I just did some experiments testing out the stability of various positions for sandbags, seeing what would allow the longest boom extensions of the heaviest loads without the stand becoming unstable and potentially tipping over.

Here's what I learned, and just wanted to check that others agree:

On C stands where one leg is longer and taller than the others it's best to put all the sandbags on the longest leg, and have that leg pointing in the direction of the boom/load. Using a single 25 pound sandbag with rectangular sides that lays nice and flat off the ground is more stable than using two smaller square sided 15 lb sandbags stacked on top. If I want to add another sandbag, it's better to put it on top of the other(s) on the long leg pointing towards the boom rather than distributing the weight to the other legs.

With conventional stands such as the Manfrotto 1004BAC (http://www.bhphotovideo.com/bnh/controller/home?O=&sku=644444&is=REG&Q=&A=details) it is not a good idea to attach a boom. Doh! I snapped off the stud on mine by attempting to hang a weight off a grip arm. Luckily Manfrotto makes it easy to order replacement parts, so it's only a $30 lesson. The lesson is don't attach loads that apply significant torque to aluminum stands.

On folding boom stands where all the legs are the same length such as my Manfrotto 420b or on the conventional folding equal length leg stand Manfrotto 1004BAC, when used to support background crossbars, I place the sandbags on the flat metal supports under the sloping legs, not on the legs themselves:

I will put the first sandbag under the leg pointing 180 degrees away from the crossbar load, and further sandbags will be placed so that they are on top of two of the three leg supports, so I don't overstress any one of the leg supports with too much weight. Same thing when putting a light like a heavy fresnel on these stands: first sandbag opposite the load, subsequent ones distributed around the center.

Great information here, Tom! We just have 25 lb bags, so I hadn't considered the one vs. two bag thing. On larger light stands, we can fit the 25 lb bags over the bottom crossbars. On smaller stands, we just put them on the diagonal legs.

Also, great information about C-stands vs. light stands for torquing loads. C-stands are heavy and expensive, but they really do their jobs well, don't they.

A couple tips (unrelated to sandbags)...

* Always put the knob on the right of the c-stand extension bar. As gravity pulls the bar down, it tightens the clamp.

* You can use a C-stand, extension bar, clamps, and a monopod to create a poor-man's jib for static shots. It's not as easy as a well-balanced jib and tripod head (just move the camera into position and it sits there), but it's just as effective in the final shot. Yeah, you have to loosen/tighten when making adjustments, but you can place the camera at unique positions and angles, which is great for macro shots and odd perspectives. Note that this setup will bounce, so you need to push REC, damp the vibrations and wait a few seconds before calling "Action!"

Anyway, great tips on sandbag usage - an essential part of any grip kit.

I just want to start a poostorm here by saying that that is generally the way I do it with c stands, but i have known many legit long time professionals who will bag the two back legs on a c stand rather than the longest leg under the weight. Also a big debate can always be had about whether the bag should hang so low as to touch the ground (some say if touching ground its not doing anything, some say if NOT touching the ground its not doing anything). Some say its better to wrap the bag around the vertical column of the stand so that weight is right in the center rather than on the long leg.

Its the "how to clean a lens?" Debate all over again. WHAT HAVE YOU DONE????

That's not how I do it. I put the longest leg under the load, then wrap the sandbag around the riser to put the weight opposite of the load. This way I only need the one sandbag, and it guarantees the bag doesn't touch the floor for all but the strangest bags.

Here's an example from a client's living room shoot:

it begins...

That's not how I do it. I put the longest leg under the load, then wrap the sandbag around the riser to put the weight opposite of the load. This way I only need the one sandbag, and it guarantees the bag doesn't touch the floor for all but the strangest bags.

Here's an example from a client's living room shoot:

Bruce has good technique.

I just tested out Bruce's placement, and it did hold a bigger boomed load than putting the sandbag flat on any single leg. But the wrinkle is that it's unstable with my sandbags and stands. The handle to release the turtle base of my stand points toward the long legs, holding the sandbag away from the center column, so the corner of the sandbag just barely touches the lowest/shortest leg and could easily fall off.

