MicrobeHunter.com Microscopy Forum

I'm looking to examine some minerals and am looking at one of these 20x L Plan lenses, with LWD so I don't damage the sample or lens. Does anyone have good experience with these, or the fall apart from being built down to a cost?
https://imgur.com/a/hiRV56O

Some chinese objectives are very good, some are very bad, many are in between. It's not easy to tell what you're getting from a picture either because very different designs are sometimes put inside very similar shells. It's probably OK, but you'd have to try it to be sure.

Generally, the formulas they use for the objectives work. Achromat , planachromat, planF/planfluar and planapo because more often than not the design originated elsewhere, either through the purchase of older designs that have been sold off, reverse engineering, use of obsolete patents, or licensing agreements. This is especially true with the better colour corrected types. You also won't find made in China on an objective, at least I have never seen it.
That is because India is also a big player and components from each country can show up in the other country's stands. They also sometimes contract smaller Japanese manufacturers to do custom runs but that is usually only for expensive stuff.
However, any of these objectives are relatively cheap, even in comparison to modest optics from Germany or Japan. Prior to 1990, there were about 15 well establish companies world wide that made high quality microscope optics and now 35 years later, there are similar optics available from China/India for 1/2 the 1985 price.
One cost saving factor is through economy of scale. China and India need a lot of microscopes, so the number of units of the basic grade objectives made and sold are huge. They also have to be economical, so even though the optical performance is theoretically within spec., and tens of thousands of individual lens components are churned out efficiently, they still need hand assembly and final adjustment. That is where the skimping takes place and the quality control of the system breaks down. Each objective has to be hand assembled from bins full of like components. The through put time for the mechanical parts required has to be just as fast as that of the lenses, so the machining and finishing is rough, requiring more expertise in assembly because air gaps and centering even in the simplest of objectives needs to be within .02-.03 mm maximum. I have been cut by the threads on a cheap oriental objective. The brass is crude with impurities, made from old light bulb bases and rifle shell casings. Machining is rapid. You can see chatter marks.
It takes time to adjust the spherical aberration in an objective and time is money in manufacturing.
I have been into oriental objectives, where you had to rotate the lens cells in order to use their inherent wobble to adjust for s.a. instead of shims. Certainly under the circumstances not a bad way to do it but that speaks to a parcentering problem that is at the core of the deficiencies of cheaper oriental objectives.

If it were me, unless I had some reason to trust the particular Aliexpress seller, I would try to buy through Ebay/Amazon with a 30-day return policy, even at a higher price, just in case the objective turned out to be junk.

I agree with Scarodactyl, some Chinese objective lenses are good, some are bad and you can't always tell by its price. Many times it is difficult to determine if the unknown objective lens you are viewing through is good, mediocre or bad. If you have some present objective lenses that you know are of good optical quailty, placing the unknown optical quality objecctive on the same revolving nosepiece of your microscope, next to the known optical quality objective and flipping back and forth between the two while examining a slide will give you a subjective opinion as to its quailty. Not a very scientific way of determining objective optical quaity but it works for me. In addition to Chinese lwnses, I have had very positive experiences with objectives made in India.

My experience with eyepieces has shown me that just about any eyepiece will yield good optical quailty if viewed with a good objective. Other than field of view, and a few other unexplainable issues, differences in eyepiece optical quality has been far less of a problem.