Dealing with the problem of Stiction

[dklimek1]

I have been on a quest to lighten my load as I’m scrambling over the rocky coast of Downeast Maine, and am using the MonoGimbal to connect my Nikon D7500 / Tamron 150-600 to a Feisol monopod. I am very pleased with the combination except for one problem - Stiction. I often find myself tracking birds in flight. This is often thru 90+ degrees horizontal motion. With a tripod I was frustrated in that I had to be moving my body around the tripod while trying to keep aim on the bird. With the monopod, I can twist at the waist, and move the camera around me. Unfortunately, with the foot of the monopod fixed, the rotational angle of my camera (around the optical axis of the lens) is constantly changing. I loosen the mounting ring on the Tamron to allow the correcting rotation, but that’s where Stiction is a problem. Stiction is that initial resistance to sliding. Once it is overcome, the sliding is very fast do to this excess force necessary to start the rotation, and I over compensate. The same problem happens when I try to back correct. I’ve tried various oils and greases with limited success. I was wondering if you know of the best sort of lubricant to solve this problem. The Wimberley rotation is very smooth. Most of the lenses I have used zoom with a very smooth motion with very little of this initial resistance to rotation, so I would think there is a solution. Thanks.

PS. Stiction is also why I rarely use a ball head mount. No mater what the setting on the friction screw, I find my self jumping back and forth trying to set the desired camera angle.

 

[Rassie]

I wouldn't bring any wet lubricant near my lenses due to the risk of it getting into where it should not be. The only lubricant that I might consider would be a very limited application of a dry lube such as graphite powder. Even that may be risky, but I can't think of anything else.

 

[DRwyoming]

I agree with Rassie above. I wouldn't get any kind of liquid lubricant anywhere near a lens, particularly a zoom lens where the zoom action could pump a bit of that inside and onto the optical elements. I'd also say that often these kind of irregular rotation issues that cause stiction are the result of small machining tolerance errors where surfaces are not mating perfectly. IOW, lubricant might not resolve the issue if it's really a mechanical tolerance issue.

 

[Andrew Lamberson]

Stiction is best thought of as the amount of force needed to get to adjacent surfaces to start to move. It's the sequel you here when a cheap pump starts up. It is also why the paper drawer on your printer is hard to open, but once it starts to slide is gets easier.

Even more critical is when the nurse is giving you an injection and how hard they have to push to get the plunger to start moving (a project I worked on for an engineered thermoplastics company).

Since you cannot use an external lubricant to solve the problem, the manufacturer would have to spend some $$ for a thermoplastic that is designed for minimal stiction. The most common thermoplastic has PTFE (brand name: Teflon) in the formula and there are a number of other additives that work very well. They are known as "internally lubricated" thermoplastics.

People whine that something is made from "cheap plastic" but believe me, engineered thermoplastics are not cheap! They can also outperform metals in a lot of applications, at a significantly lower weight. They don't rust and can be very chemical resistant.

So, you might look for Gimbal made from an engineered thermoplastic. It probably won't be cheap...but it would work a LOT better! Or look for a Gimbal that has a thin "plastic" washer (so to speak) between the two surfaces. It's really there to reduce the stiction.

 

[dklimek1]

I certainly agree with the concern about lubricant near my lenses, but there are option with very low vaporization and high viscosity that may be safe enough. This reminds me back when I was a graduate student and working with glass vacuum systems. There were specially design stopcock greases which could provide lubrication over a large temperature range and would not be contaminating the vacuum innards. However, after looking at the rotating ring on my Tamron 150-600 mounting foot, it may be that the problem is that it was never designed for smooth motion with minimal stiction. Taking the ring off, there are stainless steel posts that hold the ring in place once it is rotated away from the entrance slot on the ring. These then rub against other parts of the rings a the lens is rotated. There is a plastic sheet on the inner surface of the ring, but it is not Teflon, and the opposing surface on the lens is a matted surface like the outside of the rest of the lens housing. I was looking at pictures of the Nikon 200-500 f5.6 and it looks like it has a similar design. Not sure where to go from here (other than put up with it).

I was wondering if the high priced lenses (like the Nikon 500mm f/5.6E PF) have a better design that provides smoother rotation of the mounting foot ring.

Thanks for the comments on this issue.

 

[Graham Clark]

I was looking at pictures of the Nikon 200-500 f5.6 and it looks like it has a similar design.

There is a degree of stiction with the OEM 200-500mm f/5.6 collar, changing to the aftermarket Kirk replacement solved it for me. Not sure if they do a replacement for the Tamron though?

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[dklimek1]

Graham,
Thanks, I'll look into it.
Dan

 

[dklimek1]

Arrgggg!! Kirk Enterprise Solutions doesn't make such a Lens Collar for the Tamron 150-600. Looking at their description for the Nikon 200-500 Lens Collar I can see how it would make a big difference on the Stiction issue. The entire inner surface of the collar is machined out of Delrin, including the slot for the stainless steel posts. Maybe I'll contact them and see what it would take for a special order. The relevant diameter of the Nikon lens is a liitle more than a mm smaller than that of the Tamron lens so maybe its just another pass on the lathe. Then again, things are never that simple.