Polarizing filter for Sigma 150-600mm lens.
Jul 12, 2020 14:41:51 #
its the way the light pasess trhough the lens which confuses the autofocus system. Circular Polarizers contains a Linear Polarizer component that does the main work of polarization, as well as a second layer inside the filter called a Quarter Wave Plate, which “spins” the light after it goes through the linear layer and before it enters the camera lens. In still photography, SLR cameras and DSLR cameras have a mirror, which a linear polarizer can cross polarize, causing the image to darken or go black.
Jul 12, 2020 15:08:42 #
One more comment: The linear polarizer element in a circular polarizer needs to be out front, pointed at the world, with the quarter wave plate on the rear side, the camera lens side. A circular polarizer doesn’t work if you get it in backwards. With a screw-in filter that’s no issue, there's only one way you can screw it on the lens..
Jul 12, 2020 15:09:46 #
travisdeland wrote:
I bet your camera does not autofocus at f/8. You said you were using AF. If the lens is at full extension, and you add a CPL, you are probably over f/8. Which camera body are you using. The lens is f/5-6.3.
Roger that. The CPL will cost a stop at best and more like 1-1/2 stop I use the B+W F-PRO C-Pol on my Tamron 150-600mm G2. AF likely marginal or useless then.
Jul 12, 2020 17:20:33 #
Jul 12, 2020 20:58:34 #
Longer focal length lenses exacerbate any defects in filter qualities of front mounted filters - which is realized in lowering optical acuity .........that is why they work better on shorter lenses. And, no I cannot explain this scientifically but I am satisfied knowing the possibilities of the results !
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Jul 12, 2020 21:18:27 #
Jul 13, 2020 01:37:27 #
imagemeister wrote:
Longer focal length lenses exacerbate any defects in filter qualities of front mounted filters - which is realized in lowering optical acuity .........that is why they work better on shorter lenses. And, no I cannot explain this scientifically but I am satisfied knowing the possibilities of the results !
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I have the B+W F-PRO C-Pol on my Tamron 150-600mm G2 mounted on the D810. The AF worked fine and the images were sharp as usual viewing objects a few meters away for both 150mm and 600mm focal lengths. This is a more stressing case than when the object is very distant. If the OP was able to focus the camera/lens w/o the CPF using the AF and obtained good imagery, then either the camera AF sensitivity is inadequate or the CPF is flawed. There are three versions of the GOBE CPF with the lowest level having common glass for the substrate up to excellent quality glass for the professional version.
Jul 13, 2020 01:43:26 #
travisdeland wrote:
I bet your camera does not autofocus at f/8. You said you were using AF. If the lens is at full extension, and you add a CPL, you are probably over f/8. Which camera body are you using. The lens is f/5-6.3.
This is the correct answer! AF does not work well at small apertures. I had the same problem with a Nikon 80-400mm lens. Take the filter out and it AF works like a charm.
Jul 13, 2020 11:01:35 #
I tried to manual focus as well and cannot get any sharper with the filter on. Is it possible that the $70 I spent just does not cut it and i have to buy a more expensive filter?
Jul 13, 2020 11:16:48 #
I agree and suspect the small aperture created by the loss of 1.5x is the issue. But the one obstacle to my statement is the fact you tried to focus manually and it's still blurry. You need to confirm you manually focused correctly; however that is not possible with using the viewfinder icon or green light, since it has the same loss factor of the aperture and will not display properly. You should try to observe the image and guess when its best in focus. Difficult process without the aid of the screen, maybe you can use the scale on the lens to approximate the setting with a known distance.
Jul 13, 2020 11:21:24 #
Jerry Bruzek wrote:
I tried to manual focus as well and cannot get any sharper with the filter on. Is it possible that the $70 I spent just does not cut it and i have to buy a more expensive filter?
A more expensive filter will have the same exact effect; do not waste any money on a new expensive filter.
You have two options here: 1) Use the lens without a polarizer filter or 2) buy a faster lens.
Jul 13, 2020 11:23:09 #
Jerry Bruzek wrote:
I tried to manual focus as well and cannot get any sharper with the filter on. Is it possible that the $70 I spent just does not cut it and i have to buy a more expensive filter?
Jerry,
From what you have written, it sounds like a bad filter since you can't focus manually. For $70, it would appear that you purchased the entry level version of the GOBE CPF. When I bought my Tamron 150-600mm lens, it came with a bunch of stuff, most of which was of no value to me. It included a set of filter that contained a CPF that I found was next to worthless. The image degraded a bit and the degree of polarization was poor. As usual, I purchased a quality B+W CPF and it was excellent. Maybe you can return the GOBE and trade up to a B+W.
Doc Barry
Jul 13, 2020 12:54:39 #
Jul 13, 2020 12:54:54 #
Jul 13, 2020 12:55:34 #
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