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Emicimoli

Very particular underwater task requires advice

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Hello to everyone,

 

I am writing in order to seek some advice regarding a particular task I am working on. As a side part of my research, I need to take high quality pictures of the sea ice sub surface from a Remotely Operated Vehicle (ROV). The aim is to be able (at least try) to capture the relief of the underside of the ice. It is quite challenging, and I lack some expertise in the underwater photography perspective, any advice from some underwater veteran would be extremely appreciated!! I would need your help mostly for choosing the camera and some clue on the housing and lens port.

 

As you can imagine:

 

  1. the camera is upward looking,
  2. the under ice is very low lit,
  3. the images arise from transmitted light trough the ice (thus not reflected),
  4. imaging the under ice has very high dynamic range; light varies a lot in small spatial scales because of the overlying snow
  5. the ROV is moving so we need fast shutter speeds
  6. we want to cover as much area possible per frame
  7. the ROV with the camera will be approximately 1-2 meters from the target thus the the focal range is quite narrow
  8. we would like to have the images as geometrically correct as possible
  9. very low temperatures
  10. we would hope not to need active light sources, but advice's with/or and without are very much appreciated!

HAHA! Well i know it sounds that we want it all and it is kind of impossible but if you have any ideas advice for the idea gear please let me know you opinion.

So far, I think that the SONY a 7s is the better option for this task due to its low light capability and is very compact and light (mirror less) and is very fast! However which lens? What do you think?

 

 

Here some pictures of how its looks like under the ice and what is the target for inspiration:

 

https://www.google.com.au/search?q=under+sea+ice&espv=2&biw=1396&bih=668&source=lnms&tbm=isch&sa=X&ved=0ahUKEwj33vDA4anQAhVDm5QKHZrWCawQ_AUIBigB#imgrc=pEGLldNuugZHvM%3A

 

 

Thank you all for your attention hope I can get your precious advice!

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Hmm.. interesting. Are you trying to obtain still images, or video footage?

 

It's also important to understand I think what kind of resolution and magnification scale you need from the images. What are you trying to identify using them? Are the features you're interested in centimeters in scale, meters in scale? That might impact the lens recommendations.

 

Furthermore, why the aversion to using active light sources? Fill lights could help overcome the high dynamic range. Would it interfere with what you're trying to capture/measure?

 

Low distortion speaks to a "normal" focal range (e.g. 50mm full-frame equivalent or longer) lens. However, generally, you want a wider lens underwater as this allows you to get closer to the subject of interest and reduce the filtering effects of the water. This is particularly important in turbid water, which may or may not be the conditions you operate in. Does the ROV have to operate 1-2 meters away from the ice? 0.5m would be more ideal from a photographic perspective.

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Thanks for your reply and interest!

 

We would like to capture the topography of the under ice, which can vary at centimeter and meter scale. Thats why we would like high resolution and possibly still images and as geometrically correct as possible. Hopefully a a mm/cm pixel size. We where also thinking on a wide angle lens, but the tradeoff is the geometric distortion and the need to use a dome port which makes it expensive and difficult to set up in terms of enclosure i guess?`

 

Your guess is right, we use also use light sensors thus thats why active light sources are not best option but still could be considered. Active light sources will influence the measurements and is very difficult to remove their influence of the sensor measurements.

 

0.5 m is also an option! we prefer to stay distant to the ice to avoid collisions but it can be done! :)

 

Water is pretty much clear! thats a positive aspect :)

 

I understand is impossible to have it all, but would be awesome just an opinion on the best camera and lens option available out there! :)

 

Thanks again and let me know if you have ny more questions!

 

cheers

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I don't have any specific camera advise but I will say this - practise with whatever you get. Before you get to the Arctic or wherever. Because whichever setup you use, there will be an optimum angle, distance from the ice, aperture, shutter speed, ISO, speed of the ROV and number of photos required for coverage. And you may find you can change one setting to give you better results in a couple of other settings, like slowing down the ROV to decrease the shutter speed and avoid the use of on board lighting. I have done some photo and video runs to map cave tunnels and the first run never works properly. Depending on the program we used to stitch things, completely different technique was required. Much easier to sort that stuff out standing waist deep in a well heated pool a few evenings a week and downloading images for pool tile analysis each time.

 

On the dome port front, if you use a rectilinear lens (as opposed to a fisheye which distorts things) you will need a relatively high f stop to avoid blurry edges. Either that, or consider a wider angle lens where you crop the result and discard the outside of the frame. Flat ports underwater magnify the image and are unusual for wide angle. You may like to consider having a ruler/fixed measurement in the frame for reference.

 

On the Sony 7s, consider the battery life (not much!). How often will you be pulling the camera up? Do you plan to shoot tethered with results coming up as you go?

