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Polar Pro Variable ND - Zoom camera Blur?

ClearPropMedia

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Hi everyone,

I’m using the PolarPro Mavic3 variable ND on my drone, and I’ve noticed something odd at longer focal lengths. In the past, I’ve only used regular NDs, and not the variable kind.

When I use the Zoom camera, at the longer zoom of say 20x through 28x, the higher stops on the variable ND cause considerable blur.

Stops 2 and 3 look fairly sharp but 4 and 5 are very blurry. I switched the filters out to DJI filters and tried no ND at same focal length and things look “sharp” by the Mavic 3 zoom standards. Any ideas what is going on?

Do variable NDs cause more blur on zoom lenses?
 
So you tried DJI's ND filter of the same stops, and there is no blur?
 
Yep! The issue isn’t the regular ND. It’s the variable ND at long focal lengths.

Does the blur only occur for zoom camera, or for main camera as well? If it is only for zoom camera, what is the shutter speed of the image, when it occurs?
 
Does the blur only occur for zoom camera, or for main camera as well? If it is only for zoom camera, what is the shutter speed of the image, when it occurs?
Yeah, the regular lens looks okay. At least on my phone screen. I haven’t compared video yet or photo at wider focal lengths. Seems to be the higher the ND used on variable ND, the more blur on the image. Not sure on the shutter speed as the the zoom lens only shoots in auto.
 
Yeah, the regular lens looks okay. At least on my phone screen. I haven’t compared video yet or photo at wider focal lengths. Seems to be the higher the ND used on variable ND, the more blur on the image. Not sure on the shutter speed as the the zoom lens only shoots in auto.

You should examine the blurry images and find out the shutter speed used for these images. A slower shutter speed might be the reason for the image blur. When you change VND from stops 2/3 to 4/5, the zoom camera has to lower the shutter speed considerably, in order to capture the same amount of light.
 
You should examine the blurry images and find out the shutter speed used for these images. A slower shutter speed might be the reason for the image blur. When you change VND from stops 2/3 to 4/5, the zoom camera has to lower the shutter speed considerably, in order to capture the same amount of light.
Just did that. I attached the image samples. You will see that the ND16 by DJI is much sharper than the ND16 Variable ND by Polar pro at the same focal length. In fact, the Polar Pro lens has 3 photos below Stop 2, Stop 3, and Stop 4. You can see each one gets progressively worse in image quality. The shutter speed is coming down on each one. It comes down to 1/20 on Stop 4... BUT the shutter speed is also 1/20 on the DJI ND 16 filter too. And that shot is much sharper. So I don't think this is a shutter speed problem.
 

Attachments

  • DJI ND 16.JPG
    DJI ND 16.JPG
    3.9 MB · Views: 7
  • NO ND.JPG
    NO ND.JPG
    3.9 MB · Views: 7
  • POLAR PRO VARIABLE STOP 2.JPG
    POLAR PRO VARIABLE STOP 2.JPG
    3.8 MB · Views: 7
  • POLAR PRO VARIABLE STOP 3.JPG
    POLAR PRO VARIABLE STOP 3.JPG
    3.5 MB · Views: 7
  • POLAR PRO VARIABLE STOP 4.JPG
    POLAR PRO VARIABLE STOP 4.JPG
    3.3 MB · Views: 8
Variable NDs have a more complex design than single strength NDs. A variable relies on two polarizing filters overlaid, so it might be that the tolerances between the two are off, and since you're shooting at high magnification through the "corner" of the filter, it's further exacerbating an IQ issue.

The CA appearing in the variable stop 3 image makes this seem even more likely, IMO.
 
Just did that. I attached the image samples. You will see that the ND16 by DJI is much sharper than the ND16 Variable ND by Polar pro at the same focal length. In fact, the Polar Pro lens has 3 photos below Stop 2, Stop 3, and Stop 4. You can see each one gets progressively worse in image quality. The shutter speed is coming down on each one. It comes down to 1/20 on Stop 4... BUT the shutter speed is also 1/20 on the DJI ND 16 filter too. And that shot is much sharper. So I don't think this is a shutter speed problem.

This is very strange indeed. Because the kind of blur showing up on the last two images (stop 3/4) look like to be caused by camera shake. I would suggest doing another test to completely rule out this possibility. Just place your drone on the ground/bench/table, and shoot with VND at 3/4/5 stops. If the final images have no blur, then we know the previous problem (blur) was caused by camera shake. If the blur still occurs, then you may have a faulty VND. You should ask Polar Pro for a replacement.
 
1/20 sec is a very slow shutter speed, especially for the zoom camera. Any tiny amount of movement is going to cause motion blur. I'd try at least 1/200 sec. No reason to be at that slow of a shutter speed when shooting in daylight unless you purposely want to blur something (like cars or water).
 
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