3A Arm type

[Eric Fletcher S.O.C.]

Both have extremely low friction due to new bearings and more iso capability, i.e., the potential for a flatter response curve.

 

BTW, all the G series arm's response curves can be flat or steep (user controllable) and also have a non-flat section near each end of boom travel.

 

 

Now hang on a second Jerry, a few things. First of all YOU are trying to redefine what iso is. This whole bit about the PRO and 3A arms and iso is all new on your part, post's from you in the past have stated unequivocally that they are not, now they are. Seems like revisionist history, no? You accuse me of trying to redefine it which I'm not I'm just using the correct terminology for the behavior of the arms so that we can actually discuss what they are doing.

 

You also are now characterizing the response curve (You have always used the term Ride, so are we changing that term now also?) as flatter or steeper. In the past you called this "more Iso" or "less iso" and this has always been the way that Tiffen workshop students have come to the board asking about arms. Is this the new terminology? I'd like to make this clear so everyone can follow along.

 

Question about the "X" Series arm. Has there been geometry changes or just bearing changes because if it's just bearing changes, the only way to increase "iso" is to have reduced friction. If that's the case then wouldn't that empirically prove that "iso" is friction?

[James Davis]

Anyone interested in trying out a new arm should get themselves to the Tiffen factory or a workshop or trade show.

 

Both the G-50 and G-70 have been improved and have new designations, the G-50x and the G-70x.

 

Both have extremely low friction due to new bearings and more iso capability, i.e., the potential for a flatter response curve.

 

BTW, all the G series arm's response curves can be flat or steep (user controllable) and also have a non-flat section near each end of boom travel.

 

The G-70x has some additional geometry tricks that make it a joy to use....

 

But, as it is ultimately about user preference, I suggest users try the new arms and compare them to any other arm out there.

 

Jerry

 

Anything available online yet about these new arms Jerry, and do they have them in house at Tiffen in Oval (London) to try?

[Jerry Holway]

No, Eric, I'm just trying to explain, using some of your concepts/words, and other words, what is and has always been the definition or concept of "iso-elastic." Which, has always referred to the relative effort required to boom up and down fully from the float point. Iso-elastic (or more iso) arms take little or less effort, less or non-iso arms require a lot, or more effort.

 

I've always and consistently said that friction is a different thing, and that it affects how any arm behaves, and generally in a negative way. So we all agree on that. Surprisingly, the original Flyer arms were too friction free, but I've said this before as well.

 

What I've always said about the PRO arm is that it is iso-elastic, and the PRO achieved an iso-elastic response curve through different springs and a different geometry than used in other arms.

 

What I've always said about IIIa arms is that they are iso-elastic at high loads, and less and less so and the load is decreased. A gold spring arm with the springs relaxed to lift only 37 lbs (the bottom of the lift range) is not very iso-elastic. Or to consistently put it another way, when carrying a light load, IIIa type arms are very reactive to vertical changes, or to put it another way, they seek the float point strongly, or to put it another way, they take a lot of effort to boom up and down.

 

All arms take progressively more effort to boom further and further from the float point; it's just a question of how much effort is required, or in some cases like the IIIa arm, how much effort is required depends on how much load is being lifted.

 

Some folks at Tiffen labeled the "iso" knobs "Ride" - thinking that would make it easier for some to comprehend. No change in concept.

 

Yes, there have been some subtle geometry changes in the G-70x to increase the iso, flatten the response curve, etc. Again, this is separate from friction. And some other tricks to improve the overall performance, which I believe everyone should experience

 

Jerry

[David M. Aronson]

How about we forget about brands and go back to how a spring works.

For the sake of argument, Let's say that springs follow a perfect cubic curve. It takes 1 Unit of Mass(uom) to stretch the spring 100%, it takes 4 UOM to stretch the spring 200%, 16 UOM to stretch it 300% inches, etc.

 

If you have a spring diagonally across a parallelogram and put a load on one end, It's going to very strongly seek the float point. That's because of how a logarithmic scale works. If you stretch a spring, it gets exponentially harder to stretch. If you Use the range of a spring from 0% to 300%, you have to lift up or push down 16 UOM. If you only use from 0% to 100%, you only have to lift up or push down 1 UOM. You decrease the range of the arm by 300% though. That's why arms use pulleys and cables(the older ones at least). They use a ratio so that the are will still have the same amount of travel, but only use 0% to 100% of the spring travel.

 

Good arms take very little force to boom up and down. They don't seek their float point strongly because they're tuned to the weight that's on them and because the springs aren't deflecting that much. An arm that uses friction to stay put is like one of those arms for a computer monitor. They don't care how much weight is on them, thy have enough friction that they stay put.

 

I'm not a physicist so feel free to correct anything that's wrong mathematically.

 

Also, we all know which arms use pulleys and cables, which use compression springs, etc, but for the sake of science, let's not use brand names!

[Jerry Holway]

 

Now I'm wondering about how to adjust the arm. I've heard that it's supposed to adjust the 4 screws pretty much the same. (I'm working with lighter cameras too, what forces me to relax the springs - Certainly it becomes less "iso-elastic" then.

 

Yet, playing around with it I found it better to have the lower bones (regarding only one arm section!) tighter/ the upper ones more relaxed. This makes it feel easier for me to boom it up and down, even with lighter loads.

But now I'm concerned about the mechanics. Could this adjustment be any bad for the arm/springs?

 

One more thing - What grease would you recommend for this arm if squeaking occurs? And also where to grease??

 

 

Fabian-

 

It's generally considered better if both arm sections work together; i.e., that one arm section does not lead or lag, as that will or can produce a "bump" or lack of smoothness in booming. Typically 3A type arms are set so both arm sections float slightly down from horizontal, but level or slightly up probably won't make much of a difference, and it might help you get a particular shot, or you just might like it that way.

 

While I suspect that your method of adjusting the arm doesn't get the most out of the arm, you should videotape yourself as you boom up and down as well as recording what you shoot - if you see any issues, change how you adjust your arm.

 

I don't know the Artemis arm very well, so you should contact them for grease info. I used to use a teflon grease (low friction, non-dirt-attracting) - and not a lot of it - in the trunion bearings when I greased my arms.

 

Jerry

[Matteo Quagliano]

Hi Jerry and Eric,

 

With all the due respect I suggest a match. Same path, same op, same camera, same sled but different arms (G70 and PRO). Then edited in split screen left and right.

 

maqu

[Eric Fletcher S.O.C.]

Hi Jerry and Eric,

 

With all the due respect I suggest a match. Same path, same op, same camera, same sled but different arms (G70 and PRO). Then edited in split screen left and right.

 

maqu

 

 

Just Demo the two, you'll pick the arm that is used by most....