Field Test - Purple Fringing of PL25/1.4 on EM1

Started Feb 3, 2015 | Discussions
slartz
slartz Senior Member • Posts: 1,691
Field Test - Purple Fringing of PL25/1.4 on EM1
2

Today I took my PL25 for a "field test" regarding the Purple Fringing issue on Olympus bodies (compared to the Panasonic bodies that have a better UV filter on their sensor...)

The purpose of the test was to see how much it is, and does it justify seeking out some of the complex solutions regarding a rear UV2 filter (front is problematic as noone is doing them in 46mm)

The test was conducted shooting leaves on a very bright sky - that always brings the worst of purple fringing

Conclusions:

  • Yes, the problem is there
  • It is very visible at f/1.4 - Even at a relatively small viewing size.
  • It is becoming much less apparent in f/2.0. In fact at first I thought at f/2.0 it's not there, but when viewing at 1:1 it is still definitely there.
  • It is gone completely by f/2.8. Even at 1:1 I could not see any of it. 

Bottom line for myself - I will not seek a UV2 filter for this lens (unless someone starts making high quality, multicoated, 46mm threaded ones).

The issue is really only annoying at f/1.4 in very high contrast situations which are already likely to justify stopping down. I mostly use it at f/1.4 at dark conditions/portraiture where this issue is not so dramatic.

If I will shoot landscape with this lens, I will stop down to f/2.8-4 anyway for the better sharpness.

In the remaining cases (probably single instances over the year...) - I will use PP to get rid of it.

I will repeat this test with the PL15/1.7 when I get it. Though I assume similar results

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Skeeterbytes Forum Pro • Posts: 12,001
Re: Field Test - Purple Fringing of PL25/1.4 on EM1

As a data point, the 75 fringes wide open with strong backlighting (E-M5/M1) and is likely a product of the lens design rather than any inherent camera shortcoming. Luckily, Lightroom's correction tool can usually handle it.

Cheers,

Rick

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Anders W Forum Pro • Posts: 21,466
Re: Field Test - Purple Fringing of PL25/1.4 on EM1
1

slartz wrote:

Today I took my PL25 for a "field test" regarding the Purple Fringing issue on Olympus bodies (compared to the Panasonic bodies that have a better UV filter on their sensor...)

The purpose of the test was to see how much it is, and does it justify seeking out some of the complex solutions regarding a rear UV2 filter (front is problematic as noone is doing them in 46mm)

The test was conducted shooting leaves on a very bright sky - that always brings the worst of purple fringing

Conclusions:

  • Yes, the problem is there
  • It is very visible at f/1.4 - Even at a relatively small viewing size.
  • It is becoming much less apparent in f/2.0. In fact at first I thought at f/2.0 it's not there, but when viewing at 1:1 it is still definitely there.
  • It is gone completely by f/2.8. Even at 1:1 I could not see any of it.

Since what we are talking about is essentially a form of longitudinal CA, it is expected to decline with the aperture (proportionally to its diameter to be precise). I would in this particular case expect the PF to be more pronounced towards the edges/corners than in the center (which is not always the case with respect to LoCA, as it is with LaCA). Did you look for that and if so, what was the result.

Bottom line for myself - I will not seek a UV2 filter for this lens (unless someone starts making high quality, multicoated, 46mm threaded ones).

I think Formatt would provide a Wratten 2A at 46 mm for you if you asked them. But I am not sure you'd be able to get one with multi-coating.

The issue is really only annoying at f/1.4 in very high contrast situations which are already likely to justify stopping down. I mostly use it at f/1.4 at dark conditions/portraiture where this issue is not so dramatic.

If I will shoot landscape with this lens, I will stop down to f/2.8-4 anyway for the better sharpness.

In the remaining cases (probably single instances over the year...) - I will use PP to get rid of it.

I will repeat this test with the PL15/1.7 when I get it. Though I assume similar results

 Anders W's gear list:Anders W's gear list
Panasonic Lumix DMC-G1 Olympus OM-D E-M5 Olympus E-M1 Panasonic Lumix G Vario 14-45mm F3.5-5.6 ASPH OIS Panasonic Lumix G Vario 7-14mm F4 ASPH +28 more
slartz
OP slartz Senior Member • Posts: 1,691
Re: Field Test - Purple Fringing of PL25/1.4 on EM1

Skeeterbytes wrote:

As a data point, the 75 fringes wide open with strong backlighting (E-M5/M1) and is likely a product of the lens design rather than any inherent camera shortcoming. Luckily, Lightroom's correction tool can usually handle it.

