Jostein,
That (a reflection off the sensor) could only happen if the rear element had
a concave external surface. According to exif data, Arnie was using a 50mm
lens at f1.4, and AFAIK none of those has a concave surfaced rear element.
If the source of the reflection was the sensor, then any reflected light
rays would be spread, not focused, at their secondary reflection from the
rear of the lens. As well, a ghost from this source would have the same
orientation as the image on the sensor.
Ghost images can occur between any two or more lens or filter surfaces, and
can appear erect or inverted depending on their relative curvatures, because
they are are in effect a secondary imaging system superimposed upon the
primary one. Arnie's example shows a reflection that has either not been
inverted as a normal projection is, or has been inverted twice by multiple
mirror-foldings. While at its worst with uncoated glass, it can still occur
with coatings (otherwise you wouldn't see ~any~ reflections in lens). The
fact that Pentax introduced "ghostless" SMC when they already had SMC is
proof enough that multicoating itself is not immune to ghosting.
Some film emulsions are quite shiny yet ghosting off the film hasn't been
observed AFAIK. However a CCD as in the *istD is surfaced with tiny
lenslets and is unlikely to act as a mirror. While I haven't seen one with
my own eyes, photos of sensors I have seen show a satiny sheen rather than a
mirrorlike glaze, and are unlikely to support a coherent reflection over the
approximately 8cm from themselves to rear element and back again.
regards,
Anthony Farr
Quoting Anthony Farr <[EMAIL PROTECTED]>:
> That's a "ghost image", a reflection from the front surface of one of your
> lens elements onto the rear surface of the filter, and then back through
the
> lens in parallel with the desired image. It is most pronounced when a
lens
> has any uncoated elements, or the filter is uncoated.
I thought ghosting between the front element and a filter would produce a
reflection with the same orientation as the reflected object?
Jostein
_______ AND ________
----- Original Message -----
From: "Jostein" <[EMAIL PROTECTED]>
> Hi, Arnie.
>
> I think it looks like a reflection off the sensor, back onto the rear
element of
> the lens.
>
> I have been wondering if lenses with large rear elements could be causing
this
> problem. I have noticed that the FA*24/2 gives more glare and less
contrast
> than the FA20/2.8, and the only explanation I have come up with is just
that.
> When shooting film, there's not much difference between the two.
>
> From the metadata, I saw that you have used a 50mm f/1.4. So it doesn't
> contradict the theory, at least...:-)
>
> If it's right, there's not much we can do about it except to avoid using
lenses
> with large rear elements for this type of photography...
>
> Cheers,
> Jostein
>
