Use of polariser

[glamy]

Did that happen because I was pointing up? Sometimes I have a problem on the sides.

Cheers,
Gerard

[owen]

Hi mate. This happens because the wide angle of the lens is capturing the un-evenness in the sky. One of the things about using the polariser.

[glamy]

Thanks Owen,
How come that does not show the problem, it has been taken with the same lens.

Cheers,
Gerard

[owen]

Could be a number of reasons, the sky in the second one looks slightly overexposed; could be a different level of polarisation; the position of the sun could be different, etc...

a polariser works best pointing 90 degrees from the sun. I quite like the effect of the changing tones in some images,, but a lot of people don't.

[sirhc55]

Angle along with the time of day (i.e. sun position) will affect a CPL. I have always found that a polariser is a hit and miss affair

[stubbsy]

Gerard

The effect in #1 is because you've rotated the polariser too far - once you get the hang of it you can see this in the viewfinder (the image gets VERY dark in the V in the middle). When you see this in the viewfinder you rotate the CP a touch and you're home & hosed. In the second shot you either (a) didn't rotate the CP quite so far, or the orientation relative to the sun was different. In other words you need to deal with both angle to the sun (90 deg being optimal) AND, in wide shots, back off a little with the polarisation to avoid the V effect.

[owen]

Something I only learnt about a few months ago is that you'll notice a line on the rim of your polariser, if you rotate this to point in the direction of the sun then you'll get the maximum effect.

[ozczecho]

Great thread.

I just got my CPL and also have exp. the effect of #1. I always thought that the line on the CPL should match the white line on the lens doh.

[daniel_r]

Great thread.

I just got my CPL and also have exp. the effect of #1. I always thought that the line on the CPL should match the white line on the lens doh.

As Owen mentioned, the white line or arrow on the rotating ring on most CPLs is supposed to be pointed in the direction of the sun (usually says so in the little paper slip that comes with the filter, as well as other info on how many stops it reduces and so on).

In image #2 it looks like the sun was in front and slightly above the field of view (from a guess).

The polarisation effect is minimised when the sun is infront or behind you, and maximised when pointing 90 deg away from the sun (or light source in other types of shots such as minimising reflection off glass)

Another thing to lookout for is if you're wearing polarised sunglasses, and using a CPL - you'll need to take off / look over the sunnies to get your CPL effect right. As Stubbsy said, the "V" in #1 is caused by overdoing the polarisation in wide angle shots - if you rotate the filter slowly, you'll see a dark band moving slowly across the frame.

[ozczecho]

<snip>
(usually says so in the little paper slip that comes with the filter, as well as other info on how many stops it reduces and so on).

No such beast in my packaging

Anyway, great info daniel_r, btw you mention a dark band moving across the frame. I have noticed that aswell and always thought it should be where the sky is. Is that right or is the CPL working when there is no dark band?

TIA

Mike

[glamy]

Thank you all for the infos. As my CPL is not graduated I thought the position did not really matter. I did notice the two marks on the filter after a while and I thought they were supposed to line up with the horizontal...':oops:
I discarded the notice in the box thinking it was useless like in the others. I tend to agree with Chris about the hit and miss affair. I wear glasses that darken in the sun, combined with the view finder of the D70 it makes it a bit hard...

[daniel_r]

No such beast in my packaging

Anyway, great info daniel_r, btw you mention a dark band moving across the frame. I have noticed that aswell and always thought it should be where the sky is. Is that right or is the CPL working when there is no dark band?

TIA

Mike

The dark band is actually the "V" you see in image #1, but it's less pronounced in the D70's viewfinder (because it's so small). Say you had a identical filter on say a 20mm lens, and a 105mm lens with the CPL rotated to the same position and focused on the same object in the middle of the frame. If the 20mm was showing the "V" in the middle of the frame, you probably wouldn't be able to see it with the 105 as it has a much narrower angle of view, and the the middle of the "V" is filling the frame.

The "V" mainly shows up with wide angle lenses as they capture such a large angle of view, and polarisation varies across a given scene in reference to where the sun is.

For example the angle of view of a 20mm lens on a 35mm body is 83 deg horizontal, while 105mm is 19 deg horizontal. Essentially with the 105 you're cropping (eeek, I hate using such a term but cant think of an alternative) down to the middle of the V.

What you're aiming for when figuring out where the CPL should be rotated to comes down to and/or:
* minimise the presence of the dark band (the "V") in the viewfinder in a scene that has a large amount of sky
* maximise the contrast / minimise the amount of reflection in glass or scenes with lots of foliage (leaves will go very green with a cut in the white washed-glare.

Good experiment for figuring out your CPL and how it works is car windscreens on sunny days.

Hopefully I've got all this right from memory, been a while since my physics days and wave properties of light (slit polarisation and wavelengths)

[Potatis]

I have always found that a polariser is a hit and miss affair

Me too! Like the rest of my photography.

[SteveGriffin]

I think that this thread is the most educational thing that I have read on DSLR. Thankyou

[glamy]

Thank you very much for the info, I'd better practice!
Cheers,
Gerard