Circular vs Linear Polarizing Filters

Hi,

Seeing we haven't had a really dumb question for a while means Mac has been slacking-off.

Well, I'm back, and need some help understanding Circular PL filters - which I believe were necessitated by auto focusing lenses being fooled by linears.

- If they're circular, how come we still have to align them - just like linear?

- They seem to cost two-to-three times more than linear, and on a manual focus rig, perform the same?

Thanks

Mac (from Montreal)

Here is a pretty good tutorial on polarizers.
http://www.luminous-landscape.com/tutorials/polarizers.shtml

Drew (from BC)

Circular polarisers filter the polarised light in the same way as linear polarisers (and so still need rotating in the normal way) , but then they 'scramble' the filtered light afterwards so as not to fool autofocus and AE sytems that use half silvered mirrors.

Calling them circular polarisers is a bit confusing and not an acurate description of what they do.

Thank you, Gentlemen from opposite sides of the pond and continent.

The tutirial explained other issues I've had with PL's on wide angle lenses - thick rims = vignetting and uneven sky effect.

I never knew that linear PL's could confuse TTL light meters on newer camers (Post 1970) which also use partially silvered mirrors. (I am so pre-1970).

I guess the safest way to go is to always pony up for thin circulars - ouch.

One reason I like Pentax is that 49mm covers a lot of lenses - in my case, six. So investing in a B&W high end, Circular PL makes sense.

Appreciate your help!

And just to add, that if you have several lenses then the Cokin A or P system may be cost effective
In addition, the polarisers fit snugly in the first slot, so they're better for wide angle lenses.

...now I'm just waiting to find out if I can still use the Cokin-P on the new 12-24mm which is 77mm filter. The X-Pro/Z-Pro are scarily expensive! (I daren't even look at the cost of the polarisers!)

Matt

Matt,

Now you've done it!

Satisfied one question about Circular vs Linear PL's and opened up another about Conkin.

I inherited a very banged-up Conkin frame designated 49, simply marked Conkin made in France. There was also a box of pre-shaped cutouts and two frames to hold them, which slide into the camera mount. The pre-shaped frame box says A 397. Is that "A" a hint?

In playing around a little, I noticed that the cutouts really only have the desired effect on my 28mm, yet are the kinds of things you'd use for portaits usually taken with 55mm, 100mm or 135mm? (That's when I threw them in a drawer).

Now, my interest is reawakened if Conkin makes high quality, lower priced filters.

Can you tell me the difference between A and P, and if pursuing Conkin glass is a good way to go?

The A filters are, I think, 75mm square, and the P ones 100mm square, for use on larger lenses and medium format.

Cokin isn't glass, but dyed optical quality acrylic of some kind (forget what exactly).

Perhaps predictably, I prefer "proper" glass filters, when I use filters, and that usually means SMC Pentax, B&W or Heliopan. Part of the reason is the superior coating (Colkin are not coated at all, are they?), the more compact design and the potentially higher image quality.

With digital photography, I rarely use filters at all, adding the effects in Photoshop. CS2 is especially good for this, with its series of photographic filters. Want an 81A, then just dial it in!

Hi Mac,
Sorry to have added to the confusion
There are four Cokin sizes:

A - cover 36mm to 62mm
P - cover 48mm to 82mm (filter is 84mm square)
Z-Pro - cover 49mm to 96mm (filter is 100mm square)
X-Pro - cover 62mm to 112mm (filters are 170mm x 130mm)

You'll find plenty of "A" series filters second hand. There are a few "P" ones around. The X-Pro and new Z-Pro series are mindblowingly expensive, but then are manufactured to higher standards, or so I'm told!

You are right, A397 is an "A" style filter
In the UK, www.speedgraphic.co.uk do nice neutral density starter packs (e.g. P121L, P121S, P121M). Personally I use P121F (full length ND grad), and P121S, along with a Kenko circular polariser - there are plenty of third party P and A fitting filters (e.g. from www.srbfilm.co.uk )

Hope that helps!
Matt

John,

Thank's, based on your reply, I have the "A" series holder with the 49mm attachment.

As I tend to be a fumbler, I can just imagine what I could do to acrylic filter inserts!

I have a lot of good 49mm screw-in filters from Hoya, Olympus and Tiffen and a 58mm B&W UV on order for my f2.5 135, and I think I'll stick with glass as well.

Cheers

Matt,

Thank you for your detailed reply. I'm always amazed at how much selection and availability you folk have in the European arena!

I can see that the Conkin type of filter system could be very attractive to a professional photog - especially the P series. You could have every type, intensity and combination of filter known to man - and probably invent a few - for a relatively reasonable expendature, and not spend hours screwing and unscrewing dedicated filters to try things out.

WAY above my simple needs and abilities (I'd never snap a picture - by the time I'd have decided on the two or three filters I'd like to try, the sun would have set - on my sunrise photo!)

Appreciate the input very much!

Cheers

I'm not sure what you have when you say cutouts and frame, but I sometimes cut out shapes(hearts,stars etc) from black cardboard and tape them to my uv filter.
try photographing a person with those cutouts with city/xmas lights (anything that'll make specular highlights) in the background and the check your out of focus background for (heart/star etc) shaped highlights!
cokins have holders for four filters, on a wide angle, I'd got with the largest filter that'l fit my largest lens, and cut the filter holder to remove 2 or 3 of the extra filterslots to avoid vinetting.

I meant try that with a medium telephoto, not your wide angle.

Oh, one more thing, then I'll shut up for a while...
stacking 2 polarizers will give you an infinately variable nd filter.
great for 1-8 hour exposures to remove traffic and people from cityscapes during daytime.

Cokin, Conkin, Colkin................
If I remember correctly, the Hoyarex system is essentially the same and there are other makes too.

Mac, don't discount acrylic filters entirely, even cheaper ones can have their uses. They are lighter than glass and being flat, can fit snuggly inside a credit-card type wallet. They are particularly good for those occassional special effect shots where you want a graduated or coloured filter and the holder can be rotated, accomodate more than one filter and the same filter can be fitted to a number of lenses with different thread sizes - all you need are the appropriate adapter rings.
For a bit of creative fun, the holder is a convenient way to fit a mask eg. a keyhole for that 'what the butler saw' type shot.

Why not look around for a cheap set, quality doesn't have to be great if it's just for a bit of fun and you never know when they might come in handy

Kimbo - and I didn't even SPELL it right!

If I come across a set -I'll get them - I just looked on the Cokin site, and there are countless numbers of them! (And the permutations and combinations are endless).

My head hurts!

Don,

What came with my 49mm ring and A series holder, were a bunch of cutouts which work on wide angle, but the openings may be too large for anything longer. There may be another series with smaller openings - or, now that I have the dimensions I can make my own - as you've done.