GH2 Variable ND Filter Users - Input Wanted

[Tim Polster]

Hello,

I have been trying some variable ND filters with my GH2 and have found a strange issue when filming outdoors. When there is sky in the frame I see horrible banding. This happens at all angles related to the sun and is not really present when shooting stills. I can't really see the effect anywhere but when sky is present.

So I wanted to ask: Have you seen this? Or could you test with your filters to see if this happens?

I want to go with the variable because it is so flexible, but it looks like a topographical map wherever there is sky.

Thanks for your help!

[Jeff Harper]

I'm guessing it has to do with the model of filter and you might need to find a different one. I've read of some older/less expensive filters that are prone to banding.

[Tim Polster]

I don't want to name names but this is a new model. Do you know of a brand or two that does not act this way? I am kind of looking for some user experiences to see if I have any options.

Thanks

[Jeff Harper]

If it's inexpensive then that it your problem. Older or cheaper ones are said to be prone to banding. If it were me I would go to B&H website and look at the variable ND filters and read the reviews and you'll find reviews that may contain the information you seek.

If you are getting banding it is the filter, pure and simple. Cheap filters of any brand, even UV filters, can cause distortion. Variable filters, the good ones, tend to run several hundred dollars to $600.. I had a variable polarizer that cost $300, and it was very nice. I also had a cheaper one that I got with a used lens and it was quite different, didn't like it at all, but I couldn't put my finger on what was wrong with it.

All the filter manufacturers, I believe, manufacture economy filters, as well as better ones. It's not so much the brand but the price point you jump in at.

I'm betting your filter cost between $100-$250, probably closer to $150. Is that about right?

[Bob Richardson]

I'm respectfully skeptical... If it's solely the fault of a cheap filter, then why, as the original post mentions, doesn't the problem manifest in still photos?

I'm more inclined to blame the codec. AVCHD (like many forms of compression) looks for was to ditch detail in areas the eyes aren't inclined to notice in a moving image. This often leads to dismissing information from graduated colors, such as a sky that ranges from light to dark, in favor of detailed/contrasting information, such as leafy trees, anything with an edge.

The reason you may not see this without the ND filter is that your sky is near the maximum exposure and actually lacking in graduation of lightness or color. Introducing the filter introduces the variation, and the codec degrades that a bit too much.

[Jeff Harper]

Bob, in line with your thinking I would adjust shutter speed and aperture and see if a different combination helps.

[Tim Polster]

Thanks for your input guys. I am just looking for a workable solution. So far i have tried a $70 vari ND and now this one ($200). Both show the same behavior. So I am looking for a GH2 user who HAS found a variND solution that does work.

I too think it has something to do with the codec or the way the chip gets a video image from a higher resolution imager.

Either way, I don't want the banding in my footage. So if anybody with a GH2 has a variND that can be used outisde pointed at the sky in video mode at wide aperatures I would love to hear from you.

Thanks

[Jeff Harper]

Let us know what happens when you try adjusting your shutter speed and aperture. I'm curious, which lens are you using? I think if you under or overexpose a touch your problem might vanish, but I could be wrong.

I have used solid ND filter (not variable) on numerous occasions with sky in the shot and not experienced any issues. I've shot some beautiful video of the Cincinnati skyline with 50% or more of blue sky in the shot from the Kentucky side of the Ohio river with no ill effects.

I would suggest trying a non-variable filter and trying the same shot, and if you lose the issue than you either need to change your settings when using the filters you have or going with a solid.

[Tim Polster]

I am considering just going with a few different solid filters for different situations. Three solid filters can be had for the price of the variable filter.

But I hope to hear from some vari ND users that have a product that does not give the banding while shooting a sky in video mode.

[Hamish Reid]

I get noticeable banding on the beautiful deep blue Californian skies around here and out in the Valley and desert with my GH2 with or without filters, which is depressing. It's not always particularly bad (a lot of people don't notice it), but it gets somewhat worse when using a polariser. So I suspect the codec really doesn't do nice skies justice -- and that changing the filter will have some impact, but not a lot.

[Eric Stemen]

This is a guess but...

When making ramps or gradients in After Effects they look smooth in the program because it's not compressed, but when I export to ProRes422 the files generally show banding because information is lost(to get around this I usually add noise to the image)

Variable ND filters are just two circular polarizers.
If you use a regular polarizer and make the effect as strong as possible and shot up towards the sky you may notice certain parts of the sky are much darker than usual and other parts of the sky have very little effect....you could say the sky has more of a "ramp" or "gradient" than usual when using a polarizer.

From my explanation in the first paragraph certain types of compression will exhibit banding in gradients....I assume because they can't display all the levels of brightness and color we can see....and when you use your variable ND filter you have really just attached two polarizers to the front of your camera which can change how the sky looks.

An interesting experiment(which you probably don't want to take the time and try) would be to hack your GH2 so that the noise pattern is very visible(not like with the stock bit rate which is lower and "smooths" the noise out) then shoot at a high ISO and see if the sky still shows banding. I would think the banding would be reduced since this would be similar to adding noise in After Effects.

Hopefully I didn't put out any false information in this post....mostly just ideas.

[Tim Polster]

Anybody else use variNDs with their GH2?

[Dave Mercer]

I use a L.C.W. Fader ND MKII 72mm with step-up rings. It's certainly not perfect (occasionally will vignette, occasional banding, and have seen some weird ghosting a few times) but I've been pretty happy with it for the price.

Oh, and I also dropped it ... little crack but held up pretty well.

Hope that helps.

[Tim Polster]

Thanks Dave. Do you see banding when there is sky in your frame?

[Jeff Harper]

I still think if you over or underexpose a bit you might get rid of the banding. Have you tried that?