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on Dec 27, 2018 8:59:02 GMT
Last Edit: Dec 27, 2018 10:20:36 GMT by Deleted
A couple of examples below of a protrusion that exists on all C/Y lens mounts but I've never figured out what it does. Does anyone know? It's in the same place on all lenses and the same height. Can vary a bit in shape and sometimes it's just inside the aperture actuation lever (first example) and sometimes in line with it (second example). It doesn't connect to anything on any of my cameras. Edit: These are Zeiss lenses. I've noticed that some Yashica lenses don't have this extra lug though I have a late 50mm f/1.9 that does.   |
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on Dec 30, 2018 9:54:57 GMT
Posted: Dec 30, 2018 9:54:57 GMT
I think you'll find the same feature on all Yashica C/Y lenses as well, but they might take the form of an L-shaped bar that's screwed onto the rear cover plate, or as a separate and stationary tab or post. It's there to provide the lens's max aperture for metering in whatever Yashica or Contax body it was attached to. The 'flat' indicator on it isn't identical in position on every lens - but - it might appear that it is at first glance. I think the only interchangeable lenses of any mount that won't have some similar type of setup might be M42 or M39 screw-mounts, but there has to be a way for the the metering system to be aware of what that f-stop value is in order to function in TTL mode... unless the meter can only do stop-down readings. A photo I posted in another thread shows the 3 pins/tabs/posts/levers as they were designed to work on a 50mm f/1.9 and a 50mm f/2, and labeled for what they do. |
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on Dec 30, 2018 11:47:18 GMT
Posted: Dec 30, 2018 11:47:18 GMT
I think you'll find the same feature on all Yashica C/Y lenses as well, but they might take the form of an L-shaped bar that's screwed onto the rear cover plate, or as a separate and stationary tab or post. It's there to provide the lens's max aperture for metering in whatever Yashica or Contax body it was attached to. The 'flat' indicator on it isn't identical in position on every lens - but - it might appear that it is at first glance. I think the only interchangeable lenses of any mount that won't have some similar type of setup might be M42 or M39 screw-mounts, but there has to be a way for the the metering system to be aware of what that f-stop value is in order to function in TTL mode... unless the meter can only do stop-down readings. A photo I posted in another thread shows the 3 pins/tabs/posts/levers as they were designed to work on a 50mm f/1.9 and a 50mm f/2, and labeled for what they do. Thanks for the reply but that's not the same tab. The maximum aperture link is on the other side of the mount. The tab I'm asking about is right next to the aperture actuator (the lever that stops down the lens) which is at the bottom of the mount when the lens is on a camera. The max aperture link is at the top. As an aside, it's not necessary for the camera to know the maximum aperture to be able to function in TTL mode - it only needs to know by how much the lens has been stopped down from maximum. The maximum aperture is only needed if the actual aperture is displayed in the viewfinder. Examples would be the Yashica FX-3 or the Contax S2, neither of which have a maximum aperture coupling in the camera but both do full aperture TTL metering. |
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on Dec 31, 2018 0:53:43 GMT
Posted: Dec 31, 2018 0:53:43 GMT
@peterr ... I've been staring at ML lenses for far too long. You're correct about them not being the same. (I should remember to 'engage : brain' before 'running : mouth/fingers' :) ). These show up on all the Zeiss glass I have - even the diminutive 45mm Tessar. They all seem to have that perpendicular face aligning with the end of the stroke from the DOF lever at the bottom of the mirror box. It's possible they act like a hard-stop to keep from pushing the preview too far - or - they might be some kind of guard to keep the lens-attached aperture actuator from being jammed past it's limit. As for the max aperture and TTL metering... that might be the case for many brands, but as I understand it, not all. I.E., Nikon still uses a variation of Aperture Indexing (the 'notched' lip at the lower edge of the barrel), and everything that was AI-s and earlier couldn't calculate exposure properly without knowing the max aperture because of the linkage needed to activate and 'sync' the metering system. Even the Nikkoex F and FTn Photomic uses an indexing arm on their optional slide-in/on meters to get the max setting directly from the lens - assuming it has the prongs to engage with the lever. ( Nikkorex F w/o a pronged-lens, and FTn Photomic w/ 2.8 max aperture showing in the meter's front cutout) |
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on Dec 31, 2018 6:57:27 GMT
Posted: Dec 31, 2018 6:57:27 GMT
As for the max aperture and TTL metering... that might be the case for many brands, but as I understand it, not all. I.E., Nikon still uses a variation of Aperture Indexing (the 'notched' lip at the lower edge of the barrel), and everything that was AI-s and earlier couldn't calculate exposure properly without knowing the max aperture because of the linkage needed to activate and 'sync' the metering system. Even the Nikkoex F and FTn Photomic uses an indexing arm on their optional slide-in/on meters to get the max setting directly from the lens - assuming it has the prongs to engage with the lever. ( Nikkorex F w/o a pronged-lens, and FTn Photomic w/ 2.8 max aperture showing in the meter's front cutout) Huh? What's a 'Nikon'? LOL. I was really just referring to anything that uses the C/Y mount. Beyond that, who knows? And this from someone who used to work for Nikon would you believe... But, in theory, a metering system doesn't need to know the actual aperture, just how much the lens is going to stop down from the aperture which is used to take the meter reading. |
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