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Drop times for real


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#1 Jerry Holway

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Posted 26 April 2007 - 12:01 PM

All-

I was taking some time exposure "drop time" pictures for the Ultra2 manual the other day, and I suspect that I'm not counting my seconds very accurately...

Back in the days when we all had more or less the same rigs (when was that?) and GB counted for us all at the workshops, I think it was not too important to get an accurate timing.

But now with all the different rigs and different counting... All the drop time numbers we all talk about is misleading, confusing, inaccurate, etc.

Regardless, it would be interesting if several ops could take a video of their normal length rigs during several drop tests, transfer the footage to an editing program, and count the frames from horizontal to vertical, and compute the real drop time.

Then come back to the forum and say that you were using a rig about X inches long (measured camera c.g. to battery c.g), and that you FEEL that you use a normal, a more bottom heavy than normal, or a more neutrally balanced than normal rig. Or any other words to describe your rig's bottom-heaviness during the test. Someone really industrious might even balance their rig three differnt ways and give us the timings.

It still isn't scientific (the sled's inertia will alter the time as well.. it's a static vs. dynamic sort of thing ? for the old time ops on the forum, it's the Betacam effect...)

The reason for all this (beyond curiosity) is that I fear new operators hearing about 4 second drop times and actually trying to work with rigs with a drop time of 4 actual seconds, not a count.

Anybody game?

Jerry
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#2 Afton Grant

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Posted 26 April 2007 - 12:33 PM

Hi Jerry,

I'd be game... I'll let you know what I come up with.

Just curious, however. Wouldn't a 2 second drop time be 2 seconds, regardless of the rig? Assuming my counting (one-thousand-ONE, one-thousand-TWO) is relatively accurate. From horizontal to vertical, we're all just counting the time it takes for our sleds to move that 90 degrees, correct?

I do understand where it may be misleading, however. If the sled is longer, the speed at which its base sweeps past 6 o'clock will be faster. Is this the fudge factor you are talking about?
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#3 Eric Fletcher S.O.C.

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Posted 26 April 2007 - 01:39 PM

I was taking some time exposure "drop time" pictures for the Ultra2 manual the other day, and I suspect that I'm not counting my seconds very accurately...



Drop time is drop time. Length doesn't matter. Think of it more as Degrees per second. Infact why don't we just call it that.

I like a drop time 22.5 DPS (Degrees per second) or less. That would be a 4 second or longer drop time.
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#4 Bryan Fowler

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Posted 26 April 2007 - 02:22 PM

Anybody game?


I should have time to. I don't own a video camera though.. funny huh. I can borrow one from work.

BFo
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#5 Charles Papert

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Posted 26 April 2007 - 02:25 PM

I guess the confusion is that the longer the rig, the faster the base will swing through the air given the same exact drop time as a shorter rig, as the length of the arc is greater. My question is, does this result in a different feeling to the rig? In other words, does a 3 second drop feel the same on a 3' long rig as a 6' long rig? Does it require more force to tilt up with the longer rig? I suspect yes, but not having a long post I don't know the answer. if so, is there something empirical that can be drawn about a constant rate of descension at the bottom of the rig, i.e. the batteries move through 1 ft of arc per second for a 3 second drop time on a 3' rig which delivers the same feel as a 6 second drop time on a 6' rig, etc.? OK, now I've confused myself.
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#6 Jerry Holway

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Posted 26 April 2007 - 02:56 PM

I guess the confusion is that the longer the rig, the faster the base will swing through the air given the same exact drop time as a shorter rig, as the length of the arc is greater. My question is, does this result in a different feeling to the rig? In other words, does a 3 second drop feel the same on a 3' long rig as a 6' long rig? Does it require more force to tilt up with the longer rig? I suspect yes, but not having a long post I don't know the answer. if so, is there something empirical that can be drawn about a constant rate of descension at the bottom of the rig, i.e. the batteries move through 1 ft of arc per second for a 3 second drop time on a 3' rig which delivers the same feel as a 6 second drop time on a 6' rig, etc.? OK, now I've confused myself.


Yes, Charles, here we all are confused again.

A "3 second drop time" ? if normal with a short rig ? would be terribly bottom-heavy, nearly impossible to tilt, and very pendular with a long rig - so length matters, just you suspect!

Longer rigs need correspondingly longer drop times... this we know. Little rigs like the Merlin much shorter ones...

Regardless, what I wanted to find out was what the normal range of drop times actually was (in, at least, agreed-to-seconds) - knowing that how rigs are configured is going to alter this somewhat, along with what each operator perceives as normal, bottom-heavy, more neutral, etc.

I didn't proof-read the last sentence very well either - my suspicion is that what I would call (have been calling) a four second drop time is in reality more like 2.5 seconds or less, and if I told folks I had such a drop time and they duplicated it, they might not be so happy.

I was working with 2 second exposures and a rear curtain flash to get a 90ยบ drop nice for the photos, but we cheated with the moment of the drop... and I don't remember how the rig was balanced or anything... and I stopped it from swinging through, so I have no accurate time...

