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#1 David Desio

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Posted 15 December 2010 - 09:54 AM

On a shoot yesterday I was using some BPM filters for a few shots when the Gaffer, who has years of experience on me pulled me aside and asked if I knew the rule for using pro-mist filters in relation to the focal length of the lens. I gave him a blank look and said I did not. He said that he thought the rule was that the longer the lens, the higher the pro-mist value should be, but he wasn't certain. Anyone know of this rule of thumb?

Edited by David Desio, 15 December 2010 - 09:55 AM.

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#2 linus rosenqvist

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Posted 15 December 2010 - 11:00 AM

I think that depends on why you are using pro mist, what lenses you are using and if you are using it for all shots. Are you using it to lower contrast or are you using it in a "leading lady" way?
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#3 David Desio

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Posted 15 December 2010 - 11:40 AM

a little of both, I wanted the highlights to bloom a bit and have the overall look be different from the video look of some other shots.
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#4 Tom Jensen

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Posted 15 December 2010 - 11:57 AM

On a shoot yesterday I was using some BPM filters for a few shots when the Gaffer, who has years of experience on me pulled me aside and asked if I knew the rule for using pro-mist filters in relation to the focal length of the lens. I gave him a blank look and said I did not. He said that he thought the rule was that the longer the lens, the higher the pro-mist value should be, but he wasn't certain. Anyone know of this rule of thumb?


Think about the filter in relation to the area it covers. If you are wide, you are covering a huge area of the scene. The tighter you go the area the filter covers is much smaller so you need to go stronger with the filter.
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#5 Dror Dayan

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Posted 15 December 2010 - 12:05 PM

Think about the filter in relation to the area it covers. If you are wide, you are covering a huge area of the scene. The tighter you go the area the filter covers is much smaller so you need to go stronger with the filter.



That´s also what I know. because the BPM is made up of tiny particals in the glass, if you use a longer lens you have less particals and the spaces between them are relativly bigger, hence less of a promist-effect, hence you need a denser filter...

all the best,

Dror
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#6 David Mullen ASC

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Posted 15 December 2010 - 01:32 PM

That's more true with nets in front of the lens, you are looking through less material and more open spaces, but with glass diffusion, generally the defocusing particles are also getting enlarged, and the front-focus is more critical on longer lenses, so the general rule is that longer lenses need less diffusion, not more.

However... we mainly use diffusion to soften detail, and closer shots (not longer lensed shots, but generally they go hand-in-hand), tighter shots, enlarge detail in the subject and therefore may need more diffusion. On wide shots, our eyes expect to see more detail than in close-ups. So in that case, we tend to go heavier on diffusion as we use longer lenses because we are using the longer lenses to get tighter, and vice-versa. However, if you decided to shoot a wide shot on a 100mm, for example, you may want to back off on the diffusion to hold more detail.

So in the end, I wouldn't blindly follow any rule of thumb on diffusion, as if you could just do it by the numbers, it's really an issue of the needs of the shot. Or, you can just decide that if you were shooting filterless, you'd just use a set of lenses that match fairly well, so you could take the approach of using the same diffusion filter on everything as the base level of diffusion and not necessarily have to vary it except for special occasions, like shooting wide-open or in foggy weather, times when you don't need as much diffusion.
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#7 David Desio

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Posted 15 December 2010 - 04:00 PM

Awesome, thanks for clearing that up guys. I guess it turns out that my Gaffer had it right, eh, you learn something new on every shoot don't you?
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#8 David Mullen ASC

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Posted 15 December 2010 - 06:40 PM

Awesome, thanks for clearing that up guys. I guess it turns out that my Gaffer had it right, eh, you learn something new on every shoot don't you?


I'd actually disagree with your gaffer, my point is that there aren't any "rules" to blindly follow, you actually have to stop and think about the amount of diffusion you want for each shot and each lens.
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#9 David Desio

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Posted 16 December 2010 - 05:25 PM

Thanks for the clarification David.
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