Archived posting to the Leica Users Group, 2020/02/19

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Subject: [Leica] Leica response to Tri Ermar (28/35/50) is retrofocus?
From: ken at iisaka.com (Ken Iisaka)
Date: Wed, 19 Feb 2020 12:42:41 -0800
References: <CAOgCMTQqxjhsg2NO34uV8j4HK8c1KEf2_E44NCk+fh=0Wd2LDg@mail.gmail.com>

I think there is more to it.

Tri-Elmar 28-50 is basically a zoom lens with two groups: a positive
focusing lens group closer to the film, and a negative group up front. The
distance between them is what determines the effective focal length of the
lens.

To have a negative group up front and having a positive group in the back
is the definition of a retrofocus design.

At 28mm, the centre of the lens is well ahead of the focal plane, certainly
further than 28mm. This indicates that it is effectively a retro focus
lens. At 50mm, it is less so.

On Wed, 19 Feb 2020 at 11:21, Frank Filippone via LUG <lug at 
leica-users.org>
wrote:

>  It is not considered a retrofocus design.
>
> That's it folks.... Final answer
>
> Frank Filippone
> BMWRed735i at gmail.com
>
> _______________________________________________
> Leica Users Group.
> See http://leica-users.org/mailman/listinfo/lug for more information
>


-- 
Ken Iisaka
first name at last name dot org or com


Replies: Reply from roark.paul at gmail.com (Paul Roark) ([Leica] Leica response to Tri Ermar (28/35/50) is retrofocus?)
In reply to: Message from bmwred735i at gmail.com (Frank Filippone) ([Leica] Leica response to Tri Ermar (28/35/50) is retrofocus?)