Monday, May 28, 2012

Tips for the Opteka Steavyvid Pro - Part 2

Balancing the Steadyvid Pro
  1. Strip camera to components to be flown
  2. Find the camera's weight
  3. Find the camera's center of gravity (COG)
  4. Mount camera to stage aligning for COG
  5. Mount the plate to have camera COG over gimbal
  6. Expand the stabilizer arch
  7. Attach the weights
  8. Use trim controls to adjust balance
  9. Adjust drop time
Strip camera to components to be flown
Make sure to remove the camera strap and lens cap. You want the camera to be in a ready to shoot state before attempting to balance. If there is a fold out screen set it up. If the lens is not an internal zoom you'll want it locked into position.

Find the Camera's Weight
It might be a good idea to find out what your entire camera weighs. For camcorders it's not so hard. For DSLRs and Micro 4/3 it will vary on the lens attached. Some lenses will put the camera over the weight limit. Any accessories such as a sliding mounting plate will add to the overall weight. If you're worried by the accesories you've added use a kitchen scale. You only have three available weights standard with the Steadyvid Pro. Though the box says it should take 5 lbs (2.26 kg) that might be a stretch.

Example Weights
ItemWeight
Canon 7D Body only842g
Canon LP-E6 battery77g
Canon 7D + Battery919g
Giottos MH621244g
Canon 70-200mm 4.0 + Filter + Ring924g
Canon 100MM 2.8 Macro + Filter664g
Sigma 17-50mm 2.8 EX HSM + Filter618g
Tokina 11-16mm 2.8 + Filter593g
Sigma 30mm 1.4 + Filter424g
Sigma 30mm cap14g
Canon 7D + Tokina 11-16 + Filter1512g
Canon 7D + Sigma 30 + Filter1348g
GoPro HD Hero 2 + 3D Hero Kit + Mount455g
Using metric units for the precision

Find the Camera's Center of Gravity (COG)
My technique for finding the center of gravity is to mount the camera on a plate then roll it around a cylinder like a ballpoint pen. I do this for front to back and side to side. For the Canon 7D it's toward the EOS-mount and the right edge of the viewfinder port. This is your target for the gimbal.



Another way is to support the camera with one hand and feel for the point where it starts to balance with your finger. Other cameras a regular enough shape that you could pretty much guess it should be the geometric center. The mounting hole for the camera is close to the camera's center of gravity, so it's always a good starting point.

Mount camera to stage aligning for COG
If we assume the gimbal is presently set for center of the stage, you want the camera COG right above the gimbal. The gross control for this is the mounting hole for the camera plate. There isn't an Opteka cookbook out there as of this writing. This will have to be accumulated by the user community. For this example I will be balancing the Canon 7D + Sigma 30mm + 67mm Filter. In the case of the 7D, I used the rear most position on the cross. This is not the optimal position but close enough. There is an even closer position which is the left rear hole. The trouble with that position was grip on the camera. Unless tightened enough there was a tendency for the camera to turn with heavier lenses. What matters is the camera stays in the position you set and is close enough that trim doesn't go out of range.



Mount the plate to have camera COG over gimbal
Now you should be able to mount the plate onto the stage. There is some left-to-right adjustment possible when mounting on the stage. Use the rear screw as a guide and compare it to the current gimbal position. Once your have the left-to-right position fairly close to the COG the next step is to deal with the arch. For the Canon 7D + Sigma 30mm + Filter I set the plate to align the left edge with the stage's left edge. This put the Camera COG on top of the gimbal.

Expand the Stabilizer Arch
To start with you will want the arch expanded to full. To do this turn the knob counter clockwise when you're facing its front. This arch has some flex to it which doesn't appear to affect it much in operation. But in build quality it's not quite a precise as the Blackbird I've had before.



At maximum expansion the counterweight's effect is maximized. This affects drop time. Hold that thought, more on that later.

Attach the weights
You want just enough weight to balance the camera. Too little weight and the stage will tilt-up or dive down. Too much weight and the camera will be too bottom heavy making it erratic. You only have three weights. Only the Start and Middle weights are able to attach to the arch. The minimum counter weight is 81g using the Middle Weight. This might be a challenge for very light cameras. In those cases you may want to add weight to the camera using a sliding mount like the Giottos MH621 Quick Release Adapter with Short Sliding Plate camera mount.
Counter Weights
Start Weight 335g
Middle Weights 162g (2x 81g)
Finish Weight 78g

Total 577g
So how can we find how much weight to use? I start by mounting all the weights then recombining them experimentally. The arch should still be at maximum extension at this point. For the Canon 7D + Sigma 30mm + Filter I took away the Finish weight (Start+Middle = 497g). The camera remained upright with a slight tilt. When I took out even the middle weight the camera totally tilted up (Start = 335g). When I added back the Finish weight (Start+Finish = 413g) it wasn't enough to counter the camera's 1348g. So I settled with the Start+Middle weight as the correct combination for my rig.