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You mentioned above mm accuracy. I am sure you already are aware of it, but, just a reminder: depending on the type of ice, there might be a very transparent glass/waterlike underlayer of the ice. Even when viewed ortogonally from an opening in the ice, it might be very difficult to distinguish the underneath surface of ice from clear water. Thus, you might endup focusing, shooting and analyzing the next more visible layer with more frost/pores/whiteness. If you yourself are not diving beneath the ice, you might not even notice or realize this difference. The transparent layer can be surprisingly thick. I've seen transparent ice layers of 20 cm thickness and without any pores/frost. I wouldn't be surprised that you could encounter even thicker transparent layers in the Arctic.

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The largest most gaping detail you have failed to supply is what budget are you talking here as with out knowing it is hard to say. The only clue you give is your dome port comment which implies it is a pretty small one. If you want the highest resolution and quality of shot, be prepared for a shock.

 

I am sure others who know a lot better will chime in (I hope they do!!) but I would say you would be best served by making three basic decisions and sticking to that path.

 

1 - still or video - which is your primary focus as this will obviously lead you down different paths, especially if you are on a tight budget. You say high resolution and possibly stills. Does that mean video first and maybe the odd still if possible?

 

2 - Ambient light only or not.

 

3 - what is the minimum quality acceptable and what detail level is needed.

 

Once you make clear decision on what is and is not acceptable the choices will narrow themselves down and people may be able to give you more specific advice. Oh.. And did I mention budget?

 

I think you will struggle in the thicker ice to get the sharpness and clarity by just using ambient light, especially if the ROV is moving. As Errbrr said, a reference/scale could be a very good idea.

 

How long is your expedition as if it's not too long you may want to think about renting the gear as you could possibly get a lot higher end equipment if you only need it for a few weeks. Plus you could then trial some out in similar lighting conditions as see what results you get.. Far better to know if it will do what you need it to do before you leave so there is still time to change it!!

 

Have you contacted the Australian Antarctic Division and asked them what they used?

 

 

 

 

 

 

Sent from my iPhone using Tapatalk

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Hello all, thank you very much for your advices! All of you give privided great imput! Here some replies to some of your perplexities:

 

I have worked a lot with imaging and digital photogrammetry from UAVs in the high arctic (snow mapping), so I am well aware of imaging from moving platforms, of plannining, failing, and the trials of it :)

 

I want to mention that this is not the principal payload ( and objective) of the ROV and light sensors are the main component, thats why I would like to avoid active light sources if possible.

 

The ROV is thethered, thus I think power supply will not be a conncern, can fit plenty of weight there aswell for extra powersupply to the camera.

 

I have supervisors from the AAD ( I am a PhD student), however they have just used video imagery for assessment of the under ice. I would like to obtain relatively high quality pictures. I say video because sometimes i think that it would really make it easier but i prefer pictures.

 

The type of ice we are looking at is usually very thick and not transparent so it is difficult to not to see the difference.

 

Regardng the budget thats something we reserve for later, i would like to have an idea of the relatively best out there in terms of camera and lens. I say that dome port is expensive because the underwater enclosure will be customized. A flat port would greatly simplify the complexity of building such enclosure. Flat port would be great if you think we dont sacrifice too much quality considering that we are going to use a wide angle lens most porbably.

 

Thanks guys!!!

 

Peace and love

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Well, if you want to know the best out there, I would say your best bet would be the new Red WEAPON 8K S35... It shoots at 8k, has a massive dynamic range and can take 35.4mp stills but I think it is something like $59k just for the body... I am having a guess that you are not talking that sort of price point though! ;)

 

If you don't already have a camera brand you have lenses for and are free to choose I would say the best cameras for low light stills are probably

1) Nikon D5

2) Sony A7S II

3) Canon 5D MkIV

 

Again, how long is the trip as you can rent a D5 for a week for about $350... Could be option... A Canon MKIII I think is about $130 for a week.

 

Once you pick a camera body then you can nail down the lens. I personally don't have any experience with trying to shoot a wide angle through a flat port but I think you would have a whole heap of problems trying to do so. Anyone here managed to get good results? I am also not familiar with Nikon and Sony lenses so will leave that for the people that are but if quality is key then I would go for a good prime rectilinear lens like the 35MM F/1.4L II if it's canon or possible the 50mm f/1.2L . The worry I would say with needing to use such a wide aperture is getting the DOF you may need.

 

I would take a guess that your best bet is to shoot with a 4K camera that can also take stills. That way if you are finding that the stills are not working you can still get some footage.

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Im not sure to understand exactly how you will manage to get a link between ice color and lightness to dimensional characteristics of it, meaning thickness and surface shape (if this is what you're looking for)

 

Just a thought (not an expert at all in this kind of systems), but seems to me that what you're interested in is the opposite of trying to map the depth of sea bed.

 

Maybe a kind of sonar system, opperated from the rov with known depth should give you the rov to ice distance ?(not sure solid water to be different enough from liquid for the sonar to work well)

 

More is needed to get the thickness but you start with quantitative measurements.

 

Sounds dumb ?

 

 

Envoyé de mon D5803 en utilisant Tapatalk

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