Ghost of the moon

[roland.rash...@virgin.net]

Here is a post from another newsgroup describing the problem
of ghost moons and suns when taking photographs. The same
would apply for light entering the lens at an angle.

Roland

Subject: Re: ghost of moon in evening shots! HELP!
From: twr...@silcom.navu.com (Bill Wright)
Date: 1997/09/21
Message-ID: <3424ab7b...@news.silcom.com>
Newsgroups: rec.photo.misc

jayf...@aol.com (JayFromLA) posted:
>whenever I take pictures at night with the moon or sunsets where the
>sun is still visible, I always get that damn "ghost" image of a second
>moon (or sun) in the picture.

If the sun or moon is in front of the camera, such that sunlight
or moonlight enters directly into the lens, you may have a number of
problems, including the one that you've mentioned.
However most of us have photographed the setting sun or the moon
without ghosts or diffractions or excessive flare.
So it's a matter of knowing when you're in trouble, and when
you're not.

The viewfinder does -not- tell you whether the sun/moon is
shining directly into the lens. If sunlight or moonlight enters the
lens from an angle, and strikes just inside the front end of the lens
barrel, it may not travel directly to the film or viewfinder. It may
take several bounces inside the barrel and eventually reach the film,
but you may not see it in the viewfinder.
Experience teaches photographers to be aware of the warning
signs, but none of us see them 100% of the time.

As a starting point, hold your finger or pencil in front of the
lens and look into the barrel (from the front of the camera) without
blocking any direct sunlight/moonlight that may be entering the lens.
Move your finger or pencil around. If you can see the shadow moving
inside the lens barrel (anywhere inside the barrel), you have a
potential problem(s). Most likely you should abandon the photograph
unless.....

If you -want- to include the setting sun or the moon in your
photograph, don't base your exposure on the sun/moon itself.
Point the camera off to one side and set your exposure. After you've
done this, if the sun or moon is 3-4 stops brighter than the exposure
you've chosen, you're in 'problem territory.' Perhaps you'll want
to shoot regardless; but think about shooting later (sunsets) or
earlier (moons) when the contrast isn't so extreme.

Here are some other comments, in no particular order:

Even if you ignore the issue of a flare bouncing around inside
your lens barrel, it's also a fact that your viewfinder does not show
exactly what your lens sees. Viewfinders vary from 90% to 110% of
the lens's coverage, depending on the details of each particular
system. In my Nikon FM2, I think I get 106%.
Thus you may think that you excluded the sun or moon from your
image, but you didn't.
Since the optical path to the viewfinder is not identical with
the optical path to the film, the viewfinder may not see the same
thing that film see, even after accounting for differences in
coverage.

If you mean that the "ghost" is sharp-edged and distinct,
identifiably separate from the "real" image, and located in a
different portion of the photograph, then you are dealing
with a reflection.
If the ghost is somewhat fuzzy, or has noticeably less detail,
then there are a number of possibilities that involve flare and/or
high humidity (water vapor can cause halos) and/or small apertures
(large f-numbers).

In addition to inside the lens, a reflection can happen in the
space between filter and lens, or between multiple (stacked) filters.
Also, you may want to inspect the inside surface of your lens hood
(if you're using one). Does the hood have a shiny area, perhaps
polished by usage or damage? Does the lens (or a filter) have a
scratch or abrasion on it? Some lenses are better protected (better
constructed) to minimize internal reflections.

Finally, I would recommend that you take a few examples to a
full service camera store or photolab, not to a drug store or place
that sells only point & shoot equipment. You may discover that what
you are describing as a 'ghost image' is really something else.

Good luck.

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