Effects of using a circular Poleriser?

kingy

kingy

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I've started to ake my first tentative steps into the world of filters. I was in a camera shop on friday afternoon and and picked up a CAMLINK 67mm Circular Polerising filter for my Nikkor 70-300VR lens

My thinking is, as most of thime I point it at cars in the sunshine this would be a good filter to have?

I tried it out at Goodwood Festival of Speed yesterday on the Porsche Cayenne Off Road area but found that I could not get a focus if I zoomed anymore than say 120mm.

I'm wondering is this is a normal effect of a CP filter or if I need to alter settings in the camera to compensate.

Any thoughts or suuggestions would be much appreciated. I have a couple of shots that I could post but am away in an hour or so and won;t be back near my PC until Tuesday evening.

Thanks for reading:thumbs:
Stu
 
when you pop your cp filter on, dont polarise until you have focussed first. Then polarise, it alters the the way the light is transmitted through to the camera, if you polarise and then focus, this could cause af difficulties, it has at least done so in my experiences in the past.
If your lens does not have internal focus, it will be spinning your filter around which will give the same effect as actually turning the polariser. Hope this makes sense
these filters are great for reducing reflections, and enhancing blue skies and clouds, so very usefull indeed
 
It adds roughly one and a half stops to the lens ,so with a zoom 70-300f/ 4.5
Say,it will make the f/4.5 into nearly f/8 .
For a camera to auto focus it needs to do so properly under f6.3 so the 70-300 might not auto focus at the big end.....:'(
 
towershot said:
It adds roughly one and a half stops to the lens ,so with a zoom 70-300f/ 4.5
Say,it will make the f/4.5 into nearly f/8 .
For a camera to auto focus it needs to do so properly under f6.3 so the 70-300 might not auto focus at the big end.....:'(
Click to expand...

The polariser won't change the aperture, it simply reduces the amount of light passing through the lens. The camera will auto focus fine as long as there's enough light.
 
A circular polariser should have no effect on auto focusing or auto exposure control. It doesn't matter if you do it before or after adjusting the polariser for effect. A polariser does not alter the f/number - just makes things darker, which is not the same thing.

Basically, a circular polariser should not produce the effect you have got. Does it actually say 'circular' on the filter itself? If is is a linear polariser, in which case it will probably just say 'polariser' then this might well be the problem.
 
I've just bought a circular polariser myself, and I have to admit I'm finding it very confusing... I'm never 100% sure if it's working or not! Is there a good 'guide for dummies' aywhere online?
 
Thiefree said:
I've just bought a circular polariser myself, and I have to admit I'm finding it very confusing... I'm never 100% sure if it's working or not! Is there a good 'guide for dummies' aywhere online?
Click to expand...

You can see the effect through the viewfinder. Blue sky is polarised, so if you rotate the filter it will get darker. Cloudy sky has very little polarised light, so very little effect.

Reflections are also polarised. If you stand at 35 degrees to the reflection and rotate the filter, the reflections will come and go.
 
It's easy to see if it's working, guess which part of this shot is using a CPL ;)



polarizer.jpg
 
Hoppy's correct.
Lee for instance have 2 types of polarising filters, both physically circular in shape, but one has linear polarising and the second (and more expensive!!) one has circular polarising.
The first is for film cameras, the second is for digital use, precisely for the autofocus issues mentioned elsewhere.
I'd check it is indeed a filter with circular polarisation, not just a circular shaped polariser!!
George
 
HoppyUK said:
You can see the effect through the viewfinder. Blue sky is polarised, so if you rotate the filter it will get darker. Cloudy sky has very little polarised light, so very little effect.

Reflections are also polarised. If you stand at 35 degrees to the reflection and rotate the filter, the reflections will come and go.
Click to expand...

As I understand it, blue sky often/usually contains a lot of UNpolarised light - ie light that has been scattered and is heading in all directions; the polarising filter removes this, returning the sky to its pristine and beautiful blue self. But the filter will not remove haze, which consists of actual particles suspended in the atmosphere.

