polarized filter issue

[Bobo Hodls]

Well, there are only three alternatives, poor equipment, incorrect technique or optical physics property of the hardware, but I don’t think its any kind of birefringence. I can see that in the second photo the top left and bottom right corners look sharper than the rest of the image. If it was me I would put the camera on a tripod, remove the filter and hold half of it over the lens with my fingers, then rotate it in quarter-turns for four test shots.

Or just buy a new filter.

A keen observation about the corners, I think I'll try yours suggested experiment, just for the heck of it.

Bob (and all)

A bit more about the setup for the comparison 'tree' shots: I used a tripod, the camera was in apeture priority mode and OIS was set to the ON position. So in A mode at f5.6, the first tree shot without filter was 10/1000sec, and the second shot with the filter was 10/3200sec..... so addition of the filter is something on the order of losing 1 1/3 stops? Obviously, this old filter is not of suitable quality. Will a typical high(ish) quality polarized filter block the same order of light? or is what I'm seeing just another side effect of the lens quality?

The first shot was actually 10/10000s (1/1000s).

You have not yet determined the filter is inadequate, and most polarizers are expected to hold back about 1.5 stops of light. It may well be, but your technique needs to be verified.

OIS while on a tripod is asking for trouble, try it w/o OIS enabled with and w/o polarizer.

--
...Bob, NYC
http://www.bobtullis.com

"Well, sometimes the magic works. . . Sometimes, it doesn't." - Little Big Man
.

 

[Jim T]

Did you try setting OIS off. When using a tripod OIS can introduce something like this.

Well, there are only three alternatives, poor equipment, incorrect technique or optical physics property of the hardware, but I don’t think its any kind of birefringence. I can see that in the second photo the top left and bottom right corners look sharper than the rest of the image. If it was me I would put the camera on a tripod, remove the filter and hold half of it over the lens with my fingers, then rotate it in quarter-turns for four test shots.

Or just buy a new filter.

A keen observation about the corners, I think I'll try yours suggested experiment, just for the heck of it.

Bob (and all)

A bit more about the setup for the comparison 'tree' shots: I used a tripod, the camera was in apeture priority mode and OIS was set to the ON position. So in A mode at f5.6, the first tree shot without filter was 10/1000sec, and the second shot with the filter was 10/3200sec..... so addition of the filter is something on the order of losing 1 1/3 stops? Obviously, this old filter is not of suitable quality. Will a typical high(ish) quality polarized filter block the same order of light? or is what I'm seeing just another side effect of the lens quality?

steve

 

[micksh6]

Sure filter effect may depend on focal length. I suppose it has something to do with magnification. If you photograph small spot at the same distance with wide and telephoto lenses the spot will look bigger with telephoto. Same is with filter imperfections - they are magnified with longer focal length.

Several months ago when I found out how crappy filters can ruin pictures I shot resolution chart with different lenses.

And, for example, $15 Polaroid CPL was not noticeable on 20mm lens but significantly degraded sharpness on 50mm lens.
http://forums.dpreview.com/forums/read.asp?forum=1023&message=39132232

Take a picture of resolution chart with and without filter at different focal length and you will see. The resolution chart will likely show that bad filter will affect microcontrast even at short focal length. You may or may not notice it on real images depending on how you look, but the image quality will not be optimal with bad filter. Cheap filter will eventually hit you when you will want to crop your photo or to resolve some fine details.

Once I did these tests I ditched all my cheap filters. Bought B+W MRC and top of the line Marumi (2filters.com is a good place to buy). These don't make noticeable impact on image quality. I can even stack several of them (I tried up to 3 without significant impact).
http://forums.dpreview.com/forums/read.asp?forum=1041&message=39428099

PS. Polarizer will reduce the light by between 1.1 and 1.5 stops depending on how much light is polarized. You may see metered exposure changing when you rotate polarizer.

 

[Klarno]

I've had it since the slr days. Maybe someone can offer up a technical reason why this is causing an issue?

I'm surprised you have a problem with m4/3 but it could possibly be that the filter is a linear polarising filter, and you were using automatic focussing. If your SLR was manual focus and was not using a split image system. you would never have known you were probably going to have a problem in the far distant future. But your m4/3 isn't using split image either, which is why I'm surprised,

My guess is that the problem became apparent above 100mm simply because that is when a focus issue would come into play when shooting at that distance.

Two possibilities:

Your camera may have alternative focussing methods and one of the others may work.

If you try a circular polarising filter, you will probably find all is well.

I have no problem using a linear filter on a P&S and I understand that they are only a problem on DSLRs.

Anyway, I'm very relieved that it's not an issue with the lens!!

And the filter is probably fine too - on another camera. But, if it is a circular, then who knows?!

There's some confusion here that I have to resolve.

For the same reason that polarizers cut reflections on glass, water, etc. linear polarizers also can cut reflections off of the semisilvered mirror that exists in all autofocusing DSLRs. This impacts metering and composition but not autofocus (which is dependent on light passing through the mirror). If you shoot with an SLT instead of a DSLR, the problem is reversed; metering is fine, but as autofocus is dependent on reflection off of the semisilvered mirror, you may have autofocus performance issues crop up sooner.

