polarized filter issue

I was out at the river this past weekend hiking with the wife and kids, of course snaping photos. I'm using the gh2 with the 140. I started to notice that anything over 100mm was slightly out of focus. I tried upping the shutter speed, setting the camera on a rock with timer, nothing seemed to help.

I got home and examined the photos, sure enough, everything over 100mm was blury. I looked back thru my photos to do a comparison. I previously had crisp focus on images at 140mm, but none focused out to infinity. Ugh, maybe I have a bad lense, or I've changed a setting? What has changed? I couldn't think of anything I've done.





Today, I wanted to try a more controlled experiment to try and figure out what was going on. I set up my tripod on the front porch and proceeded to take photos at various focal lengths, 14, 25, 50, 70, 100, 140. Then it hit me as I was taking off the lens cap.... I put on a polarized filter yesterday. I shot a round without the filter, then put the filter back on. Sure enough, things stay clear without the filter but, they started getting blury with the filter beyond 100mm.

I'll spare you all the focal lengths and jump straight to 140mm.

Without the polarized filter:





With the polarized filter:





Anyone else experience this? I recall others using a polarized filter. It's a promaster spectrum 7, I've had it since the slr days. Maybe someone can offer up a technical reason why this is causing an issue?

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

thanks,
Steve

lowpine said:

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

Click to expand...

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.

lowpine said:

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

Click to expand...

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

Looks like a bad quality filter, quite a noticeable color cast there as well.

I'd get a good quality filter.
--
http://www.flickr.com/photos/30225435@N00/

Likely just a bad filter. Linear polarizers work fine with the m4/3 cameras a circular polarizer is needed for a slr type AF camera and since m4/3 isn't an slr the linear or cicular both work.

nickoly said:

lowpine said:

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

Click to expand...

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.

nickoly said:

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

Click to expand...

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

Click to expand...

On reflection, I reckon you're right.

Jim T said:

Likely just a bad filter.

Click to expand...

I haven't experienced this myself, but I have seen more than one example of it happening with telephoto lenses and so-so quality polarizers. This is a pretty dramatic example, I think I may have seen something this dramatic with the Canon 100-400L once a few years back on the Fred Miranda forums. Usually the problem is more subtle.

I've never heard a compelling reason for why this occasionally happens though!
--
Ken W
See plan in profile for equipment list

I have a G2 and G3 have used both cameras with a circular polarizing filter and have never had this issue.
--
Ellen McIlroy

Jim T said:

... Linear polarizers work fine with the m4/3 cameras a circular polarizer is needed for > a slr type AF camera and since m4/3 isn't an slr the linear or cicular both work.

Click to expand...

Is this true? Is AF different on µ4/3?

BTW Buy the best filters you can afford! At least B+W that will run you ~$40 for a 52mm circa. pol. No sense in buying great glass and filtering it through junk. Not to suggest your filter is junk but a general point that many people miss. Even the best filters will have some adverse effect on the best glass...

Warren

thanks for the replys. I did a bit of googling, but was unable to find any specs on the filter, so I'm not really sure what kind it is. Like I said, I got it over 20 years ago and I don't remember what I paid or anything about it really. I am sure that it's going in the garbage though .

So it sounds like either linear or circular varieties will work with the m43.

thanks,
steve

WAGeo said:

BTW Buy the best filters you can afford! At least B+W that will run you ~$40 for a 52mm circa. pol. No sense in buying great glass and filtering it through junk. Not to suggest your filter is junk but a general point that many people miss. Even the best filters will have some adverse effect on the best glass...

Click to expand...

Haha, make B+W reach

I use circular pol filters from 37 to 77 mm - price $4.99 - $5.99 (incl. ship.), all excellent!

More money = wasted money.

Both photos with same ($4.99) pol filter, G3

WAGeo said:

Jim T said:

... Linear polarizers work fine with the m4/3 cameras a circular polarizer is needed for > a slr type AF camera and since m4/3 isn't an slr the linear or cicular both work.

Click to expand...

Is this true? Is AF different on µ4/3?

Click to expand...

Yes, µ4/3 uses contrast detection AF (CDAF), SLRs use phase detection (PDAF). It relies on an optical element that splits the light from the lens into two beams. I think it is the function of this element that's affected by the linear polarizers.

Linear polarizers are more efficient than circular ones (less light loss), but so far they had less resale value, because SLRs and DSLRs could not use them. The future is murky. On the one hand, contrast detection in mirrorless system became a lot better, and the cameras became more common, so there may be enough market to support the second-hand market.

On the other hand, if mirrorless cameras adopt the on-sensor PDAF in the future, then this limitation may enter our world too. I don't know if it's effected by polarizers in the same way as SLRs. If it is, then we may have to start bying circular polarizers to keep it working.

At any rate, if you plan on selling the filter in the future, buy the circular. If you don't care about the resale value, buy linear.