That's my understanding anyway; perhaps one of you guys with the degree in photonics would like to confirm this or otherwise?;)

I agree that if the outer rim of your lens rotates when focusing, using the polariser should be the last thing you do. Otherwise, they're really very easy to use. TTL metering will sort everything for you. Remember that they are most effective at 90 degrees to the angle of the sun.
 
jerry12953 said:
As I understand it, blue sky often/usually contains a lot of UNpolarised light - ie light that has been scattered and is heading in all directions; the polarising filter removes this, returning the sky to its pristine and beautiful blue self. But the filter will not remove haze, which consists of actual particles suspended in the atmosphere.

That's my understanding anyway; perhaps one of you guys with the degree in photonics would like to confirm this or otherwise?;)

I agree that if the outer rim of your lens rotates when focusing, using the polariser should be the last thing you do. Otherwise, they're really very easy to use. TTL metering will sort everything for you. Remember that they are most effective at 90 degrees to the angle of the sun.
Click to expand...

You're not quite right Jerry, but let me clarify. Light from the sun is polarised, and the atmosphere de-polarises it somewhat, but bright blue sky is pretty clear and polarisers cut it out a lot and have a strong effect. I have some pictures taken in Greece (nearer equator, sun directly above) where the sky is almost black. Clouds however scramble it up pretty effectively though, so polarisers don't do much to darken skies on overcast days.

Polarisers can reduce haze, I think in theory, but my experience is not by any noticeable amount. The theory here is that if the atmosphere contains a lot of dust particles which polarise light through reflection off their surfaces, then the polariser can have a go at them, but really not worth bothering about.

Some other points: you need a circular polariser with DSLRs because the AF system polarises the light off the semi-silvered mirrors used in the focusing system and this can get confused with a plain linear polariser. It's the same with some metering systems also, but this is a camera design effect, not a film/digital thing. A circular polariser is actually a linear polariser with a quarter wave plate stuck to the back, so that the light is polarised in the nromal way, but then scrambled by the plate so that the camera sensors get an even helping of light regardless of the rotation of the filter.

Polarisers are also very effective with reflections, provided the angle is right - optimum is 35 degrees from the surface. They work well with lanscapes, even on cloudy days, as all reflections are polarised, ie of leaves and grass etc. You can't really orientate the filter much to modify this effect, but some leaves will randomly fall at the right angle for the filter to get to work on them. It looks good.

Polarisers are very effective in getting rid of reflections of cars, but only from one angle at a time. For example, they will work on the windscreen and bonnet, but not on the side at the same time. You have to rotate it 90 degrees for the other option. And if you use it on the sides of cars, the toughened glass used for side windows often shows stress marks - a mottled pattern (windscreens are laminated these days).
 
Lots of posts for me to think about here - so thanks for all the input :)

Here's the brand/model of filter (ignore the size) for those that asked about the filter type.

41Yu0eRAInL._SL500_AA280_.jpg
 
George said:
Hoppy's correct.
Lee for instance have 2 types of polarising filters, both physically circular in shape, but one has linear polarising and the second (and more expensive!!) one has circular polarising.
The first is for film cameras, the second is for digital use, precisely for the autofocus issues mentioned elsewhere.
I'd check it is indeed a filter with circular polarisation, not just a circular shaped polariser!!
George
Click to expand...

Not quite, the type of camera doesn`t matter (ie. film or digital) it`s just that linear polarises don`t allow AF to work correctly, so if you use af lenses (which most of us do) then you need circular polarising filters.
 
kingy said:
Lots of posts for me to think about here - so thanks for all the input :)

Here's the brand/model of filter (ignore the size) for those that asked about the filter type.

41Yu0eRAInL._SL500_AA280_.jpg
Click to expand...

You're welcome, and thanks also Chumpalot.

The reason I asked about your filter Kingy is that I wondered if the wrong filter had been put in the box, ie a linear one.

Anyway, my guess is that you just got unlucky and that if you try again all will be well.
 
Well it's definitely a circular polariser...... What was light like at Goodwood? By adding the filter, it makes it harder for the lens to focus by reducing the amount of light, and if it was a bit dark or dingy maybe the AF on the camera was struggling a little? Or it could be a dodgy filter I guess, could you borrow another and try it out?