Circular polarizers are comprised of two layers-- a linear polarizer and a quarter wave plate. First light passes through the linear polarizer, that's what gives you the desired visual effect. Then it passes through the quarter wave plate, converting that light into circularly polarized light--which is, for the purposes we care about, not polarized. Its behavior with transparent reflective surfaces doesn't change based on its angle.

When you're shooting on a camera that doesn't have a semisilvered mirror, it doesn't matter what kind of polarizer you use. They'll both work equally well. If you also want to use it on a DSLR or an SLT, buy circular. If you're sure you'll never have a lens that size for a DSLR or SLT, buy linear and save a few bucks.

Generally, linear polarizers and circular polarizers in the same product group will have equal strength. The strength is dependent on the linear polarizing film used, and this film is typically made by a big materials company such as 3M.
--
http://www.photoklarno.com

 

[Midnighter]

Ahhh... ! OFF and repeat. OIS does not like living on a tripod, not at all. I think the gremlins inside the lens that move the element to compensate for hand movement become enraged when the camera is rock solid still.

lowpine wrote:

A bit more about the setup for the comparison 'tree' shots: I used a tripod, the camera was in apeture priority mode and OIS was set to the ON position.

 

[weesam]

Bobs on the money here.

Polarisers give you a two-stop penalty.

Stick the camera on a tripod (or better stuck snugly deep in a bean bag!) so there is no movement at all . Switch all the image stabilisation to off. Switch on the anti-shock device on your camera, preferably 5 or 6 seconds for this test.

Then shoot. Don't go near the camera until the photo has been taken. If it is windy stand as a wind break for the camera. (telephoto shots need very little movement to be ruined, and wind can and will blur a shot!)

Your image should be perfectly sharp. If it isn't sharp, then maybe you do have a dodgy filter, but I doubt it. Those images look like camera shake rather than image degradation (which is usually manifest as loss of contrast and detail rather than blur).

Sharp telephoto shots are not easy. Take a little bit of practice to get the knack, if you are handholding knowing how to brace the camera against your body and what shutter speeds are good; and if on a tripod, setting up for minimum shock and movement when you hit the shutter.

 

[weesam]

so addition of the filter is something on the order of losing 1 1/3 stops? Obviously, this old filter is not of suitable quality. Will a typical high(ish) quality polarized filter block the same order of light? or is what I'm seeing just another side effect of the lens quality?

light is a travelling electromagentic wave. As it travels forwards in one dimension, "corkscrews" in the other two dimensions. Your filter "filters out" one of these dimensions, so the intensity of the light is reduced accordingly, plus you lose a bit because the filter, like any such object, is not totally transparent. (cheaper filters may be less transparent than more expensive ones, but it is not always the case, and the effect is so minimal, and the improvement in image quality by using one makes it not worht worrying about.

So, you will ALWAYS lose light with a polariser. If you have two polarisers put them together see what happens when you rotate them.

 

[lowpine]

The first shot was actually 10/10000s (1/1000s).

You have not yet determined the filter is inadequate, and most polarizers are expected to hold back about 1.5 stops of light. It may well be, but your technique needs to be verified.

OIS while on a tripod is asking for trouble, try it w/o OIS enabled with and w/o polarizer.

--
...Bob, NYC
http://www.bobtullis.com

"Well, sometimes the magic works. . . Sometimes, it doesn't." - Little Big Man
.

Out at the river I did try a couple with the OIS off (and filter on as I didn't suspect it being an issue at the time), these were blurry too. I did not try any on the tripod with OIS off. I'll try your suggestion.

thanks!

 

[Bobo Hodls]

Out at the river I did try a couple with the OIS off (and filter on as I didn't suspect it being an issue at the time), these were blurry too. I did not try any on the tripod with OIS off. I'll try your suggestion.

Weesam went into more depth about technique, which I was assuming didn't need to be said. But it all matters when isolating such results, so do heed those practices.

--
...Bob, NYC
http://www.bobtullis.com

"Well, sometimes the magic works. . . Sometimes, it doesn't." - Little Big Man
.

 

[lowpine]

thanks again to all that have provided input, in as far as the effort to isolate the issue and for the additional info..... On to the latest set of shots.

OK, I think this was the suggested method? tripod, stable ground, out of wind; timer; manual mode to keep the shutter at 1/800 for all shots. For some unkown reason I had the iso at 800, meh.
Shot A: OIS ON, polarizer ON
Shot B: OIS OFF, polarizer ON
Shot C: OIS ON, polarizer OFF
Shot D: OIS OFF, polarizer OFF

I have to tell ya, I think the filter is the cause of the blur problem... plus it's got some kind of discoloration in the corners, especially apparent in the sky. Earlier someone noted that the corners were more in focus the center of the frame with the filter.

Shot A: OIS ON, polarizer ON





Shot B: OIS OFF, polarizer ON





Shot C: OIS ON, polarizer OFF





Shot D: OIS OFF, polarizer OFF





steve

 

[weesam]

did you manually focus with the live view to X10 or so?

was it blurred then - or just after the shot?

