Is it possible to use 4-5 of the $30 standard halloween fog machines and get the effect of a very foggy exterior area? Or do I need a special fog machine?

Much will depend on the weather conditions at the time. Low temps, High humidity and NO wind... and you're in good shape. (Of course, I've basically described the conditions under which fog exists.)

The industrial strength machines will put out a denser fog. Ive used both, and prefer the heavy duty machines. BUT you can get by with the cheaper ones. Lay the fog in the scene, maybe even use a fog filter on the camera to accentuate it, and go for it. Fog in between shots to keep it going.

But if there's a breeze... your S.O.L.

Also define in your mind what "fog" is. The machines you describe make smoke, although they're often called fog machines. But real fog hugs the ground while smoke rises up into the air.

For theatrical effects if a true fog is needed we would use a dry ice fogger since they produce a heavy water vapor that hugs the floor. You can also buy/rent "chiller" accessories for commerical fog machines which make the smoke lay low.

Also realize there are very real health/safety concerns for glycol based fog machines (which is what the ones you describe use). All the technical, musicians and actors unions have adopted some rather strict rules about their use.

Consider renting a more powerful fog machine from a local theatrical supplier, it will have a much higher output than the cheapo halloween store junk. It will also use fluid which have known composition. The best machines are made by LeMaitre, Rosco, MDG and CITC. A little Googling will get you lots of info.

Also, try experimenting around a bit in post. Apple Motion has some really nice fog effects which can be modified as needed. Try overlaying these on another video track and varying the transparency - I've gotten some good results this way.

Also define in your mind what "fog" is. The machines you describe make smoke, although they're often called fog machines. But real fog hugs the ground while smoke rises up into the air.

For theatrical effects if a true fog is needed we would use a dry ice fogger since they produce a heavy water vapor that hugs the floor. You can also buy/rent "chiller" accessories for commerical fog machines which make the smoke lay low.

Also realize there are very real health/safety concerns for glycol based fog machines (which is what the ones you describe use). All the technical, musicians and actors unions have adopted some rather strict rules about their use.

Consider renting a more powerful fog machine from a local theatrical supplier, it will have a much higher output than the cheapo halloween store junk. It will also use fluid which have known composition. The best machines are made by LeMaitre, Rosco, MDG and CITC. A little Googling will get you lots of info.

Also, try experimenting around a bit in post. Apple Motion has some really nice fog effects which can be modified as needed. Try overlaying these on another video track and varying the transparency - I've gotten some good results this way.


Ahhh...the fog machine thing again. I remember the thread from awhile back discussing glycerine based fog. Keep in mind however, that if used in a confined area, the use of dry ice (frozen CO2) could liberate too much carbon dioxide and lead to an oxygen deficient atmosphere leading to asphyxiation. Keep in mind, I'm talking about confined space use, not a large theatrical environment. but wanted to present that as a 'don't do this' sort of warning.

-gb-

If you end up going the post route, you'd do well to investigate Particle Illusion (http://www.wondertouch.com/). I have a copy, myself, and while I've never done fog personally, I understand there are some out there who have; successfully, I might add. I've done a test here and there that looked quite good, but my standards may be too low. Heck, you don't have to take my word for it, try the demo (http://www.wondertouch.com/downloads.asp) and see what you think.

For a brief, but nonetheless interesting look at some serious fog done in post production, check out the extras on the DVD for "The Others" (with Nicole Kidman). The relative merits of the film notwithstanding--I liked it, but what do I know--the technical stuff they show is pretty cool. Not too detailed, and no verbal explanations, but they show you how they pulled off the thick white fog outside of the house, with a before, after, and four-way split screen of all the different layers involved in one of the shots. None of the fog was there during production, apparently, which blew my mind. Just a couple guys walking along behind Ms. Kidman with a Photoflex-style greenscreen to help separate her from the background.

Much will depend on the weather conditions at the time. Low temps, High humidity and NO wind... and you're in good shape. (Of course, I've basically described the conditions under which fog exists.)

That's hilarious, Richard!!!

Anyway, Drew....We rented a fog machine from a local music store and did pretty much what Richard suggested in his post (minus the fog filter). It worked well enough and only cost about $35. It didn't produce VERY foggy outdoor conditions, like what you mentioned, but it was dense enough for our needs. Maybe you could rent a couple of them.

I remember the thread from awhile back discussing glycerine based fog.

Not to nitpick, but I specifically said glycol based fog which is very different from glycerol based fog fluid. Glycol is somewhat similar to auto antifreeze, like alcohol, and there has been extensive testing done of these fluids which are the source of a lot of controversy. Glycerol is actually edible and used less frequently in fog machines so there is much less test data and hence less controversy (which doesn't necessarily imply it's safer though). The glycerol fluids are used in "haze machines" which are intended to create a more evenly dispersed atmospheric haze effect that hangs in the air a long time. We use the LeMatire G-300 as a haze machine with glycerol based fluid, but the same machine can also operate in fog mode with glycol fluid. However our singers have only approved its use with the glycerol based fluid.

Your point about the dry ice machines is well taken, but I think it would have to be a very confined space to be an issue, and of course the topic of this thread was outdoor use :-) I don't think a dry ice fogger would be effective outdoors personally.

To address the original question of "how is it done in movies," for many years Hollywood used "oil crackers" to fill large areas with haze. These machines use mineral oil, and there are even greater health concerns with these.

In 1999 the University of British Columbia did a study of the effects fogs used in the film and TV industry. If you plan to work with this stuff very often then you should read their report, it's pretty sobering:

http://www.shape.bc.ca/resources/pdf/summary.pdf

Compared to the control group, the entertainment industry employees had lower average lung function test results and they reported more chronic respiratory symptoms: nasal symptoms, cough, phlegm, wheezing, chest tightness, shortness of breath on exertion, and current asthma symptoms, even after taking other factors into account such as age, smoking, and other lung diseases and allergic conditions.