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04-07-2018, 06:42 PM - 1 Like   #31
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QuoteOriginally posted by Dewman Quote
the Hoya brand is heads and shoulders above all the rest.
Schott [ B+W ] would have a thing or two to say about that, I'm sure Lee filters would too.

04-08-2018, 03:05 AM   #32
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QuoteOriginally posted by amoringello Quote
Things change. Don't get stuck living in the past and repeating old information that no longer applies.
You didn't proof that the information are not correct.


QuoteOriginally posted by amoringello Quote
If first hand experience didn't "change the basics" the issue would still be present and this conversation would not be happening. Scientific studies are proven "wrong" all the time as more information becomes available, or as current technology changes.
First hand experience cover just a small area and not the whole topic. AF will be compromised in low light situations with LPL.


QuoteOriginally posted by amoringello Quote
"However, I actually have never seen an ill effect from mounting a linear; maybe it’s all not data, just lore."
Mounting a LPL isn't the topic, it's about the AF with LPL in low-light.


QuoteOriginally posted by amoringello Quote
The other link has this to say;
"If you have a modern AF SLR the answer is almost certainly "yes"."
Still thought of as not definitive,100% certainty. It is quite possible there is no effect, as many will attest to.
The page is also heavy on description of film and slide. So maybe out of date??
PDAF technology has evolved since film days, but not changed in construction yet.
Maybe Image sensors with integrated PDAF sensors can change that.


QuoteOriginally posted by amoringello Quote
Sorry, but until you can borrow a LP (no need to buy something you won't use, jeesh) and give us your first hand results, I really don't put a lot of faith in your opinions, over first hand experiences.
I don't have to proof anything, since yoU#re the only one not believing public information but someone without any professional optic background who'd try something and didn't see anything.
Metering sensors have problems with polarized light rays, so that's another point why CPL instead of LPL on AF cameras.
Lineare und zirkulare Polfilter
Welcher Polfilter ist richtig ? linear oder zirkular? » Objektive24.de Blog
Der Polfilter in der modernen Digital-Fotografie - nützlich oder überflüssig? - gwegner.de
Wie funktioniert ein Polfilter? - Objektivfiltertest
Polarisationsfilter - Mythos und Praxis
04-08-2018, 04:57 AM   #33
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QuoteOriginally posted by angerdan Quote
... since yoU#re the only one not believing public information but someone without any professional optic background who'd try something and didn't see anything.
Only if you choose not to read nor understand what has been written...

You also know nothing of my background nor that of the background of the people I have spoken with.
Don't you dare pull that sort of thing without first presenting your own qualifications and professional credentials.
It's both ignorant and rude.

Who are you that anyone should pay any attention to your *opinions*, other than being one who can Google for a few links to pages with old and weak information? At least presenting some first hand experience would foster a bit of credibility.

Sadly, I probably won't take the time to translate the latest set of links.
Do any of these contain a scientific study and comparison with modern technology?
If it's just more repeated lore built upon old tech, they aren't worth the time.
04-08-2018, 05:59 AM   #34
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QuoteOriginally posted by amoringello Quote
Don't you dare pull that sort of thing without first presenting your own qualifications and professional credentials. It's both ignorant and rude.
Who are you that anyone should pay any attention to your *opinions*, other than being one who can Google for a few links to pages with old and weak information? At least presenting some first hand experience would foster a bit of credibility.
Do any of these contain a scientific study and comparison with modern technology?
If it's just more repeated lore built upon old tech, they aren't worth the time.
That's the difference between science and religion. One can believe or stick to proven facts. Personal insults shouldn't be used in a forum, respect should be. You can find this in the forum rules.
You don't need to ask about scientific studies, because you believe in some tests which only lits one of many aspects of LPL. Where are your asked scientific studies about linear polarizers don't effect exposure measuring or AF at all?
Again, basics like aperture or PDAF sensors don't change much, so the age of informations from the AF era isn't that relevant like with image sensor technology.

04-08-2018, 06:19 AM - 1 Like   #35
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Here's another 2 pence worth, generated from both internet and personal research (which gleaned me some odd looks from my wife...).

The Bob Atkins article is interesting but maybe needs taking with a pinch of salt, as checking on the Wayback Machine reveals the article to be substantially unchanged since 2008, so his references to "a modern AF SLR" are actually to ten year old technology.

Once again I've mounted up both a linear and CPL filter to my K-1 and M85/2, as I don't have an AF lens which fits the filters. So, just on exposure, the linear gave me between 1/60 and 1/40, where the CPL gave 1/50 at all angles. With both I could see a distinct colour shift (blue to yellow) in the OVF as I turned the filter. Images taken at fixed WB and 1/40 don't show a colour shift and appear very similar, though there's some evidence I didn't quite achieve non-polarised incoming light.

