.

Much easier to find information in wild microscope models, for some reason, than Nikon.

Scarodactyl
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Re: What are the quality criteria for stereo microscopes?

#15 Post by Scarodactyl » Sun May 30, 2021 6:53 am

The smz 1 and 2 models are greenoughs, as well as the recent 440/460, 640/660 and 745. All the Nikon cmos are modular units, separate zoom body and heads, while the greenoughs are one piece. That's sort of a general pattern across stereos with very few exceptions.
Nikon does use the terms greenough and cmo.
There is quite a bit of info out there about nikon scopes, in some cases it may take a little more digging but it's not so bad.

farnsy
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Re: What are the quality criteria for stereo microscopes?

#16 Post by farnsy » Sun May 30, 2021 7:15 am

Scarodactyl wrote:
Sun May 30, 2021 6:53 am
...cmos are modular units, separate zoom body and heads, while the greenoughs are one piece. That's sort of a general pattern across stereos with very few exceptions.
That is a very handy bit of info that will help a lot when answering basic questions like this. Thanks!

MichaelG.
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Re: What are the quality criteria for stereo microscopes?

#17 Post by MichaelG. » Sun May 30, 2021 8:48 am

farnsy wrote:
Sat May 29, 2021 7:18 am
I would really like to purchase a stereo microscope, but I'm frustrated with the lack of availability of knowledge on the subject.
.
Have you read these ?

http://www.microscopy-uk.org.uk/mag/art ... tereo1.pdf

MichaelG.
Too many 'projects'

Rorschach
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Re: What are the quality criteria for stereo microscopes?

#18 Post by Rorschach » Sat Jun 26, 2021 6:31 am

I would vote for a CMO/infinity design. It gives so much more modularity and flexibility. You can add very useful components such as photo tubes, coaxial lights, drawing tubes, ergo wedges etc. You also have a large selection of different heads available (can tailor the system to your specific ergonomic needs) and often also several different focus carriers to choose from.

Also, some CMO models will have the possibility to slide the objective to coincide with just one of the two optical paths - clear benefits for photography. I don't think this possibility exists with greenough stereos.

Regarding the zoom vs turret design, I think the turret design does have one advantage over a zoom system: less glass in the light path --> more light gets through the system to your eyes/camera. Also, the more lenses and lense surfaces on the way (as typically in a zoom system) , the bigger the risk of losing image contrast (depending on lens coatings and overall quality, of course). This would be an argument for preferring a system with just a moderate zoom but with an objective slider/revolver (another CMO special, correct?) over a system with an incredibly wide zoom range.

jfiresto
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Re: What are the quality criteria for stereo microscopes?

#19 Post by jfiresto » Sat Jun 26, 2021 7:26 am

Hi Riku!
Rorschach wrote:
Sat Jun 26, 2021 6:31 am
Also, some CMO models will have the possibility to slide the objective to coincide with just one of the two optical paths - clear benefits for photography. I don't think this possibility exists with Greenough stereos....
Since a (competent) Greenough always coincides, the standard trick is to tilt the specimen or the observing objective, 5–6°: to make them parallel.
-John

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