CPL + GND/ND Filters - order matters?

chickenandavocado · 04-12-2012, 06:45 AM

Can someone tell me if it matters whether I put a CPL before the GND/ND filter, or after?

I was told by someone the GND/ND should always be put before the CPL if you use them in combination

Can anyone explain why?

Thanks!

eddie1960 · 04-12-2012, 06:53 AM

Actually if you use a square filter system the CPL is always first so i'm not sure it's an issue

Na Horuk · 04-12-2012, 07:10 AM

Well, lets think about this.
GND CPL LENS means the light is first darkened, then the light is polarized, and then the lens catches it.
CPL GND LENS means you first polarize and then you darken only the remaining light. (so GND has less light to even work with and its all polarized). Who knows, the GND might even de-polarize some of it.

VictorDA · 04-12-2012, 07:39 AM

Originally posted by Na Horuk

Who knows, the GND might even de-polarize some of it.

Well no, no filter can "de-polarize" light, just like no filter can get back the missing colors after using a red filter.
If I understand correctly, the CPL does not actually change the light, it just transmits one part of it and absorbs another. That missing part can never be retrieved.
I don't really see why there would be a preferable order... maybe it's just about which one flares the most?

chickenandavocado · 04-12-2012, 07:40 AM

Well I still use screw in polarisers and looking at getting grad nds in a square system to match without buying new cpls

Still unsure of the logic as to why the order matters

eddie1960 · 04-12-2012, 07:42 AM

Originally posted by chickenandavocado

Well I still use screw in polarisers and looking at getting grad nds in a square system to match without buying new cpls

Still unsure of the logic as to why the order matters

If you are going to a square system then even if you get the CPL it will be first before the lens so no big difference than using the screw on CPL and then adding the filter holder with the exception that you will have vignetting issues on wider lenses possibly

Na Horuk · 04-12-2012, 08:00 AM

Originally posted by victordeamorin

Well no, no filter can "de-polarize" light, just like no filter can get back the missing colors after using a red filter.

I assume you can scramble polarized light, thus depolarizing it or changing its polarization. But that wasn't even the main point of my post, just an afterthought.

VictorDA · 04-12-2012, 09:59 AM

Back to topic, this has been in my head all afternoon, I think I just understood why you would put the CPL between the GND and the lens: probably to reduce or suppress any light reflections (a common application on CPLs) that might happen on the GND and lead to flare! Please be aware that this is just an opinion of why that advice was given to you... I personnally hadn't ever heard it or given it myself!

chickenandavocado · 04-12-2012, 09:29 PM

thanks for your input, however i was told it should be the other way around i.e. the CPL -> GND -> Lens

i found this on another forum, but it still doesnt seem like a reasonable explanation:

Lee Filters - SLR gear - Photography

VictorDA · 04-12-2012, 11:07 PM

Originally posted by chickenandavocado

thanks for your input, however...

Oops, OK, I'm going to forget about this now.
I have no idea!

chickenandavocado · 04-13-2012, 01:00 AM

no worries

hopefully someone will know the answer so everyone can benefit!

**Ron Boggs** · 04-14-2012, 11:52 AM

A couple thoughts...Usually the GND is the farthest from the lens simply because that's the easiest place to manipulate it. I frequently hand hold the GND in place over the top of a Kaseman circular polarizer and forgo the square holder altogether. Prolific photo author Tim Fitzharris uses electrical tape to tape GND filters in place which also places the GND farthest from the lens. That's just his way to speed the process and avoid the square holder.

Note that I have one lens that won't tolerate the addition of both polarizer and GND out front. It's a very high quality * telephoto lens and the optical formula is just too touchy for all the extras...image goes soft...I found a drop-in polarizer (some extreme tele's have a drop-in filter drawer) that places the polarizer back near the lens mount and now I can use GND filters out front with no softening effect.

Since virtually every brand that makes telephoto lenses also offers drop-in polarizers placing the polarizer back toward the camera end of the lens, I have to presume that it's OK and maybe even preferable to keep polarizers closer to the camera and the other "junk" goes on farther out front.

So from my experience and from extrapolating from the manufacturer's drop-in polarizer offerings I'm suggesting that you screw on your polarizer and then affix GND out front farthest from the lens noting that adding an additional ND as well may be too much "junk" for many lenses. I recommend getting up early so you don't need to use the multi-stop ND filter since a polarizer and GND is already lots to add.

chickenandavocado · 04-16-2012, 03:11 AM

thanks for your response, i can certainly see the points you're making

so far it seems there's no definitive answer as to why some people say its best for the CPL to be outside, i will stick with utilising the CPL inside (obviously easiest way to control the amount of polarisation especially with a solid ND which is difficult to see via vf / live view).

Cheers!

04-12-2012, 06:45 AM	#1
chickenandavocado Veteran Member Join Date: Oct 2010 Location: Hong Kong Posts: 327	CPL + GND/ND Filters - order matters? Can someone tell me if it matters whether I put a CPL before the GND/ND filter, or after? I was told by someone the GND/ND should always be put before the CPL if you use them in combination Can anyone explain why? Thanks!