Oly and Pana have different approach regarding filtering of this type of purple. Olympus does that with some coating on the lens, whereas Panasonic does that with the UV filter placed in front of the sensor.

As a result, this type of purple fringing is less common with Olympus lenses on Olympus bodies or Panasonic lenses on Panasonic bodies. When using some of these Panasonic lenses on Olympus bodies, this becomes very apparent (the most famous of course it the Panasonic 7-14).

There is a solution brought by Anders W to place a UV[2] filter (either in front or in the rear of the lens) that eliminates this.

Of course PP can be used, but some of us prefer to use as little PP possible.

 slartz's gear list:slartz's gear list
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slartz
OP slartz Senior Member • Posts: 1,691
Re: Field Test - Purple Fringing of PL25/1.4 on EM1

Anders W wrote:

Since what we are talking about is essentially a form of longitudinal CA, it is expected to decline with the aperture (proportionally to its diameter to be precise). I would in this particular case expect the PF to be more pronounced towards the edges/corners than in the center (which is not always the case with respect to LoCA, as it is with LaCA). Did you look for that and if so, what was the result.

It's slightly more pronounced in the corners though it appears in the entire frame. I can later try and load some samples... I'm adding a sample image at the end of this message at f/1.4. You'll be able to see it is quite strong in the center as well.

Bottom line for myself - I will not seek a UV2 filter for this lens (unless someone starts making high quality, multicoated, 46mm threaded ones).

I think Formatt would provide a Wratten 2A at 46 mm for you if you asked them. But I am not sure you'd be able to get one with multi-coating.

I doubt I'll want to useĀ a filter which is not MultiCoated on the front of the lens as a regular filter. the cost of IQ in this type of filters is usually far greater than the issue of PF wide open... it's not like the horrendous 7-14 fringes ;). I could in theory just put one on if I get to such scenarios, but really if I get to such scenarios I can stop down a bit or PP

 slartz's gear list:slartz's gear list
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Skeeterbytes Forum Pro • Posts: 12,001
Re: Field Test - Purple Fringing of PL25/1.4 on EM1

Confess this is the first I've heard of filtration to combat fringing, as opposed to veiling flare (big purple blotches). I'm skeptical the 75's fringing wouldn't occur on a Panny body, but since I don't have one with which to make the test I'm open to the possibility.

Cheers,

Rick

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Anders W Forum Pro • Posts: 21,466
Re: Field Test - Purple Fringing of PL25/1.4 on EM1

Skeeterbytes wrote:

As a data point, the 75 fringes wide open with strong backlighting (E-M5/M1) and is likely a product of the lens design rather than any inherent camera shortcoming. Luckily, Lightroom's correction tool can usually handle it.

Any fast lens is likely to have some LoCA wide open. In the plane of focus, it is very well controlled on the 75/1.8 but in the OOF area just in front of that plane, it can get pretty bad.

However, on top of the LoCA inherent in the lens design itself, there is a special problem with purple fringing when using Pany lenses on Oly bodies. The optical CA correction of Pany lenses is premised on a stronger on-sensor UV filter than the one used on Oly bodies. Therefore, you can expect to see more PF when using a Pany lens on an Oly body than when using the same lens on a Pany body (or when using an Oly lens on a body of either brand). This problem can be eliminated by putting a strong UV filter (Wratten 2A) on the lens (or in front of the sensor inside the body if you are daring) so as to bring UV filtering up to the strength expected by Pany lenses.

 Anders W's gear list:Anders W's gear list
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Anders W Forum Pro • Posts: 21,466
Re: Field Test - Purple Fringing of PL25/1.4 on EM1

slartz wrote:

Anders W wrote:

Since what we are talking about is essentially a form of longitudinal CA, it is expected to decline with the aperture (proportionally to its diameter to be precise). I would in this particular case expect the PF to be more pronounced towards the edges/corners than in the center (which is not always the case with respect to LoCA, as it is with LaCA). Did you look for that and if so, what was the result.

It's slightly more pronounced in the corners though it appears in the entire frame. I can later try and load some samples... I'm adding a sample image at the end of this message at f/1.4. You'll be able to see it is quite strong in the center as well.

