[Leica] Re: darkroom focusing

[creativevisions at verizon.net (Michael J Herring)]

Hi Henning,

In your experience, how do the Leitz Focotars compare with their German
cousins and the infamous Apo-Nikkor enlarging lenses?

Thanks,
Mike
----- Original Message -----
From: "Henning Wulff" <henningw@archiphoto.com>
To: "Leica Users Group" <lug@leica-users.org>; <lug@leicausers.org>
Sent: Thursday, June 16, 2005 2:38 AM
Subject: [Leica] Re: darkroom focusing


> At 7:18 PM -0700 6/15/05, Herbert Kanner wrote:
>>I think focus shift is a myth. If the focus were to shift when stopping
>>down, this would indicate that spherical aberration is so poorly
corrected
>>that the portion (a ring) of the lens that is active between say f/8
(the
>>enlarging aperture)and say f/2,8, the focusing aperture, has a marked;y
>>different focus distance than the portion (a circle) from the center to
>>the periphery at f/2.8.  If this were true, the lens would suck; it
would
>>be noticeably fuzzy at f/2.8.
>>
>>Herb
>>--
>>Herbert Kanner
>>kanner@acm.org
>>650-326-8204
>
> It's no myth. Check it out; most enlarging lenses, especially the f/2.8
> ones and older 4 and 3 element ones, suffer from it to a noticeable
> degree. I use a Micromega focusser that I bought in the 70's, and it has
> no trouble detecting the difference in focal plane if I don't have a
sheet
> of paper in the easel. It corresponds with the results I get from
> printing, so it's accurate enough.
>
> Anyway, print one picture after focussing on the grain stopped down, and
> then open it up and print again. Then print the picture with the lens
> focussed wide open. Do this for a 16x print. You'll probably see the
> difference, unless your lens is one of those few that really doesn't
have
> any focus shift.
>
> Some lenses I've had or used that have had focus shift problems:
> Various 50mm f/2.8 Rodagons of different eras (all)
> 50mm f/2.8 Componons - same
> 40mm Focotar
> 240 Componon
> 150 Rodagons and Componons of various ages
> 75 Nikkor
> 50/2.8 Nikkor
> 105 Rodagon (slight)
> WA Componon 60
>
>
> Lenses that have negligible or no focus shift:
> Nikkor 80/5.6
> Nikkor 63
> Focotar 50 (second)
> S-Orthoplanar 60
>
> There were others, but I can't recall, because they were all good lenses
> and I focussed them stopped down, so it doesn't matter.
>
> On 8x10's, it rarely matters. On 16x20's, it almost always makes a
> difference, just like aligning your enlarger.
>
> For many pictures, it doesn't matter very much if the grain is crisp; on
> others it does make a difference. YMMV :-)
>
> --
>    *            Henning J. Wulff
>   /|\      Wulff Photography & Design
>  /###\   mailto:henningw@archiphoto.com
>  |[ ]|     http://www.archiphoto.com
>
> _______________________________________________
> Leica Users Group.
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>


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