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Member Since 25 Jun 2011
Offline Last Active Today, 04:29 AM

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In Topic: Vacuum for Neutral Bouyancy

26 August 2015 - 10:18 PM

This makes absolutely no sense. Did I miss a smiley?

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Typos are a feature, not a bug

Ultimately the housing will have a centre of gravity and when it goes up and down you can approximate the whole item to a single point. In absence of external forces the housing will not rotate around its centre of gravity. If you induce a force and make the item rotate on an axis this will continue to spin.
When people say the macro port makes the rig heavy in the front or the acrylic dome makes the rig light in the front is because the centre of gravity moves and now you have a torque on the axis between the handles of the rig if the overall system is negative or positive. When the rig is neutral it will stay in any position you leave it so if you are within grams this doesn't really matter much. In most cases though rigs are around 1 pound negative or less but not really 0.
So to have a perfectly balanced rig you need to ensure that the centre of gravity is on the axis between your two hands. Inducing an additional vacuum of 200-300 Mbar over a rig of more than 5 kg such as the gates housing in the clip will have an effect of few millimetre in determining the centre of gravity and therefore will be completely irrelevant

In Topic: Living on black sand - Lembeh

26 August 2015 - 12:59 PM

Are you watching this back on 4K monitor or what? 4K is not relevant if you watch back on a 1080p display.

I have a 4K TV thanks very much besides this video is actually 720p but still looks excellent


Correction she has a pro account it is 1080p

In Topic: Living on black sand - Lembeh

26 August 2015 - 09:37 AM


Not sure how you held the camera but the footage is very stable and sharp that makes up for the issues of the camera codec

Well done, this is better than other clips I have seen with 4K and similar!

In Topic: Vacuum for Neutral Bouyancy

26 August 2015 - 08:26 AM

Makes no sense whatsover

Archimedes Principle: Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.


The vacuum created is around 200-300 mbar so the reduction in the number of air moles is only 20/30%.


So he is making it lighter say 25% of the weight inside. The weight of the air is only 20-25 grams as a starter so 20% less is 5 grams


The explanation is incredible too


thanks for checking it out Erik. the reality is sucking the air out of the housing is just one step to help balance. it does in fact close the seal but if there is air in there, no matter how little, the housing tends to bubble it up on either end and the camera will start to teeter. majoritatively however, the housing requires specifically placed weights to counter the teetering which took about an hour for us to set up.


The reason why the housing will be more buoyant in one part than another is because of the specific weight of the part. The port for example will be lighter if acrylic than the rest, for glass instead could be the opposite. So once you work out how much weight or float you need to make it neutral you need to put it in the right place so that there are no rotation. If there are areas that are very dense the specific weight will be higher than areas that have gaps. But vacuum does not change anything really.


What does vacuum have to do with this????

In Topic: LX100 - Underwater video shot on the Red Sea

25 August 2015 - 12:08 PM

Did you try setting the focus mode to macro with the dome? I heard the camera can't focus when you zoom in with the dome but it should at least work until 40mm or otherwise it is a total waste of money


Coming to the video the definition is there but I don't particularly like the colors, which is a panasonic issue as things are on the green side, and the clip look a bit jumpy probably when you were pressing record and stop and the camera has a sudden shake. You could try cutting more and eliminating those parts to make it a bit more pleasant