P filter onto Cpl?

Yes, you could but there's little point unless the outside pol is linear. That setup (Lin Pol, Circ Pol, Lens) will effectively give you a variable neutral density filter but a Circular pol on a circular pol will just cut the light levels a fixed amount (as well as giving the usual polarisation).

The reason for this (if I remember the basics of optical theory from my long past schooling!) is that a circular polariser basically re-randomises the light after it's done its magic while a linear pol leaves it oscillating in one plane, allowing the 2nd pol to re polarise it in its own plane. Someone else will hopefully be able to explain it better (and possibly more correctly!)
 
Oops! Duplicate post.
 
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Er, Nod, where did he mention using two polarisers?

AIUI the OP wants to attach grads or NDs to the outside of a CPL.

Yes, it will be possible, but you run the risk of vignetting due to the depth of the setup. If you want to go down that route it might be worth buying another cheapo P series holder off ebay for a couple of quid and hacking it down with a saw to just one slot to make it a little shallower.

The very rearmost slot on a P series holder (the one nearest the lens) is thinner than the others and is designed for a CPL. I seem to remember Kood make a P series CPL which slots into that thin slot and has a toothed outer ring to allow you to rotate it independently of the other filters used.
 
markmullen said:
Er, Nod, where did he mention using two polarisers?

AIUI the OP wants to attach grads or NDs to the outside of a CPL.

Yes, it will be possible, but you run the risk of vignetting due to the depth of the setup. If you want to go down that route it might be worth buying another cheapo P series holder off ebay for a couple of quid and hacking it down with a saw to just one slot to make it a little shallower.

The very rearmost slot on a P series holder (the one nearest the lens) is thinner than the others and is designed for a CPL. I seem to remember Kood make a P series CPL which slots into that thin slot and has a toothed outer ring to allow you to rotate it independently of the other filters used.
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Yeah Mark, you're spot on. I don't know if I'll suffer from vignette on my lens, I'll play about with my gear later and see. Will have a look into Kood polarizer later.
 
You're completely right! That'll teach me not to wear my reading glasses at 0:mygodit'searly o'clock!

TBH, in that instance, I would be tempted to get a P fit circ pol (as mentioned by Mark) to use when using other filters - it's a bit fiddly to adjust a screw in pol then get the holder level for the grad etc but, as John's said, he's going to have a play!
 
Hi, Nod is perfectly right in what he says but one thing that has been omitted is that using a linear polarizing filter with auto focus can in some instances cause the auto focussing on some cameras to misbehave. Also vignetting could be a problem, other than that it should work. Hope this helps.
 
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