Re: [Leica] Filter designations

["Henning J. Wulff" <henningw@archiphoto.com>]

At 10:20 AM -0700 7/8/00, Tom Schofield wrote:
>My tests show that a tiffen 60-62 step up works fine with the Noctilux.  No
>step downs work.  Even the E60 C-Pol from Leica vignettes with it because of
>the thickness of that filter.  That lens is the first Leica lens I have used
>that has a problem with moderate step-downs.  I have even stepped down to
>49mm on the 100 APO, 60, and 35mm R, without vignetting. The 35mm going from
>55-49 was a pleasant surprise, but look at how small the front element is
>and you'll see why it works.  The last 28mm R with 48mm (Ser. VII) does not
>work well with a 48-49 step up but a 48mm-55mm works fine.
>
>Some people have expressed the myth that with the Noctilux if you stop down
>the filter does not vignette because "you are only using the inside part of
>the lens."  Not true, the entire lens surface affects pictures at all
>apertures.  In fact, vignetting from filters always worsens when stopping
>down because of the increasing DOF -- the black triangles in the corners get
>darker and more defined.  To check for vignetting with a reflex camera
>always check stopped down.
>
>Tom
>
>----- Original Message -----
>From: "apbbeijing" <apbbeijing@yahoo.com>
>To: <leica-users@mejac.palo-alto.ca.us>
>Sent: Saturday, July 08, 2000 2:06 AM
>Subject: [Leica] Filter designations
>

I've posted this before, but I think it bears repeating:

- ---------------------
Vignetting cannot be reliably checked through any viewfinder. The following
is a procedure which does work reliably, whether a rangefinder or SLR:

<snip>

In any event, if you mount your lens of concern on your camera, open the
camera back and lock your shutter open with a cable release or whatever,
hold it up to a brightly lit surface such as a window, you can look through
the front of the lens and see the film aperture through it. Look for the
corners, and stop your lens down. If you have a 50/1.4 lens on your camera,
you probably have to stop the lens down 4 stops to f/5.6 or so before it is
the aperture blades that are cutting off the light coming from all
directions, rather than part of the lens barrel. A 105 macro lens with an
aperture of f/4 might need to be stopped down only one stop, or also to
f/5.6 before the same condition applies. Only at this aperture or smaller
does physical vignetting cease, and the only vignetting that still applies
is optical vignetting due to the cos^4 law and other design issues.

<snip>

You can also check for filter or hood vignetting this way. If the filter
cuts into the light path while you can still see the corners of the frame,
it vignettes at that aperture and that focussing distance (and that focal
length, if a zoom)
- -------------------------

   *            Henning J. Wulff
  /|\      Wulff Photography & Design
 /###\   mailto:henningw@archiphoto.com
 |[ ]|     http://www.archiphoto.com