The most surprising thing I learned while doing this testing is that if I take a 40" grip arm and grip the stud of a C stand with the fixed grip head, the righty-tighty rule that John mentioned does not apply. Just the opposite: it needs to be oriented such that the arm faces left as you are looking at the tightening knuckles.

Thinking about it a bit more, I suppose this configuration probably shouldn't be used at all; typically you put the non-fixed grip head on the stand, and put the fixed end of the grip arm on your light or flag. So no need to learn exceptions to the righty tighty rule, just learn "don't do what I did" (gripping the C stand stud with the fixed grip head on the arm).

(Puts on best Lady Bracknell voice):
A sandbag?

Sorry - someone had to say it. Carry on - this is interesting.

According to the Set Lighting Technician's Handbook you put the sandbag on the top leg, so that the weight is resting on the leg not the floor. Although,I notice that didn't apply in the illustration with an arm fitted to the C stand, when you place the longest leg under the extended arm. You work with gravity, so that when you put weight onto the arm, it tightens it, which means that with the arm facing away from you, the knuckle should be on your right.

I just tested out Bruce's placement, and it did hold a bigger boomed load than putting the sandbag flat on any single leg. But the wrinkle is that it's unstable with my sandbags and stands. The handle to release the turtle base of my stand points toward the long legs, holding the sandbag away from the center column, so the corner of the sandbag just barely touches the lowest/shortest leg and could easily fall off.

The most surprising thing I learned while doing this testing is that if I take a 40" grip arm and grip the stud of a C stand with the fixed grip head, the righty-tighty rule that John mentioned does not apply. Just the opposite: it needs to be oriented such that the arm faces left as you are looking at the tightening knuckles.

Thinking about it a bit more, I suppose this configuration probably shouldn't be used at all; typically you put the non-fixed grip head on the stand, and put the fixed end of the grip arm on your light or flag. So no need to learn exceptions to the righty tighty rule, just learn "don't do what I did" (gripping the C stand stud with the fixed grip head on the arm).

As Tom has discovered there are differences in gear which may require alternate methods. As far as the righty tighty rule the adjustability of grip head and arms should allow you to always let the head tighten as the weighted end falls. Sometimes you have to figure out that correct orientation for this as it is not always the way you need it at first.

As Tom has discovered there are differences in gear which may require alternate methods.

Indeed. Here's someone who looks knowledgeable that suggests two sandbags on the legs opposite the load (at about 3:06):

All About C-stands on Vimeo Video School on Vimeo (http://vimeo.com/videoschool/lesson/168/all-about-c-stands)

And because those sandbags look like they are applying significant weight to the legs even when touching the floor, I think he made a good call. If I had enough of those sandbags I would probably do the same. But I don't; I mostly have sandbags that would put all of the weight on the floor on the lowest leg so I'll continue to put them on the tallest leg to get them off the floor.

You work with gravity, so that when you put weight onto the arm, it tightens it, which means that with the arm facing away from you, the knuckle should be on your right.

For those who aren't clear, this means the knuckle on your right as you stand on the opposite side of the stand from the boom. Not as you are facing the stand from the boom side, where it will be on the left.

At the risk of beating a dead horse... The interesting thing for me was that when, for some crazy reason, you have the stand gripped in the grip head on the fixed end of a grip arm, then it's the stand that needs to be applying the torque to tighten the grip knob not the arm. Which means the stand has to apply pressure in the rotational direction that would move the arm upwards not downwards. This is why it's Lefty-tighty in that situation as I said earlier. Anyway, don't mean to confuse things by talking about a configuration that should probably never be used. Right on for Righty-tighty.

Indeed. Here's someone who looks knowledgeable that suggests two sandbags on the legs opposite the load (at about 3:06):

All About C-stands on Vimeo Video School on Vimeo (http://vimeo.com/videoschool/lesson/168/all-about-c-stands)

Funniest thing about that video is he has the scrim in the picture (under Anatomy of a C-stand: section) on the wrong side.

