D300 Focus Problem with CPl

Joined
Mar 26, 2008
Messages
57
Location
Northern Illinois USA
I ran into a rather strange problems when using my D300 with the Nikon 70-300VR lens. If I use a circular polarizer on the lens I can only get out of focus images. If I take the polarizer off it focuses fine. I have tried manual focus, Liveview Tripod mode and normal AF with the same result. I had the camera mounted on a tripod with VR off and used shutter delay, just to be safe. I was shooting outside during a very bright day. F5.3 at 200mm and around 1/120 I believe.
I don't mean a little soft, I mean very out of focus.
I suspect it is the filter. It's not a real expensive one (Sunpak) but I would have never guessed it would be that bad. It appears clear and undistorted to look thru it. I even cleaned it, which made no difference.
 
Joined
Oct 28, 2006
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I use a CPL (Hoya S-HMC) on my 70-300VR quite often with no issues.

I'm bettin' you're right - it's a filter issue. Perhaps a linear filter was packaged incorrectly.
 
Joined
Oct 6, 2005
Messages
1,490
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California
The CP reduces the amount of light hitting the sensor by a stop or two. Even though the camera reads f5.3 you're only getting light equivilent to an f8 to f10 lens, which is beyond what the camera needs for reliable AF.
 
Joined
Mar 26, 2008
Messages
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Location
Northern Illinois USA
Well, that's what I thought too. But when I thought about it, it really is no different than shooting on a dark day. I was in "A" mode and the camera set the shutter speed.
Also when you look at the image you will see it has a strange smeared look. There was no camera movement and the subject (a dumpster) weighs several hundred pounds so it doubt it was moving either.
Here is a shot without the filter:
original.gif
Subscribe to see EXIF info for this image (if available)


And here is one with the filter on:
View attachment 239954
 
Joined
Oct 6, 2005
Messages
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Location
California
I got the same results with manual focus as well, so even if the AF had a problem with the "filter factor" of the CPL, manual focus should have worked OK.

True. Maybe some internal reflections then between the lens and filter. Save it to use a "drop shadow" effect filter. :biggrin:

I have some windows in my house with a coating on them that do a similar thing.
 
Joined
Jun 5, 2008
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Location
Alberta
Put a $15 doller filter on a $500 lens and your lens suddenly turns into a $15 lens. Take it off your lens and smash it against a wall:eek. To extreme? Okay, take it and put in on the ground and walk away:biggrin:. Filters are another layer of the optical formula(Image chain), which on a zoom lens is already very complicated. If you want to use filters on your zoom than get the very best B+W is good start. What ever brand you choose, make sure its coated. The reason that really good filters cost so much is that they are optically flat. And use the same multicoatings as you quaility lenses. And if possible also use a lens hood. Good luck

Gregory
 
Joined
Mar 26, 2008
Messages
57
Location
Northern Illinois USA
Thanks Gregory. I have had the filter for a number of years but hardly every use it as I am not really into landscape photography. And when I have used it for that I haven't really noticed a problem (though I last used it on my CP8800). I suspect it is more noticable on telephoto.
The next one will be of better quality. The one I have was part of a package - I guess all filters aren't equal :). All my other filters are Hoya HMC or SMC and I have never noticed a problem. Might be an interesting exercise to test them all. I can't imagine any are as bad as this.
 
Joined
Mar 26, 2008
Messages
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Location
Northern Illinois USA
Well, the sample shots were both taken on the same heavy duty Bogen tripod using the mirror up shutter delay and even the shot with the filter was at 1/200 sec (VR off). There was no wind to speak of and no seismic activity in the area. The "model" weighs hundreds of pounds.
I don't think it was camera shake :)
 
Joined
Oct 9, 2005
Messages
29,624
Location
Moscow, Idaho
A CPL is a sandwich of two glass layers over a plastic polarizing film. I think maybe your CPL has separated (delaminated) and you are seeing ghosting.
 
Joined
Mar 26, 2008
Messages
57
Location
Northern Illinois USA
Thanks Nick. Yeah, that makes sense. I wasn't aware that they were constructed that way, but that would likely cause the distorted image I am seeing. It would also explain why I didn't notice it in the past.
I still have the box it came in and it says "Lifetime Warranty" - not sure I would want another one, though... ;-)
Thanks for the info.
 

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