On Mon, 03 Mar 2003 09:58:25 -0600, Don Stauffer
<stauffer@usfamily.net> wrote:
>I tend to not believe this. A piece of uncoated glass can have about a
>5% reflectance.
Say we have a scene with about a 1000:1 contrast. That
>is not unreasonable for a sunlit scene, even
conservative. Say film
>surface is also 5% (I think this is even low for film-
I'd guess most
>are about 10 %.
Anyway, a single reflection from film to uncoated
>surface gives us 0.25% of light from highlight back on
film. But 0.1 is
>amount of light in shadow detail, so flare is 2.5 times
shadow exposure.
>
>Now, what about focusing or defocusing? A flat plate perpendicular
>actually AUTOCOLLIMATES, so flare light IS focused near
edges of
>highlights. So if you have a shadow right next to highlight,
it WILL see
>flare.
>Neuman - Ruether wrote:
>> On Sat, 01 Mar 2003 02:39:10 GMT,
"jriegle"
>> <jriegle@att.net> wrote:
>>
>>
>>>I agree. Hold a lens up towards a bright window,
but not directly at it and
>>>look into the camera end. You should see faint
reflections off the coatings.
>>>Now hold an uncoated filter in front. You should
see a large increase in
>>>reflections. With a multi coated filter, there
will be increased reflections
>>>but not nearly as much as the filter with no AR
coatings. So in my test, AR
>>>coated filters do reduce reflections. Does this
mean it will make a
>>>difference on film? Maybe, maybe not. It depends
on the lens and lighting
>>>situation.
>>>
>>>A lighting situation that caused annoying flare
in a shot may still have
>>>shown some flare even without a filter attached
so it is best to avoid these
>>>situations if possible.
>>
>>
>> If you figure the percentage of "flare
light" introduced
>> by even an uncoated filter compared with the total
light
>> going through the lens, the amount is almost always
below
>> the threshold for shadow exposure on the film, and
is
>> not seen... In conditions where the added light is
not
>> diffuse (when light sources are much brighter than
the
>> rest of the image, and are relatively small in the
image),
>> the filter coating can make a difference, but it is
>> slight...
>> David Ruether
>>
d_ruether@hotmail.com
>>
http://www.David-Ruether-Photography.com
>> Hey, check out www.visitithaca.com too...!
On Mon, 03 Mar 2003 09:58:25 -0600, Don Stauffer
<stauffer@usfamily.net> wrote:
>
>I tend to not believe this. A piece of uncoated glass can have about a
>5% reflectance.
Say we have a scene with about a 1000:1 contrast. That
>is not unreasonable for a sunlit scene, even
conservative. Say film
>surface is also 5% (I think this is even low for film-
I'd guess most
>are about 10 %.
Anyway, a single reflection from film to uncoated
>surface gives us 0.25% of light from highlight back on
film. But 0.1 is
>amount of light in shadow detail, so flare is 2.5 times
shadow exposure.
The key is, "the threshold for shadow exposure on the
film".
Scenes appear with 20-stops of illumination difference (I
used to shoot these on Tri-X at 25 ASA, processed in POTA),
but most film is "stretching it" to cover 7 stops
in a
printable way, and low levels of flare exposure slip off
the end of the scale of recorded light...
>Now, what about focusing or defocusing? A flat plate perpendicular
>actually AUTOCOLLIMATES, so flare light IS focused near
edges of
>highlights. So if you have a shadow right next to
highlight, it WILL see
>flare.
Again from my post above, "In conditions where the
added
light is not diffuse (when light sources are much brighter
than the rest of the image, and are relatively small in the
image), the filter coating can make a difference, but it is
slight..."