Convert 25/2.8 Biogon ZM for M8 viewfinder

[lecycliste]

Has anyone changed the stock mount on their 25mm f/2.8 Biogon ZM to bring up the 24mm frame on the Leica M8?

Mark Bohrer
Mountain and Desert Photography
www.mountain-and-desert.com
Wildlife on the urban edge

[Side Dish 小蔡]

I'm not convinced such a change is necessary, especially if you have a M8 classic without the frameline upgrade. It seems to me that it is just as well to use the entire VF as a guide, and in critical situations you can manually flip to the 24 framelines (which are only accurate at minimum distance on an un-upgraded M8).

[lecycliste]

popflash.photo sold me a 25mm f/2.8 Biogon T* that brings up the 24mm frame lines in my M8. Those lines are about right for 25mm coverage beyond 2m. The lens is sharp, contrasty and pretty flare-resistant wide-open to f/8.

[Doug]

I've sent my 25 Biogon to DAG, along with the 18 Distagon and 35/2 Biogon. The 25 comes with 28/90 bayonet and the 18 comes with a 50/75 bayonet. He will switch mounts between the 25 and 18, and grind the 50/75 bayonet to be a 24/35. Then I'll use the Zeiss 25/28 finder with the 18mm lens. He'll code the lenses as appropriate; the 18 gets the same code as the new Leica 18.

[lecycliste]

I've used DAG for repairs to my M3 and 50mm Noctilux. He's good, but it may take awhile if he's backed up.

[Doug]

True, I expect his workload varies... He had my 28 Summicron in February for coding and focus adjustment, and it took six weeks including shipping both ways. I believe he sends the mount flanges to John Milich for machining the coding, so that should tend to extend the time.

I'd like the 25 Biogon to bring up the "correct" 24mm framelines automatically, even if less accurate at distance than desired, as that's probably more useful than seeing 28 frames and maybe just using the whole window (which loses parallax compensation).

Then the mount flange's frameline "code" apparently must be consistent with the 6-bit coding to ID the lens to the camera so that the EXIF will be correct and the camera can apply appropriate corrections to corner fall-off and IR filter cyan fringing. All in all, I think getting the right framelines triggered and some reasonable 6-bit coding is worth the bother and expense.

Oh, and kudos to Tony at PopFlash for arranging more useful mounts for Zeiss ZM wide-angles!

[Doug]

As a follow-up... In the last post I mentioned sending my 25 Biogon to DAG for flange change and coding... He received it March 13, and he was done and shipped it back on April 27. Six weeks, same as back in February for the previous coding job.

The newly-coded 25mm is recognized by the M8 as a 24mm, and the photos include more than had been enclosed by the viewfinder framelines, especially for subjects at distances of several meters or more. At the RF's close-focusing limit, framing is fairly tight and accurate. Example below...