Sigma 12 - 24

I am unsure whether I can use a Sigma 12-24 lens in my Subal D70 housing. The lens can't take any filters so if dioptre correction is needed for focussing then that is a problem. The lens' minimum focussing distance is 28mm. Anybody able to give me a definitive answer before I spend lots of money on the dome port?

Hi Morris,

First of all, welcome to the forum.

Well, let me start by saying that Sigma's 12-24 minimum focussing distance is 28cm (11 inches), not mm! Nikon's 12-24 has a minimum fucussing distance of 30cm (11.8 inches) and doesn't require a diopter to be used behind Subal's fisheye domeport (with the appropriate extension ring). So, I am pretty sure that a diopter won't be necessary with the Sigma. Now, what I don't know is if Subal makes zoom gears for that lens. Maybe you should send them an e-mail and ask.

Luiz

I use the Sigma 12-24 behind the big Sealux Dome. Focus begins just a few cm in front of the dome. I don't know the several different Subal domes in terms of size and radius. I only know that the Sealux glass is identical to some Subal domes(kind of standard european glass blown in one factory and shipped to several manufactures). If you have the correct extension ring I strongly believe there shouldn't be a focus problem.

Julian

I use the Sigma 12-24 behind the 9" Seacam dome with no diopter.

HTH

James

Configuration for Sigma 12-24 Lens in Subal Housings:

Dome Port FE2

Extension Ring 40 (EXR-40 or EXRX-40)

No Zoom Gear Required (Zoom Drive fits against Rubber Zoom Ring on Lens)

No Diopter Lens is Required

Installation:

Install camera in housing

Install Extension Ring onto housing

Pass Lens through Extension Ring and "carefully" mount onto camera

Install Dome Port FE2

Note: Using EXRX-40 (wider aperture) will simplify the installation process.

Hi all,

Thanks very much for the helpful advice. I now feel much happier knowing I will be spending my hard earned cash on a set up that will work.

Morris.

why is it necessary to mount the camera without the lens on first? That seems to be very risky of getting debris on the mirror or sensor.

I am not convinced about this lack of dioptre for these 12-24s. The need for a dioptre is determined by the size of the hemisphere that the dome would prescribe - and is not really related to the lens. And the Subal FE2 therefore requires a dioptre.

I know that this is Subal's official line. But I think that they are wrong.

Lenses have always "worked" behind domes without a dioptre, but a dioptre is required for the best image quality and to enable the lens to focus over its full range on the virtual image created by the dome.

All the knowledgeable photographers I know who have a 12-24mm use it with a dioptre. And now I have one I intend to.

Alex

The Sigma 12-24 that was referenced in this post is the one designed to cover a full frame sensor Alex, not the DX that you have.

Even if I wanted to use a diopter with the Sigma 12-24 it would be impossible because there is no front thread, just a built-on petal hood.

Cheers

James

I had subsequently realised that, James!

I know that this lens only takes rear filters (gels) which are 25x23mm in size.

But I still maintain that these lenses should be used with dioptres behind a domeport and if they are physically incapable of taking them then they may not be the best choice for UW shooting.

Also does the built-on hood not cause problems when mounting it behind a dome.

Alex

why is it necessary to mount the camera without the lens on first? That seems to be very risky of getting debris on the mirror or sensor.

<{POST_SNAPBACK}>

Because the front of the lens is too large to pass through the standard extension ring. Using the X type extension ring resolves this problem.

Hi Alex,

The built-on hood is quite small and doesn't cause problems. It looks like the hood on the Sigma 15mm fisheye for example.

I'm still not sure if I understand this one Alex - my lens will focus at 9" - so why do you think it would perform better with a diopter?

I'd hate for it to focus on bugs inside my dome-port (inside joke for Lionfish43).

Cheers

James