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..."