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Member Since 15 Aug 2013
Offline Last Active Mar 22 2014 11:54 AM

Posts I've Made

In Topic: Sigma 15mm fisheye focus problem

18 March 2014 - 10:04 PM

To follow up on this, I added the 10mm extension ring, and that fixed my focus problem.


The 15mm isn't happy behind a small dome, quite apart from alignment of the dome with the nodal point or the entrance pupil and physical obstruction of the lens. That said, I've never felt the need for manual focus with a big dome or even with a smaller dome and teleconverter.


The Nauticam port chart recommends either a 4.3" or 8.5" dome.  I've got a 10" dome that I haven't used in years because the 4.3" creates less drag when mounted to the scooter.  The video I shot after adding the ring was nice and crisp, though, so I think the 15mm works pretty well with the 4.3" dome.


In the PNW, our waters are usually murky, which necessitates getting pretty close to the subject.  At those distances, I find manual focus a lot easier, especially when combined with the focus assist mode of the SmallHD monitor.

In Topic: Canon 550D and Nauticam Housing $1500

18 March 2014 - 09:49 PM

Hey AzNativ1, it seems I've been shooting my 5D exclusively and there are some lenses I'd like to get, so selling the T2i setup makes sense.  PM me if you're still interested and let me know where you're located.

In Topic: Sigma 15mm fisheye focus problem

16 February 2014 - 05:27 PM

One of the main requirements of using the appropriate extension ring is to ensure the centre of the dome port is aligned with the entrance pupil of the lens:





Awesome, thanks for the links.  I'll be ordering a 10mm extension ring tomorrow!

In Topic: Sigma 15mm fisheye focus problem

16 February 2014 - 05:14 PM

Um, I feel embarrassed about even responding now.  Just checked out your photostream on Flickr.  I'm simply not worthy... <hangs head in shame>


Ha, that's hilarious.  I'm a long-time technical guy (computers), but haven't had time to really dig into the technical details of photography, and I'm pretty much still winging it.  I'm hoping to have more free time this year and change that, though.

In Topic: Sigma 15mm fisheye focus problem

16 February 2014 - 02:59 PM

You mention having difficulty with manual or auto-focus so I assume it's not an issue with not finding a good high-contrast point for the autofocus to work with. 


I'm usually using this lens for video, and I always manually focus video since the continuous focus on most DSLRs is slow.  I've got a SmallHD external monitor with focus assist that helps, too.  But even when using auto-focus and getting the "green box" focus confirmation, the video will still be out of focus.  So I'm thinking you're right about moving the dome out.  I've never had this problem with other cameras/lenses/ports, but this is the only lens where I'm not following the manufacturer's recommendation.