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Re: Wide lenses for 12x20 @ 300mm

Vritually all normal Series III Dagors, of 12" focal length or less, are of
f/6.8 aperture (from 14" to the largest sizes the aperture is f/7.7). The
Zeiss wide angle Dagor is an f/9 lens as I recall, but Kerik can verify
this since I believe his 240mm Dagor is of this type.

There was also once (pre World War II) a Series IV Dagors, of maximum
aperture of f/11, designed for copy work. The Goerz Blue Dot Triogor, which
is also an f/11 lens, may have evolved from the Series IV.  However,
specifications for the original Seres IV Dagors indicated coverage of up to
90 degrees at the smallest apertrue, whereas it is generally stated that
the Blue Dot Triogor has less coverage than nomral Dagors.

I have also seen reference to a Super Dagor of f/8 (Neblette) which covered
a field of approximately 100 degrees. This may in fact be nothing but an
Angulon, which has a circle of illumination of over 100 degrees but, as
Richard pointed out in an earlier message, the useful circle is about the
same as that of a regular Dagor.

People state coverage in varius ways. My method for determing coverage is
as follows. Mount the lens on your camera and center all shifts, tilts and
swings. Focus on an object at infinity, then look the image through the
corners of the ground glass with the lens wide open. If the lens covers the
format at maximum aperture you should see a round image through the lens.
If you see an ellipse there is vignetting. Stop the lens down until the
ellipse changes to a round image. Full coverage begins at the point where
you first see a round image through the lens when looking through the
corners of the ground glass. With my 12" Goerz Dagor the round image begins
at about midway between f/45-f/64 when the lens is focused on infinity.

Sandy King

>Sandy,
>
>You mentioned that the "wide angle Dagors" were not made in the 300mm focal
>length.  How do you determine if a Dagor is a WA dagor?  I don't think I have
>seen any Dagors that have any designation other than "Dagor".  Is it
>determined
>though maximum aperture (as is the case in some other lines.)?
>
>Thanks,
>
>---Michael