Black magic 6k and underwater lenses

[Ar Splujer]

Good day,

I would like to improve my nauticam system for filming in wide angle.

I have a bmpcc6k with the nauticam housing. Above I have the 11-20mm ef 2.8 tokina with the 8.5” dome. And the 100mm with port 87 +CMC2. As well as the 60mm ef-s canon.

I find the Macro side excellent. Top images quality. On the other hand, I am less happy with the wide angle side. I find the sides very blurry and the average image not sharp enough. It gets better of course at f8 but I can't always be like that because I don't to get to much ISO.

My idea would be to have a better lens instead. Or maybe the glass dome would greatly help with sharpness?

Otherwise I was thinking of going with the 40mm ef canon + MWL1. Maybe this is a bad idea? What do you think? I don't have anyone around me with this system.

Another idea would be to go with the 24-70mm ef ii 2.8 usm from Canon. I already have the dome, maybe it would save some money?

If any of you have any feedback, I would be happy to hear it. Thanks in advance !

 

 

 

 

All reaction

 

[Davide DB]

Hi Yann,

 

You linked that image from FB so I had the chance to see some WA video you published and you are right, borders are terrible.

Out of curiosity, what's your aperture? At 11mm I guess that F11 or F16 are mandatory.

 

I went on the Nauticam port chart and I didn't find you lens listed. I see the Tokina AF 11-16mm f/2.8 and Tokina AF 12-24mm f/4.

lens dimensions are nearly the same but IDK their entrance pupil. Anyway, assuming it's the same,  for both the lens listed, the best combination is the 250mm dome port!

 

 

 

 

[Ar Splujer]

Hi Davide,
Thank you for your reply.
You are right, the lens is not listed anymore.

But I've got the 60 ring extension with the 8,5'' dome. That was the best before.
 

The problem is when I close at F11, I have to put to many ISO that the picture is not really good. The water isn't really clear everytime so I would like to find an other solution.

The glass dome will really help a lot in better sharpness ?

Edited September 11 by Ar Splujer

[Davide DB]

3 minutes ago, Ar Splujer said:

The problem is when I close at F11, I have to put to many ISO that the picture is not really good. The water isn't really clear everytime so I would like to find an other solution.

 

I think that F11 is really the minimum at that FOV.

 

1 minute ago, Ar Splujer said:

The glass dome will really help a lot in better sharpness ?

 

I don't know. let's see if members much more technical than me intervene.
It doesn't depend on the material, and the dimensions alone (215mm vs. 250mm) don't tell the whole story because they might have different curvature. 

 

Would you mind to share/embed a video showing the problem?

A YouTube link will automagically embedded.

[Ar Splujer]

Of course, here is a link. We can see all the borders are really smooth. This is in Brittany so closing at F11 will put a lot of noise on the images.

 

It is better in mediteranean sea if course, because I can close a bit more : 

 

[Davide DB]

In some points it seems to me that shallow DOF is also the problem but with a crop factor of 1.5 you have an FOV of a 16.5mm. Impossible to get sharp edges at F4 F5.6 with any dome I think.

You can try zooming in a little bit and that way you would also be facilitated with tilt and pan movements.

 

[Ar Splujer]

Thanks Davide. I will try that tomorrow. 

 

That's also why I wanted to get a better lens, 24-70mm Canon "L".

I don't know if it could help in farpness. I will keep reading around.

[Ar Splujer]

If you look at this video, I've got the same issue. But it was so dark that I couldn't open so unless zooming in a bit I don't know what else I can do.

I'm also wondering if a 40mm lens with port 12 and a MWL-1 could help with that problem...?

[Davide DB]

43 minutes ago, Ar Splujer said:

If you look at this video, I've got the same issue. But it was so dark that I couldn't open so unless zooming in a bit I don't know what else I can do.

 

Do you remember or you can check on your files which aperture did you used?

[Ar Splujer]

On this on I was really open, like f3.5... So yes it makes sense for the borders to be so smooth...

[Davide DB]

6 minutes ago, Ar Splujer said:

On this on I was really open, like f3.5... So yes it makes sense for the borders to be so smooth...

