Hugyfot housing for D500: questions about building setup

[MichaelB 2]

Hi everyone, first post on here! It involves a couple of different questions, so thanks in advance for your attention... 

I've recently upgraded from a compact to a used Hugyfot DSLR housing for my Nikon D500 that I already used for topside photography. The purchase included: Sigma 10mm EX DC HSM f/2.8 fisheye lens, 20mm & 50mm extension rings, 6.5" acrylic dome port (note: I do not know if the true diameter of the dome is 6.5"; it is not a full hemisphere, but I don't have it to hand right now to measure). 

In addition to this, I already have a Sigma 105mm OS HSM f/2.8 macro lens and a Tamron 10-24mm Di II VC HLD rectilinear wide-angle (both good lenses in their own right - at least above water) that I am hoping to be able to use with the housing.

My first questions are: does anyone have experience using the Sigma macro and Tamron wide-angle lenses underwater, and if so are they worth building my setup with? The Nikkor 105mm VR Micro is the direct competitor of the Sigma, but I would prefer not to have to upgrade if possible. 

If they are indeed worth using underwater, does anyone know the correct extension rings for using i. the Sigma with a Hugyfot flat port, and ii. the Tamron with the 6.5" dome port? Hugyfot lens compatibility charts aren't super comprehensive, and I don't trust myself to correctly identify the entrance node of the Tamron. I am also considering selling the 6.5" dome port and getting the 7" fisheye port instead if the dome optics with the Tamron wide-angle would work fine, but I can't find any comparative info using my lenses. 

Final question has to do with some wear on the housing anodisation itself. It seems that something rough has come into contact with the rear of the housing and (I think) exposed the aluminium in two small areas (the damage is half the size of a pea). Thankfully the housing was mostly used in a freshwater pool previously, but obviously I want to prevent any corrosion ASAP and would welcome any advice on this. I attach a photo of this damage. 

Thanks again,

Michael

[ChrisRoss 150]

Which specific Sigma macro lens? - is it one of the lenses that extends as it focuses closer?  These are generally not as suitable for use underwater as the dome port needs to be longer and you may have trouble using closeup lenses with them. 

You may find a 6.5" dome port is a bit small for your 10-24mm which means corners won't be as sharp as they could be.  As you already have the 6.5" port so you might as well try it out to see how you like the results.  As for the right extension, a starting point is to see if other manufacturers list both the Nikon and Tamron 10-24 lenses.  Ikelite does and they recommend 6mm more extension for the Tamron lens over the Nikon lens.   Seeing as how you have the 50mm extension recommended for the Nikon I would start with that as there is a little less extension so it shouldn't vignette, it will be about 6mm forward of the optimal point.  You could buy the 55mm ring, but I would try the 50mm first.  Ikelite is the only manufacturer listing the Tamron lens - there may be a reason for this as it may not perform that well UW - as I said try it first.   Depending on the type of diving you do you may find you don't use the 10-24 range that much.

The port chart recommends the 5" and 7" domes for the 10.5 mm fisheye lens, and as you note they are full hemispheres, you could use the 10.5mm fisheye behind the the 6.5" dome port but would have to place it well forward of the optimal position to prevent vignetting and the port chart doesn't provide guidance on the right extension with the 6.5" port.  The fisheye ports should perform better, but again try what you have out first.  The small port for the fisheye would be better for CFWA work.

[MichaelB 2]

Thanks Chris, that’s very helpful and a great idea to compare other manufacturers’ lens data. The Sigma is the internal zooming 105mm OS HSM, fairly similar to the Nikon 105mm VR in length I think.