Diffusion Filters

[gx42]

Hi all and thank you to Roger and team for this community forum, excited to have found it. I am prepping for a music video and am interested in having a discussion on diffusion filters.

The script is a mix of night time interiors and daytime exteriors. Dark living room scene with TV on and practical lamps in frame. Exteriors are urban streets and beach dunes at different times of day.

I am considering using a set of vintage lenses I own, but am curious about some tech on diffusion filters if I go with modern lenses. What adjustments should be made as you move from say a 24mm to an 85mm for consistency in the same scene?

Do filters behave differently on an indoor practical bulb vs outdoor highlights (like on water or reflected off a building)?

I also heard of filters that create the illusion of atmosphere/haze in a room which could be interesting on the interior. If anyone has experience with these i’d be interested to know more!

Also, any recs on which filters you’ve used/ prefer would be interesting to know as there are tons of options, and my personal experience is limited with lens diffusion.

Thank you and hope this wasn’t too long winded!

Topic

[Stip]

I personally would advise against physical filters. You cannot undo the effect. Luckily, filter diffusion is the one thing that actually makes sense to do in post imo. There is a plugin that emulates all popular diffusion and haze filters called Scatter from Video Village. It’s visually indistinguishable and you have infinitely more control than with physical filters. I think they have a demo version you can try.

[gx42]

This is a good point, and i’m definitely interested in using diffusion in post production on other projects! The flexibility makes a lot of sense, and thanks for the plugin suggestion! For this video I have the freedom to experiment and “bake-in” effects like this, so i’m less concerned with flexibility. I’m curious to use more traditional glass filtration, and make creative decisions in pre-prod and on set rather than make them in post for this project. Thought it would be a good exercise to learn about diffusion choices and do them in-camera!

[Stip]

Using post-diffusion does not mean that you make the decision in post. Usually you do tests before shooting and decide on what you are going for then.

But of course you can use physical filters if that is what you want.

[gx42]

That does make sense, I suppose I could create a file with the look and then monitor it on set. I have been a little headstrong on doing mostly practical/physical effects work on this video, but there’s no reason not to be open to this idea. Anything to make things easier and less complicated on set right? Appreciate the insight!

[Stip]

Yes the advantage of a physical filter is that you see their effect while shooting and may adjust lights ect accordingly. It might also be more fun 🙂

I didn’t want to talk you out of trying things the way you want to!

[Matt Stahley]

I would use physical filters personally. It’s just an added step in post that needs applied and adjusted for every clip. Like Stip said if you see what it actually looks like on set you can decide to fix it etc. I say get the image as close as you want the final look to be in camera.

[dmullenasc]

A diffusion filter has some element that causes light rays to be diffracted, throwing them out of focus, but has to have some clear areas to allow a sharp image to pass through — it’s the overlay of a sharp and soft image that creates diffusion.

There is another category of filters that have particles that spread and halate light: low-cons, fogs, and mist filters… but by virtual of having particles, they also cause some diffusion.  Some are designed to soften less but lower contrast more, some are designed to soften more but halate less. Tiffen Smoque filters are a type of low-con filter that gives the impression of haze in the air if any bright areas are in the frame like a daytime window.

There is seemingly opposite advice regarding filter strength, one is that the tighter you go on the subject, the heavier the filter needs to be; the other is that the longer your focal length lens gets, the lighter the filter needs to be. But these are two separate issues, the first addresses the viewer’s need to see fine detail in wider shots versus close-ups of faces, the second is a technical issue that often the elements that blur focus on a filter get enlarged on longer focal lengths so you might have to reduce the strength.  Ultimately this is why you have to make a judgement by eye.

If you want the look of diffusion filters, then use them! Just remember that it is safer to go lighter because you can easily make it heavier in post.

[Roger Deakins]

I have a box of around 40 filters of various kinds; fog filters, diffusions, black and white pro mists, even a series of stockings. The last time I opened the box to use one on a film was in the 1980s and I regretted doing so later.

[gx42]

Thank you all for the responses! I appreciate your individual perspectives on the topic as well as the technical information. It all comes to creative choices and this is the conversation I was looking for. I’m doing a test with light diffusion filters, and then with no diffusion and adding in post. We’ll see where I end up, thank you again!

[Author]

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