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04-18-2018, 08:04 AM   #16
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QuoteOriginally posted by BruceBanner Quote
.................Two more points;

1) You can't vary the 'strength' with linear, like rotate it like you can a CPL and decide how much polarising effect to go for, with linear it's all or nothing?

2) Can you use linear (or even CPL for that matter) with ND filters if you feel you want to block out even more light. Perhaps for example a 1-2min very bright day with clouds scene to get the clouds really moving etc.
1) I think you're missing something here Bruce. A CPL is a linear polarizer (with a retarder) hence they both behave almost identically. The difference is that with a CPL the polarized light produced by the linear polarizer is "scrambled" so it doesn't affect those AF systems which are susceptible to polarized light. So yes, you can vary the strength of either - they both behave identically relative to the scene. If you hold a linear and a CP side-by-side and look through them, you would see exactly the same thing and as they rotate, the changes would be identical.

2) Yes, an ND filter doesn't care is light is polarized or not (nor linearly or circularly). It just reduces light intensity. Therefore, you can use a standard ND with a polarizer with no issues. (Exception: Variable ND filters use crossed polarizers and aren't compatible with polarizers). It could be argued which should be on the camera side, but technically, it makes no difference. (One thing to keep in mind is that with wide-angle lenses, stacked filters may start to show and produce vignetting in the photo - just watch out if the filter rims are wide.)

And - that one point is well taken - it may be harder to find a quality linear polarizer these days since both to address the issues with some camera's metering systems, and as a market ploy (to imply a CP is has some advantage over a LP), many manufactures only offer CPs and have discontinued LPs.


Last edited by Bob 256; 04-18-2018 at 08:17 AM.
04-18-2018, 08:19 AM - 1 Like   #17
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QuoteOriginally posted by Bob 256 Quote
And - that one point is well taken - it may be harder to find a quality linear polarizer these days since both to address the issues with some camera's metering systems, and as a market ploy (to imply a CP is has some advantage over a LP), many manufactures only offer CPs and have discontinued LPs.
Lee still make linear polarisers, which are high quality by definition, but not so useful if you don't use the lee filter system - cheaper than circular, though
04-18-2018, 09:19 AM   #18
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QuoteOriginally posted by Ontarian50 Quote

Most cameras, and I think including all Pentax SLRs and DSLRs, had the meter cells beside the eyepiece and looking straight at the focus screen - and didn't have any beam splitting going on, and didn't need a costly circular polarizer (they were rarer and more pricey back then).

So, while a linear polarizer will muck up your AF system, if you've got AF turned off you've got no problem. But it should have no effect on your exposures, since Pentaxes don't employ beam splitters in the meter path.
I forgot the one exception - and of course it's the exceptional LX. The LX has a beam splitting main mirror, to direct some light down to the meter cell in the base, via the smaller secondary mirror. That's needed in the LX because the prisms and accessory finders don't contain the meter cells.

But aside from the LX, no other Pentax meters through the mirror or a beam splitter, as far as I know. Evaluative (segmented, matrix) meter systems work best with the meter cell situated right beside or above the eyepiece and looking straight onto the focusing screen. No beam splitter required.
04-18-2018, 10:15 AM   #19
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QuoteOriginally posted by Ontarian50 Quote
I forgot the one exception - and of course it's the exceptional LX
I remember this problem of Pentax LX which is the cause of the introduction of CPLs to replace PLs in this article.

QuoteQuote:

The first analogue SLR to present problems with exposure due to the presence of the polarizing filter was the splendid Pentax LX. The LX display system, a real innovation at the time,
used only one silicon cell placed inside the unit under the moving mirror. This cell was directed inwards towards the film plane and measured before and during the exposure itself the light reflected
from a surface with a particular reflective treatment on the first curtain and/or from the emulsion of the film itself. This is why the problem of circular and linear polarizers was created with the Pentax LX.
With linear polarizers, the light arriving on the mirror has a different intensity than the initial one, depending on how the filter is rotated. Since sensors behind mirrors in cameras such as Pentax LX
are calibrated to receive a fixed percentage of total light (in the case of LX 15%), if they receive more light than they expect, they will lead the photographer to underexpose and receive less overexposure.
Circular polarizers, on the other hand, polarize light in different ways, without changing its intensity: therefore, the same percentage of light that would arrive without filter continues to arrive on the sensor
through the semi-reflective part of the mirror. It goes without saying that the problem only arises when working manually using the viewfinder LEDs: working automatically,
with the LX there is continuous real-time exposure control even when the mirror is raised.