Yes, at f/1.4, I'd certainly expect to see some of it even in the center, especially in a maximally PF-prone scene like this. But I'd expect it to be worse at the edges and remain visible there for longer as you stop down.

Bottom line for myself - I will not seek a UV2 filter for this lens (unless someone starts making high quality, multicoated, 46mm threaded ones).

I think Formatt would provide a Wratten 2A at 46 mm for you if you asked them. But I am not sure you'd be able to get one with multi-coating.

I doubt I'll want to use a filter which is not MultiCoated on the front of the lens as a regular filter. the cost of IQ in this type of filters is usually far greater than the issue of PF wide open... it's not like the horrendous 7-14 fringes ;).

You mean the 7-14 purple flare (not fringes). And yes, that's worse and above all far more difficult to handle in PP.

I could in theory just put one on if I get to such scenarios, but really if I get to such scenarios I can stop down a bit or PP

 Anders W's gear list:Anders W's gear list
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OrdinarilyInordinate
OrdinarilyInordinate Veteran Member • Posts: 3,675
Re: Field Test - Purple Fringing of PL25/1.4 on EM1

Would it help to use a Hoya UV(0) HMC type filter, or UV(2) is needed?

EDIT: I guess it wouldn't help as much--just found this:

http://www.dpreview.com/forums/post/51786560

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slartz
OP slartz Senior Member • Posts: 1,691
Re: Field Test - Purple Fringing of PL25/1.4 on EM1

Anders W wrote:

It's slightly more pronounced in the corners though it appears in the entire frame. I can later try and load some samples... I'm adding a sample image at the end of this message at f/1.4. You'll be able to see it is quite strong in the center as well.

Yes, at f/1.4, I'd certainly expect to see some of it even in the center, especially in a maximally PF-prone scene like this. But I'd expect it to be worse at the edges and remain visible there for longer as you stop down.

I agree with you that I'd EXPECT it to be more apparent in the edges but it's only marginally the case. I'm looking now at the 1:1 view of the f/2. It's not visible (entire frame) in normal display, and it's visible at 1:1 in both center and corner, though not very strong. At f/2.8 it's not even apparent at 1:1 - either in corner or center. The diff is surprisingly small between center and corner.

 slartz's gear list:slartz's gear list
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slartz
OP slartz Senior Member • Posts: 1,691
Re: Field Test - Purple Fringing of PL25/1.4 on EM1

OrdinarilyInordinate wrote:

Would it help to use a Hoya UV(0) HMC type filter, or UV(2) is needed?

EDIT: I guess it wouldn't help as much--just found this:

http://www.dpreview.com/forums/post/51786560

Not only UV[0] doens't help...

interestingly enough - a polarizer did not help either. I thought it might as it swallows a lot of light to begin with, and I Assumed it may cut out some of the visible fringe light, but it doenst... I tried it with a Hoya HD CPL today and the same result appeared at f/1.4

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Anders W Forum Pro • Posts: 21,466
Re: Field Test - Purple Fringing of PL25/1.4 on EM1
1

OrdinarilyInordinate wrote:

Would it help to use a step-up ring and a good multi-coated filter, like Hoya UV(0) HMC?

Unfortunately, a Hoya UV(0) or any other ordinary UV or skylight filter won't help at all. You need something significantly stronger. A 2A (Wratten 2A) is the minimum strength I'd expect to have much of an effect. The slightly stronger 2E is likely to work as well but might be slightly overkill.

Regrettably, there seem to be no multi-coated 2As and 2Es on the market. Part of the explanation may be that these filters were originally meant for a very different purpose than the one we now use them (haze reduction in B&W film photography). And since that purpose isn't exactly "hot" these days, we might be grateful that they are available at all.

As to step-up as well as step-down rings, they will work fine as with any filter (as long as you don't step-down so much as to get vignetting).

But one other solution is to use a gel filter affixed by means of thin (not thick) double-sided adhesive tape on the ring surrounding the rearmost element of the lens. That's what I use with my 7-14/4 (where there is also the worse problem of purple flare to be reckoned with) although for that particular lens it is possible to get a special gel filter holder to keep the filter in place as you can see here. Gel filters aren't multi-coated either but their location at the rear might alleviate any problem with flare.

