ND mmm

[Miguel Bunster]

Hi just curios about it.

 

I am shooting with 5279 in exterior work for a film and I want to shoto at 4.0 on the stop and will be using heavy ND which I have done before and NP but was testing a couple things and in a couple i got some color shift. Not so much on a single ND85-1.8 btu combining two NDs. I u nderstand this as adding characteristics of the filters but wanted to ask peoples experince in this.

Thanks!

M

[Kevin Zanit]

Heavy NDs tend to have some magenta shift to them. A solution is to use PANCRO ND filters which are two-way mirrors.

[Nick Mulder]

I dont know if you were doing it but if you sandwich glass or resin filters together closely (matte box type filters, not screw ins) you'll get interference patterns about the wavelength or so of the distance between them - I cant remember the physics/math exactly but its the same thing as a thin film of oil on water. Depending on the separation and consistency of the separation (i.e. how flat and clean your filters are) you can get some strong color cast, I've seen it turn up in print in medium format stills I have done ... I learned there is a good reason not to stack them directly and keep a distance apart of more than 1mm or so.

 

Kinda like this:

 

But the 'oil' is the gap of air between the two filters - same phenomenon, different set up ...

Edited October 9, 2007 by Nick Mulder

[Miguel Bunster]

Interesting for sure.

Thanks for the replays.

I printed a test of 5279 using an ND85-1.2 plus a ND3 and had no problem so most probable thing i will go with a 1.8ND85 and avoid extra glass...any thoughts?

M

[Hal Smith]

I dont know if you were doing it but if you sandwich glass or resin filters together closely (matte box type filters, not screw ins) you'll get interference patterns about the wavelength...

A good demonstration of this sort of interference is "Newton's Rings". In this case it's a spherical glass surface (like a lens) touching a flat glass surface, therefore you get concentric circular bright and dark rings.

 

http://en.wikipedia.org/wiki/Newton%27s_rings

[Miguel Bunster]

O yes got hta tbefore in HD jajaj really nice effext if you go for it....annoying in the other cases....but this is something you can acutally see as you are shooting unless i putting the name to another effect..

M