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a low cost substitute for the cult JML 21mm f/3.5

The Otamat 20mm f/2.8 microfilm lens is a small microfilm lens that appeared on ebay in late 2012 and was quickly picked up by the extreme macro crowd as a low cost substitute for the cult JML 21mm f/3.5.

Otamat 20mm microfilm lens, a low cost substitute for the fabulous JML 21mm f/3.5.

The lens performs well at 4:1-6:1, costs less than a tenth as much as the JML and is (currently) quite easy to source.

Using A 20mm Microfilm Lens

The lens has a complex asymmetrical design and can only be mounted in one direction, and its the working distance is short, about 8mm.

it comes on a 22 mm diameter barrel without any thread, and is intended for the Otamat 101/R microfilm projector.

Otamat 20mm microfilm lens, mounted using a spare objective adapter. I used a double sided rubber tape from the motor industry round the lens, which allowed it to be screwed into the adapter nicely.

According to the seller, the lens has a centre resolution of 200 lp/mm and an image circle of 18 mm. The microfilm lens can be used both with an infinite tube and as a finite, on its own, system.

You will need to build an adapter to mount the lens. A nice way to do this is to buy a metal M42 lenscap and drill a big hole in it, the width of the lens. Alternatively, use a spare adapter like I did.

Then use a couple of rubber retaining rings round the lens to fasten the lens into the lenscap.

Buying An Otamat 20mm Microfilm Lens

The dealer distributing these lenses through eBay seems to play an unappealing lens pricing game. It was initially priced at £17.99, then went up to £777.95, went back down to £17.99 and currently stands at £39.95. an unappealing lens pricing game When I bought one at £17.99, I was told there were actually none left and given a refund, but at the same time the lens was put back up by the same seller for £777.95. Strange sales practise.

I objected to this and made this obvious in the feedback, at which point the seller demanded I change the feedback, and via multiple emails, he threatened to report me to eBay for being an unreasonable buyer. I instead reported him to eBay for this and they have censured him. I have not heard again from him.

Extreme macro robberfly studio stack shot using Otamat lens, reworked from original.

Extreme Macro Results

Because of its f/2.8 resolution, best results will be obtained using this lens below 6:1. Beyond that, diffraction will set in.

The lens exhibits transverse chromatic aberration (colour fringing around in-focus hairs) also longitudinal chromatic aberration (green vs magenta casts in dark areas in back and in front of focus).

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