DPChallenge: A Digital Photography Contest You are not logged in. (log in or register) 
 

DPChallenge Forums >> Hardware and Software >> circular polarizer filter
Pages:  
Showing posts 26 - 50 of 57, (reverse)
AuthorThread
 06/05/2007 01:42:54 PM · #26
Originally posted by soup:
ETA A: the light source wouldn't matter if the parabala were repeated to make a bowl that is perfect. any refelcted light would have to be focused to a floating point inside the bowl. sort of like how a satellite dish works...?


That's a concave surface...
 06/05/2007 01:45:01 PM · #27
it would scatter the same amount. but i think it would be possible.

the light we see as blue in the sky is, or green on a leaf is also randomaly scattered, but the particles that are scttering them are also absorbing some of the light.

at the right angle - a choppy water surface 'might' be able to not absorb any light, and would act like metal.

i would think this would possible in the opposite... or at leats be mimicked?

Originally posted by SamDoe1:
Originally posted by soup:

--------------------------------------------------------------------------------
then we need to make it ;}

Well thinking about it some more, wouldn't a shiny convex surface scatter MORE light than a flat one?


Message edited by author 2007-06-05 13:45:58.
 06/05/2007 01:55:31 PM · #28
Please, please, please...
Keep in mind that if you do not adjust your circular polarizer for your shots then you should not even have it mounted; if it is not adjusted it does little more than reduces the speed of your lens.
 06/05/2007 02:27:08 PM · #29
I get that effect with my polarized sunglasses while driving, you dont see much glare on windshields and windows but chrome bumpers etc still glare like crazy.

Originally posted by kirbic:
One thing to remember about polarizers and reflections... a polarizer will *not* reduce reflections off of metal surfaces. It has to do with the physics of the surface; light reflected from metal surfaces is not polarized.

06/05/2007 02:28:48 PM · #30
yeah i know, brain is all over the place lately...

Originally posted by SamDoe1:
That's a concave surface...

06/05/2007 02:31:15 PM · #31
not necessairly a bad thing though. if you are using it to serve a certain purpose... sort of an ND filter as mentioned earlier...

Originally posted by stdavidson:
Keep in mind that if you do not adjust your circular polarizer for your shots then you should not even have it mounted; if it is not adjusted it does little more than reduces the speed of your lens.

 06/05/2007 02:40:56 PM · #32
Originally posted by soup:
use your hand like a hand gun, and point at the light source. the arrow on the filter should aligned with where your thumb is pointing...

Is this correct? Or should the arrow on the filter align with where your index finder is pointing (towards the source)?

Message edited by author 2007-06-05 14:42:13.
 06/05/2007 02:41:18 PM · #33
If you need an ND filter then use one. But polarizers make lousy ND filters. I, for one, think we pay a lot of money for faster lenses and it does not make sense to throw that away with an improperly adjusted polarizer filter.
Originally posted by soup:
not necessairly a bad thing though. if you are using it to serve a certain purpose... sort of an ND filter as mentioned earlier...

Originally posted by stdavidson:
Keep in mind that if you do not adjust your circular polarizer for your shots then you should not even have it mounted; if it is not adjusted it does little more than reduces the speed of your lens.

 06/05/2007 02:51:32 PM · #34
Originally posted by drewbixcube:
Originally posted by soup:
use your hand like a hand gun, and point at the light source. the arrow on the filter should aligned with where your thumb is pointing...

Is this correct? Or should the arrow on the filter align with where your index finder is pointing (towards the source)?


Quote from article:

1. First, locate the arc of target directions.
Point an index finger at the light source and hold the attached thumb at 90° to the finger.

Now rotate the thumb around the index finger to sweep out the arc of maximum scatter polarization. These are all target directions.
2. Arrange to shoot your subject with your camera pointed in a target direction as best you can.

3. With your camera aimed, turn the polarizer dot (or blocking axis) 90° to the direction of the light source to block the target polarization.
 06/05/2007 04:03:54 PM · #35
Originally posted by giega:
Quote from article:

1. First, locate the arc of target directions.
Point an index finger at the light source and hold the attached thumb at 90° to the finger.

1a. Now rotate the thumb around the index finger to sweep out the arc of maximum scatter polarization. These are all target directions.
2. Arrange to shoot your subject with your camera pointed in a target direction as best you can.

3. With your camera aimed, turn the polarizer dot (or blocking axis) 90° to the direction of the light source to block the target polarization.