Vlad

lowpine said:

thanks for the replys. I did a bit of googling, but was unable to find any specs on the filter, so I'm not really sure what kind it is. Like I said, I got it over 20 years ago and I don't remember what I paid or anything about it really. I am sure that it's going in the garbage though .

So it sounds like either linear or circular varieties will work with the m43.

Click to expand...

1. This filter sells on eBay for 9 USD, so it can't be particularly advanced. The lack of the overall contrast tells me that it's probably the optical quality of the filter, rather than the focusing issue. I submit that you did not see degradation in quality at shorter FL because the details at infinity were not magnified enough to see it.

2. Linear polarizers most definitely work on µ4/3. I have used them myself, and there are ample examples if you search for these words on this forum and on the net in general.

Vlad

kenw said:

I haven't experienced this myself, but I have seen more than one example of it happening with telephoto lenses and so-so quality polarizers. This is a pretty dramatic example, I think I may have seen something this dramatic with the Canon 100-400L once a few years back on the Fred Miranda forums. Usually the problem is more subtle.

I've never heard a compelling reason for why this occasionally happens though!
--
Ken W
See plan in profile for equipment list

Click to expand...

We had the same kind of issue on the PBase forum. A guy had a Canon 'L' telephoto,I forget the focal length...had almost the same problem, and with a polarizer I'd have thought was OK, (think Hoya's better line, is it HFC?) if remembering right...and although there were quite a few knowledgeable photographers on there, If I'm not mistaken it seemed no could quite answer why. Quite a few theories, but nothing really definite. He kept trying different tests, solutions, etc. but nothing seemed to work. The lens was fine without the filter.
--
http://www.pbase.com/madlights
http://barriolson.aminus3.com/



Like the Joker said: Why so serious?

Knallberto said:

Both photos with same ($4.99) pol filter, G3

Click to expand...

Nice,

While both shots look fine I suggest you look at again at the OP and his issue with cheap filters.

I have had problems with cheap filters in the past. This was mostly in my film days and I learned top avoid bargain filters. Digital allows a wider easier contrast range that seemed to be the issue with cheap glass.

Issues with filters will be more apparent with varying angles of light as well.

For me it's good to know I don't have much of a wild card in my bag when reaching for a filter.

Warren

lowpine said:

I was out at the river this past weekend hiking with the wife and kids, of course snaping photos. I'm using the gh2 with the 140. I started to notice that anything over 100mm was slightly out of focus. I tried upping the shutter speed, setting the camera on a rock with timer, nothing seemed to help.

I got home and examined the photos, sure enough, everything over 100mm was blury. I looked back thru my photos to do a comparison. I previously had crisp focus on images at 140mm, but none focused out to infinity. Ugh, maybe I have a bad lense, or I've changed a setting? What has changed? I couldn't think of anything I've done.





Today, I wanted to try a more controlled experiment to try and figure out what was going on. I set up my tripod on the front porch and proceeded to take photos at various focal lengths, 14, 25, 50, 70, 100, 140. Then it hit me as I was taking off the lens cap.... I put on a polarized filter yesterday. I shot a round without the filter, then put the filter back on. Sure enough, things stay clear without the filter but, they started getting blury with the filter beyond 100mm.

I'll spare you all the focal lengths and jump straight to 140mm.

Without the polarized filter:





With the polarized filter:





Anyone else experience this? I recall others using a polarized filter. It's a promaster spectrum 7, I've had it since the slr days. Maybe someone can offer up a technical reason why this is causing an issue?

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

Click to expand...

The blurry ones are under 1/500s, the sharp one 1/1000s. At the equiv. 280mm FOV you should have been safe hand held, but that shutter speed had me going. Looking closely at the originals to one side I see movement, on another side I don't (it's just soft). I feel there's a slight movement with the shutter release, maybe ever so slightly circular.

Because the evidence of moment is so slight (and more on one side or the other, not throughout), it does bring to mind a filter. But I've only seen this exhibited on 200mm+ Canon L glass with cheap protection filters (and with a Sign-Ray fading ND on a 70-200/2.8 at max zoom). Like the others, no real rhyme or reason was ever documented - answer being: if in doubt remove the filter.

But I'm stuck on that slight evidence of blur. There was no mention of OIS in the mix, and it's easy to forget to turn it off for the tripod (or leave it in the wrong mode). . . and the shutter speed difference is not insignificant. Just food for thought. I certainly wouldn't worry for the lens itself. I'd just put it though some further tests, and not use the CP until/unless reassured by them.

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

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

WAGeo said:

Is this true? Is AF different on µ4/3?

Click to expand...

DSLRs typically use phase detect, M4/3 doesn't.

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.

I think OP has an (very) old (and expensive?) pol filter. He should buy a new for $ 4.99 and problems are gone.

Knallberto said:

I think OP has an (very) old (and expensive?) pol filter. He should buy a new for $ 4.99 and problems are gone.

Click to expand...

The issue doesn't arise with the sort of studies you enjoy, K.

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

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

Midnighter said:

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.

Click to expand...

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