 

[Midnighter]

Must be the filter.

 

[kenw]

Yeah, that looks like it is the filter unless there was some sort of gross focus error.

Can I ask one favor, if you end up deciding to throw away this filter please send it to me instead - I'm curious and will pay shipping!
--
Ken W
See plan in profile for equipment list

 

[micksh6]

did you manually focus with the live view to X10 or so?

was it blurred then - or just after the shot?

Obviously filter does the blur. It doesn't matter how you focus. If you focus manually the blur will be visible in magnified live view. You can only notice it if you know how sharp the view should be without filter.
But I bet OP used AF and didn't look at magnified view.

Besides, all these fears about leaving OIS on tripod are exaggerated. I agree that IS should generally be disabled on tripod. But chances of blurring the picture with IS on tripod are low, especially with such fast shutter speed as OP uses.

Anyway, this is exactly what some bad polarizers do to the picture. I don't know what additional proof is needed.

 

[LincolnB]

Yes, the shots without the filter look sharper but none of the shots look sharp. They're all hazy and lack contrast, with or without the filter. Perhaps ther's a lens flare thing going on or something. So I think this is not a conclusive test unless you're trying to figure out the best technique for shots that are going to come out hazy anyway.

Are these shots cropped?

 

[lowpine]

did you manually focus with the live view to X10 or so?

was it blurred then - or just after the shot?

Obviously filter does the blur. It doesn't matter how you focus. If you focus manually the blur will be visible in magnified live view. You can only notice it if you know how sharp the view should be without filter.
But I bet OP used AF and didn't look at magnified view.

Besides, all these fears about leaving OIS on tripod are exaggerated. I agree that IS should generally be disabled on tripod. But chances of blurring the picture with IS on tripod are low, especially with such fast shutter speed as OP uses.

Anyway, this is exactly what some bad polarizers do to the picture. I don't know what additional proof is needed.

I did use AF.

I agree with your estimation. I couldn't see much of any difference in sharpness or blur between C and D, OIS ON and OFF respectively. It seems it doesn't matter if the OIS is on with a tripod.

 

[lowpine]

Yes, the shots without the filter look sharper but none of the shots look sharp. They're all hazy and lack contrast, with or without the filter. Perhaps ther's a lens flare thing going on or something. So I think this is not a conclusive test unless you're trying to figure out the best technique for shots that are going to come out hazy anyway.

Are these shots cropped?

not cropped.

It was noon hour with overhead light, a bit of a hazy day to begin with, then I shot over the river. This wasn't an exercise in composition or getting the sharpest image, just trying to determine if the polarized filter is causing the blur at long focal lengths.

OK, what would be a conclusive test then? I'm satisfied that the filter is no good over 100mm, at shorter focal lengths it's OK but I don't have high expectations.

 

[LincolnB]

I think a more conclusive shot would be one that's closer to what you'd consider a "keeper, something that had acceptable sharpness. As in: sample "A" with the filter is unacceptably fuzzy, sample "B" without the filter is acceptably sharp.

Yes, the shots without the filter look sharper but none of the shots look sharp. They're all hazy and lack contrast, with or without the filter. Perhaps ther's a lens flare thing going on or something. So I think this is not a conclusive test unless you're trying to figure out the best technique for shots that are going to come out hazy anyway.

Are these shots cropped?

not cropped.

It was noon hour with overhead light, a bit of a hazy day to begin with, then I shot over the river. This wasn't an exercise in composition or getting the sharpest image, just trying to determine if the polarized filter is causing the blur at long focal lengths.

OK, what would be a conclusive test then? I'm satisfied that the filter is no good over 100mm, at shorter focal lengths it's OK but I don't have high expectations.

 

[kenw]

I think a more conclusive shot would be one that's closer to what you'd consider a "keeper, something that had acceptable sharpness. As in: sample "A" with the filter is unacceptably fuzzy, sample "B" without the filter is acceptably sharp.

Personally I'd say this test was that. Did you click on "Original" and compare the two side by side at 100% ? The polarizer shots are absolutely horrible - nothing subtle at all about it. The non-polarizer are sharp (if low contrast) and the polarizer shots are really, really, really soft.

--
Ken W
See plan in profile for equipment list

 

[lowpine]

I think a more conclusive shot would be one that's closer to what you'd consider a "keeper, something that had acceptable sharpness. As in: sample "A" with the filter is unacceptably fuzzy, sample "B" without the filter is acceptably sharp.

Yes, the shots without the filter look sharper but none of the shots look sharp. They're all hazy and lack contrast, with or without the filter. Perhaps ther's a lens flare thing going on or something. So I think this is not a conclusive test unless you're trying to figure out the best technique for shots that are going to come out hazy anyway.

Are these shots cropped?

not cropped.

It was noon hour with overhead light, a bit of a hazy day to begin with, then I shot over the river. This wasn't an exercise in composition or getting the sharpest image, just trying to determine if the polarized filter is causing the blur at long focal lengths.

OK, what would be a conclusive test then? I'm satisfied that the filter is no good over 100mm, at shorter focal lengths it's OK but I don't have high expectations.

both A and B have the polarized filter, C and D don't......