1. Got it!
1a. um...what?
2. so my camera is aimed where my thumb rotated...or where my index finger was pointing?
3. this is getting more confusing...

How 'bout this:

I want to take a picture of a tree directly North of me. So I face North.
The sun is in a 4 pm sky (to my left, say up at a 45 degree angle).
With my lens level and facing North, I want the dot on my CPL to face my right (East) at approximately the same heading (45 degrees) as the sun is to my left.
If you were standing behind me and drew a line from the sun to my lens and from my lens to where my CPL dot is pointed, it would make a 90 degree angle...correct?

Thanks,
-drew
 06/05/2007 04:20:48 PM · #36
i am sorry, i still haven't got it.
if i want to shoot in a dark room with windows and bright sunlight outside, and want to get more light on the room but still don't wash out the windows - what should i get? a polarazing filter, an uv filter, something else?
i like when bright light comes into a dark rom, but have never been able to capture it right. i always have to combine two images: one for the windows and another one for the rest of the room.
thank you!!
 06/05/2007 04:25:18 PM · #37
Originally posted by silverfoxx:
i am sorry, i still haven't got it.
if i want to shoot in a dark room with windows and bright sunlight outside, and want to get more light on the room but still don't wash out the windows - what should i get? a polarazing filter, an uv filter, something else?
i like when bright light comes into a dark rom, but have never been able to capture it right. i always have to combine two images: one for the windows and another one for the rest of the room.
thank you!!


I'm not entirely sure what exactly you want to do but I don't think there is a filter for that. Polarizing filters are used to cut the glare and improve contrast while UV filters are used to protect a lens and cut a little haze out of the scene. What you're talking about, if I'm taking it the right way, is using a filter to increase the dynamic range of the scene right? If so, then there's no filter that will do that and you're doing it the only way I know of.
 06/05/2007 04:27:02 PM · #38
LOL

Let's try this way.

You're the center of the clock. The sun shines from 3 o'clock at 45 degree angle. To get best results you have to face your camera at 6 or 12 o'clock (index finger and thumb thing). If you face towards 6, rotate CPL 45 degrees to the right, if you face 12, rotate CPL 45 to the left.

So your camera has to be at 90 degrees to the sun. If you draw a vertical line down from the marker on CPL, that's your blocking axis. Rotate it so that it is perpendicular to the sun's angle.

That's the best explanation I can come up with.
 06/05/2007 04:28:29 PM · #39
Originally posted by SamDoe1:

I'm not entirely sure what exactly you want to do but I don't think there is a filter for that. Polarizing filters are used to cut the glare and improve contrast while UV filters are used to protect a lens and cut a little haze out of the scene. What you're talking about, if I'm taking it the right way, is using a filter to increase the dynamic range of the scene right? If so, then there's no filter that will do that and you're doing it the only way I know of.


ah, oh
but more money saved:)
thank you! i just thought that polarizer reduces bright light and i could use it
 06/05/2007 04:30:04 PM · #40
I heard you use your thumb and first two fingers, at right angles. Set your thumb and first finger (like a gun) and point your middle finger at 90 degrees to the plane formed by the thumb and first finger (bend it at the knuckle only).

IIRC, Point at what you're going to shoot with the first finger, the thumb goes toward the sun, and the middle finger shows the direction to set the polarizer.

But I just look through the viewfinder for the darkest blue sky when I rotate the polarizer (or for reflections on glass to be minimized).
 06/05/2007 04:31:35 PM · #41
Originally posted by silverfoxx:
ah, oh
but more money saved:)
thank you! i just thought that polarizer reduces bright light and i could use it


It does...just not the way you want it too, haha. It will act as a neutral density filter but won't do as well as a dedicated one. But a neutral density filter (non-grad) will just darken the WHOLE scene, what you want is for it to darken the window but not the room. The only way to do that, for now and that I know of, is to merge 2 or more frames together.
 06/05/2007 04:36:04 PM · #42
Originally posted by SamDoe1:

It does...just not the way you want it too, haha. It will act as a neutral density filter but won't do as well as a dedicated one. But a neutral density filter (non-grad) will just darken the WHOLE scene, what you want is for it to darken the window but not the room. The only way to do that, for now and that I know of, is to merge 2 or more frames together.


thank you:) i finally got it
oh my, i was thinking all the time: hmm, how does the filter know exactly what part of an image to make darker?
hehehe :)
 06/05/2007 04:39:49 PM · #43
So point the dot on the filter to where the arrow is pointing? (Up and to the left of the diagram)

-drew

ETA: Why wouldn't they put the dot on the filter a quarter turn and say, "Point the dot at the light source."? Just a thought.