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04-12-2012, 06:53 AM	#2
eddie1960 Veteran Member Join Date: Aug 2010 Location: Toronto Photos: Gallery \| Albums Posts: 13,667	Actually if you use a square filter system the CPL is always first so i'm not sure it's an issue

04-12-2012, 07:10 AM	#3
Na Horuk Veteran Member Join Date: Feb 2012 Location: Slovenia, probably Photos: Gallery \| Albums Posts: 11,186	Well, lets think about this. GND CPL LENS means the light is first darkened, then the light is polarized, and then the lens catches it. CPL GND LENS means you first polarize and then you darken only the remaining light. (so GND has less light to even work with and its all polarized). Who knows, the GND might even de-polarize some of it.

04-12-2012, 07:39 AM	#4
VictorDA Pentaxian Join Date: Sep 2010 Location: Lyon area, France Posts: 718	Originally posted by Na Horuk Who knows, the GND might even de-polarize some of it. Well no, no filter can "de-polarize" light, just like no filter can get back the missing colors after using a red filter. If I understand correctly, the CPL does not actually change the light, it just transmits one part of it and absorbs another. That missing part can never be retrieved. I don't really see why there would be a preferable order... maybe it's just about which one flares the most?

04-12-2012, 07:40 AM	#5
chickenandavocado Veteran Member Join Date: Oct 2010 Location: Hong Kong Posts: 327 Original Poster	Well I still use screw in polarisers and looking at getting grad nds in a square system to match without buying new cpls Still unsure of the logic as to why the order matters

04-12-2012, 07:42 AM	#6
eddie1960 Veteran Member Join Date: Aug 2010 Location: Toronto Photos: Gallery \| Albums Posts: 13,667	Originally posted by chickenandavocado Well I still use screw in polarisers and looking at getting grad nds in a square system to match without buying new cpls Still unsure of the logic as to why the order matters If you are going to a square system then even if you get the CPL it will be first before the lens so no big difference than using the screw on CPL and then adding the filter holder with the exception that you will have vignetting issues on wider lenses possibly

04-12-2012, 08:00 AM	#7
Na Horuk Veteran Member Join Date: Feb 2012 Location: Slovenia, probably Photos: Gallery \| Albums Posts: 11,186	Originally posted by victordeamorin Well no, no filter can "de-polarize" light, just like no filter can get back the missing colors after using a red filter. I assume you can scramble polarized light, thus depolarizing it or changing its polarization. But that wasn't even the main point of my post, just an afterthought.

04-12-2012, 09:59 AM	#8
VictorDA Pentaxian Join Date: Sep 2010 Location: Lyon area, France Posts: 718	Back to topic, this has been in my head all afternoon, I think I just understood why you would put the CPL between the GND and the lens: probably to reduce or suppress any light reflections (a common application on CPLs) that might happen on the GND and lead to flare! Please be aware that this is just an opinion of why that advice was given to you... I personnally hadn't ever heard it or given it myself!

04-12-2012, 09:29 PM	#9
chickenandavocado Veteran Member Join Date: Oct 2010 Location: Hong Kong Posts: 327 Original Poster	thanks for your input, however i was told it should be the other way around i.e. the CPL -> GND -> Lens i found this on another forum, but it still doesnt seem like a reasonable explanation: Lee Filters - SLR gear - Photography

04-12-2012, 11:07 PM	#10
VictorDA Pentaxian Join Date: Sep 2010 Location: Lyon area, France Posts: 718	Originally posted by chickenandavocado thanks for your input, however... Oops, OK, I'm going to forget about this now. I have no idea!

04-13-2012, 01:00 AM	#11
chickenandavocado Veteran Member Join Date: Oct 2010 Location: Hong Kong Posts: 327 Original Poster	no worries hopefully someone will know the answer so everyone can benefit!

04-14-2012, 11:52 AM	#12
Ron Boggs Site Supporter Join Date: Feb 2008 Location: MT Photos: Gallery Posts: 1,350	A couple thoughts...Usually the GND is the farthest from the lens simply because that's the easiest place to manipulate it. I frequently hand hold the GND in place over the top of a Kaseman circular polarizer and forgo the square holder altogether. Prolific photo author Tim Fitzharris uses electrical tape to tape GND filters in place which also places the GND farthest from the lens. That's just his way to speed the process and avoid the square holder. Note that I have one lens that won't tolerate the addition of both polarizer and GND out front. It's a very high quality * telephoto lens and the optical formula is just too touchy for all the extras...image goes soft...I found a drop-in polarizer (some extreme tele's have a drop-in filter drawer) that places the polarizer back near the lens mount and now I can use GND filters out front with no softening effect. Since virtually every brand that makes telephoto lenses also offers drop-in polarizers placing the polarizer back toward the camera end of the lens, I have to presume that it's OK and maybe even preferable to keep polarizers closer to the camera and the other "junk" goes on farther out front. So from my experience and from extrapolating from the manufacturer's drop-in polarizer offerings I'm suggesting that you screw on your polarizer and then affix GND out front farthest from the lens noting that adding an additional ND as well may be too much "junk" for many lenses. I recommend getting up early so you don't need to use the multi-stop ND filter since a polarizer and GND is already lots to add.

04-16-2012, 03:11 AM	#13
chickenandavocado Veteran Member Join Date: Oct 2010 Location: Hong Kong Posts: 327 Original Poster	thanks for your response, i can certainly see the points you're making so far it seems there's no definitive answer as to why some people say its best for the CPL to be outside, i will stick with utilising the CPL inside (obviously easiest way to control the amount of polarisation especially with a solid ND which is difficult to see via vf / live view). Cheers!