17 Dec 2017>> I'm returning to my review of this lens after Amazon disallowed my review of a similar set of 3 Sciencent lenses I had just purchased, saying that my review of a prior purchase of the Sciencent lens back in February showed a "relationship to the product or seller [that] may be perceived as biased". I found no review of mine for that purchase, so I guess it was deleted for some reason, and perhaps that reason will surface with what I'm about to say here. My opinions are not biased in favor of a seller, they are biased only in favor of one product, regardless of seller, that is demonstrably of higher quality than a similar product of another seller.The Sciencent double concave 75mm diameter, 20cm focal length lenses are "good" lenses at at about $8, roughly 33% cheaper than this Eisco Labs lens. I bought the Sciencent lenses for that reason, to save some money on the purchase of 3, and not recalling having any problems with the lens previously purchased. Upon receipt of the 3 new Sciencent lenses however, I was reminded of why I favor lenses from Eisco Labs....Eisco lenses seem to higher quality lens in both consistency of size and the edge finishing of the lens. My Eiscon lens measure 13mm thick, whereas 2 of the Sciencent lenses were 9.5mm thick and the third was a little under 9mm. For anyone purchasing these lenses for use as a precision top spin stage, it isn't a biased opinion to state the fact that a thicker double concave lens should prove to be a bit more robust, even if the different thicknesses of lenses were all found to be the same thickness at the lens center. For lenses priced as economically as the Sciencent lenses are, I consider that acceptable but still merely a "good" lens, where I'd call the Eisco lens "excellent" in comparison. It is up the buyer to decide upon what they find acceptable. As far as the lens edge is concerned, the Sciencent lenses are a straight ground edge, with a sharper corner at the lens face, whereas the Eisco lenses have a ground bevel that makes for a nicer handling lens if not really affecting the performance. With the exception of one Sciencent lens having an acceptably small chip at the edge of one lens, the lenses from Sciencent were free of any chips. I've never received an Eisco lens that was chipped, but I suspect they do surface every now and then. "biased or from ScPurchased for use as a spinning top platform, this lens works quite well but I actually observed longer spin times on a 10X magnification, 5-inch diameter mirror. I'm guessing the mirror was a little less concave, thus there was probably less surface contact with the spinning point of the particular top I was using (ShadowSpin stainless steel). Another advantage was that the larger mirror gave more room for error in placing the top when trying to attempt a good strong spin. The lens is nice for the conveniently pocketable size but just be advised it may not be the very best spinning platform, but that is no fault of the lens itself.Purchased for use as a spinning top platform, this lens works quite well but I actually observed longer spin times on a 10X magnification, 5-inch diameter mirror. I'm guessing the mirror was a little less concave, thus there was probably less surface contact with the spinning point of the particular top I was using (ShadowSpin stainless steel). Another advantage was that the larger mirror gave more room for error in placing the top when trying to attempt a good strong spin. The lens is nice for the conveniently pocketable size but just be advised it may not be the very best spinning platform, but that is no fault of the lens itself.

I got my nephew a professionally spun and tuned spinning top for Christmas. These lenses were recommended for use as a base on which to spin the top as the gentle concave shape keeps the top towards the center and the glass surface provides a smooth surface with little friction. Using this as a base he was able to spin his top several times that night for 4 to 5 minutes and it spun so perfectly it would often hardly look like it was even spinning.

I have numerous precision tops (AKA Pocket tops, Spinning tops) by various makers from 5/8" to 2.1" in diameter. This type of surface is ideal for many styles except for flat-bottom-tops with a shallow clearance for bearings in tops that are greater than 1.2" in the realm of beginning collectors (as made by people like Twisted Tops, Fludunlimited/BW Flud, Charles Symeonides, and Patrick Ober). The concavity tends to interfere with larger tops with that particular diameter/design. For intermediate/advanced top collectors, this lens should be suitable for your use.This lens works well for tops with stainless, ruby, or ceramic genre of bearings. It also even works well with tops that do not have bearings such as the Inception top, Tippe top, Lance Barnett tops (some select tops that don't have bearings), or Franz Tommasi Delrin/Polymer tops.My lens did have a tiny chip on the edge of the lens but since my purposes were not for optical use, I didn't return it. However, it raises the questions of quality control for my experience.Overall, I am quite pleased with the performance of smaller tops with a wide basilar clearance for my tops, especially from makers such as Blake San (Mountain Tops EDC), Steven Robbins Fine Pocket Tops, the Inception top, Symeon Metal Works, the Tippe/Tippie Top, Twisted Tops, Marke Dalpe, and Fludunlimited/BW Flud.

I got this on a whim for some spinning tops and a cotton supported spindle. It works well for the tops, but I think I need more practice for the spindle. It's been a cool item to interest my grandkids with the optical effects. The lens is very well done with clean smooth edges. I have used it at work to clarify engineering drawings after I noticed the lens making some parts of the drawing clearer even though it was making it smaller; counter intuitive but handy.

It's just OK.. I'm a newbie when it comes to spinning tops. This lens is a great idea, however the edges all around are sharp which puts bad scratches in the bottom or your tops. The edges needs to be covered in some manner. Like a rubber wrist band, or tape. I wish someone would have told me.

I have no idea what was responsible for the complaints that others have experienced. My lens arrived in what looked to me to be perfect shape in spite of obvious (mis)handling of the package. This lens is a much better base for spinning Forever tops than the one provided at a much higher price by Forever Spin. Unlike the commercial product, the lens not only seems to keep the top spinning longer and more centered, at the end of every spin, at least so far, the Forever Spin Titanium top stays in the lens when it drops. Sometimes the excess energy is depleted by a rocking motion that sounds a bit like a ticking clock and is tres cool. I will soon try my Vorso top in it and see if it just a one top base or a universally great deal.

I use this product as a spin station for my tops. It works very nicely and is a good size for portability. Also having it double sided should I get any scratches on it is a plus. Price is very reasonable.

Good price and well made, good for spinning tops

The glass was cracked when it arrived.