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Leica IIIf viewfinder optical diagram


fuchs

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All Leica direct viewfinders from the A to the IIIf are simple reverse Galilean telescopes: One flat-concave negative lens in front, and a biconvex positive one for an ocular.

 

That of an M is in principle just the same, but with a beamsplitter inserted for the rangefinder. But that of the classical LTM camera lives all on its own.

 

The old man from the Age of the IIIa

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Hi Lars, thank you. Is it really that simple? A two-elements galileian design? I'd at least expected an achromat on the front.

 

Anyways, I will modify the front lens FL, either by replacing it or by attaching a second plano-concave element to attain a larger FOV to cover 35mm. I find the 50mm lenses a little too long for what I am used to and I'd never been really fond of external VFs either.

 

cheers

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Hi Lars, thank you. Is it really that simple? A two-elements galileian design? I'd at least expected an achromat on the front.

 

Anyways, I will modify the front lens FL, either by replacing it or by attaching a second plano-concave element to attain a larger FOV to cover 35mm. I find the 50mm lenses a little too long for what I am used to and I'd never been really fond of external VFs either.

 

cheers

 

You can... after all it is the method that Leitz used for its "goggles" for 35 and 135 ... with a patient work, you can make a fine swing-unit that attaches to the accessory shoe: of course, in the LTMs Leicas the RF aligning image would maintain the same dimension (that is not the same as the VF image) : in the goggled lenses for M, on the contrary, they had to modify accordingly also the RF projected image.

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Hi to all,

I am looking for the optical schema of the Leica IIIF viewfinder. Can anyone point me to a source where I can find this info?

 

It's a reversed Galilean telescope but with a prism to deal with the offset between the eyepiece and the finder window. According to the IIIf "Servicing Instructions" the front lens is epoxied to the rangefinder module, while the rear lens is retained by the eyepiece.

 

The "Servicing Instructions" include exploded diagrams and parts lists showing all components. I found mine a year or two ago after a few minutes' web search.

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You can... after all it is the method that Leitz used for its "goggles" for 35 and 135 ... with a patient work, you can make a fine swing-unit that attaches to the accessory shoe: of course, in the LTMs Leicas the RF aligning image would maintain the same dimension (that is not the same as the VF image) : in the goggled lenses for M, on the contrary, they had to modify accordingly also the RF projected image.

 

Salve Luigi,

Appunto per questo la mia scelta di una leichina a vite: possibilità di modificarne il visore senza dover complicarmi con il telemetro, accoppiata alla sua altissima tascabilità (soprattutto usando un Summaron 35/3.5). In realtà, pensavo di supplementare l'obiettivo del visore o addirittura di cambiarne completamente la lente un'altra corretta per il nuovo FOV. Niente accessori da staffa, visto che questa è ormai occupata dal fotometro VC-II.

Grazie

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It's a reversed Galilean telescope but with a prism to deal with the offset between the eyepiece and the finder window. According to the IIIf "Servicing Instructions" the front lens is epoxied to the rangefinder module, while the rear lens is retained by the eyepiece.

 

The "Servicing Instructions" include exploded diagrams and parts lists showing all components. I found mine a year or two ago after a few minutes' web search.

 

Thanks. I have no problems with the idea of either replacing the whole VF objective lens or gluing an additional (negative) lens to the front of the VF/RF casing. The goal will be to have a very compact -pocketable- package with a 35mm VF FOV.

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You are right of course that from the IIIb on, the finder has a prism because the eyepiece has been moved over toward the rangefinder eyepice, while the front window remains centered above the lens. But the image optics is still reverse Galilean, just like the little WEISU finder.

 

The old man who forgets

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