Cokin polarizing filter help please

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Brad
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#1
Hello all,

I have brought a second hand Cokin screw on polarizing filter, Once screwed to the lens the glass will rotate, as I've never used one before am I surposed to rotate the glass to get the affect ?
I have tried it quickly it takes a stop of light away but does not seem to make a lot of difference if rotated !
 
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#2
You need to be looking at blue sky (which is slightly polarised) or a shiny surface (like glare on water) then you can see it working as you rotate.
 

Asha

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#4
A couple of other things to mention
If the sun is behind the camera as opposed to the side then the effect will be less pronounced.
Also the filter will darken blue sky which can have a nice effect on the image however if using wide angle lenses the effect can be patchy and make some areas of sky appear darker than others.
Down to about 35mm focal length is generally ok. Wider than that and care needs to be taken to see wether the sky is ‘balanced’ before firing the shutter.
 
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#5
Thanks,I didn't know whether (from a not very educated stand point) the rotation was only for the more modern circular filters, when I tried it and realized the filter rotated I thought it must be for all of them. Another lesson learnt !
 
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Asha

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#7
Look through it at your TV :)

I might try that to see if it offers anything more interesting to watch!:LOL:

I find them more useful for reflections than skies.
Yes this is true, witout a doubt they help cut through reflections very well indeed (OP: Think of photos taken through glass or shooting fish / plantlife in a pond etc)

If you have TTL metering then any loss of light will be automatically compensated for.
If you're reliant on external (handheld) metering then don't forget to take into aaccount that you have a filter attached.
 
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#8
O.k the sun has just shown it's face for a few minutes, I pointed the SLR at the wife's black car at about 90 deg to the sunny the glare was terrible from both the back window and the shiney black paint a quick rotation and it all vanished to a sharp black car, fantastic! This has led me to a few more questions, Could I mark the filter for easier lining up or will it depend on the actual situation ? ( it will only be used on one lens) if this is possible could I then leave the filter on but in the off position ( if that makes sense) ? I'm quessing rotating the filter just alters the angle from which the light is allowed to enter am I right ? The metering is TTL on this particular camera but I did think of going up one film speed to 400 ASA (from 200) to help with the range of usable light I just have to find some cheapish film at 400ASA .

Cheers all
 
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#9
You'll need to fine tune the rotation each time to suit the angle at which the light is being reflected from your particular subject.
 
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#10
Thanks Mr Badger ,Next daft question I was just looking for 400ASA film and wondered if the filter would still work with B&W film ? I'm guessing it would ?
 
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#11
Thanks Mr Badger ,Next daft question I was just looking for 400ASA film and wondered if the filter would still work with B&W film ? I'm guessing it would ?
Yes, it does work with B&W film. Also wrt the position of the filter, bear in mind if you change to portrait format you still have to orient the filter the same wrt your subject.

In colour they will often make clouds more dramatic, rther like an orange filter does for b&w.
 

Asha

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#12
the glare was terrible from both the back window and the shiney black paint a quick rotation and it all vanished to a sharp black car, fantastic!
(y) Pretty cleva innit?!!;)
Like most gear, it's a handy tool to have if you know how to get the best from it.
 
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#14
Thanks,I didn't know whether (from a not very educated stand point) the rotation was only for the more modern circular filters, when I tried it and realized the filter rotated I thought it must be for all of them. Another lesson learnt !
All polarisers - linear and circular - require rotation to work.

IIRC I still have a Cokin linear polariser and 'pro' filter holder left over from first time around - you need the circular polariser allegedly to work with AF, but when I bought the kit originally it was for my Bronica, and a linear was about half the price.
 
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#15
I've read about the differences between linear and circular polarisers several times. Still no flaming idea! :)
 

StephenM

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#17
I've read about the differences between linear and circular polarisers several times. Still no flaming idea! :)
Imagine you're holding one end of a piece of string that is fixed at the other end, and moving your hand up and down so that you get a wave passing along the string. That wave is only in an up/down plane (assuming your hand is moving up and down). That corresponds to a linear polariser. Now start moving your hand more diagonally, through a horizontal and back to up/down. The plane of the wave is now rotating round a circle - that's circular polarisation.

A polariser also increases colour saturation for reasons too complex for me to explain without a diagram...
 
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#18
"I've read about the differences between linear and circular polarisers several times. Still no flaming idea! :) "

You only really need to use Circular, Linear can screw up camera metering, not always but sometimes
 
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#19
You only really need to use Circular, Linear can screw up camera metering, not always but sometimes
I'm willing to accept this as fact, I'd just like to know why...
Imagine you're holding one end of a piece of string that is fixed at the other end, and moving your hand up and down so that you get a wave passing along the string. That wave is only in an up/down plane (assuming your hand is moving up and down). That corresponds to a linear polariser. Now start moving your hand more diagonally, through a horizontal and back to up/down. The plane of the wave is now rotating round a circle - that's circular polarisation.
OK, that explains (a bit) how light could get to be polarised in both senses, but not how the filters work... because in either case, presumably the end result is that waves in one direction go through and waves in another don't. (And that circular wave you mentioned is surely something like a vector sum of a vertical and horizontal wave anyway...)

In your first case, I can imagine a slot in a piece of card with the string going through it. If the wave and the slot are aligned, the wave gets through if perpendicular, the wave is blocked (imperfect analogy because of the other effects of such a slot, but good enough for this purpose maybe). What's the analogy for circular polarisation?
 
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#21
I'm willing to accept this as fact, I'd just like to know why...


OK, that explains (a bit) how light could get to be polarised in both senses, but not how the filters work... because in either case, presumably the end result is that waves in one direction go through and waves in another don't. (And that circular wave you mentioned is surely something like a vector sum of a vertical and horizontal wave anyway...)

In your first case, I can imagine a slot in a piece of card with the string going through it. If the wave and the slot are aligned, the wave gets through if perpendicular, the wave is blocked (imperfect analogy because of the other effects of such a slot, but good enough for this purpose maybe). What's the analogy for circular polarisation?
A circular polarizing filter has 2 parts - the outside one is a linear polariser so all the light going through it end up linearly polarised, any light vibrating in the wrong direction gets blocked, the next (inner) layer (known as a quarter-wave plate or retarder) imparts a twist so the light now vibrates evenly in all directions so it can work with autofocus and exposure systems.
 
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#23
A circular polarizing filter has 2 parts - the outside one is a linear polariser so all the light going through it end up linearly polarised, any light vibrating in the wrong direction gets blocked, the next (inner) layer (known as a quarter-wave plate or retarder) imparts a twist so the light now vibrates evenly in all directions so it can work with autofocus and exposure systems.
Like I said, magic and voodoo.
 
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#24
If you want real magic try a Cokin Pola Red-Blue 171 or Purple-Orange 172 that tints polarised light different colours, makes for funky skies man!
Like I said, magic and voodoo.
 
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#25
A circular polarizing filter has 2 parts - the outside one is a linear polariser so all the light going through it end up linearly polarised, any light vibrating in the wrong direction gets blocked, the next (inner) layer (known as a quarter-wave plate or retarder) imparts a twist so the light now vibrates evenly in all directions so it can work with autofocus and exposure systems.
Thankyou David, that makes proper sense to me now! Although it's a wonder the little elves can turn the rope fast enough to twist the waves circularly...
 
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