The intention is to have the rig slightly bottom heavy. Taking away weights or adding them back changes the COG of the entire rig. Notice the distinction! Before we were talking about the Camera's COG with respect to the gimbal. Now that you have the camera mounted you are trying to manage the Steadyvid Pro and Camera's overall COG. You want this to be slightly below the gimbal which acts as the fulcrum. Why? It has to do with Physics. Some people smarter than I am could probably work the math out for me. If you would like to take a shot here are some references:

http://www.ehow.com/how_7525395_calculate-weight-balance.html
http://www.school-for-champions.com/science/gravity_center.htm
http://www.grc.nasa.gov/WWW/k-12/WindTunnel/Activities/balance_of_forces.html

What I took away from this was the see-saw example. The heavier child, the camera in this case, has to be counteracted by the lighter child by varying either weight or distance. Now there could be cases where the camera is too heavy for the rig. My Canon 7D + Sigma 17-50mm 2.8 + Filter + Giottos MH621 could be balanced static but was too sensitive in motion. The Opteka website doesn't sell the weights separately on their catalog. You might have to get creative with washers to get more granularity.

Use Trim Controls to Adjust Balance
Now there is the infuriating part. I would find a sturdy table with empty space underneath. Merlin and WSCALTERs alike can sit on the handle when the camera is fairly close to balanced. With this you can use both hands to practice balancing. Once you get used to it, you should be able to balance it one handed while holding the camera with your dominant hand.





Keep and eye on the bubble level. If your camera has an electronic level that would be even better. For this exercise we stick to the standard equipment, hence the bubble level. If the bubble is to the right, you need to roll left a bit. Use the knob on the stage's side and twist clockwise to move the bubble left. The bubble might also be slightly back, use the knob on the rear and twist clockwise to move the bubble forward. Alternate between knobs until you get the bubble center. Move the arch out of center then let it fall to confirm it will sit center. Once you have a good balance tighten the silver locking bolts on the sides and bottom of the stage. You are almost there. This is what they call static balance.

One thing I don't like about the trim knobs is they tend to stick. I have to periodically check the gimbal to see if it's moving. The Blackbird was much smoother and precise. I'm comparing a Kia to an Audi here. Just letting you know.

When first learning to make adjustments, you should use whole rotations until the stabilizer leans in the opposite axis. Then dial it back. Over time the number of twists start to become intuitive. If you look inside the stage you will find it is manipulated by long screws. The reason for the stickiness is friction between the locking nut and the stage. This may wear down over time making it easier to move even with the silver locking bolts tightened. For alignment of the gimbal by sight, on the bottom the space between the silver bolts is center. On the side, the silver bolts are fixed to the sliding stage. When the rear silver bolt is close to the rear end of the groove you are at maximum aft.


Now pick up the handle and lift the rig from the table. It may get a bit squirrely then tilt in some odd direction. Adjust any major tilting with the same technique as you had. Now we need to work on dynamic balance and drop time all at once.

Adjust Drop time
If you move your hand left to right, then front to back you may notice it acting like a boat in rough seas. The rig is too sensitive because it is too bottom heavy. If the weights came in finer increments we could have added or removed more weights. Since we don't have this option we'll have to raise the weights/contract the arch.

Try pulling the weights to the left so the camera and weights become horizontal. This would be a good time to remember if all your silver locking and plate bolts are tight. You don't want the camera to fall off the stage! Then let go of the weights and count how long it takes for the it to cross vertical. With my rig setup it was less than 1 second. I reckon about .5 seconds it was already dropped. Yes, this is drop time.

The rule of thumb is you want anywhere from 1 to 2 seconds of drop time. On the Blackbird I liked 1.5 seconds, but when I started I did 2 seconds. For Merlin's they recommend close to 1 second. On the Steadyvid Pro, I'm still at 2 seconds. You'll have to get a feel for it depending on your camera. The end state you want is for the entire camera and arch to move together as a unit. When you stop you don't want it to overly tilt or rotate. If it does rotate as it falls then adjust the camera a bit backward then try again.

For the Canon 7D + Sigma 30mm + Filter it took about 15 clock-wise twists to get to the point where I was happy. Do a few twists at a time, move the camera around a bit, and observe how steady the head remains. Test the drop time. Then trim the balance. As you contract the arch the rig's COG changes so you have to continually adjust balance.



Whew, if you've gotten this far you should be able to walk around a bit with the footage being fairly stable. There may be some effects of inertia where it acts like a boat. Or maybe an unruly helicopter. That could mean more tuning. What it probably means is the need to practice flying the stabilizer. Here's a hint: use both hands!

On to Flying the Steadyvid Pro

6 comments:

JP said...

great article! when it's part 3 coming?

Mike said...

It's out now.

Mr.Smad said...

Great article. But I'm a bit confused by the weighing the camera part. Should the counterbalance be the same weight as the camera and lens? I only have about 800g of weight and my camera with lense is 1100g.

Thanks for any help

Mike said...

The further away the spur holding the counterbalance to the camera increases it's weight. Think of a lever or a seesaw. With the longer end of the pole you can counter a heavier weight with a lighter one.

だれ? said...

I am trying to stabilize my Canon T3i Rebel + 50mm f/1.4 but so far I haven't been able to balance it a bit. I think it has to do with the drop time being less than a second. However, when I adjust the arch it tilts backward way TOO much. Any suggestions?

Mike said...

Try reducing the weight on the spur by one unit. You want the drop time to be at 1.5 to 2 seconds to start with.