Ah, thanks Tom,
That is precisely what I wanted to know.
Bernd
----- Original Message -----
From: <Tom@xxxxxxxxxxxxx>
To: <olympus@xxxxxxxxxxxxxxx>
Sent: Friday, January 11, 2002 12:00 AM
Subject: Re: [OM] [OT] two OM items for sale -> browsers -> darkrooms
> On Thursday, January 10, 2002 at 22:01, Bernd Moeller
> <olympus@xxxxxxxxxxxxxxx>
> wrote re "Re: [OM] [OT] two OM items for sale -> browsers -" saying:
>
> > Wow. But do you actually work with the aperture wide open? Usually I
> > step down my Rodenstock 3.5/50 to f11 or f16 in order to achieve good
> > DOF and better consistency of exposure time.
>
> >From http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=001Kur
> "You may be surprised that I suggest using these lenses at full aperture.
> However, diffraction effects swamp improvements in optical distortion
> even
> closed down a single stop. Howard Bond has done extensive testing in this
> area (as readers of Photo Techniques will recall), and I concur with his
> conclusions. I should also mention that most LF lenses (with the possible
> exception of certain fast -- i.e. faster than f5.6 -- press lenses) are
> sharpest wide open (assuming you have adequate coverage for your chosen
> format at that aperture). If you were comparing prints made with your
> lenses stopped down, you were not seeing either at its best. Try them
> both
> wide open, compare them against each other and against prints made at
> smaller apertures. Then decide which you prefer. "
>
> There is a lengthy discussion there. The smaller apertures are useful to
> lengthen exposure times for easier manipulations.
>
> The diffraction limit in lines per mm is equal to the f/stop times the
> wavelength for a high-contrast target:
>
> The diffraction limits in lines per mm for blue and red light are:
> F/stop Blue(400 nm) Red(700nm)
> 1.0 2500 1429
> 1.4 1768 1010
> 2.0 1250 714
> 2.8 884 505
> 4.0 625 357
> 5.7 442 253
> 8.0 313 179
> 11.3 221 126
> 16.0 156 89
> 22.6 110 63
> 32.0 78 45
> 45.3 55 32
> and so on.
>
> DoF doesn't matter for enlarging if the film carrier, lens, and easel are
> properly aligned (using levels) and the lens' curvature of field is
> minimal, which is normal for an enlarging lens.
>
> Stopping down will usually reduce any disparity in exposure between centre
> and edge.
>
> tOM
>
> ------------------- http://groups.yahoo.com/group/ottawa-
> photo-clubs
> tOM A. Trottier, ICQ:57647974 http://abacurial.com
> 758 Albert St, Ottawa ON Canada K1R 7V8
> +1 613 860-6633 fax:231-6115 N45.412
> W75.714
> "The moment one gives close attention to anything,
> even a blade of grass, it becomes a mysterious,
> awesome, indescribably magnificent world in itself --
> Henry Miller, 1891-1980
>
>
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