Removable rear achromat at
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Old March 30th, 2010, 07:37 AM   #1
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Join Date: Jan 2008
Location: Central Coast, NSW Australia
Posts: 119
Removable rear achromat

I just got a Letus Extreme (see previous post re paint flakes) but the previous owner had a different camera and I need to get a 77mm Lens adaptor for my EX-1. I found this EX-1 optimisation kit at B&H ( but I am not sure whether my Extreme has a removable rear achromat. How would I know if it does or not?
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Old March 30th, 2010, 09:40 AM   #2
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Join Date: Dec 2003
Posts: 4,475

If you look closely at the rim of the achromat in back of the Letus after you have taken the adaptor ring off the outside of the shoulder around the achromat, you will see a seam about 1mm forward. This is the face of the body where the rim of the achromat beds down.

On the face of the rim you will see two slots. This is where a lens spanner is used to unscrew the achromat. The proper tool for doing this is a Rolyn spanner, which is an adjustable bar and legs with blades on them. You could make a blade wrench and use that, making sure the edge of the blade does not contact the convex surrface of the glass.

Please "DO NOT" attempt to chisel the slots in the rim by engaging a screwdriver in the slot and hitting it to loosen the achromat. The Le brothers used a hard bond, UV cure I think, to secure the optic in the metal rim instead of the pliant material they were using in their older models. If you whack it, you "WILL" damage the glass at the bond points.

You could try engaging two screwdrivers in the slots and use a third laid across the face of the rim between them to twist them and unscrew the achromat. If it is tight you will likely experience the screwdrivers jumping out of the slots.

At about 00:37 of this clip, you will see how the Rolyn spanner is used to extract the achromat from the Letus Extreme.


The Canon 5D and 7D may have arrived but the Letus Extreme and other similar products are still cool devices.


If you replace the achromat, don't give the old one to the kids to use as a sunglass for scorching the hawkmoth caterpillars and locusts you should be getting about now after the heavy rains. Keep it safe for you might need it if you upgrade to a SI2K and want to shoot groundglass images with it.

Last edited by Bob Hart; March 30th, 2010 at 10:11 AM. Reason: error
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