Dome for Sigma 15mm on Sony

Hello Everyone!!  Thank you for your input thus far.  It means a lot. 

So I have the 15mm Sigma fisheye with the MC11 adapter for my Sony A7iii.  I have an Isotta Housing.  I'm torn on which type of dome I should get.  Would a 4inch glass dome be okay with this?  Or perhaps a 6inch acrylic?  They both cost about the same.  I'm not sure if either makes too much of a difference.  Would love to hear your thoughts.  Thank you so much.  

Generally if choosing between acrylic and glass domes there are a few pros and cons to each. 

Acrylic domes are lighter (good for travelling) but that also means they are often very floaty underwater, especially 6" and up. 

Acrylic domes scratch easier, but if they do, you can usually polish it out. Glas scratches harder, but if it does you will have to live with the damage or prepare for an expensive repair bill.

Glass domes are said to be better for splits and also resist flare better, but generally image quality between both is very similar.

1 hour ago, hyp said:

Generally if choosing between acrylic and glass domes there are a few pros and cons to each. 

Acrylic domes are lighter (good for travelling) but that also means they are often very floaty underwater, especially 6" and up. 

Acrylic domes scratch easier, but if they do, you can usually polish it out. Glas scratches harder, but if it does you will have to live with the damage or prepare for an expensive repair bill.

Glass domes are said to be better for splits and also resist flare better, but generally image quality between both is very similar.

Thank you so much!!  Will there much of a difference in image quality between the two if I"m using the Sigma 15mm fisheye?

I have no particular experience with the Sigma Fisheye or the Isotta port system. If you're going with a similar port size I would suspect that the IQ difference will be marginal. Isotta recommends all those domes for the 8-15 fisheye zoom, but then they also recommend the 4,5" dome for the Panasonic 8-18 in MFT and that will definitely not give nice results so their port charts are pretty bare bone...

If you want to do splits and don't mind the additional volume get the 6,5" glass or 6" acrylic (mostly depending on your budget). If you want to keep a compact setup for travel you should be able to get away with the 4,5" glass dome. That's probably what I would do but I'm not sure how the requirements are for FF.

The other consideration is what you will be shooting with it - the 4" dome is more compact and you can get closer to your subjects.  Fisheyes are less impacted by dome size than rectilinears but the general concensus is that the image quality will be a little less in the 4" .  People use the 4" for CFWA as it allows them to get into tighter spots .

I would also check if the sigma fisheye is feasible in the 4" dome, it has pretty large petals on the lens hood as I recall and it's not removable.  I know for example it doesn't fit in theZen 4" dome.

I used to use a 100mm  Zen mini dome with the Canon 8-15 fisheye on my crop sensor DSLR and was very happy with the results.  However, when I used the same combination on my full frame Sony A7RIV the resulting images were nowhere near as good.  I got a Nauticam 140mm dome and am once again very happy with the results from the Canon 8-15.