I could conceive of very tricky subjects where the complementary colour shift at the AF sensor might fool it, but it was subtle, so I think you'd be in trouble with the AF anyway.

As noted before, this is one person's actual experience with a 2016-model DSLR. In all but exceptional circumstances I'd guess one could ignore the +/-0.25 stop apparent possible exposure error. I'd be very interested to hear of similar experiments done by someone using a 2008-vintage DSLR, both for exposure and AF, and of course something modern for AF.

As ever, while it's worth getting others' opinions so as not to waste your time and money, there's no substitute for trying stuff out yourself so you know how your kit (mis)behaves in likely scenarios, so you can shoot with confidence when the moment is fleeting...

Cheers

Jonathan
04-08-2018, 06:22 AM   #36
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QuoteOriginally posted by amoringello Quote
I'm hoping Pentax doesn't use plastic lenses.
Hybrid aspherical elements have been used in Pentax lenses for some time now, they are basically a shaped high optical grade polycarbonate plastic bonded to a glass substrate. The highly regarded DA15mm f/4 Limited ASPH has one.

QuoteOriginally posted by angerdan Quote
Mounting a LPL isn't the topic, it's about the AF with LPL in low-light.
If it has no effect on AF in good light, chances are the use of a Linear PL filter will have negligible effect on AF in low light. In any case, who would want to use a PL filter in dim lighting anyway?

QuoteOriginally posted by angerdan Quote
AF will be compromised in low light situations with LPL.
My own experience with Linear PL filters used on Canon, Nikon,Leica and Pentax AF cameras proves the explicit requirement for a circular polarisers for accurate AF and AE are long behind us. There have been only a handful of cameras where that caveat applied.
04-08-2018, 07:35 AM   #37
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QuoteOriginally posted by angerdan Quote
Lineare und zirkulare Polfilter
Welcher Polfilter ist richtig ? linear oder zirkular? » Objektive24.de Blog
Der Polfilter in der modernen Digital-Fotografie - nützlich oder überflüssig? - gwegner.de
Wie funktioniert ein Polfilter? - Objektivfiltertest
Polarisationsfilter - Mythos und Praxis
First one: 2005-2009, no evidence quoted/linked
Second one: 2012, no evidence
Third one: 2015, no evidence, though there's an evidence-free assertion in the comments that "really modern mirrorless system cameras work perfectly with linear polarizing filters" (my italics)
Fourth one: no reliable date that I can see, no evidence
Fifth one: 2016, no evidence

QuoteOriginally posted by angerdan Quote
Again, basics like aperture or PDAF sensors don't change much
Which is not quite the same as saying they don't change at all... Maybe a "minor change" is that they now work OK with LPL filters.
QuoteOriginally posted by Digitalis Quote
My own experience with Linear PL filters used on Canon, Nikon,Leica and Pentax AF cameras proves the explicit requirement for a circular polarisers for accurate AF and AE are long behind us. .
Hooray, there's at least two of us who've actually tried it then!
QuoteOriginally posted by Digitalis Quote
There have been only a handful of cameras where that caveat applied.
Is it possible to give an example or two? Is this fairly historical now or are there any current models out there?
QuoteOriginally posted by kaseki Quote
OK, I'll bite, being old. On page 71 of the 645N Operating Manual, a paragraph on polarizing filters concludes with: "Use a CIRCULAR POLARIZING FILTER for proper autofocus operation."
Thanks for that. So the manufacturer themselves recommended it, on a camera introduced in 1997; I've just checked the PDF manual for the 645N II (2001) and that repeats the advice, on page 85. That gives us a reference point to work from.

This is probably one of those debates where the answer is more interesting than useful, as it appears fairly unlikely that any of us is going to be caught out by using an LPL filter on a camera old enough to be affected. But I'm still interested to know when the advice was first given, by whom, and when (or more usefully, for/from which models) it became irrelevant.

Cheers

Jonathan

04-08-2018, 08:10 AM - 1 Like   #38
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QuoteOriginally posted by h4yn0nnym0u5e Quote
Is this fairly historical now or are there any current models out there?
Little more than a historical footnote these days, The Canon A-1 [ C.1971] and The Canon Pellix [C.1965] and the subsequent Pellicle based Canon and Nikon F mount SLRs and later the Canon EOS RT [C.1989] would experience AE and AF anomalies when linear polarisers were used. There are some Pellicle mirror based Sony cameras: but at that point in time circular polarisers were ubiquitous and thus, there were only isolated and easily remedied AF and AE issues regarding Linear Polariser filters.

