Darkening the Sky (Double 85 Filtering)

[Evin Cameron]

Hey everybody, I'm currently in the planning phase for a very minor project - shot on 16mm, half of it will consist of daylight exteriors, and the other half will be nighttime exteriors. There's a lot of surreal themes, so I've been trying to find different ways to convey this - and I stumbled across an old video recently from KINETEK (Matthew Rosen) showcasing different ways to apply filters to darken blue skies. 

In particular his examples of his work using double 85 filters really caught my eye, and it was something I had never heard of before - and aside from a few brief mentions elsewhere on these forums I couldn't really track down another source of information for this and it leads to a lot of questions I'd have before testing it for myself. 

Does doubling up with 85 filters on tungsten stock lead to this much additional warmth as a general rule? And would anything be lost color-wise from correcting it back to a neutral balance in post? It's hard to tell because a lot of the example work is post grading, and has a very stylized look to it. 

I'm also a bit confused on exactly how much each of these filters cuts light down from the sky, and if you still have to deal with an overall filter factor as it's said that since the filter is mostly blocking this blue wavelength of light and allowing most of the warmer wavelengths of light through, it's able to darken the sky and equalize the exposure between the sky and subject - but on a sunny day isn't everything being lit by this same blue wavelength of light? Or am I misunderstanding the concept entirely? All of the 85 Filters I'm looking at have a 0.6 Filter factor, so would I truly be opening up 1.3 stops and then getting this effect? Or am I ignoring the filter factor to a degree as that's what's cutting the blue sky? 

And as a very quick final question is there any extreme difference in performance between the traditional matte box 85 filters and the circular lens mounted ones? 

Any help/examples and resources on this topic would be much appreciated. A lot of this information has become incredibly hard to look for on the internet. Hopefully soon I can just bite the bullet and do a complete round of testing myself, but gathering as much info as I can before hand could save me a lot of money/time. 

 

 

[Mark Dunn]

Selective darkening of a blue sky isn't what an 85 is for- it's to correct a film balanced for artificial light to daylight, and it won't have quite the effect you desire; as you say it affects the entire image.

In digital photography I would darken a blue sky by increasing the saturation of the blue channel, or preferably by reducing the luminance. There's a limit to how much you can do this without affecting the rest of the scene.

But the most effective way to end up with a deep blue sky is to start with one.

Edited February 19 by Mark Dunn

[David Mullen ASC]

In that example, there was a lot of overall contrast added somewhere in the chain, probably in color-correction.

And of course, in digital color-correction, you can isolate the blue channel and darken it.

The first 85 filter on tungsten stock just gets you to neutral, as if you shot daylight stock. The second one warms up the image quite a bit; that will slightly darken a blue sky but it's more that by making the image more orange, the blue sky stands out a little more (of course, the orange filter also makes it less blue, it shifts a bit to the green.)

If you have a really blue sky like that, a pola filter will do more to darken and saturate it, but if you like the orange highlights, then go ahead and use the extra 85 filter. Or do both, or use an 85/Pola combo so there is only one piece of glass.

But keep in mind that your reference photo is higher in contrast than normal, and increasing the contrast tends to increase the saturation.

[Evin Cameron]

15 minutes ago, David Mullen ASC said:

If you have a really blue sky like that, a pola filter will do more to darken and saturate it, but if you like the orange highlights, then go ahead and use the extra 85 filter. Or do both, or use an 85/Pola combo so there is only one piece of glass.

Funny coincidence here, I actually just ordered an 85/Pol after finding a great deal on eBay. 
 

20 minutes ago, David Mullen ASC said:

The first 85 filter on tungsten stock just gets you to neutral, as if you shot daylight stock. The second one warms up the image quite a bit; that will slightly darken a blue sky but it's more that by making the image more orange, the blue sky stands out a little more (of course, the orange filter also makes it less blue, it shifts a bit to the green.)

Much appreciated on this info, hopefully I can independently test the information from this video - it was claimed this orange shift was kept from the double 85 being used, but that you could fairly easily correct back to a neutral balance and that both 85 filters were able to knock the sky down by at least a stop or two - which was definitely confusing as all three example videos shown had this exact same high contrast orange look to them.

 

I think the video might be oddly presented as there also seems to be a more neutral video captured in the desert and the sky is much more in line with what you’d expect - just darkened slightly as though a polarizer was used, however it’s stated to be just two 85 filters knocking the sky down by “about two stops”. (2:56) 

I think the lack of raw out of camera stills / prints of these examples is what’s tripping me up here, seems like a lot of color and post work going on. This example in the desert is a much more desirable effect for me, but all these other examples had me skeptical with their high contrast look. 
 

The reply is much appreciated, I’ll be sure to share my findings on this thread once I run some tests for myself. 

[David Mullen ASC]

It would be easy to take stills to see the effect of using two 85 filters on a blue sky and correcting back to neutral versus normal filtering, but again, assuming digital color-correction, it's just as easy to darken the blue channel in post if that's what you want.