[LRflex] Re: PS RE: Angle of View
- From: Thomas Schofield <tdschofield@xxxxxxxxx>
- To: leicareflex@xxxxxxxxxxxxx
- Date: Sat, 26 Jan 2008 07:36:54 -0800 (PST)
Frank,
We appear to be saying the same thing in different
words. I was probably adding confusion by using angle
of view in the sense of the angle of the apex of the
cone of light that is projected, as I have seen it
used in specification charts for Schneider/Rodenstock
large format lenses. Perhaps angle of coverage is a
better term for what I was talking about. Generally,
a different lens formulation gives a different angle
of coverage, which in combination with focal length,
determines coverage for different formats, such as
whether a particular 75 or 90mm will cover a 5x7 neg
as well as 4x5, or the extent to which the lens will
allow shifts with a particular format size. You were
using the angle of view as in relation to the diagonal
(or possibly horizontal or vertical angle of view) for
a particular size of sensor or film, in essence, we
were looking down opposite directions of the cone of
light.
The specification that is in use that is similar to
Doug's proposal is "35mm equivalent focal length", but
is expressed in focal length referenced to a 24x36mm
film/sensor size, instead of angle of view. Doug's is
more useful in terms of referencing in degrees that
you are viewing.
Alternatively, you could reference magnification
ratio, which refers to the size of the image on the
sensor, but that would really confuse people!
Tom
--- Frank Filippone <red735i@xxxxxxxxxxxxx> wrote:
Tom.. the Angle of view is determined by the sensor
> format and the FL of the
> lens, only. ( Lens Vignetting is a totally other
> issue, and further may
> limit the useable AOV given a specific format.).
> Image Circle is totally lens dependent. It is the
> circle of light (
> actually a cone, but who is quibbling...) thrown by
> a lens onto a target
> without regard to sensor size. It is dependent on
> lens design.
>
> All 50mm lenses have the same angle of view FOR THE
> SAME SENSOR. Different
> Sensor = different AOV. But they each may have a
> different Image Circle.
>
> Or I misunderstood your point....
>
> Frank Filippone
> red735i@xxxxxxxxxxxxx
>
>
> And don't forget formats bigger than 35mm. ;-) The
> LF
> potographers on the list would also point out that
> focal length and angle of view are not the same --
> two
> lenses with the same focal length but differing
> angles
> of view will have different circles of coverage;
> i.e.
> able to cover different formats or allow more or
> less
> shift movements. All 50mm lenses do not have the
> same
> angle of view. E.g. a 50mm f.l. designed for medium
> format has a wider angle of view than a 50mm f.l.
> made
> for 35mm.
>
> Tom Schofield
>
>
>
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