GH13 Getting uneven ND coverage with 77mm Singh Ray vari-ND + Lumix 20mm f1.7

[Dvader]

I'm using a 77mm Singh Ray Vari-ND with my lumix 20mm 1.7 lens and I'm getting dark spots on the left and right of the image when I stop down the filter towards the max end. Is this because 20mm is pushing the very wide end of what the filter allows? (Singh Ray says not use lenses wider than 35mm still) I'm kind of confused since this article http://philipbloom.net/2011/06/04/the-best-variable-nd-filter-i-have-used/ talks about using a 11mm tokina lens with a similar filter.

I don't notice the effect very much when I'm filming indoors but when I go outside on a sunny day it becomes really noticeable. I'm also using 2 step up rings to make the 46mm thread of the lens fit the 77mm thread of the filter but that would be normal right?

 

[aljudy]

My guess is the step up rings. I have a 55mm ND (different brand) and use one step-up 46-55 and haven't noticed the problem you mention. I wonder if there is light bouncing in there from the edges?

 

[Dvader]

The step up rings are really really thin, practically 3mm thick. I'm going to try to see if I can get some test footy today and try holding the filter in front of the lens and see if the results duplicate. I've seen a ton of people comment about using a 77mm version, which on most lenses would need some step up rings so I'm surprised this hasn't been a problem for others.

I also was shooting wide open at f1.7 which this lens review seems to state that at that aperture the center of the image of 1 stop hotter than the sides. If it's true perhaps that's contributing? http://www.slrgear.com/reviews/showproduct.php/product/1295

 

[bitcrusher]

The 20mm vignettes about a 1.5 stops wide open. There is no way that a 77mm filter will cause any vignetting on that lens. Unless you are using adapters 3cm thick.

 

[jeree]

The step up rings are really really thin, practically 3mm thick. I'm going to try to see if I can get some test footy today and try holding the filter in front of the lens and see if the results duplicate. I've seen a ton of people comment about using a 77mm version, which on most lenses would need some step up rings so I'm surprised this hasn't been a problem for others

I also was shooting wide open at f1.7 which this lens review seems to state that at that aperture the center of the image of 1 stop hotter than the sides. If it's true perhaps that's contributing? http://www.slrgear.com/reviews/showproduct.php/product/1295

shouldnt you not get small step up rings as it is really flimsy