Don't try this lens changing technique at home.

[evacguy]

Don Pettit on Instagram: "Changing my camera lens."

128K likes, 2,168 comments - astro_pettit on January 17, 2025: "Changing my camera lens.".

www.instagram.com

 

[Unframed Dave]

Probably a dust free environment.

 

[evacguy]

Probably a dust free environment.

It would be pretty dust free, apart from flakes of dry human skin!

 

[AlphaWorld]

Would you care to suggest how you might improve on this lens changing technique?

Yes, you might be lacking free-fall, but apart from that, it seems a reasonable approach.

 

[iain clyne]

At least there is very little chance of dropping them.

 

[evacguy]

Would you care to suggest how you might improve on this lens changing technique?

Yes, you might be lacking free-fall, but apart from that, it seems a reasonable approach.

Last time I checked, if I let my lens go in mid air, it would fall rather rapidly to the ground. One of the advantages of changing lenses in micro-gravity environments.

 

[AlphaWorld]

Last time I checked, if I let my lens go in mid air, it would fall rather rapidly to the ground. One of the advantages of changing lenses in micro-gravity environments.

So that what was meant - fair enough. I was wondering if it was a comment about maybe taking too long to cap the lenses, or something like that. One thing is true - can’t complain about not holding the camera downwards

Is it a micro-gravity environment, though? The photographer, the lenses, the camera, and indeed their entire surroundings are all in a gravity field, and the field is changing their direction of travel continuously (if it wasn’t, they would be travelling in a straight line, not orbiting). They are in free fall, because they are all be acted on by the same force equally. But should that be called a “micro-gravity environment”?

 

[evacguy]

So that what was meant - fair enough. I was wondering if it was a comment about maybe taking too long to cap the lenses, or something like that. One thing is true - can’t complain about not holding the camera downwards

Is it a micro-gravity environment, though? The photographer, the lenses, the camera, and indeed their entire surroundings are all in a gravity field, and the field is changing their direction of travel continuously (if it wasn’t, they would be travelling in a straight line, not orbiting). They are in free fall, because they are all be acted on by the same force equally. But should that be called a “micro-gravity environment”?

Hi Tony, yes what you say is correct, but not quite the full picture. It is a little complex to explain, but the gravitational field at the orbit of the ISS is approximately 89% of that on the Earth’s surface, so they experience almost as much gravitational acceleration as we do no earth. They appear 'weightless' because they are in free fall as they orbit the earth at 8 km/s. The perception that objects are weightless arises due to the orbital motion of the ISS, and the ‘balance’ between the two key forces acting on ISS and everything in it i.e., the astronaunts and the camera and lenses - the gravitational force (pulling them ‘down to earth’) and the centrifugal force (pushing them ‘out’ in the circular motion. This is often described as a 'zero gravity’ environment but that is incorrect, they are exposed to 89% of the force of gravity at the earths surface, and they are in free fall. As the speed around earth is not actually constant (hence magnitude of centrifugal force varies) and earth is not a perfect sphere (hence gravitational force varies), these two forces don't exactly balance all the time and so they feel a very, very, very, small pull of gravity and the magnitude acutally changes as they orbit, this is the so-called ‘microgravity’. At least that is my understanding.

Another interesting feature is that they also experience what is known as g gitter. The magnitude of the net gravitation force does not only change but so does the direction of the net gravitational force due to small irregular vibrations on board the space station which are caused by a variety of factors such as crew movement, equipment operation and small changes in the space station attitude control. While g gitter is very very small, it does create measureable issues with fine sensors and equipment.

 

[AlphaWorld]

Hi Tony, yes what you say is correct, but not quite the full picture. It is a little complex to explain, but the gravitational field at the orbit of the ISS is approximately 89% of that on the Earth’s surface, so they experience almost as much gravitational acceleration as we do no earth. They appear 'weightless' because they are in free fall as they orbit the earth at 8 km/s. The perception that objects are weightless arises due to the orbital motion of the ISS, and the ‘balance’ between the two key forces acting on ISS and everything in it i.e., the astronaunts and the camera and lenses - the gravitational force (pulling them ‘down to earth’) and the centrifugal force (pushing them ‘out’ in the circular motion. This is often described as a 'zero gravity’ environment but that is incorrect, they are exposed to 89% of the force of gravity at the earths surface, and they are in free fall. As the speed around earth is not actually constant (hence magnitude of centrifugal force varies) and earth is not a perfect sphere (hence gravitational force varies), these two forces don't exactly balance all the time and so they feel a very, very, very, small pull of gravity and the magnitude acutally changes as they orbit, this is the so-called ‘microgravity’. At least that is my understanding.

Another interesting feature is that they also experience what is known as g gitter. The magnitude of the net gravitation force does not only change but so does the direction of the net gravitational force due to small irregular vibrations on board the space station which are caused by a variety of factors such as crew movement, equipment operation and small changes in the space station attitude control. While g gitter is very very small, it does create measureable issues with fine sensors and equipment.

Thank you. That’s a much more detailed explanation than I’d have managed. 8km/s doesn’t sound like a lot, but if we call it 8 x 60 x 60 = 28 800 km/hour it suddenly sounds like a lot!

I do have a question: is it “g gitter” of “g jitter”? (I’m wondering if “gitter” Is an in-joke conflating g and jitter?) Makes sense, either way - small changes would be a lot more perceptible up there - I doubt anyone on the planet surface has ever felt lighter when the space station passed overhead

And let’s just leave “centrifugal force” as something for the pedants to argue about