Too bad there's no saying that goes: "What goes down, must come up." At least that would give shareholders of 3D Systems (DDD -2.65%) something to hold on to.

It's been a rough 2014 so far for owners of 3D Systems as shares of its stock have tumbled nearly 50%. While seemingly outrageous valuations have been the norm for 3D Systems and its 3D-printing brethren, the promise of massive future industry growth kept investors confident during the stocks' crazy run over the past few years.

But now many of those same investors are having second thoughts and abandoning the high fliers.

Whitney Tilson isn't one of them. He didn't own 3D Systems during the torrid upswing, and he doesn't own it now. In fact, Tilson's hedge fund, Kase Capital, is short 3D Systems stock and has shorted even more of the stock as it's plunged.

How ugly could it get? Tilson pegs the company's per-share intrinsic value at just $10 -- which suggests significant further downside from today's near-$50 price tag.

In the video below, Tilson outlines his case against 3D Systems. A transcript follows the video.

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Tilson: The stock went from $10 to $100, and I was short it from $60 on up, and kept pounding the table and warning people.

Really, the peak of it was at the Consumer Electronics Show in Vegas in January. I was out there and they announced that they had just appointed a new creative director,, the singer. I said, "This is the sign of a top."

Koppenheffer: That's the jump the shark moment, right there.

Tilson: Yes, exactly, and sure enough that day was the stock's peak at $98. Today it's down more than 50%, three-four months later. I just feel bad for the retail investors who got sucked into a giant promotion.

At that point it was trading at something like 20x revenues. I actually posted an article about this --, and this is the sign of a top -- on one of the websites, and someone in the message board said, "Oh, Tilson doesn't know what he's talking about. It's a good company; it's only trading at 20x earnings."

I slapped my head and I said, "That's the problem here. There are people being drawn into this stock who don't understand the difference between 20x earnings and 20x revenues.

Koppenheffer: Kind of a big difference.

Tilson: That's all the difference in the world.

By the way, I haven't covered a share. I shorted more on the way down at $60, stock's in the $40s today. I think intrinsic value is $10. It's not a fraud -- it's not going to $0.

Koppenheffer: There's a business there.

Tilson: Yeah, and it's probably worth 2 to 3x revenues, so my price target is $10. Now, there's enough hype around it that I'll probably cover most of it before it really gets down there, because once it gets down to a low level, you never know. It can get promoted back up, so as a short sell you can't be too greedy.