I still have a mix of circular and linear polarisers in my photography kit, all are of the highest quality. Most of the linear pol filters I have are for lenses with bizarre filter diameters* or require bayonet filters.

*53mm,80mm,87mm,44mm,51mm,112mm,103mm,69mm all verified with digital calipers- I suppose the lens manufacturers used such threads the ensure that people would only buy their filters.

Last edited by Digitalis; 04-08-2018 at 08:24 AM.
04-08-2018, 04:56 PM   #39
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QuoteOriginally posted by angerdan Quote
Model line of an filter brand has more influence about the quality than the brand.

Every Made in Germany filter I have owned has been top quality, far better than most made elsewhere.

Chris
04-08-2018, 10:47 PM - 2 Likes   #40
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This continuing argument is hard to believe. I have no dogs in the linear vs. circular fight for cameras I do not own, but I do not think the case has been made for circular polarization belonging to the scrap heap of history.

First, there are members here who shoot with film with autofocus (AF) cameras. The fact that a camera was built before 2005 or some other arbitrary date doesn't automatically designate it as obsolete.

Second, if the light path used for auto focus involves one or more mirrors, and one such mirror is not actually silvered, but dielectrically coated to act like a mirror over some wavelength band, it will be polarization sensitive, particularly near Brewster's angle of incidence. (This is true of any surface where a transition between two indices of refraction is present.) If there weren't such an effect in the AF path, there would never have been any reason to use circular polarization to ensure that light is available in both polarization directions when exiting the lens.

Third, it seems extravagant to believe that an entire filter industry would continue to "waste" resources providing the added coatings needed to synthesize an effective quarter wave plate behind the polarizing sheet material if there were no merit to doing so because the requirement for circularity -- restoring light with both directions of polarization -- was a photographic old wives tale.

Fourth, I have provided a reference from Pentax for the 645N (film camera) asserting the need. Do we have a reference from any of you with 645D or 645Z cameras where circular polarization is explicitly no longer required or not mentioned at all in their respective Operating Manuals? Any other AF Pentax camera? Are you certain that accurate P-TTL measurement is equally immune to polarization effects as you are that AF is immune? Are the dielectric color coatings on your imaging arrays unaffected by polarization for the more extreme ray angles at the edges of the field of view, or even at the center of the field of view for short focal-length lenses?

Last, should we believe that the effort put into the measurements at Polarizing filters test 2015 - Introduction - LensTip.com referenced earlier in this thread was performed in 2015 just for nostalgia's sake?
04-09-2018, 12:37 AM   #41
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I have been using a Lee 100X100mm linear polariser filter with just about every camera and lens the Lee filter system is suited for - some cameras were manual AF and AE cameras, and some had highly advanced AF and AE systems.

I cannot recall if I have ever experienced difficulties that were a direct result from the use of a linear polariser filter. While I work with a lot of cameras, I can tell if any of them are misbehaving as I exhaustively calibrate the AF of each camera and lens combination.

QuoteOriginally posted by kaseki Quote
it seems extravagant to believe that an entire filter industry would continue to "waste" resources providing the added coatings needed to synthesize an effective quarter wave plate behind the polarizing sheet material if there were no merit to doing so because the requirement for circularity
What do filter companies stand to gain by offering a plethora of exclusively circular polarising filters?

Simple: Money. I know, this sounds like the proselytizing of a foil hat wearing conspiracy theorist. But i'm coming up short on ideas on why Hoya,B+W,Marmumi,Tiffen,Cokin,Signh-ray et al would be doing this if the advice is utterly outmoded.
04-09-2018, 07:12 AM - 2 Likes   #42
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Addendum

On page 2 ( Polarizing filters test - About light and polarization - LensTip.com ) of the 08.2009 study report referenced by the 2015 study, the need for circular polarization is described with DSLRs included in the scope of the argument. A useful diagram is included.

On the other hand, I just rummaged through an on-line copy of the 645D Operating Manual and there seems to be no mention of filters in any of the places where I might expect to find such a description. This may be an oversight, or an indication that the generic optical layout of the 08.2009 study doesn't apply to the 645D.

On the third hand, In SMC PENTAX-DA INTERCHANGEABLE LENS OPERATING MANUAL, page 21, there is the text: "Use a circular polarizing filter with Autofocus camera for proper exposure and autofocusing." Filters - Pentax Digital Camera Lens Operating Manual [Page 21]
This message is repeated on page 14 of a shorter lens manual PENTAX DA Operating Manual (Page 14 of 20)

Without checking all Pentax lens manuals, my preliminary conclusion is that Pentax intends that the output of the polarizing filter be circularly polarized.
04-09-2018, 08:20 AM   #43
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Kaseki is right. I, too, have seen variations and errors in exposure metering with linear polarizers that don't occur with circular ones. And the physical cause is the use of half-silvered reflex mirror (splitting the light between the focusing screen & AF system) which reflects more of one polarization than the other.

