Archived posting to the Leica Users Group, 2000/11/30

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Subject: Re: [Leica] CoF and Macro
From: "apbbeijing@yahoo.com" <apbbeijing@yahoo.com>
Date: Thu, 30 Nov 2000 19:51:48 +0800

Hi Jacques, Yes - I have one book which says the APO100 is actually a 92mm
at 1:2. Of course all lenses shift focal length slightly as they are
focussed closer but the additional lens group of the APO100 and the IF
structure of some other fixed focal length lenses as well as the more
complex zooms exacerbate this shift IME: and I cannot help feeling that
extension tubes are not optimal for these lenses. After all when you add
tubes or a bellows behind a regular lens (where the entire optical group
moves forward to focus closer) you are merely doing more of the same but
with these other lenses you are at least fighting against the aberration
controls designed in to the unencumbered lens. Anyhow proof of the pudding
is IME the pictures and so far zooms or IF lenses with tubes are not that
good so far as I have seen. The 100APO, which I must acknowledge I do not
have, may of course be an exception to this though it has adopted the Elpro
approach...

Anyhow, if anyone knows or can find out it must be Erwin so let's see what
he uncovers! In the meantime I am more than happy struggling on with my 60
Macro and my 70-180 with close-up lens when necessary!
> 
> My understanding is that as the APO macro 100mm is focused at close
> distances it acts like not like a regular 100mm on the end of a bellows but
> rather like a lens of shorter focal length focused at a close distance. I
> think this is what Adrian was referring to when he stated that this lens
> shares some attributes with a zoom lens.


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