Help me understand Circular Polarising (CP) filters!

Wail

Wail

Messages
6,671
Name
Wail
Edit My Images
No
OK, there have been a number of threads about CP filters, but I just can’t seem to figure this filter out!

I’ve not used CP for a very long time, and at the suggestion of another forum member I opted for Marumi CP for my Nikon & Sigma lenses.

I’ve managed, with a huge struggle, to see the difference a CP does with water. I was out in Black Mountains and shooting some stream of water, when I managed to see the difference; but it was a huge struggle to see the difference.

That same day, I tried to see how this filter would give me a “bluer” sky, but to no avail! I tried rotating the CP a notch at a time and taking a shot with every slight movement, but still nothing seen!

Can someone please shed some light on what am I not doing right.

Thanks,
 
Wail, they wont work if your shooting into the light source your best off at 90 degrees. Then hold it up to the sky and look through with one eye. while looking twist the filter to see how it makes a difference, not which bit of writing is at the top on the filter then attach to camera making sure the same bit of writing is at the top.

HTH
 
Toothie,

Thank you for the ultra quick reply. I've done the bit with the 90 degrees. I've also done the bit with the one eye (it's how I've managed to notice the slight improvement in water), but didn't help with the blue sky. I've even done the bit with the text on the filter, to monitor how much I move / rotate the CP while shooting.

My only thoughts, at the moment, is may be :shrug: I wasn't at 90 degrees to the light source (sun) ... but I just can't figure it out at all :thinking:
 
A polariser filter just polarises the light into one plane. A circular polariser has the polarising lines in a circular plane whilst a linear polariser has the lines in a straight plane. It has nothing to do with the physical shape of the filter Linear polarisers can be round and Circular polarisers can be square.

See here for info!

the effect of a polariser will be dependant on the amount of unpolarised light that is available and the angle that you are to that light, best results are typically found at about 90 degrees from the light source. It will not work on reflections from metallised surfaces.

Hope this helps!
 
EdBray,

Thanks for the info., and not wanting to sound rude but all that stuff I already know!

The problem is that when applying it with my Marumi CP (mouted on Sigma 10-20, or Nikon 24-70) I don't get the blue sky I was hoping for ... I am sure it is something to do with my application :shrug:!

I am hoping for some feedback / pointers on how to shoot & position myself for best effects.
 
It's ok, thank you for the effort to help out; I am almost sure it is something to do with my application! I will give it another try next time the sun is out.
 
I have noticed that the CP effect I use to get with film is impossible to get with digital - I've no idea why and have basically given up using it to get a rich sky - I use post-processing to add the effect back in!

There are a couple of photohop actions on my web site, that will do that for you without having to make any selections.
This one http://www.broadhurst-family.co.uk/lefteye/MainPages/skydarkening.htm is better (IMHO) than the one on this page http://www.broadhurst-family.co.uk/lefteye/MainPages/actions.htm

Hope that is a little help for you - but it doesnt really answer your question - sorry!

PS - Sun in Wales! hope you dont have to wait too long!
 
davidbridges said:
Maybe you've got a dud filter ...
Click to expand...

It's possible, you really should be able to see the filter doing its thing on glass/water and skys.

A side by side comparison is in order here I guess.
 
With such wide angle lenses it can sometimes be hard to get the darkening of the sky across the whole scene. That said, with a polariser on a Sigma 10-20mm lens you should, depending on your angle to the sun, see a moving section of the sky getting darker as you rotate the polariser.
 
Thank you all for the latest update & feedback.

I am not so sure about it being a dud filter! I've done the lazzy-person test and used it infront of my laptop screen and it does work! My screen does go from normal to dark to impossible to see .. so, I figure it is somewhat OK.

Then, it did work with water, and the effect was very hard to see .. but I was using a Sigma 10-20mm :shrug:

The last thing, and please no one kick my behind for this .. it is my birthday today ... but may be it was a cloudy day when I tried to get a blue sky!


Again, thank you for trying to help me sort this out.
 
but may be it was a cloudy day when I tried to get a blue sky!
Click to expand...
:LOL::LOL::LOL::LOL::LOL:

happy birthday, have a very good one. May you get a year of blue skies and great shots. :D
 
Wail

I use a cheap KOOD CPL on the sigma 10-20mm and it has a very visible effect..

harbour2.jpg
 
Simple answer is time of day.

Polarisers do the dark blue sky thing when the sun is to the right or left of you when you are pointing the camera forwards - not with the sun overhead. Middle of the day and it will do next to nothing apart from reduce the light a bit and take some reflections off water.
 
Many years ago in the days stuff called film I used to check the position of the polariser by wearing a pair of Polaroid sunglasses and then looking through the filter which in a certain position would appear almost black.

Paul
 
dazzajl said:
:LOL::LOL::LOL::LOL::LOL:

happy birthday, have a very good one. May you get a year of blue skies and great shots. :D
Click to expand...

Thank you so much, I've had one of the best birthdays of my life ... I just can't tell you how wonderful it went :):):)
 
Dogfish_magnet said:
Wail

I use a cheap KOOD CPL on the sigma 10-20mm and it has a very visible effect..

Lovely shot, and thank you for letting me know that even a cheap Kood can give such wonderful results.

If my Marumi doesn't work out well in the end, I may opt for a Kood before I pull the trigger on getting something like a heliopan or B+W, which I am not too keen to spend £££ on!
Click to expand...
 
RobertP said:
Simple answer is time of day.

Polarisers do the dark blue sky thing when the sun is to the right or left of you when you are pointing the camera forwards - not with the sun overhead. Middle of the day and it will do next to nothing apart from reduce the light a bit and take some reflections off water.
Click to expand...


Thank you so so so much, I think you may have nailed the whole issue for me. I was out about mid-day when I was testing the CP. This makes me believe it was the approach I've used since it may well have been mid-day AND cloudy :nono::nono::nono:.

I will have to wait for a nice sunny day and head down to the beach front to give it a full and better test .. keeping what you've said in mind.
 
Hobbytog said:
Many years ago in the days stuff called film I used to check the position of the polariser by wearing a pair of Polaroid sunglasses and then looking through the filter which in a certain position would appear almost black.

Paul
Click to expand...


Nice reason to buy one of the not-so-cool Polariod frames :p
 
Another demonstration to show the CP working is to look through it at a TV (switched on) and slowly turn the filter and then the TV will slowly look like it is switched off.
 
ThisPhotoGuy said:
Another demonstration to show the CP working is to look through it at a TV (switched on) and slowly turn the filter and then the TV will slowly look like it is switched off.
Click to expand...

Yeah, I love to show the kids this effect .. it always gets and "oooooh" :)
 
Smiffy said:
Just wait until you buy them some toys
;););):D
Click to expand...

Thank you so much for the comment, you seem to think I am a young teenager! :):):) I am almost a grandfather :LOL:

Still, seeing the amazements on a child's face when they see something for the first time is just mind-blowing ... makes me appreciate the All Mighty all the more.

Yesterday, in spite of sever pains, I took my kids to The Natural History Musuem in London ... they just couldn't stop asking questions after questions after questions ... made me feel so alive.
 
You must log in or register to reply here.
Back
Top