Polarizing filter...

Felisek

Senior Member
Unlikely. The filter would have to either lose its transparency or be distorted to affect sharpness. I don't think even the cheapest filters suffer from such problems. The biggest issue with cheap filters is the coating. Poor coating leads to reflections at filter surfaces, which in turn can create flares and reduce contrast.

A dirty filter can affect sharpness. I recall photographers smudging glycerin on a clear glass to create a simple soft filters for portrait photography :)
 

Jules

Senior Member
Not a stupid question at all!
As Felisek says, a clean filter is your biggest buddy but a dirty one is your worst enemy, as always get the thinnest rim on the filter you can to avoid vignetting, I didn't and am currently experiencing huge vignetting problems on my 18-35 AFS G, due to using deep 77mm filters on it's 77mm thread. I need to move up to 82mm to keep the corners clean, my own fault and more expense but forewarned is...

Cheers Jules...
 

alfaholic

Banned
Hmmm, strange... I never noticed any difference while using polarizer, some cheap one from eBay, Massa I think, but I just returned from Greece with 16 gb of photos, now I am looking at some of them and I can not believe what is happening... :confused:

I do not know, maybe I am pixel peeping, but here you go, look for your self:

https://www.sendspace.com/file/z181wj
 

Jules

Senior Member
Can't get hold of em on my PC, could you post a couple up here? Gladly take a look to see whats up...

Cheers Jules...
 

Horoscope Fish

Senior Member
It's possible, however remote, that your polarizing filter is screwing with your camera's ability to auto-focus. I've seen it happen. Again, the possibility is remote, but it *IS* possible. Good quality polarizing filters will not do this. I swear, personally, by Hoya HD polarizing filters for many reasons; one of them being they transmit more light than other polarizing filters and so are far less prone to issues like this.

...
 

Eyelight

Senior Member
A linear polarizer will mess with the AF. Needs to be a circular polarizer, which has an extra layer to avoid the AF and metering problems.
 

Horoscope Fish

Senior Member

I've looked at your photos and I would have to say that something is not right. The EXIF tells me everything should bee good: taken with a Nikon 18-105mm at ISO 100, f/8, 1/250 yet the shots do not look good to me. I'm posting one for other opinions on the matter.

This shot of yours is a straight RAW to JPG "Save as" via Photoshop:

BBA_8571.jpg
 

Blade Canyon

Senior Member
One local camera shop here in Raleigh (we are down to only two!) stopped carrying some cheaper filters because they noticed softness when they tested them. I think the DigitalRev TV guys on Youtube also tested some filters and pointed out softness in the final images.

Alfaholic, why not do before and after shots? It would be easier to tell what's up than with the two pics you shared. Looks like you were in a beautiful spot, however.
 

alfaholic

Banned
The strange thing is that I made A - B test with, and without filter as soon as I noticed something is wrong, and I could not see any difference in sharpness. I would do it again.
Also, not all photos look like this, there is many which are soft, but there are also many that looks good.

I will find another two and post here JPGs...
 

alfaholic

Banned

Attachments

  • With Polarizer.jpg
    With Polarizer.jpg
    102.7 KB · Views: 70
  • Without Polarizer.jpg
    Without Polarizer.jpg
    199.1 KB · Views: 110
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Horoscope Fish

Senior Member
Both are RAW files just saved with Photoshop. But, PS adds sharpness 25 of 100, so even if not by much, it is edited. For my eyes, they look the same at 100% magnification, both looks bad and soft. First one is With, second one is without polarizer.
Well you do understand that all RAW files coming out of your camera are going to *require* post processing, right?

Are you familiar with how to post-process a RAW file?

...
 

Jules

Senior Member
First one looks ok to me but it's hard to tell from a web jpeg, pretty much like most unprocessed Raws, I take it you were at the wider end of your zoom on this shot? I only ask as I think I can see the sky darkening a bit on the right side of the beach. That will happen with any polariser whether its fron B+W or B&H!
Second looks like mis-focus or lack of depth of field to me, some of the foreground foliage looks quite sharpish and yet the Bridge is a little soft for sure. It's not easy to tell, you got any settings saved anywhere?

Oh I see some in the earlier part of the thread, in which case you need to get the 18-105 checked out!
Do you have the same trouble with those two lovely little primes you have?
 
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alfaholic

Banned
My 35mm and 50mm are super sharp. Of course, 50mm is a little bit soft at f1.8 with a lot of CA, but from f3.5 and up it is good.

All my lenses are checked few months a go when I had some focusing problems with my 35mm, and all passed at Nikon.

This 18-105 is sharp when subject is close, or when it is zoomed, but at 18mm it is soft, even at f8.
I focused on something 2 or 3 meters away, so at 18mm with f8 everything from 0.8 meters to the infinity must be in focus, which is not the case here.
It is not out of focus, it just looks weird,I do not know...
 

alfaholic

Banned
OK, here is the ZIP file with 3 folders:

18-105 Bad
18-105 Good
35mm

https://drive.google.com/file/d/0Bz565Iyy7PBXcDNkT2d1X2l6Sk0/edit?usp=sharing

This "Bad" folder contains 4 photos, two photos with, and two without polarizer, at 18mm and 50mm, all with f8. I named it "Bad" because I did not screwed the filter to the end, so it was loose.
The folder named "Good" contains the same, but this time I screwed the filter to the end hard, so it was on it's place.
The third folder is named "35mm", and it is made with 35mm f1.8 G with some cheap Baner polarizer, just two files "with", and "Without" filter.

I would like to hear your opinions, how much my cheap filters are affecting IQ.

Thank you...
 
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