Major issue with HVX and ND

smelni

smelni

Veteran
First let me preface this with saying I love the HVX and we are shooting our feature with it.

But we have run into a major issue - it appears that the HVX, for whatever reason is not compatible with large amounts of ND. I have seen this with both filters and ND on windows.

In low abounts (.3) it is fine and the filters and/or gels cut the light correctly. But in higher amounts (.9 and higher) the ND turns the light pink. So much so that it is noticable. If you use white balance to correct it, the scene turns green to offset the pink.

This has happens with me with tiffen ND filters and with roscoe nd gels on windows. My understanding is that ND is color agnostic and should not cause this.

So this limits creative use of bright exterior lighting with interior scenes and is causing huge issues for our production.

Has anyone else seen this, have an explanation or a suggestion.

Jan - panasonic - any reports of this from other users?
 
What you're describing is fundamentally not possible. An ND filter is, by definition, neutral -- it cannot impart any sort of color cast to the footage.

Cheap filters are made from so-called "green glass" and could impart a small green tint to the footage; if you're using screw-on Tiffens I'd suspect this could be what you're running into.

You've got six stops of ND filtration built into the camera (on 1/64) and there's no pink or green cast when using that, right?
 
Barry - beleive me - I understand it is theoretically fundamentally impossible. But it is happening for sure and is repeatable and has been seen by our AC and another DP on set.

We have seen it with tiffen 4x4 - only at ND .6 or more.

We saw it today with 1.8 total of ND on the windows- and it was roscoe gels - the skylight was pink - very obviously pink - and if we white balanced on that the sky was white but the room was green (cause the green and red channels are opposite i guess).

It is baffling - try it - on a sunny day (very sunny) put 2 layers of .9 on a window and then point the camera at it. It is repeatable - and very disconcerting - we had to frame windows out of the shots and even black them over cause they light coming through was tinted

Fundamentally impossible - in theory only - cause it is happening on our set.

Any frustration in this message is not towards you Barry - you know I have the upmost respect for you - the frustration is at a seeming impossible and therefore insolvable problem

By the way - i would LOVE to be proved wrong as this is killing us

Oh and yes - the internal ND does not have the issue
 
I know you're not frustrated at me, no problem, don't worry 'bout that.

But this line is telling:
the internal ND does not have the issue
Click to expand...
That in and of itself leads me to say that it's not any sort of issue with using ND with the camera, obviously. So I'm left to wonder about the quality of the ND stuff you're using. And the only thing I can think of is to say "try a different camera for a test" -- preferably a different brand. Would a Sony or a JVC also go pink in the same circumstances? If so, it lets you know what I suspect to be the case: that the color tint is due to the ND filters you're using, not due to any fault of the camera itself. They're supposed to be color-neutral, but apparently they're not.


Not that I'm blindly defending the camera, but that it simply doesn't make sense. The camera doesn't know whether you're using ND or not; if you use a .6 ND, or you just close the iris by two stops, the net effect to the camera is the same.

If the HVX footage is turning pink, then I'd expect that any other camera in the same conditions would also turn pink.

I'll dig through my stuff and see if I have any window gel here and try to replicate it. In the meantime, I'd suggest trying to add a bit of whatever the color complement of pink is -- would that be blue? blue-green? anyway, whatever it is, a mild shade of that should compensate and get you back under proper color conditions. Might keep you up and running until you can get to the bottom of it.
 
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It would help if you could be much clearer about what you are seeing and doing. I am confused about whether you are using rosco window gel or ND filters on the lens.
I have definately seen problems with rosco gel not being truly ND. In my case I remember seeing significant magenta casting and I have a vague recolllection of seeing that compound with heavy layers of ND. Also have seen it on 85ND and blue correction. Its probably a general problem with that kind of material, simply doesn't have the same standards as glass filters and even those differ in their standards. I've had bad polas and bad ND's . Its not uncommon and Tiffen may be more prone than say heliopan. Usually you can tell just by looking carefully at the ND with your eye

Seems to me I started using Lee and Cinemills gel because the colors were more reliable but that was some time ago.

