New Dome for my RF15-35

Hey,

last weeks/month i do many dives with my new Canon R5 in the Nauticam housing. It is a great combo. But i have to do little tweaks to make it perfect  

Actually i use the RF15-35 and the 8-15 with the 8,5" Acryl Dome. 

With the 15-35 and the 70mm extenion the camera will make a backward roll (i add many balance weights to the dome who made it better but not perfect) and the corners are not as good as I would like.

So i have to decide what i will do in the future.... buy the 230mm Dome or a WACP. With the WACP i cant use the 15-35, not the 8-15 and i cant do Splitshots.... 

I keep reading here many times about the correction filter from S&S. Is it really worth the money? 

So my questions: S&S has the correction Lens... What's the deal with B&W filters costing a small fraction of that? 

Would love to hear about your experiences  

1 hour ago, michaelgeyer said:

So my questions: S&S has the correction Lens... What's the deal with B&W filters costing a small fraction of that? 

 

I've not used the S&S lens but it's designed to compensate for the curvature of the virtual image to help improve the sharpness of the corners. So bringing the corners of the image more into focus. It's not a close-up diopter but a distortion correction lens

B&W filters are traditional close-up diopters and don't compensate for the curvature.

There's a good explanation of the S&S here:

https://www.bluewaterphotostore.com/sea-sea-internal-correction-lens

There's plenty of posts on here discussing the S&S lens including this one:

View archived post in: Which Nauticam 9" dome with Sony 16-35gm?

in particular Phil Rudin posts that he has used the S&S lenses with many port combinations and it assists to a greater or lesser extent varying with port size.  The gold standard for a 15-16mm lens on full frame is 230mm dome stopped down to f11-16 and this is improved further with the S&S lens.  Your 8.5"dome is going to very close to the 230mm dome in performance as it it will have similar radius of curvature.

The bluewater photo link is good as it has test images to compare taken with the 240mm dome from S&S.  As the domes get smaller the radius of curvature changes - unfortunately the manufacturers seem to want to keep radius of curvature of their domes a state secret, but many of these domes have similar curvature of around 110-120mm radius, if the radius of curvature is reduced then the S&S lens will be less effective.  In the link  phxazcraig posts about the S&S lens and says he now shoots at f5.6 with a 16mm lens and 230mm dome. 

I would note that I don't believe the bluewater post is entirely correct regarding how the S&S lens works.  The problem with dome ports is the virtual image is curved so the corners of that curved image are physically closer to your lens.  Because it is so close the corners are out of focus, they fall outside the depth of field. 

This is because the plane of sharpest focus at the sensor is curved .  The lens acts to change the shape of zone of sharpest focus so that it is flatter and within the range that the depth of field is sufficient to bring the corners into focus.  Technically it is a field flattener and brings the corners into focus at the setting as needed for the centre  of frame.

For your situation the 15-35mm has an 82mm filter thread so can accept the S&S lens directly.  What will also help corners is to zoom in slightly.

Regarding your buoyant dome if you are handy you could make something similar to this and use a dive weight to help balance the dome:

https://www.ikelite.com/products/trim-weight-system-for-dslr-mirrorless-housings

On 1/26/2021 at 1:01 AM, ChrisRoss said:

Regarding your buoyant dome if you are handy you could make something similar to this and use a dive weight to help balance the dome:

https://www.ikelite.com/products/trim-weight-system-for-dslr-mirrorless-housings

You can also print a 3D part that fulfills the same role.

https://www.thingiverse.com/thing:4586545

Not exactly apples to apples but I shot this with the Tamron 17-28 F/2.8 for Sony at F/10 in a Nauticam 180mm port with a Sony A7R IV 61MP camera.I am using the 77mm S&S correction lens with a 67 to 77mm step-up ring. I also shot the same lens in the Nauticam 230mm optical glass port and as you would expect I gained about one stop +/- better results out of the larger port. So about 1 to 1.5 stops with 180mm and about 2 to 2.5 with 230mm. This is very subjective so you should try to  test with your own equipment to draw best conclusions. I also tested the Rokinon 14mm F/2.8 for Sony (now widely available for Canon mirrorless) no filter threads with an Aquatica 200mm acrylic port and was impressed with the results for a on sale $500.00 lens.   

so you can say that glass is preferable to acrylic, especially with the the filter ?

The difference is related to the larger size of the port not the material. My personal preference is for glass over acrylic but not because of image quality at a given size. 

Yeah i read a lot of .... but on the paper the 230mm is larger then the 8.5" Acryl :)? Or is it not? And the few milimeters are negligible

I have used the Aquatica 200mm, Ikelite eight inch and eight inch compact plus others but if you are referencing the Nauticam 8.5 inch acrilic I have never used it so can only speculate on any difference v. the Zen 230mm port I own. My issues with acrilic over glass involve buoyency and more reflections from the lens back onto the sensor shooting at the surface, splits.