JML 64mm f/0.85

Lou Jost · Post by **Lou Jost** » Wed Nov 01, 2017 6:53 pm

This is one of the cheap but exotic lenses I brought back from the US on my last trip there. It cost $50 (https://www.ebay.com/itm/ULTRA-HIGH-SPE ... 4d617d21d7). Lots of them are available from the same seller I bought mine from. I can't find much useful info about it on the internet. So I have begun to explore its properties empirically.

The first weird thing about it is that when the lens is focused at infinity, the image is in focus almost right at the rear lens surface. And if the lens is reversed and the back side is aimed at an object at infinity, the image is in focus right at the surface of the front element. I'd never seen a lens do that in both directions. So it probably can't be used at infinity and must be optimized for close-up work. But at what m, and in what orientation? Anyone know anything about this lens?

By eye it seems that for m>1 it is better reversed. I tried it today at 2.2x (the magnification obtained by mounting it on a Nikon PN11 extension tube). Working distance was a respectable 38mm. It was soft but surprisingly sharp and clean for such a fast lens wide open. If I make a paper aperture to stop it down one stop, and if I control stray light better, it will still be at f/1.2 (EA= 4.0) and I suspect it will be very sharp. When time allows, I'll explore this lens more to find its optimum magnification range.

Here is a 100% crop on an MFT 20Mp sensor, with and without post-processing, stacked with Zerene PMax:
With PP:

Straight from camera 100% crop:

Lou Jost · Post by **Lou Jost** » Wed Nov 01, 2017 7:16 pm

Forgot to mention one other interesting thing about this lens. When I aimed it it at a slanted ruler, the ruler lines showed no parallax. So at this magnification it may be approximately telecentric. The scale factor at the end of the 88-image stack was 1.0003, pretty close to unity, suggesting that it really is almost telecentric.

A real (and quite expensive) telecentric lens I also brought back with me, the Sill Optics lens for m=1, is far less sharp than this cheap lens. More on the Sill Optics lens when I have some time. Meanwhile here is the short version of what I'll write: don't waste your money unless you need perfect telecentricity and can afford to stop the lens way down.

ray_parkhurst · Post by **ray_parkhurst** » Wed Nov 01, 2017 8:11 pm

I bought one a while back but have not tested it yet. It's a big lens, hard to adapt.

Lou Jost · Post by **Lou Jost** » Wed Nov 01, 2017 8:24 pm

Yes, it is big and heavy! I take that as a sign of quality usually.

I epoxied step-down rings onto the front (unthreaded) end. They are holding. Then I attached a Nikon BR2 reversing ring which gives it an F mount.