04-18-2018, 01:20 PM - 1 Like   #20
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QuoteOriginally posted by pentaxfall Quote
There was a lively thread about LPL and CPL comparison. I am not able to find the actual thread
Could have been "The difference in brands of polarizing filters?" maybe? Kinda fizzled without reaching a definitive conclusion IMHO, but I suspect the reality is most modern cameras don't react too badly to LPLs, but some older ones did. The LX didn't come up, interesting to know that it was one.

There seems to be a lot of quite old (for the internet..) information which is still regarded as current, not helped by many site authors not dating their reports or documenting which cameras were tested. So "CPLs good, LPLs bad" seems to have passed into the realm of Folklore What Everyone Knows Is True.

As Pentaxians seem to like using older kit, it would actually be quite useful to have a list of equipment with notes of how much AF and metering are affected for each item. Can't help much there...

Cheers

Jonathan
04-18-2018, 01:33 PM   #21
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QuoteOriginally posted by h4yn0nnym0u5e Quote

There seems to be a lot of quite old (for the internet..) information which is still regarded as current, not helped by many site authors not dating their reports or documenting which cameras were tested. So "CPLs good, LPLs bad" seems to have passed into the realm of Folklore What Everyone Knows Is True.

As Pentaxians seem to like using older kit, it would actually be quite useful to have a list of equipment with notes of how much AF and metering are affected for each item. Can't help much there...
Jonathan
Agreed. Here is a wiki on TTL which helps to show some models (manual focus 35mm film SLRs) that had IDM or didnʻt. IDM (Integrated Direct Metering) was the more advanced metering system that was adversely affected by LPLs.

Through-the-lens metering - Wikipedia

Anyone know of a link that has the same but for AF DSLRs and FSLRs?
04-18-2018, 02:33 PM   #22
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QuoteOriginally posted by Bob 256 Quote
1) I think you're missing something here Bruce. A CPL is a linear polarizer (with a retarder) hence they both behave almost identically. The difference is that with a CPL the polarized light produced by the linear polarizer is "scrambled" so it doesn't affect those AF systems which are susceptible to polarized light. So yes, you can vary the strength of either - they both behave identically relative to the scene. If you hold a linear and a CP side-by-side and look through them, you would see exactly the same thing and as they rotate, the changes would be identical.

2) Yes, an ND filter doesn't care is light is polarized or not (nor linearly or circularly). It just reduces light intensity. Therefore, you can use a standard ND with a polarizer with no issues. (Exception: Variable ND filters use crossed polarizers and aren't compatible with polarizers). It could be argued which should be on the camera side, but technically, it makes no difference. (One thing to keep in mind is that with wide-angle lenses, stacked filters may start to show and produce vignetting in the photo - just watch out if the filter rims are wide.)

And - that one point is well taken - it may be harder to find a quality linear polarizer these days since both to address the issues with some camera's metering systems, and as a market ploy (to imply a CP is has some advantage over a LP), many manufactures only offer CPs and have discontinued LPs.
Bob... I am missing something all the time hence why I practically live on Pentax Forums

Does it matter which filter goes on a lens first, is it preferable to CPL then have a ND last or vice versa or it doesn't matter?

04-18-2018, 03:19 PM   #23
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I transcribed the text entirely from the leaflet contained in one of my circular polarizing filters (Hoya), the concept (the real sense) seems very clear.

PL-Linear

The PL polarizing filter comprises a thin, neutral grey linear polarizing, neutral grey linear polarizing sheet sandwhiched between two pieces of optical glass in a rotating frame.
Eliminates undesirable reflections from glass or water surfaces and also increases contrast in distant scenes with both color and black & white films,
infrared effects can also be produced by using PL together with a red filter with black and withe films.

