All XA has f2.8 lens, only the XA-2 to XA-4 has f3.5 lenses. You mention you
don't see vignetting in film, do you mean negative or slide? I wonder anyone
can see vignetting in negative, the contrast ratio is simply too low in
negative.
C.H.Ling
----- Original Message -----
From: "Joe Gwinn" <joegwinn@xxxxxxxxxxxx>
center of the lens (the rear nodal point, to be precise) to the film plane
(in "image space"), with respect to the optical axis.
>
> Note that theta is not necessarily the angle from lens center to the
object out in the world (in "object space"). A fisheye is the best example:
The angle to an object in the world far exceeds the angle to the image of
that object.
>
> The XA came with two possible lenses, both of 35mm focal length, the
cheaper being f/3.5, the more expensive being f/2.8. Looking through the
f/2.8 lens from the film side, I don't see any vignetting, which is
plausible given how short the lens in physically. I don't have a f/3.5 to
look at, but I would expect the same lack of vignetting, for the same
reason.
>
> A 35mm frame is 24 by 36 mm, so the corners are 21.6 mm from the center
(where the optical axis penetrates the film plane). With a focal length of
35mm, the image-space angle is therefore arctan(21.6/35)= arctan(0.6181)=
31.7 degrees, and cosine(31.7)^4= 0.524, or 0.93 stops falloff; call it one
stop.
>
> This is a property of even perfect 35mm focal length lenses used to fill a
35mm film frame. This is the best one can do; imperfect lenses will be
worse.
>
> When making a panoramic collage, I use a long lens and take lots of
photos, so I can stitch the photos together without too much disruption at
the splices.
>
> Joe Gwinn
>
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