The upshot is that the rotation angle of a linear polarizer that causes over-exposure readings will also cause the AF system to get less light than it would if a CPL were being used. That will degrade AF performance especially in low light situations. That said, today's AF systems have such good low-light performance, that it's unlikely that most photographers would notice any difference in AF performance. It would take careful scientific tests could detect the difference and we all know how hard it is to measure AF performance.
04-09-2018, 09:11 AM   #44
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Found hints to the silver foil too.
Digicam Dictionary - Steve's Digicams
steves-digicams.com/pdf/digi_dictionary.pdf#page=18
Polarizers - Luminous Landscape
ars-imago.ch/productinfos/BWCompleteBrochure_e.pdf#page=17
schneideroptics.com/pdfs/filters/BWHandbook.pdf#page=15
heliopan.de/wp-content/uploads/Heliopan-Filters.pdf#page=6
http://www.hoyafilter.com/hoya/products/generalfilters/plplcir/

Besides the explanations from B+W/Schneider Optics, Rodenstock has a more advanced describtion.
rodenstock-photo.com/Archiv/Quality filters english low res.(2MB)pdf.pdf#page=4
allphotolenses.com/public/files/pdfs/f81191e91dc75b4eea917b48147da4c7.pdf#page=2
QuoteQuote:
What are the advantages of circular polarizing filters?
Circular polarizing filters are linear polarizing filters with an additional “l/4 plate” which converts the light leaving the filter into circularly polarized light.
This is necessary in cameras with a beam splitter to visualize a portion of the light for the TTL exposure measurement or autofocus measurement.
These cameras namely also cause polarizing and, depending on the rotation of the polarizing filter, would attenuate or block the light diverted for the measurement and would result in overexposure or would prevent focusing.
Circular polarizing filters are an absolute necessity for single-lens reflex cameras.

Last edited by angerdan; 04-09-2018 at 09:17 AM.
04-09-2018, 02:24 PM - 1 Like   #45
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I'd like to think this isn't particularly a fight that you'd need a dog for! I see it mostly as a quest for The Truth* - though maybe a bloodhound to sniff it out would be handy...

Reasonably established facts so far as I can tell - please do correct me if I've put something inaccurate:
  • There has been a period when CPL filters were recommended for at least some cameras for good reason. Digitalis's knowledge suggests this was at least 1965-1989, and the 645N and N II manuals repeated it in 1997 and 2001
  • The physics of why there could be a problem, as explained on various sites, makes sense
  • Both LPL and CPL filters are still available. A quick look at the features of Hoya and Dynasun (who?) LPLs on Amazon both contain the advice to use with "manual" cameras.
  • My personal experiments suggest that there is an effect even with a modern camera (K-1), though it's minor
  • Quite a lot of the literature available on the web is fairly dated; the Rodenstock filter PDF is 2006, the Bob Atkins article is 2008, the LensTip article was originally 2009 and did NOT test for effects on AF or metering. Finding more instances of dated information does not constitute adding to the weight of the evidence, one way or the other

Now a bit of speculation:
  • There doesn't seem to be ANY comparative test on the web documenting experiments with a variety of cameras to show which are affected, and by how much. (I'd love to be proved wrong on this point...)
  • More modern cameras are significantly less problematic with LPL filters. We have my experiments, Digitalis's experience and kaseki's observation that the 645D manual no longer mentions them
  • It therefore seems likely that camera manufacturers have taken steps to mitigate the problem, possibly because they got fed up with people "getting into trouble" by using LPLs when the manual said not to, possibly because AF and exposure being sensitive to polarised light gave problems even when a polarising filter wasn't being used
  • Assuming CPLs work pretty much as well as LPLs, it makes sense for filter manufacturers to offer only CPLs, because they should work on anything no matter its vintage, and no manufacturer wants to make more products than is strictly necessary. The up to date version of the Rodenstock filter brochure (August 2017) doesn't offer an LPL option
  • As noted by photoptimist, it's pretty hard to measure the effect on AF. I suppose one could make a setup which compensated exactly for the ND effect, and then try it...
  • If you're interested in using vintage equipment, it would make sense either to use CPLs or at least test LPLs before using them on an important shoot, just in case your kit is affected

Cheers - and release the hounds!

Jonathan


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