So I thought a few brave souls with a wee bit of extra time (Brian- use a weight if you have one) might try the test... and it may be that everyone is much more accurate in their sense of a few seconds than me.

Jerry

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#7 Lukas Franz

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Posted 27 April 2007 - 02:08 PM

Hello everybody,

mmh, do you remember my question about a different drop time in low mode, I posted some days ago? Well, many of us including myself have a longer drop time in low mode. Why? Because the rig is longer as in normal mode? Porbably. I guess, there is a dependence on the length of the rig!? Mmh? Very confusing...like physics always were.

My actual thoughts: if the rig is longer the acceleration of the bottom is higher, isn't it? As more the bottom is away from the gimbal (center of circle) as faster it falls. In the following way the drop time must be increased...

I'm not shure what's deciding. The acceleration of the bottom or the degrees per second, like Eric mentioned.

I'm curious about your thoughts and clues.

Lukas
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#8 Bryan Fowler

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Posted 27 April 2007 - 02:25 PM

My actual thoughts: if the rig is longer the acceleration of the bottom is higher, isn't it? As more the bottom is away from the gimbal (center of circle) as faster it falls. In the following way the drop time must be increased...


Hi Lukas,

Yes, a longer post will mean the weight will be further form the axis point (gimbal) and will have to travel faster to reach the bottom.

But that doesn't increase the droptime, just the drop speed.


------


Jerry,

I set up my EFP like I would normally, and taped the drop. I had been counting a 3.5"second" drop.

It was 74 frames from post release to passing vertical. I did 3 different takes. They were all within a frame or two.

So that's about a 2.5 second drop. Which might contribute to me fighting to keep level. =) Maybe it's my thumb.

Let me know if that help.
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#9 Jerry Holway

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Posted 27 April 2007 - 03:20 PM

Bryan - thanks for the research.

So there's one for 2.5 seconds, thinking it was (or counting) 3.5 seconds. We need more samples!! Bryan - did you think you had a fairly normally balanced rig top to bottom?

Lukas

Unless you change the length of your rig, there's no reason to alter your drop time. High mode, low mode, it should be about the same UNLESS you are trying do do something different in either mode for a shot - (lots of tilting or standing stock still, for instance).

Longer rigs (high or low mode) require a longer drop time for the same sort of feel, ease of tilting, pendular response, etc. compared to a normal length rig.

Everyone has different preferences; Larry McConkey works with a more bottom heavy rig than most, I'm told I do too, but not as bottom heavy as Larry's.

Other folks prefer and swear by a very neutrally balanced rig; it's always a compromise between vertical feedback, ability to balance and trim, pendular response,a dn what you've trained yourself to do. Find something you like for normal work, but don't ignore the advantages of different bottom-heaviness for specific shots. Especially if you are new at this, experiment and discover what's good for you.

Jerry
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#10 chris fawcett

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Posted 13 May 2007 - 06:20 AM

Hi Jerry,

Sorry, I almost missed this post.

My standard drop time is 2.5 seconds at Lb=26"

I have no great reason for it being like this, other than that I'm well used to it.

All the best,

Chris
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#11 RonBaldwin

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Posted 13 May 2007 - 10:37 AM

Larry brought me over to the dark-side many years ago -- I use about a 1.5 sec drop. Occaisionally I try slower drops but I always end up back to the same time.

Ron B
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#12 PeterAbraham

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Posted 15 May 2007 - 08:38 PM

It's okay. We like you anyway. ;)

Length does matter ! One degree of arc, drawn with a pencil and protractor on a sheet of paper is a narrow slice. One degree of arc, at forty million miles, is STILL one degree of arc but of course is a very different kettle of fish. ( to mix metaphors ! )

That whole Big Steadicam Law- DM=DM is in play here. The distance times the mass equals the distance times the mass when finding zero G. The longer the distances involved, the greater the apparent mass- even though the true weight/mass remains a constant ( assuming the rig is not altered with lens changes, etc. )

I have always felt this is why when using a lighter broadcast camera on a heavier rig, and the gimbal is 14-16 inches from the specific center of gravity of the camera, I feel less "in control" than I do when flying say, an Arri BL III where the gimbal is perhaps 6 inches from the specific c.g. of the camera body.

Peter Abraham
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#13 Jerry Holway

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Posted 16 May 2007 - 08:56 AM

Larry brought me over to the dark-side many years ago -- I use about a 1.5 sec drop. Occaisionally I try slower drops but I always end up back to the same time.

Ron B


Ron-

did you actually video your drop time or use a stopwatch?

I'm trying to get a sense of "real" drop times vs. "how I count" drop times... and see if our estimates are realistic.

and for Peter, it's distance squared times mass....

Jerry
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#14 chris fawcett

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Posted 16 May 2007 - 11:39 AM

Aha!

I thought I had a drop time of just over 2 seconds. The video showed a drop time of within 2 frames of 2.5 seconds over 5 setups of the same length Lb=26 inches

Chris
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#15 RonBaldwin

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Posted 16 May 2007 - 12:14 PM

Hi Jerry,
I thought it would actually be 2 seconds or more, but with a stopwatch it averaged 1.5 seconds. I use a stock pro sled with the old style batteries.

rb
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