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Praktina lenses and Flange Distance
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PostPosted: Thu Jan 25, 2024 10:05 am    Post subject: Praktina lenses and Flange Distance Reply with quote
M42 has 45.46mm Flange focal distance. Exakta has 44.7 as described here: http://camera-wiki.org/wiki/Lens_mounts
Praktina: 50mm! This is serious difference and gap.

While M42/Exakta lenses many times share their optical system and just change mount construction i wonder if Praktina lenses are calculated differently? Especially wide and normal models.


PostPosted: Thu Jan 25, 2024 10:54 am    Post subject: Re: Praktina lenses and Flange Distance Reply with quote
Pancolart wrote:
While M42/Exakta lenses many times share their optical system and just change mount construction i wonder if Praktina lenses are calculated differently? Especially wide and normal models.


Hallo, I own several CZJ lenses in both M42/Exa and Praktina mounts and also Thiele books on their serial numbers. These lens models (Biotar 58, Flek 25, Flek 35) share the same optical computations. The difference in flange distance is compensated by the mechanical construction.

Last edited by Max78 on Thu Jan 25, 2024 5:18 pm; edited 1 time in total


PostPosted: Thu Jan 25, 2024 11:32 am    Post subject: Reply with quote
I only have one Praktina lens, a CZJ Flexon, forerunner of the F2 Pancolar lens. The flange distance is more, but the lens is set well back on its mount such that the rear element is very exposed when not mounted to the camera, especially when compared against competing mounts of the time.


PostPosted: Thu Jan 25, 2024 2:05 pm    Post subject: Reply with quote
No. The mount is wide enough to allow the lens element recessed inside the mount.


PostPosted: Thu Jan 25, 2024 3:57 pm    Post subject: Reply with quote
The Praktina mount is a bulky great breech-lock device, compared with the screw or bayonet of M42 or Exakta.
It can mean that the "flange distance" is measured somewhat differently.
I've got a couple of Enna Lithagons in Praktina mount, but I've not been able to make much use of them Sad


PostPosted: Thu Jan 25, 2024 7:31 pm    Post subject: Reply with quote
Still puzzles me. Nikon with its 46.5mm already requires optical element adapter for M42 lenses.


PostPosted: Thu Jan 25, 2024 8:30 pm    Post subject: Reply with quote
Pancolart wrote:
Still puzzles me. Nikon with its 46.5mm already requires optical element adapter for M42 lenses.


For the same optical calculation, the optics of the Praktina mount lenses will simply stick out a bit more from the back of the lens. As kypfer already mentioned, the Praktina is a breech-lock mount, which may affect the location of what would be considered the mount "flange".

Take that Wikipedia table with a pinch of salt though; the register value for the Minolta SR (MD) mount is incorrect; it states 43.72mm, but that is the distance from the mount flange to the film pressure plate. The distance between the mount flange and film guides is 43.5mm, therefore allowing 0.22mm for the film thickness.


PostPosted: Thu Jan 25, 2024 9:45 pm    Post subject: Reply with quote
Yes, the distance from the rear lens element to the center of the film is the same for both cameras. A must for infinity focus.

Another known problem with the Wikipedia table is the film is approximately 0.14 mm thick -- is the flange distance to the front surface of the film, the center of the film, or the back surface?
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