Chris
 
chilliz said:
Not quite, the type of camera doesn`t matter (ie. film or digital) it`s just that linear polarises don`t allow AF to work correctly, so if you use af lenses (which most of us do) then you need circular polarising filters.
Click to expand...

Well, all of my polarizers are linear (wouldn't use anything else), and I haven't had any issues with Automatic Focusing on my 400d.

A linear polarizer, may effect automatic focusing on some cameras which use split beam optics to perform the focusing (and that is basically if the beam is cheaply recombined).
 
coldpenguin said:
Well, all of my polarizers are linear (wouldn't use anything else), and I haven't had any issues with Automatic Focusing on my 400d.

A linear polarizer, may effect automatic focusing on some cameras which use split beam optics to perform the focusing (and that is basically if the beam is cheaply recombined).
Click to expand...

Absolutely, I should have said that lin. pols MAY affect AF systems. :)
 
HoppyUK said:
A circular polariser should have no effect on auto focusing or auto exposure control. It doesn't matter if you do it before or after adjusting the polariser for effect. A polariser does not alter the f/number - just makes things darker, which is not the same thing.
Click to expand...

I disagree. I suspect the almost 2 stops loss of light making the "effective" aperture f/8 means there's not enough light for the AF to work - it probably just hunted back and forth instead. The same effect can be had when using a 2x TC on say a 300mm f/5.6 lens which becomes a 600mm f/11 (effective).

The clue that it only happened beyond a certain focal length is a bit of a giveaway really.
 
Here are a couple of with and without shots.

With the filter on
DSC_0104.jpg


Same camera settings but no filter, rotated my position about 30' to take this shot.
DSC_0108.jpg
 
you just focus on something
spin the filter around until the reflective light is cancelled out



heres an example of a photo i took

3681786866_87073813a6_o.jpg



you can see there are no reflections on the bonnet
but if you look at the side you can see the reflections.. thats how it was all over
with the CPL the reflections on the bonnet went away
i think its because of a mix of wide angle + ebay CPL the cpl doesnt cover the entire view..



heres an example i took just now

x1y1ky.jpg


in the first picture you can see the cpl is reducing the reflection on the white cover on the right
and in the second picture the cpl is reducing the reflection/light on the phone screen and also the top of the cover behind it


hope that helps
 
Does the image in the viewfinder look OK?

I ask this because I had a Cokin Polariser which worked fine on my 18-70mm lens, but when I got the same filter type for my 70-300mm lens and it distorted and the camera wouldn't focus either. The chap in the shop tried to say that there was something wrong with my lens/camera, but I showed him the AF working perfectly without the filter. He got a Hoya filter (more expensive) and that worked fine. Didn't have the cash at the time, but later got a Hoya Pro 1 which works on both my lenses.
 
pxl8 said:
I disagree. I suspect the almost 2 stops loss of light making the "effective" aperture f/8 means there's not enough light for the AF to work - it probably just hunted back and forth instead. The same effect can be had when using a 2x TC on say a 300mm f/5.6 lens which becomes a 600mm f/11 (effective).

The clue that it only happened beyond a certain focal length is a bit of a giveaway really.
Click to expand...

Sorry, but that's not right, though I follow your reasoning ;)

The polariser just reduces the light level a bit, not the f/number, and two stops is nothing. No more than a passing cloud.

AF systems only stop working at higher than f/5.6 (usually up to f/6.3 if you push them) because the physical diameter of the light cone gets too narrow. It's not the light level that matters so much, and they keep on working even in candle light.

D60 with that lens, which never goes higher than f/5.6, is well within tolerance. They were made to work together.
 
kingy said:
Here are a couple of with and without shots.

With the filter on
DSC_0104.jpg
Click to expand...

That is camera shake. Absolutely 100%.

Even at fast shutter speeds you have to hold the camera as steady as possible. 1/500sec with 200mm lens on a crop camera is not that fast anyway.
 
Agree on the camera shake thing. If you look at the image there is NO zone of sharpness anywhere. If the focus had missed its target, something would have been in focus...but nothing is and there is blur on the lot.

Wiht the polariser, people have said it reduces the light input by 1.6 stops...NO, it can be as much as 4 stops when fully polarised.

