David.Boettcher
Established
A 1933 and a 1935 manual which I looked in don't go into detail about lens changing, merely remarking that "The lenses are screwed moderately tight into the changing flange" and that's it.
But here is a scan of a page from an instruction manual for a IIIc, which does give a lot more detail about deploying and changing lenses.
As can be seen the only mention of the focussing lever is when attaching a lens to a body, where it says that the lens should be presented so that the focussing lever is in front of the viewfinder window. It doesn't mention the infinity catch, but the supposition must be that it is engaged, or else the location of the focussing lever would not be relevant.
The text does not mention, and the pictures do not show, the focussing lever / infinity catch being used in either deploying the lens (drawing out and locking or unlocking and collapsing) or removing and attaching a lens. If one of these actions were the primary purpose of the infinity catch, I think it would be described clearly, but in fact the infinity catch is not mentioned at all. The text says to remove the lens one should "grasp the lens close to the camera body" i.e. on the fixed part of the mount, not the focussing ring.
The infinity catch is described in a separate section on the next page. Its action is clearly described, but not its purpose. From this description it seems clear that the writer of the manual knew how it worked but did not know the reason for the infinity lock. E.g. he doesn't say "This is used for ... " or "This is useful when ... ".
In several sources it is reported that Barnack was a keen walker and probably liked to take landscapes. Perhaps he placed the "hockey stick" infinity locks on the early Leicas so that he could lock the lens on infinity and then not worry about it being disturbed from that setting by his walking activities. With a reasonable combination of shutter speed and aperture selected he could then walk freely, and take pictures just by looking through the viewfinder and pressing the shutter without having to adjust any setting on the camera at all. Because the hyperfocal distance varies with aperture, and hyperfocal focussing isn't really vital for distant landscapes, he just made a sensible compromise and chose infinity as the setting.
When interchangeable lenses were introduced it was only the short 3.5cm and 5cm which were given the focussing lever and infinity catch, I believe, and these lenses are the ones with great depth of field and relative insensitivity to focus compared to long lenses, these are the lenses most amenable to this kind of set-and-forget treatment. My Elmar 5cm lens when focussed on infinity and set to f12.5 shows a depth of field extending from 20 feet, and my Elmar 3.5cm at f12.5 shows the depth of field extending from just under 3 metres.
In the absence of any definitive literature explaining the purpose of the infinity catch we can never be sure of course, but I think that this is its most likely primary purpose, and the other used ascribed to it are secondary spin offs.
Well it's been an interesting post trying to answer what I thought was a very simple question. I thank everyone who has made a positive contribution to it.
Regards - David
But here is a scan of a page from an instruction manual for a IIIc, which does give a lot more detail about deploying and changing lenses.
As can be seen the only mention of the focussing lever is when attaching a lens to a body, where it says that the lens should be presented so that the focussing lever is in front of the viewfinder window. It doesn't mention the infinity catch, but the supposition must be that it is engaged, or else the location of the focussing lever would not be relevant.
The text does not mention, and the pictures do not show, the focussing lever / infinity catch being used in either deploying the lens (drawing out and locking or unlocking and collapsing) or removing and attaching a lens. If one of these actions were the primary purpose of the infinity catch, I think it would be described clearly, but in fact the infinity catch is not mentioned at all. The text says to remove the lens one should "grasp the lens close to the camera body" i.e. on the fixed part of the mount, not the focussing ring.
The infinity catch is described in a separate section on the next page. Its action is clearly described, but not its purpose. From this description it seems clear that the writer of the manual knew how it worked but did not know the reason for the infinity lock. E.g. he doesn't say "This is used for ... " or "This is useful when ... ".
In several sources it is reported that Barnack was a keen walker and probably liked to take landscapes. Perhaps he placed the "hockey stick" infinity locks on the early Leicas so that he could lock the lens on infinity and then not worry about it being disturbed from that setting by his walking activities. With a reasonable combination of shutter speed and aperture selected he could then walk freely, and take pictures just by looking through the viewfinder and pressing the shutter without having to adjust any setting on the camera at all. Because the hyperfocal distance varies with aperture, and hyperfocal focussing isn't really vital for distant landscapes, he just made a sensible compromise and chose infinity as the setting.
When interchangeable lenses were introduced it was only the short 3.5cm and 5cm which were given the focussing lever and infinity catch, I believe, and these lenses are the ones with great depth of field and relative insensitivity to focus compared to long lenses, these are the lenses most amenable to this kind of set-and-forget treatment. My Elmar 5cm lens when focussed on infinity and set to f12.5 shows a depth of field extending from 20 feet, and my Elmar 3.5cm at f12.5 shows the depth of field extending from just under 3 metres.
In the absence of any definitive literature explaining the purpose of the infinity catch we can never be sure of course, but I think that this is its most likely primary purpose, and the other used ascribed to it are secondary spin offs.
Well it's been an interesting post trying to answer what I thought was a very simple question. I thank everyone who has made a positive contribution to it.
Regards - David
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