For me I always go back to what the gaffer for the underwater scenes in sphere taught me. When looking from behind the arm, nob goes on the right, and the weight being supported goes on the part of the arm away from you. This always results in a self tightening setup. He also emphasized the importance of not only sand bagging the legs (sand bag does not does the ground but is as close to it as possible), but also setting a counterbalance weight (usually another smaller sand bag) on the opposite side of the arm from the lighting instrument. That really helps to keep your rig from tipping over. He had some of the greatest grip gear in his "small" kit.

One thing I'm still unclear on is how or if the right hand rule applies when you have loads pointing straight up or straight down. Imagine a fixture or flag whose supporting pin in the fixed grip head, on the end of a grip arm, is facing straight up or straight down.

I suppose a very exacting grip or engineer could argue that since the slot holding the pin is a half inch or so from the center of the knuckle, gravity acting on that half inch constitutes a moment arm that would twist the knuckle either in the loosening or tightening direction depending on the orientation. Hence in some cases to be super-safe one might rotate the grip arm 180 degrees to switch the knuckle handle from right side (more convenient generally) to left side (generally less convenient). And if the weight is above rather than below, there's some small chance that the problem could snowball as it tilts more and its weight creates more torque. I probably should just let sleeping dogs lie here :-)

Tom, it's not a matter of where the pin is in the grip head. It's where the center of gravity is in horizontal relation to the screw on the grip head. It's pretty hard to explain without visual aides so maybe next time we see each other we can talk about it.

BTW, I'm still having to work with Stan to pull together our audio testing. I've been picking up some last minute jobs this month so I've been pretty busy. Looking to get some tests protocols set up soon. let me know if you're still in.

Cheers.

It seems to me that the purpose of a sandbag is move the center of gravity of the rig (the stand itself and everything attached to the stand) closer to the point that is the average of the locations where the stand legs meet the floor. Of course this is a bit complicated since the stability of the stand relies entirely on friction and gravity and anything attached to the stand is mechanically attached. The ideal sandbag attachment would probably be one where it, too, is mechanically attached without any room for movement or shifting relative to the system in the event of unintended forces acting upon the system.

Breaking it down, though. I would think first of all that letting a sandbag rest wholly or partly on the ground might jeopardize its connection to the stand. If someone collides with the stand, it will at first act as though there is no sandbag is on it, though hopefully once it moves enough the sandbag will finally be part of the system and may stop the movement. Better, however to avoid any movement at all since that initial movement of the stand before the sandbag is engaged might be enough to change the position of the sandbag or set in motion some other forces that would keep the stand moving even once the sandbag is engaged.

It makes sense that as long as the sandbag is placed anywhere on the base where it is supported entirely by the base and not by the floor, it won't matter much to the system if it is on a leg or around the post. However, the height of the shorter legs nearly guarantees that if the sandbag is hanging on one, it will be partly supported by the floor and will not increase the mass of the system perhaps until it is too late.

I think some may put sandbags on the back legs since it may seem to bring the center of gravity away from the load, but I think that is generally outweighed by the benefits of avoiding allowing the sandbag to be supported by the floor and of increasing the weight and therefore friction of the front leg which is by far under the most stress. Of all the legs, any slippage or movement of the front leg would be the most catastrophic, and its greater length also protects better than the other legs against the sandbag sliding off. Also keep in mind that the most stable point or the point that is the average of the positions where the legs meet the floor is not the stem/post but just in front of the post on the front/long leg since it is longer than the others.

I'd say hang off the front leg is my first choice. Wrapping the sandbag around the stem allows the bag to swing or move less but I think is a bit more prone to allowing the sandbag to be kicked off though it depends on how full the sandbag is. Wrapping around the stem is probably my second choice and the place where I'd put my second sandbag if I want to hedge against my first placement :)