 

I am not aware of any lenses and domes or wet lenses that would allow you to work with those apertures.
I've shot some clips at F2.8 but it was to get a creative shot on a subject very close in focus and a very thin depth of field.

 

The first three clip of the trailer on my channel (algae, anemone and Posidonia) are shot at F2.8 and the like on a M43 PanaLeica 8-18mm f/2.8-4.0 and a 9" Aquatica glass dome.
 

https://youtu.be/LJEuuY532Kg?si=CRdOmC4B8dghqCDS

 

IMO you cannot go below F8. On my WWL-1 on M43 Sometime I work at F5.6 but M43 has a smaller sensor.

 

[Ar Splujer]

Of course. But your sea looks more bright than mine ;)

F8 is impossible with this camera and in dark water. Even at 3200 iso.

But F5 or F6 and zooming yes.

I've got other videos in here, at 50 to 60m, completly in the dark. Even with a divers with big lights and at 3200iso, you still have to open at F4-5...

[Davide DB]

I don't know. 

 

24-70 mm F2.8 is the cheapest option for sure and you already have the port. Maybe you can find someone who can lend you the lens. Canon EF lens are very common.

 

MWL-1 route is really expensive and I don't know if things will improve. Maybe there is some member who use it? Try a forum search for "MWL-1" and ask there.

[Chris Ross]

The MWL won't help much, it is suggested to use f16 with that lens and it is said to be marginal at f13.

 

You are going to have soft edges at f8 on any lens behind a dome unless it is zoomed in quite a bit, perhaps 35mm full frame equivalent or narrower.

 

The standard recommendation if you want to shoot wide apertures would be a WACP for EF but this is big and expensive.  Fisheye lenses may be an option but not so suitable for video.  A Canon 10-17 with 1.4x would approximate a WWL field of view with reduced barrel distortion due to the 1.4x converter, but you would be needing to shoot that at f6.3-8 range as well.

[DreiFish]

Unfortunately, you're running into limitations of physics here, because of the way dome ports produce a curved virtual image, which is what your lens is focusing on/filming. On an APS-C sized sensor, that means you really can't be below F8, and F11 is probably better in order to get reasonably sharp corners.

 

The only things that can help are a larger dome or shooting at less wide focal length. Things start to improve around 20mm (FF equivalent) and get pretty good by 24-35 mm. But if you want to shoot at 11mm (16mm FF equivalent), you need both a large dome (230mm preferred) and narrow apertures in the F8-F11 range. Getting a different lens might improve things slightly, but the issue is that the center of the image and the corners are at different focal length because of the curvature of the virtual image created inside the dome. Lens quality can't solve that. Only a larger dome or a narrower aperture can. 

 

Since the Blackmagic camera is also ISO limited.. you basically either have to bring a lot of artificial light into the scene or look into wet contact optics like the Nauticam WACP-1 or WACP-2 

[RomiK]

On 9/11/2024 at 8:09 PM, Ar Splujer said:

Hi Davide,
Thank you for your reply.
You are right, the lens is not listed anymore.

But I've got the 60 ring extension with the 8,5'' dome. That was the best before.
 

The problem is when I close at F11, I have to put to many ISO that the picture is not really good. The water isn't really clear everytime so I would like to find an other solution.

The glass dome will really help a lot in better sharpness ?

 

I have had similar "effect" when experimenting with Sony 14-1.8 on 180mm glass dome.  I removed 20mm extension pushing the lens further into the dome. And it looked similar to what you had.

 

 I think you need longer extension. Perhaps another 10,20 or 30mm depending on vignetting check. Although Nauticam states to use N120 Canon EF chart it depends on sensor position inside the housing. For canon EF-S 10-22 which has length of 90mm and minimum focus 24cm they recommend 60mm for acrylic dome. But I can imagine it's for Canon 7 housing while you have BMPC housing and your Tokina has 94mm length and 28cm minimum focus distance.

 

Basically sink the lens as far back as you can so it doesn't vignette and you should be fine.

 

Edited December 1 by RomiK