 Anders W's gear list:Anders W's gear list
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Anders W Forum Pro • Posts: 21,466
Re: Field Test - Purple Fringing of PL25/1.4 on EM1

slartz wrote:

OrdinarilyInordinate wrote:

Would it help to use a Hoya UV(0) HMC type filter, or UV(2) is needed?

EDIT: I guess it wouldn't help as much--just found this:

http://www.dpreview.com/forums/post/51786560

Not only UV[0] doens't help...

interestingly enough - a polarizer did not help either. I thought it might as it swallows a lot of light to begin with, and I Assumed it may cut out some of the visible fringe light, but it doenst... I tried it with a Hoya HD CPL today and the same result appeared at f/1.4

No a polarizer won't help either. It's not the amount of light per se that matters so the fact that the polarizer takes some away is of no consequence. Polarization is of no consequence either. It's just a matter of eliminating a certain span of wavelengths close to the UV borderline and only a so-called long-pass filter will do that and do it right if you find the proper strength.

When I originally researched the problem with purple flare when using the 7-14/4 on an Oly body, I didn't have a 2A available. Those were not all that commonly used even back in the film days (when they were employed to fight haze/increase contrast in long-distance shooting with B&W film) so I never bothered to get one. But fortunately, I had some other old filters meant for B&W film lying around since way back when, and eventually had the good idea of trying the weakest long-pass filter I happened to have: A Hoya yellow K2 filter. The purple flare with the 7-14 (which was the main issue back then) went away instantly and I knew we finally had a solution to that problem. After quite a bit of additional searching on the net, I eventually concluded that a 2A should be about the right strength, doing the job but not overdoing it. The fact that the same solution helps not only against the 7-14 purple flare (on Oly bodies) but also against purple fringing with Pany lenses on Oly bodies more generally was found out a little later.

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Anders W Forum Pro • Posts: 21,466
Re: Field Test - Purple Fringing of PL25/1.4 on EM1

slartz wrote:

Anders W wrote:

It's slightly more pronounced in the corners though it appears in the entire frame. I can later try and load some samples... I'm adding a sample image at the end of this message at f/1.4. You'll be able to see it is quite strong in the center as well.

Yes, at f/1.4, I'd certainly expect to see some of it even in the center, especially in a maximally PF-prone scene like this. But I'd expect it to be worse at the edges and remain visible there for longer as you stop down.

I agree with you that I'd EXPECT it to be more apparent in the edges but it's only marginally the case. I'm looking now at the 1:1 view of the f/2. It's not visible (entire frame) in normal display, and it's visible at 1:1 in both center and corner, though not very strong. At f/2.8 it's not even apparent at 1:1 - either in corner or center. The diff is surprisingly small between center and corner.

Good. The center-corner difference may well differ depending on which particular lens we are talking about and the 25/1.4 may have less of it than some others, especially those with a wider AoV.

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slartz
OP slartz Senior Member • Posts: 1,691
Re: Field Test - Purple Fringing of PL25/1.4 on EM1

Anders W wrote:

OrdinarilyInordinate wrote:

Would it help to use a step-up ring and a good multi-coated filter, like Hoya UV(0) HMC?

Unfortunately, a Hoya UV(0) or any other ordinary UV or skylight filter won't help at all. You need something significantly stronger. A 2A (Wratten 2A) is the minimum strength I'd expect to have much of an effect. The slightly stronger 2E is likely to work as well but might be slightly overkill.

Regrettably, there seem to be no multi-coated 2As and 2Es on the market. Part of the explanation may be that these filters were originally meant for a very different purpose than the one we now use them (haze reduction in B&W film photography). And since that purpose isn't exactly "hot" these days, we might be grateful that they are available at all.

As to step-up as well as step-down rings, they will work fine as with any filter (as long as you don't step-down so much as to get vignetting).

But one other solution is to use a gel filter affixed by means of thin (not thick) double-sided adhesive tape on the ring surrounding the rearmost element of the lens. That's what I use with my 7-14/4 (where there is also the worse problem of purple flare to be reckoned with) although for that particular lens it is possible to get a special gel filter holder to keep the filter in place as you can see here. Gel filters aren't multi-coated either but their location at the rear might alleviate any problem with flare.

Multicoating is not just about flare - it is also about reflectiveness of the glass - with a non multicoated filter, u have more rays that reflect of the rear element back, then from the front element again and into the sensor with an offset and some color spread (like a prism). it's of course not dominant, but may have some effect on contrast and color. This is of course enhanced greatly with "stray" light (even if not really "flaring").

