Question Need Help with Assessing how many floats I require for my rig

[adiRHIT]

Hello
I am just buying my first underwater photography rig and have tried to make some rough calculations on what the net weight underwater and net buoyancy of my kit would be ... The gear I plan to use:

Isotta housing for Sony A7RV + Macro Port + Zoom Gear + Sony A7RV with the 28-60 lens --> Isotta says this should weigh 460 gms underwater
2 x Backscatter Hybrid Flashes --> Estimated weight in water with batteries is around 250 gms each = 500 gms
Nauticam WWL-1 Lens with the foam collar --> estimated weight in water = 160 gms

Here's the tricky part --> arms, clamps and floats:
Option 1 - as suggested by Blue Water Photo --> get UL 8" & UL 5" arms + 1 set of the Stix Jumbo floats
Option 2 - as suggested by Backscatter --> get Isotta 50mm 8" arms + UL 5 or 8" arms + 1 set of the Stix Jumbo Floats
Option 3 - get Isotta 70mm 8" arms + UL 5" arms + 1 set of the Stix Jumbo floats
Option 4 - Stick to the UL 8" & 5" arms but get 2-3 sets of the Stix Jumbo floats...
I will need 6 clamps in any case... these seem to have a weight of 60 gms each on land ... I cannot find any reference to their weight underwater ...
Similarly, the UL 8" arms appear to be 90 gms on land and the 5" arms are 60 gms on land, but again I have no reference to what they weight underwater.

I have put a chart together from my rudimentary calculations... does this make sense ... seems like a hell of a lot of floatation!

Have I made some mistakes? or does anyone have clarity about the net weight underwater of the UL arms or the UL Clamps?

Any advice will help.
Thanks guys!

 

[inquis]

Best bet is to just weigh it when submerged using a luggage scale. From past experience, I've found that spec sheets are often way off.

 

[adiRHIT]

Best bet is to just weigh it when submerged using a luggage scale. From past experience, I've found that spec sheets are often way off.

great idea ... only point is that by then I am committed to the arms which I order online and going to back change them is another headache ... the Stix Floats I can always get more of if required... just that I run out of real estate to use them if I buy the Isotta 8" arms ... then only have 5" arms x 2 --> so get limited to maximum of the 4 pieces of 1 kit of the Jumbo Stix floats

 

[tursiops]

If you ae doing anything other than macro, you NEED longer arms to get the lights away from the lens....to help with shadows and mitigating backscatter.
8 inch arms (two each side) is probably a minimum. Pleanty of room for STIX.

 

[adiRHIT]

If you ae doing anything other than macro, you NEED longer arms to get the lights away from the lens....to help with shadows and mitigating backscatter.
8 inch arms (two each side) is probably a minimum. Pleanty of room for STIX.

So your suggestion is to get 2x8" arms on each side instead of one 8" + one 5" arm?
And you feel the UL arms are a better bet to stick to vs the float arms from Isotta?

 

[tursiops]

So your suggestion is to get 2x8" arms on each side instead of one 8" + one 5" arm?
And you feel the UL arms are a better bet to stick to vs the float arms from Isotta?

UL arms are good. I do not know about Isotta, sorry.

 

[TostitoBandito]

I prefer the stix foam (on normal ULCS arms) to hollow/float arms because it's cheaper and far more customizable. You won't know exactly how much buoyancy you need to add until you get it in the water. You can guess, but adjustments are often needed and you can't adjust float arms. And if you ever change ports/lenses in the future you won't have to shelve your fancy hollow arms for buoyancy reasons. I own both the normal and jumbo stix foam, though at the moment I think I only use the normal ones, and only for macro. My wide angle config with the dome is positive, and actually requires wheel balancing weights under the dome shade to trim out.

As for arm length, 5+8 and 8+8 are both common arm configs. I personally use 5+8 on each side and don't have any issues getting my strobes out for wide angle. I find that having a shorter inner arm makes the whole rig fold up nicer because the arms usually start with added height from the housing. But either way works. I wouldn't suggest anything longer than 8+8 unless you have a specific need.

 

[hedonist222]

DIVTEK Float Arm

And stix lens port collar

I use
220, 110, 160 plus the collar

Sony a7rv
Nauticam underwater system
90mm lens
Backscatter mf-2
Nauticam smc-3
AOI UCL-90PRO

It is just a tiny bit negatively buoyant (my preference).

 

[adiRHIT]

I prefer the stix foam (on normal ULCS arms) to hollow/float arms because it's cheaper and far more customizable. You won't know exactly how much buoyancy you need to add until you get it in the water. You can guess, but adjustments are often needed and you can't adjust float arms. And if you ever change ports/lenses in the future you won't have to shelve your fancy hollow arms for buoyancy reasons. I own both the normal and jumbo stix foam, though at the moment I think I only use the normal ones, and only for macro. My wide angle config with the dome is positive, and actually requires wheel balancing weights under the dome shade to trim out.

As for arm length, 5+8 and 8+8 are both common arm configs. I personally use 5+8 on each side and don't have any issues getting my strobes out for wide angle. I find that having a shorter inner arm makes the whole rig fold up nicer because the arms usually start with added height from the housing. But either way works. I wouldn't suggest anything longer than 8+8 unless you have a specific need.

The WWL-1 is a wet lens with a glass element ... so it's heavier and negatively buoyant unlike the larger wide angle dome ports.

 

[adiRHIT]

DIVTEK Float Arm

And stix lens port collar

I use
220, 110, 160 plus the collar

Sony a7rv
Nauticam underwater system
90mm lens
Backscatter mf-2

It is just a tiny bit negatively buoyant (my preference).
View attachment 890229

View attachment 890230

do you know the buoyancy of the collar?
incidentally do you use a cmc to help focus closer?
My set up is a little more wide angle focussed... therefore not sure if the MF2's will have enough juice in them for wide angle coverage... whats your take? This is why I am looking at the Hybrid flashes... plus the fact that they have 5000 lumen continuous video lights might help in a pinch as well if I want to dive and record some video ...