On Thu, 30 Jan 2003 01:48:31 -0000, "Bandicoot"
<"insert_handle_here"@techemail.com> wrote:
>"Neuman - Ruether" <d_ruether@hotmail.com>
wrote in message
>news:3e3eef3e.4599231@newsstand.cit.cornell.edu...
>[SNIP]
>> I feel like I'm running around, sticking fingers
>> in leaks, only to have to leave, and plug yet
>> another...! ;-) OK: UV filters will have NO effect
>> on the image shot with most multi-element lenses
>> (and it cannot "cut through haze" - only
a severe
>> restriction of filter light transmission to the
>> red-IR end of the spectrum, with suitable
>> IR-sensitive film used, can do this); a skylight
>> (or even a medium yellow filter) will have VERY
>> LITTLE (as in, "mostly useless") effect
on tones
>> under most circumstances in B&W photography
>> (though a skylight can offset some bluishness with
>> color *slides*, but not negatives); filters can
>> serve well for lens front-element protection (a
>> shade also helps, and is *sometimes* necessary);
>> a good filter need not be multicoated, though
>> single-coating can be useful (and it is easier to
>> clean than MC filters); expensive brands of filters
>> offer little advantage over good medium-priced
>> filters (I like Hoya single-coated for this, and
>> dislike Tiffen); a good filter has NO VISIBLE
>> EFFECT on image sharpness with wide-angles and
>> teles, let alone normal FL lenses, *even with
>> critical observation*. All this is regardless of
>> the filter-manufacturers' sales-lit
"examples"
>> or myths propagated here, and is arrived at
>> through "real-world" tests done by me...
I
>> encourage anyone to do your own tests, being
>> as careful as possible to reduce irrelevant
>> variables, to verify the above for yourself...
>> David
Ruether
>I was intrigued by this argument so I went off looking
for some transmission
>charts for filters.
I found one from Pentax, and I'm assuming other
>manufacturers of high quality filters will have more or
less comparable
>curves for their lines of filters. I've put a copy of this chart at:
>
>http://www.bard-hill.co.uk/filters.html
>
>The charts are very interesting, showing how the UV
filter is a radically
>different animal from the Skylight. The UV behaves in a similar fashion to
>the Yellow, Orange, and Red filters, in that it passes
everything, with a
>'flat' transmission curve, above a certain wavelength,
and then cuts off
>quite sharply below it - it is just that for the UV
filter it starts to
>attenuate when we are nearly out of the range of visible
light and its 75%
>point is already into the UV, whereas coloured filters
for B&W are of course
>cutting off visible light as well.
>
>The Skylight is entirely different, behaving much more
like a light
>balancing filter - which in effect it is. Its transmission line wavers
>somewhat, having a gentle dip in mid green, and then it
too attenuates UV -
>but not as strongly as the straight UV filter does. This last point might
>be salutary for anyone going to the mountains who
assumed that the
>'stronger' Skylight filter would be better than the UV
filter for
>controlling excess UV, an assumption I might have made.
>
>A filter described by Pentax as "Cloudy" is
basically their 81A (bit like a
>Nikon A2) so this too is a light balancing type filter,
with a much gentler
>roll-off than the UV.
This filter attenuates UV more than either of the
>other two (though it lets through a little of the very
short wave that the
>UV attenuates completely) so would be a far better
choice than the Skylight
>for the mountains, or the beach.
>
>And my point is?
>
>Well, apart from all this being interesting in itself; I
can agree that a UV
>might well make no really visible difference with
B&W film versus no filter:
>any situation where there is a lot of UV around, most of
it will be
>scattered anyway, the B&W won't show a colour cast,
and so the only effect
>will be a slight softening, if there is any visible
effect. It might even
>be beneficial in some circumstances as it will reduce
shadow density. The
>UV probably still would help with distance shots where
there is a lot of
>scattered UV in the air causing 'haze' - but then a
yellow or stronger
>filter will do the same job only 'more so'. The Y, O and R filters for B&W
>all have sharp cut-offs that mean that as well as the
visible light they are
>attenuating, they are also taking out all the UV that a
UV filter would
>remove, so a Yellow filter for B&W will usually make
more sense as a 'basic'
>filter than a UV does.
>
>But I doubt that it will be true a UV makes no
difference with colour film,
>where UV light will tend to give excess blueness, as
well as to reduce
>contrast overall, and add 'haze' to shots with a lot of
atmosphere between
>lens and subject
_if_ there is a lot of UV about to start with - at the
>beach or in the mountains, or in a dry desert. (Of course, the beach and
>the desert are places where you might use a UV for
'protection' anyway.)
>Uncoated flash tubes - some older studio flash heads,
for example - also
>often give out quite a lot of UV, and the normal advice
is to filter for it.
>
>It is true that all glass absorbs some UV, but I don't
think normal optical
>glass has anything like this degree or steepness of
attenuation: I'm
>recalling that one can still get sunburn through a
window, and also that
>sunglasses don't block UV unless they are specially
formulated to do so.
>All glass absorbs some, so a multi-element zoom may well
show less effect
>from UV than a 'minimalist design' standard lens,
but _so long as there is
>UV in the scene to begin with_ I would expect some effect from the filter.
>
>David - any comments?
I know you've done some testing, but how much UV was
>actually present in the light you used for the
tests? I'm hypothesising
>based on the transmission charts, so would be interested
in anyone's
>comments.
> Peter
Whew!
But, the problem is: it is very easy to theorize,
given a bunch of data - but the "bottom line" is:
"What is the visible effect in a photograph taken
under normal conditions?" Set up a camera and lens
(preferably one of, say, 5 or more elements), and
shoot a scene at normal altitude (say, roughly
1000'), in normal weather (say, "cloudy-bright",
with some blue sky showing), with a good range
of average subjects (trees, grass, a building, a
nearby person, etc.) with a standard panchromatic
B&W film with standard processing, with in turn
no filter, a UV filter, a skylight filter, then a
light yellow, medium yellow, dark yellow, orange,
red, light green, dark green, and a blue filter,
carefully applying the appropriate filter factor
to the original exposure (instead of using the
color-inaccurate camera TTL meter). Include a
grey card for reference. Make sure that the
lighting does not change appreciably during the
shooting, and that the angles and subject
positions do not change (this takes a bit of
pre-planning and fast work...;-). Process the
film and make a contact print, being sure that
the printing illumination and sheet development
are even. This, I think, will honestly represent
the results for 99% of shooting, and I think you
may find the following: no discernable important
image differences for the no-filter, UV, skylight,
light-yellow, medium-yellow, light-green, and
blue filters (the last three may show VERY slight
differences, if you look VERY hard - but is
this worth using them for...?;-) The dark yellow
will show a slight darkening of the blue areas
in the sky; the orange will show some more, and
the red will show more yet - but not a lot, unless
the blue is quite pure (plus some slight darkening
of the brightest greens). The dark green will show
VERY slight lightening of the brightest greens,
but the effect will be very moderate. If there is
a "distant" part in the subject choice, you will
see no difference in the level of obscuring haze
with any of the filters, compared with no filter.
Sorry....! ;-)
Even "sharp-cut" filters pass some of their
opposite colors, and rarely in nature are colors
very pure, so the effects of filtration on tonal
relationships is generally subtle, with the orange
and red filters (particularly with a clear blue
sky) showing the most effect - but on a grey day,
even these strong filters will show little effect.
And, lenses do not pass enough UV to matter very
much, unless the lighting conditions are unusual.
I find instruction books and filter ad sheets
purporting to show the wonderful effects of the
various filters on images rather entertaining...;-)