I'd be very surprised if it was an HVX problem, and the first thing to do before making those kinds of claims is to compare it to another camera.
 
why not instead of trying to make the outside (EXT) less bright by using ND filters, make the indoors more bright and expose for that. That way you wont need ND filters really if the exposure of the indoor and ext is decresed? Just a thought. I could be way off from what you wanted. Just trying to give a suggestion that wouldnt involve even using the ND as much.
 
What kind of lightsource are you using for the room?

If you are using fluorescent and white balance to that, you might introduce a slight magenta cast. When the windows re blown out you won't notice this but as you bring the intensity down it might become obvious.

To test the camerafilter, try holding it with your hand in front of the lens. Then as you tilt the filter towards the camera, see if the cast intensifies. If it does it's the filter alright.

In my experience Tiffen and Format polarizers can introduce a slight green cast while schneider doesn't.
 
The problem lies with filters rather than the camera. I have had this problem on a regular filmset. We have used around 1.5 total ND and the colormeter started showing CC+sthG. The point is that sometimes filters (even glass filter for the camera) act like that below the normal "magenta introduction limit" (it is normal that after you reach 2.4 ND magenta may show even with new filters) because they are old or cheaply made.

What you should do is check the filters with a colormeter. If this problem shows on the meter not only on the camera than you now where is the problem.
 
Technically speaking, there is no truly neutral density filter if by that one means that all wavelengths of the visible spectrum are equally attenuated (absorped) across the entire visible spectrum - the power spectrum is perfectly flat. The nearest to true neutral are filters used in optics labs which rely on semi-silvering or a scattering of carbron particles (also seen in centre-filters for wide-angle lenses).

So let's assume that the best of normally manufactured filters will stop most wavelengths equally but let some through, er, a little less equally. In this case it looks like there are dips in the blue and red absorptance which become visible when you pile a lot of ND together. If there is imbalance in two axes of the chrominance, then I'd guess it is very difficult for the camera to correct - which could be why Smelni is getting green in response to his attempts to correct the magenta. It could be that Panasonic's built-in filters are matched to the absorptance bands of the sensors, so they are truly neutral but only relative to the triple-sensor set-up (in fact that is what we'd have every right to expect) - which means you may not replicate the error with another camera which uses a different sensor/Bayer filter set-up.

Solution? What about setting 1/64ND on the camera, and a lighter ND on external filters or windows - sorry, I know that won't solve the luminance balancing problem? Thanks for bringing up an interesting one.
 
Thank you all for your responses - it has been helpful to have ideas

First I am sorry if I am blaming the HVX without further understanding - after reading this I think I would have to blame the gels and filters - 2 different cases with the same results. Its odd that both the Tiffen filter and the roscoe gels (each used independently) have the same cast but that seems to be the case

To those whose suggested the internal ND and using more internal light - that really isnt an option in our case - to make up the 6 stop difference we would need so much light - and we are working on 15 amps circuits (no tie-in) so we dont have enough power - and if we did we dont have the right lights to have the proper quality of light in that intensity - besides the fact that we would cook the talent.

It is very frustrating and has led us to framing windows out of shots - but production is always a series of comprimises.

I am surprised more people dont run into this - i would think more people would be filming scenes in bright daylight indoors with windows in the shots- but if you do beware that you may not be able to get the correct ratios just by using ND.
 
Again, consider adding a slight anti-pink gel to your windows. You may not have to frame them out, you may just have to color-correct the light coming in from them...
 
Just like Barry said. Sometimes some a green filter within the gel will help. But you should check the gels also. Even with a digital camera if you don't have a meter. Tell me did you check the materials or does this shows on the LCD?
 
This is not an issue with the camera or the filters. This is totally operator error. I think Anders Holck has it nailed. If your scene is turning green when you balance to daylight or the windows are going magenta when you balance to your lights then you are using homemade flourescents that are giving you a green cast.