When shooting action with a polariser you need to open up to the maximum aperture you have available. At the sort of range you were shooting those trucks then f2.8 would be more than enough, even on a 200mm.

Looking at the non filtered shot - that doesn't look sharp to me either. SharpER, but not pin.
 
More stuff to look at and think about, I'll put up a couple more images from the same set later and see if we can bottom out the camera shake theory.

thanks for all the advice and discssion - really useful stuff :thumbs:
 
kingy said:
More stuff to look at and think about, I'll put up a couple more images from the same set later and see if we can bottom out the camera shake theory.

thanks for all the advice and discssion - really useful stuff :thumbs:
Click to expand...

TBH kingy there is nothing more to bottom out on the camera shake question. It's there without question.

Maybe you should shoot some more stuff, with and without the polariser, see what your limits are, check the polarising effect. Not sure why you used it for those pics.
 
Lensflare said:
Agree on the camera shake thing. If you look at the image there is NO zone of sharpness anywhere. If the focus had missed its target, something would have been in focus...but nothing is and there is blur on the lot.

Wiht the polariser, people have said it reduces the light input by 1.6 stops...NO, it can be as much as 4 stops when fully polarised.

When shooting action with a polariser you need to open up to the maximum aperture you have available. At the sort of range you were shooting those trucks then f2.8 would be more than enough, even on a 200mm.

Looking at the non filtered shot - that doesn't look sharp to me either. SharpER, but not pin.
Click to expand...

True, a polariser darkens some things by four stops for sure. But for practical purposes it doesn't reduce the overall exposure by that much - it just reduces the brightness of the sky by that amount, not the foregound, which is what you want.

New Hoya HD polariser only reduces exposure by 1.1 stops overall, which is handy I think :)
 
HoppyUK said:
TBH kingy there is nothing more to bottom out on the camera shake question. It's there without question.

Maybe you should shoot some more stuff, with and without the polariser, see what your limits are, check the polarising effect. Not sure why you used it for those pics.
Click to expand...

I'm not convinced:thinking: I pointed the camera out of the window this morning as I had 5 mins to spare and the camera will not focus with the filter in place at long zooms - the viewfinder image isn't sharp but the AF activity was normal.... I'll try and put some proper time into this at the weekend and get my head around what I'm most likely doing wrong!

As for why i used it, trial and error. As I said in the first post, I'm feeling my way into the world of filters. I was in a camera shop waiting for Mrs K to choose a camera bag and was nosing at the filters. From what I've read and from what the box said, this filter would cut down glare on glass and water. What I didn't realise was that the glass or water shouldn't be moving:bonk:
 
kingy said:
I'm not convinced:thinking: I pointed the camera out of the window this morning as I had 5 mins to spare and the camera will not focus with the filter in place at long zooms - the viewfinder image isn't sharp but the AF activity was normal.... I'll try and put some proper time into this at the weekend and get my head around what I'm most likely doing wrong!

As for why i used it, trial and error. As I said in the first post, I'm feeling my way into the world of filters. I was in a camera shop waiting for Mrs K to choose a camera bag and was nosing at the filters. From what I've read and from what the box said, this filter would cut down glare on glass and water. What I didn't realise was that the glass or water shouldn't be moving:bonk:
Click to expand...

TBH, looking at your pic, while there is definite camera shake, it also looks like the image is out of focus. The two affects are quite easily distinguished when they are exagerated like that.

So maybe you do have a focusing problem, either camera, lens or user ;) but it will not be caused by a circular polarising filter. Just a thought, but have you checked the dioptre adjustment of the viewfinder eyepiece?
 
Just taken some more shots. THis time on a tripod using timer so I'm not touching the body.
See how the filtered image is OOF.

DSC_0017.jpg


DSC_0018.jpg
 
As I said earlier, some cheap Polarisers are not good enough to be able to focus correctly at high zoom levels. On a wide angle you would probably get away with it, but a high zoom shows the quality, or lack of.

I hadn't heard of Camlink filters before the initial post, but a friend produced one during the week which she received by buying a magazine subscription. This leads me to think that they may not be the highest quality product. ;)
 
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