Message edited by author 2007-06-05 16:50:34.
 06/05/2007 04:46:33 PM · #44
Originally posted by hankk:
I heard you use your thumb and first two fingers, at right angles. Set your thumb and first finger (like a gun) and point your middle finger at 90 degrees to the plane formed by the thumb and first finger (bend it at the knuckle only).

IIRC, Point at what you're going to shoot with the first finger, the thumb goes toward the sun, and the middle finger shows the direction to set the polarizer.

This explains this (I think):

Originally posted by giega:
[Now rotate the thumb around the index finger to sweep out the arc of maximum scatter polarization. These are all target directions.
2. Arrange to shoot your subject with your camera pointed in a target direction as best you can.

3. With your camera aimed, turn the polarizer dot (or blocking axis) 90° to the direction of the light source to block the target polarization.
06/05/2007 05:09:01 PM · #45

.

I have inherited a polarizing filter. How can I tell if it is circular or linear?

On the side of the filter is says, "ROLEV M.G. 52mm POLARIZER". I notice that it has the ability to swivel/rotate freely once it is screwed onto the lens.

.

06/05/2007 05:12:40 PM · #46
Originally posted by giega:
You're the center of the clock. The sun shines from 3 o'clock at 45 degree angle. To get best results you have to face your camera at 6 or 12 o'clock...
So your camera has to be at 90 degrees to the sun.

Ok, so if the light source is in the yellow positions (90 degrees to the lens), you will get the most out of your CPL. If the light source is in the red positions (or any other for that matter) you need to move your camera or subject so that it is oriented at 90 degrees (aka CPL won't work as well shooting towards or away from the light source, as it will shooting 90 degrees to it). Correct?

I think I am understanding.
-drew
 06/05/2007 05:15:36 PM · #47
Originally posted by lesgainous:
I have inherited a polarizing filter. How can I tell if it is circular or linear?

Look in a mirror through the polarizer—once with the male threads toward you and then with the threads flipped toward the mirror. If the flip makes no difference, the polarizer's Linear. If the flip causes the polarizer to turn black or nearly so, it's Circular.

ETA: Filter in your hand, not on your lens for this test. And close the eye not looking through the filter.

Message edited by author 2007-06-05 17:16:55.
 06/05/2007 05:40:01 PM · #48
Originally posted by drewbixcube:
Originally posted by lesgainous:
I have inherited a polarizing filter. How can I tell if it is circular or linear?

Look in a mirror through the polarizer—once with the male threads toward you and then with the threads flipped toward the mirror. If the flip makes no difference, the polarizer's Linear. If the flip causes the polarizer to turn black or nearly so, it's Circular.

ETA: Filter in your hand, not on your lens for this test. And close the eye not looking through the filter.

Thanks...I did the mirror test and it must be a linear filter. Which makes sense, this filter is circa 1980's.

So, now that I have a linear polarizing filter, what side-effects will it have on my digital camera's lenses? I understand that digital cameras should use circular filters, what happens when a linear is used?

.

06/05/2007 06:49:36 PM · #49
You may have a problem with the camera's autofocus mechanism. I think if you use manual focus it will make no difference being linear.
 06/05/2007 07:35:14 PM · #50
Originally posted by silverfoxx:
Originally posted by SamDoe1:

It does...just not the way you want it too, haha. It will act as a neutral density filter but won't do as well as a dedicated one. But a neutral density filter (non-grad) will just darken the WHOLE scene, what you want is for it to darken the window but not the room. The only way to do that, for now and that I know of, is to merge 2 or more frames together.


thank you:) i finally got it
oh my, i was thinking all the time: hmm, how does the filter know exactly what part of an image to make darker?
hehehe :)


just wondering, could you use a graduated filter rotated so that the darker part is on the window, thus allowing it to be darkened but the rest of the room lightened? (This sounds like it would work in my little inexperience head but not certain.) If so how do you set your exposures, on the window or room?
Pages:  
Current Server Time: 08/18/2025 03:29:35 PM

Please log in or register to post to the forums.


Home - Challenges - Community - League - Photos - Cameras - Lenses - Learn - Help - Terms of Use - Privacy - Top ^
DPChallenge, and website content and design, Copyright © 2001-2025 Challenging Technologies, LLC.
All digital photo copyrights belong to the photographers and may not be used without permission.
Current Server Time: 08/18/2025 03:29:35 PM EDT.