Something new - for me

Jan 19, 2019
Leamington Spa, UK
Real Name
Thanks Paul.

We describe them to people as "something you use everyday, but have no idea it even exists...".

They are "Quarter turn" (90 degree) pneumatic actuators with electro-pneumatic positioners mounted on top of them.
The actuator is the "clam shell shaped item" beneath the rectangular shaped box on top.
The positioner is the rectanglar shaped boxes on top of the actuators. There are two variants of positioners shown. The positioner controls how far open or closed the valve is based on a variable control (input) signal. It's analogous to a "throttle" for the valve and controls the flowrate passing through the valve.

These assemblies are typically used to control valves (ball valves, butterfly valves, plug valves, etc.). The valves may control the water that feeds you home or business. The could manage the flow of waste (sewage) that leaves your house. The may control the flow of fuel in pipe lines, chemicals in manufacturing processes, or any other liquid or gas that flows through a pipe for any reason.

While the "primary" application for these devices is control of valves, there are numerous other applications. They are used to control damper drives. They are used on conveyor systems to operate divertor gates, they are used to open & close pneumatic doors on busses, they are used for waste gate control on large diesel engines, and on, and on...

One of the coolest application is precise controls in rockets (i.e. Space-X).

The pictured units are comparatively small. The models shown are slightly smaller than a basketball.

The ones shown here produce 850 in/lbs of torque, when supplied 80 PSI of air pressure.
The range is 6 in/lbs on the small end (used in soda fountains and other small applications) up to 284,000 in/lbs on the big end, with even larger models currently in design.
Fascinating - the world runs on stuff that 99% of the general population have absolutely no conception of!
Apr 1, 2019
I'm assuming the lights were outside the tent. Whether the lights were inside or outside the tent, the tent produces very soft light, especially so if the lights were outside the tent.

You're probably not aware of the correct terminology, especially considering that this might be the first time you've used it. When the light produces shadows with edges that aren't well defined, that's called soft light and soft shadows. Conversely, when the light produces shadows with edges that are clearly defined, that's called hard light and hard shadows. Notice that the shadows in your photos are very soft.

10/4... thanks. Light was all inside the tent. See attached iphone pic.

BTW - I found the book on Amazon. I tried 1/2 price, but no luck.

Fascinating - the world runs on stuff that 99% of the general population have absolutely no conception of!

Right, and this is just a drop in the ocean.

Wow -- god job on the photos and thanks for the info on what they are. Amazing!!


Thank you for the kind words, Ken.

Happy to share. Hope my explanation makes sense.


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Nov 11, 2005
Houston, TX
I have never heard anyone mention "family of angles" before today - I learned something new... I based my comments on taking photos of gold jewelry inside a light tent with external lighting - large light sources relative to subject size yields "soft" illumination of subject, as in portraiture.
Sep 13, 2007
Northern VA suburb of Washington, DC
large light sources relative to subject size yields "soft" illumination of subject

That's often correct in practical usage and is correct in the example you used of the light tent and the jewelry. But it's not correct in every situation.

Try thinking of it as follows: A relatively large light source produces soft light (and, thus, soft shadows). The important factor is that the relative size of the light source has to do both with its size and with its distance from the subject. As an example, the sun is really large, but is so far from anything on Earth that it is actually relatively small insofar as this discussion is concerned. That explains why the sun produces hard light (and, thus, hard shadows) if there are no clouds or other items such as tree leaves diffusing the sunlight. Conversely, though a light bulb is ridiculously smaller than the sun, when it is close to the subject being photographed it is relatively large -- yes, relatively larger than the sun because it is so close to the subject. That explains why it produces soft light and shadows.

This also explains why, when you place any light source close to a subject, it will produce softer shadows than when you place the same light source farther away from the subject. That's because when the light source is farther away, it is relatively smaller even though it didn't change in size.
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