Whoever is the DP or operator needs to learn about color temterature before you hall everyone out on the set. The last time you brought this up (last month) you were complaining about certain areas going green. Probably the areas that were lite with the flourescents. If you load Kino-flos with the wrong tubes you can also get a green cast.

Who do you have shooting this production for you? Fire them.
 
Greenheron - thats quite a flaming post.

You are wrong - pure and simply - I appreciate you trying to help - but that isnt a necessary tone without knowing the facts.

All lights are balanced to daylight - I have a VERY strong understanding of color temp and balance it out all the time. We are using daylight kinos and gelled tungstens. There are practicals with a greenish cast but not to the degree that the issue is showing up.

Case in point - on an overcast day where we only needed .6 on the windows everything worked like a charm. On a bright day where we needed 1.8 on the windows the windows had a pinkish (magneta I guess) tint - to white balance that out the room turned MUCH greener - FAR FAR greener then the slight tint the practicals gave.

Last month - I was talking about the same issue with the Tiffen filter - hmmm - interesting - there was not a single floro on that set - not one - in fact everything was controllable tungsten - not even a single practical - so the green/magneta issue was introduced by the filter.

From all the posts it seems that the ND material has a very slight tint that comes up more when used in large amounts in front of a bright source - I plan on doing some direct testing of this in a controlled env when time permits.

greenheron - you must be a pleasure to have on the set
 
You have at least 3 different CT light sources. Daylight Kino's (Divas ?) Tungsten which are gelled and outside daylight. There are many factors from the lighting that could cause this issue. The only precise way to correct what is going on is to use a color temperature meter to read each light source and correct each one to balance to one setting(such as 5600).

I have never seen professional nd gel add magenta to a outside scene unless there was a color temperature problem. You have now stated that you had a problem with Tiffen ND filters and Rosco ND gel. I don't believe that the problem is with these professional products or the camera. I think it is a lighting issue.
There is a great difference in color temperature in an overcast day (8000) and a bright sunny day (5600).

And yes, I am a pleasure on the set, because they pay me as a DP and Gaffer to solve problems just like this. The only difference is that most of the time we are shooting film.
 
Then you simply dont understand the problem I am describing -

I set the camera up looking at the scene - I am about 3 stops too bright - I turn on the internal ND 1/8 filter - looks great.

Then I turn off the internal filter and put the tiffen .9 in front of the lens - the window light is pink - it is the material introducing it.

I have had independent people look at it and see the issue - slide the filter in - you see it - take it out - you dont.

Perhaps you did not fully read my last post - the tiffen issue occurred when we only had 2 sources - outdoor sunlight - closer to 5600 and indoor tunsten with a range of 1/2 CTB to full CTB - so where is the green/magenta shift being introduced? And why is it introduced from the external tiffen filter and not the internal ND filter.

Other posters in this thread have commented that ND materials are not truly color agnostic - so perhaps this is causing it - I dont know for sure - hence posting here.

But I am sure greenheron, if you were on set we would have the issue solved very quickly - cause its only operator error.
 
I apologize. You are right. It must be the Tiffen filter. Or the HVX Camera not handling ND? Or it must be the Rosco gel.

It could not have anything to do with human misunderstanding. My bad.

I have to go to work.
 
I never said it isnt human misunderstanding - I was simply reacting in kind to allegations that we do not know what we are doing and we should be firing whomever is lighting and operating - that is just a silly response, and not very helpful.

I hope very much that there is an error that we can correct - cause that would solve this problem. This is generally a supportive board. - that response was not.
 
A quick note:
At NAB one of the filter companies I spoke with explained what you have mentioned here.

Some filters have added a pinkish hue to the video. I think, (but don't hold them to this), that tiffen was one of them.
I'll try and find the company and what they have done to overcome this since I believed what he told me and planned on buying thieirs.

HD has produced many new issues in our work flow. Theater blood is having to be more realistic since current blood doesn't look real in HD. Makeup is going to need better artists. You won't be able to just hire a local beautician.

We often blame user error for many issues, but HD will bring new problems that we as a community will need to resolve together. Some will be gear and other issues will be education.
I wish us all luck!
 
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