[Leica] UFO's

[imx <imxputs@knoware.nl>]

The notion of a truly flare-free lens is a fiction. When applying the laws
of refraction on a bundle of skew rays, falling on a lens surface you can
easily observe that a fair amount of light rays will stray, and will bonce
through the optical system in uncontrollable paths, sometimes forming a
secondary image, sometimes a general veiling glare. One can use the proper
techniques: blackening of lens rims, blackening of insides of mounts,
creating light traps, applying multicoating and using a properly designed
shade, but it is impossible to create a system that is absolutely flare free
in every possible shooting situation.

Even the best cars with excellent roadholding will slide out of a tight
corner when the angular speed is higher than the traction of the wheels can
handle and/or the driver does not know how to control the car.

I may state that I have in my files of test slides a number of occurrances
of flare with EVERY LENS I have ever tested, Leica and otherwise. The fact
that one may occassionally encounter flare is bad, but unavoidable.
To make the occurrence of flare more manegeable, we need to be able to
replicate the situation exactly in order to study the phenomenon. And here
lies the trap: when persons note that they have less flare with lens A than
with lens B, it is invariably in different situations. So there is no real
comparison.
I have had several occasions where photographers did send me pictures (I get
pictures every day for analysis and study, which I gladly do to help Leica
photographers to make more enjoyable pictures) with large and unusual
incidences of flare. Asked to create a picture with the same lens under
identical situations, most failed to do so. IF you wish to study a penomenon
only one occurrence, however disturbing, does not do! ANOTHER PERSON has to
create the same phenomenon, otherwise we must accept the idea of a
once-in-a-lifetime-situation.
In many cases, with guidance and perseverance, we succeed to isolate the
source of the problem. Scientific experiment means reducing the noise from
cause and effect and getting to know the source, that is being able to
recreate the same phenomenon in a series of experiments.
Sometimes we do not and we have to accept a mysterious occurrance of flare,
a socalled UFO, Unexplained Flare Occurrence.

If ever there is an unscholarly approach to discuss these problems, it  is
to allow oneself to extrapolate from one incidence to a general conclusion.
And to identify one of many possible causes as the real one. On the valid
assumption that the light patch on the example of the 2/35 ASPH is real, how
do we know without comparison and replication of this patch in a second
controlled situation that it is indeed caused by the propensity to flare of
this lens?
There are many questions to ask and verify before we can even begin to get
to grips with this remarkable phenomenon.
It is to early to jump to conclusions, as the evidence is scanty, and a
convincing explanation is fully absent. To note simply that it must be the
lens and its lack of flare control, is not the best method to get to the
truth. 
It is the same as if we accuse a person of murder, just because he happened
to be at the crime scene.
Having studied and discussed and generated hundreds of photographs with
phenomena of flare, I am not inclined to draw quick conclusions, as this is
really a complicated topic.


Erwin