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adan · 03/04/08, 07:51 PM

Derek: actually my "suggestion" wasn't directed at you - nothing wrong with asking the question at all!

A bit more detail (off the original question) for those who expressed interest:

The mask "A" is actually TWO masks, sandwiched close together.

One has slits for all 6 lenses that have internal framing (24/28/35/50/75/90 in the M8; 28/35/50/75/90/135 in a .72x film viewfinder). The other has similar slits but slightly offset from each other. This second mask SLIDES diagonally when lenses are mounted, or when the frame selector lever beside the lens is moved, so that different pairs of slits line up to adjust the framing to the lens mounted.

Slide the second mask one way, and the 28/90 lines in the first mask are revealed, but the others are blocked. Slide it the other way and only the 50/75 lines are uncovered. Leave it in "neutral" (or with no lens mounted) and the 24/35 lines are visible, but not the others.

The whole mask sandwich is linked to the focusing system, and moves down/right or up/left as a unit to compensate for parallax. In theory, some believe, this mask set could be replaced by a transparent LCD with virtual "slits" created electronically, which would allow them to change in size as well as position to make framing equally accurate at both close and long distances. I have my doubts about whether it would be practical, although I'm sure it is possible.

The optical group "B" is what moves side to side to shift the light coming from the RF window at the extreme right, and move the RF patch in the viewfinder. It is linked to the roller/feeler inside the top of the camera's lens mount by a system of bell cranks and levers. As the lens moves in and out to focus, the back of the lens, or a cam in the lens, pushes the roller in and out, and the linkage swings this lens left and right.

The white plate with a hole in it between "A" and "B" is mirror-surfaced on the left side, to bounce the maximum amount of light from the serrated window through the frameline mask.

One last note - the main viewfinder is made up of two wedges of glass, with a semi-reflective surface on the diagonal where they join (far left) that overlays the lines and the RF image on the overall view through the finder.

This solid block of glass reaches almost the full depth of the viewfinder, front to back. Which is why I am highly skeptical when some have suggested a "zooming" viewfinder for the Leica Ms. There is little empty space in which to "zoom" bits of glass back and forth to achieve this.

And in addition, there would also need to be a perfectly matched zooming system somewhere in the chain through "A" and "B" to enlarge or shrink the rangefinder image in perfect sync with the main viewfinder - and I do not see a lot of excess space there for a zooming optical system, either.

03/04/08, 07:51 PM	#12 (permalink)
adan Erfahrener Benutzer Join Date: 03/04/04 Location: Denver Posts: 1,095	Re: Newtons rings on viewfinder bar? Derek: actually my "suggestion" wasn't directed at you - nothing wrong with asking the question at all! A bit more detail (off the original question) for those who expressed interest: The mask "A" is actually TWO masks, sandwiched close together. One has slits for all 6 lenses that have internal framing (24/28/35/50/75/90 in the M8; 28/35/50/75/90/135 in a .72x film viewfinder). The other has similar slits but slightly offset from each other. This second mask SLIDES diagonally when lenses are mounted, or when the frame selector lever beside the lens is moved, so that different pairs of slits line up to adjust the framing to the lens mounted. Slide the second mask one way, and the 28/90 lines in the first mask are revealed, but the others are blocked. Slide it the other way and only the 50/75 lines are uncovered. Leave it in "neutral" (or with no lens mounted) and the 24/35 lines are visible, but not the others. The whole mask sandwich is linked to the focusing system, and moves down/right or up/left as a unit to compensate for parallax. In theory, some believe, this mask set could be replaced by a transparent LCD with virtual "slits" created electronically, which would allow them to change in size as well as position to make framing equally accurate at both close and long distances. I have my doubts about whether it would be practical, although I'm sure it is possible. The optical group "B" is what moves side to side to shift the light coming from the RF window at the extreme right, and move the RF patch in the viewfinder. It is linked to the roller/feeler inside the top of the camera's lens mount by a system of bell cranks and levers. As the lens moves in and out to focus, the back of the lens, or a cam in the lens, pushes the roller in and out, and the linkage swings this lens left and right. The white plate with a hole in it between "A" and "B" is mirror-surfaced on the left side, to bounce the maximum amount of light from the serrated window through the frameline mask. One last note - the main viewfinder is made up of two wedges of glass, with a semi-reflective surface on the diagonal where they join (far left) that overlays the lines and the RF image on the overall view through the finder. This solid block of glass reaches almost the full depth of the viewfinder, front to back. Which is why I am highly skeptical when some have suggested a "zooming" viewfinder for the Leica Ms. There is little empty space in which to "zoom" bits of glass back and forth to achieve this. And in addition, there would also need to be a perfectly matched zooming system somewhere in the chain through "A" and "B" to enlarge or shrink the rangefinder image in perfect sync with the main viewfinder - and I do not see a lot of excess space there for a zooming optical system, either. Last edited by adan : 03/04/08 at 07:53 PM.