Archived posting to the Leica Users Group, 2008/05/12

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Subject: [Leica] real focal length of M-Rokkor 2.8/28 and CV 1.9/28 mm ?
From: jean.louchet at gmail.com (Jean Louchet)
Date: Mon May 12 08:33:30 2008
References: <8094f2d10805111448o5e5987a3rd2c5b1205e7e43cf@mail.gmail.com> <000c01c8b3bb$aa735300$6b01a8c0@dadquad>

Thanks to all, I already know that. My question is not about the
framelines and I don't need to adjust the Rokkor or to replace the
adaptor on the CV. My question is about the _actual_ focal lengths of
the M-Rokkor 28 and the CV 1.9/28. At least one of them is not a 28.
Best wishes
Jean

2008/5/12 Geoff Hopkinson <hoppyman@bigpond.net.au>:
> Jean, it can get confusing with the M8 frame-lines.
> For a 28 mm lens you need the 28/90 pair to display. The 28 frames show a
> field of view on the M8 that is narrower than on a film M. This is because
> the sensor is smaller than 24x36 and so it effectively crops the image. 
> With
> a 28mm lens you are getting approximately the field of view of a 37mm lens
> on a film M.
> If you have a good 28/90 adaptor on your CV it should bring up the 28/90
> frames. If it doesn't you might be able to replace it. Not every adaptor on
> the market is of equal quality. I have one CV adaptor that brings up the
> right frame-lines and one 'no name' brand that does not work properly. You
> should ideally have the new style designed for the M8.
> Another factor is that the area indicated is approximate anyway and for
> longer distances the lens covers more than is shown too.
> You might be able to talk to a lens service agent about whether your Rokkor
> mount can be adjusted or to John Milich about whether the mount can be
> replaced. I would think that your cheapest option would be to just get a 
> new
> adaptor from Cameraquest or someone similar and fit it to your CV.
> Cheers
> Geoff
> http://www.pbase.com/hoppyman/e
> http://gallery.leica-users.org/v/gh/
>
> -----Original Message-----
> Subject: [Leica] real focal length of M-Rokkor 2.8/28 and CV 1.9/28 mm ?
>
> Hi all,
>
> I am glad to be back on this list after a couple of years off!
>
> My recently acquired M8 gave me the occasion to compare the finder
> brightlines to the actual field of view.
> One of my lenses is a 2.8/28 M-Rokkor (originally for the CLE). On a
> M6 it triggers the 35mm framelines, and on a M8 the 35 + 24
> framelines.
> My other 28mm is the cosina-voigtlander 1.9/28, which I use with a
> 28/90 adapter ring.
>
> I thought both lenses had the same actual focal length, but in fact
> the Minolta-Rokkor is much wider than the CV: on the M8 it corresponds
> to the 24 mm framelines.
>
> Does anyone have an idea of which hypothesis is the right one:
> (1) the so-called M-Rokkor 28mm is actually a 24 or 25 mm
> or
> (2) the Rokkor 28 is really a 28, the M8 framelines are wrong and the
> CV 1.9/28 is a 32mm or so?
>
> Anyway I am glad that the M-Rokkor mount  triggers the 24 mm
> framelines and I did not spend money to get a screw into the mount to
> get the 28mm framelines.
>
> Jean
>

-- 
Jean Louchet
APIS - INRIA Saclay research centre
4 rue Jacques Monod 91893 ORSAY Cedex France
----------------------------------------------------------
jean.louchet@inria.fr http://jean.louchet.free.fr/
----------------------------------------------------------

In reply to: Message from jean.louchet at gmail.com (Jean Louchet) ([Leica] real focal length of M-Rokkor 2.8/28 and CV 1.9/28 mm ?)
Message from hoppyman at bigpond.net.au (Geoff Hopkinson) ([Leica] real focal length of M-Rokkor 2.8/28 and CV 1.9/28 mm ?)