The latter, of course, is irrelevant with rear element, and I also think there might be less problematic angled rays of light, but most importantly - I think gel filters are just so much better than glass filters in regard to their reflective characteristics, so that they do not need so much coating.

I thought about trying to either adapt that rear holder to the PL25/15 or to tape a filter on the back as some people did, but in all honesty, at least for this lens, this issue is so minor (only at f/1.4, high contrast) that I can really live with it without starting to "patch" the lens. I should get my PL15 next week and will see about that.

BTW - I also tested the Panasonic 35-100/2.8. I don't know if the lens is better designed, or simply because it only opens up to 2.8 - but Icould not really get any serious PF on it. at f/2.8, in the corner, at 1:1, if you REALLY hardpress me, I could find traces of it, but it's so light I would not even bother to postprocess...

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Anders W Forum Pro • Posts: 21,466
Re: Field Test - Purple Fringing of PL25/1.4 on EM1

slartz wrote:

Anders W wrote:

OrdinarilyInordinate wrote:

Would it help to use a step-up ring and a good multi-coated filter, like Hoya UV(0) HMC?

Unfortunately, a Hoya UV(0) or any other ordinary UV or skylight filter won't help at all. You need something significantly stronger. A 2A (Wratten 2A) is the minimum strength I'd expect to have much of an effect. The slightly stronger 2E is likely to work as well but might be slightly overkill.

Regrettably, there seem to be no multi-coated 2As and 2Es on the market. Part of the explanation may be that these filters were originally meant for a very different purpose than the one we now use them (haze reduction in B&W film photography). And since that purpose isn't exactly "hot" these days, we might be grateful that they are available at all.

As to step-up as well as step-down rings, they will work fine as with any filter (as long as you don't step-down so much as to get vignetting).

But one other solution is to use a gel filter affixed by means of thin (not thick) double-sided adhesive tape on the ring surrounding the rearmost element of the lens. That's what I use with my 7-14/4 (where there is also the worse problem of purple flare to be reckoned with) although for that particular lens it is possible to get a special gel filter holder to keep the filter in place as you can see here. Gel filters aren't multi-coated either but their location at the rear might alleviate any problem with flare.

Multicoating is not just about flare - it is also about reflectiveness of the glass

Same thing to me.

- with a non multicoated filter, u have more rays that reflect of the rear element back, then from the front element again and into the sensor with an offset and some color spread (like a prism). it's of course not dominant, but may have some effect on contrast and color. This is of course enhanced greatly with "stray" light (even if not really "flaring").

I have seen that hypothesis but I am not sure there is a whole lot to it. There is some evidence of this phenomenon (reflection with the sensor involved) with certain "legacy" lenses (not multicoated on the rear side of the elements) but the symptom I have seen confirmed in those cases is a blueish spot in the center with the lens well stopped down (f/8 or so). I am not yet convinced that the multiocolored (prism-like) spread you are talking about is due to this form of reflection.

The latter, of course, is irrelevant with rear element, and I also think there might be less problematic angled rays of light, but most importantly - I think gel filters are just so much better than glass filters in regard to their reflective characteristics, so that they do not need so much coating.

Could be. Don't know for sure.

I thought about trying to either adapt that rear holder to the PL25/15 or to tape a filter on the back as some people did, but in all honesty, at least for this lens, this issue is so minor (only at f/1.4, high contrast) that I can really live with it without starting to "patch" the lens. I should get my PL15 next week and will see about that.

Whether it's worth bothering with the filter is of course much a matter of how you use the lens. If you usually shoot scenes and/or at f-stops where PF isn't much of a problem in the first place, you have less reason to consider the filter solution.

BTW - I also tested the Panasonic 35-100/2.8. I don't know if the lens is better designed, or simply because it only opens up to 2.8 - but Icould not really get any serious PF on it. at f/2.8, in the corner, at 1:1, if you REALLY hardpress me, I could find traces of it, but it's so light I would not even bother to postprocess...

Doesn't surprise me. It is partly a matter of max aperture. But based on the samples I have seen, the 35-100/2.8 is extremely well corrected fo longitudinal CA, even in the OOF areas where it shows up rather clearly with most other reasonably fast lenses. Perhaps it even merits being called an APO lens even though it isn't labeled as one.

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