PL-Circular

PL-Circular is made by sandwiching a linear polarizing sheet and a quarter wave- retardation plate between two pieces of optical glass.
The effect is the same as with PL-Linear filter but PL-Circular is used for the cameras which cannot meter exposure properly with with the other type.
In other words, if a camera is provided with a divider, refracting prism or half-mirror, these devices themselves will polarize light and affect the operation of the exposure meter.
This can be eliminated by using PL-Circular.

Another thing,

To distinguish a Circular Polarizer from a Linear Polarizer, turn the filter backwards and look through it into a mirror.
If the filter image in the mirror is black, you have a circular polarizer. If the image is clear, you have a linear polarizer.
04-18-2018, 08:37 PM   #24
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QuoteOriginally posted by BruceBanner Quote
Bob... I am missing something all the time hence why I practically live on Pentax Forums

Does it matter which filter goes on a lens first, is it preferable to CPL then have a ND last or vice versa or it doesn't matter?
I know the feeling...

See my response #2 - did mention that it makes no difference. Personally, I would place the ND filter outermost toward the scene but it can be placed between the polarizer and the lens just as well. The order could potentially affect inner-lens-filter reflections so you could try it both ways, but I doubt you'd see any differences. As far as the polarization goes - no difference.

---------- Post added 04-18-2018 at 09:48 PM ----------

QuoteOriginally posted by maw Quote
............To distinguish a Circular Polarizer from a Linear Polarizer, turn the filter backwards and look through it into a mirror. If the filter image in the mirror is black, you have a circular polarizer. If the image is clear, you have a linear polarizer.
Off Topic - Just a bit more polarizer trivia: the "sense" of circular polarized light is flipped from clockwise to counter-clockwise (or visa-versa) when it is reflected (and yes, there are CW and CCW polarizers). For an interesting demo, look at yourself wearing a pair of 3D glasses (like theater 3D) which use CP filters. Only opposite eyes can see each other (Oh, just go try it and see what I mean - it will entertain you).

Last edited by Bob 256; 04-18-2018 at 08:54 PM.
04-18-2018, 09:45 PM   #25
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QuoteOriginally posted by Bob 256 Quote
I know the feeling...

See my response #2 - did mention that it makes no difference. Personally, I would place the ND filter outermost toward the scene but it can be placed between the polarizer and the lens just as well. The order could potentially affect inner-lens-filter reflections so you could try it both ways, but I doubt you'd see any differences. As far as the polarization goes - no difference.

---------- Post added 04-18-2018 at 09:48 PM ----------



Off Topic - Just a bit more polarizer trivia: the "sense" of circular polarized light is flipped from clockwise to counter-clockwise (or visa-versa) when it is reflected (and yes, there are CW and CCW polarizers). For an interesting demo, look at yourself wearing a pair of 3D glasses (like theater 3D) which use CP filters. Only opposite eyes can see each other (Oh, just go try it and see what I mean - it will entertain you).
See Bob... I can't even read properly.. there's no hope for me :'(

Just watch me bring up this same topic 6 months from now because I have forgotten it all
04-19-2018, 07:20 AM - 1 Like   #26
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QuoteOriginally posted by BruceBanner Quote
See Bob... I can't even read properly.. there's no hope for me :'(

Just watch me bring up this same topic 6 months from now because I have forgotten it all
Make that US - I'm easily amused standing in front of a mirror with 3D glasses on, looking at myself - and the next time it's the same story since I don't remember doing it the first time.
04-19-2018, 09:11 AM   #27
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QuoteOriginally posted by Bob 256 Quote
. . . got me to thinking so I popped a linear polarizer on my . . .
There's the answer you're lookin' for -- re-purpose some of that time you've 'saved' using digital AE and AF technology to do a little personal experimentation with your own gear and you'll either learn how and when to use what you have or or else you'll have a sound basis for future GBA attacks.

IMO the single greatest advantage of modern digital gear is the ability to 'chimp' and to make instant adjustments as you shoot. We used to chimp in the film era too (with both gear and in the darkroom); it just took hours or days (or sometimes weeks) to get the results back and required much greater patience and diligent record keeping to benefit from it.

My personal experience with film, filters, meters and flashes of all types was that time spent calibrating your equipment was the key to satisfactory results.
04-19-2018, 03:11 PM   #28
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I wonder about this thread, because the exact same topic has been finally discussed just two weeks ago:
The difference in brands of polarizing filters? - PentaxForums.com
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