The Gentleman's Underwater Bubble Blower Thread

[Tom Hamilton]

This needs an explanation in simple terms.

What does a diopter do optically, in terms of focal length, focus distance, depth of field, and corner resolution?

Rudi, your knowledge of u/w optics far exceeds most on this thread, and kudos to you for that. But this is a highly mis-understood subject, or so it seems, might you explain it, slowly, for me at least, what is in fact happening?

 

[Rudi Herbert]

Tom,

Pawel might do a better job than me explaining the theory of diopters, if he doesn't oblige, then I will. More importantly, did you use the diopter on your shoot?

 

[Pawel Achtel]

As we all know there are a few problems that need to be overcome when placing a rectilinear lens behind a dome port. One of them is that the virtual image produced by the dome is projected close to the lens. Most, if not all, wide angle lenses are not optimised for such imaging and perform poorly at close range. By shifting the lens backward from the geometrical centre of the dome this performance will be somewhat improved. However, ....there is always a price to pay somewhare ..... you will introduce geometrical distortions as well as chromatic aberrations. This may or may not be better outcome depending on the lens, dome, amount of shift, f-stop,
etc..

I think a better option would be to use a diopter, as Rudi suggested. Even bettr trick is to shift the back focus backward as this does not cause additional chromatic aberrations introduced by the diopter. I believe Dave Hannan started doing this probably more than 15 years ago.... I went the other way and created a bigger dome.

Yet another option is to shoot 3k cropped with suitable S16 wide angle lenses. Remember, the resolution is limited by the optics, not the sensor, so there is no reason why 3k cropped could not deliver sharper images than full 5k. This is the very trick I discovered for macro where the resolution depends on magnification factor, not on resolution of the sensor! Not very intuitive, is it?

It's tough call....and the very reason why I decided to go Nikonos (and after having invested in a $50k 12" CinePort dome).

 

[Tom Hamilton]

Not fully understanding what a diopter does, I chose to go 'naked' for the money shots; the Rouge, behind the Aquatica 9.25 mineral glass dome port delivered some respectable imagery.

Will try the diopter tomorrow. Many thanks to you and Pawel for technical clarification.

Cheers

 

[Pawel Achtel]

the diopter brings the focus closer

 

[Mark_Thorpe]

Am privileged to be shooting with the brand new Amphibico Rouge prototype, so far, a magic housing. More to come.

Looking good Tom, eager to hear about the housing.

Cheers,
M

 

[Michael Hastings]

Not fully understanding what a diopter does, I chose to go 'naked' for the money shots; the Rouge, behind the Aquatica 9.25 mineral glass dome port delivered some respectable imagery.

Will try the diopter tomorrow. Many thanks to you and Pawel for technical clarification.

Cheers

There are two main types of diopters: 1) a simple single lens diiopter which is the most common and 2) achromatic diopter which has been corrected to make a flatter field and reduced chromatic aberration.

The diopter number tells you the amount of focus change. If you set the lens focus at infinity and then put on a +1 diopter the new focus point will be at one meter, with a +2 it will be at 1/2 meter, a +3 at 1/3 meter a +4 at 1/4 meter, etc. etc.

a negative diopter does the opposite, but doesn't have much application in photography, because the elements in the lens have been designed and positioned to focus to infinity and nearer to its near limit-typically about 1 to 2 feet on modern wide angles. So a significant negative diopter would simply push the focus point past infinity where there isn't anything . But if you are nearsighted you have a negative diopter prescription, because your eyes no longer focus to infinity. My old eyes are about a minus 2 which means I can read my computer screen fine but can't focus sharply on things past about 5 or 6 feet without glasses/contacts.


A lens is basically the interface between two different materials that have different refractive indexes - i.e. bends light more or less causing the beam of light to converge or diverge. In most lenses that is air then glass then air again and depending on the curvature of the front and back of the glass it will be bent and focused differently.

A dome port in air doesn't do much because the front and back of the dome have the same shape - so air to glass to air doesn't cause much shift optically. However when the dome touches water there is a big differene between the refractive index of the water, then the glass, and then the air - the biggest difference being between the liquid (water) and the gas (air) so the dome creates a fairly strong negative lens.

a 6" port moves the focus point of a distant (technically infinity) object to 9" inches in front of the port (3 times the radius) so since 9'' is just under 1/4 of a meter we can consider a 6" dome to be about a -4 diopter. An 8" dome moves infinity to 12"(again 3x Radius) - about 1/3 of a meter so we can consider it a -3 diopter.

By using a +4 diopter you can offset the refocusing of the 6" dome and your focus scale on the lens will be correct again. (actually slilghtly off since the diopter isn't exactly matched - it should actually be a +4.38 but those are hard to find, plus the lens is usually a bit behind the dome as well)

As in Rudi's example above, people sometimes use a lower power diopter than an exact match because it brings the focus range to a more manageable range but doesn't have as much of the other optical issues (field curvature/chromatic aberration) as the higher power.

 

[James Killion]

Great explanation All, Thanks for sharing the engineering side of glass!

 

[Pawel Achtel]

One small clarification: neither diopter nor back focal length adjustment can correct for image plane curvature.

 

[Tom Hamilton]

Having tested the +2 diopter today, there seems an increased sharpening across the frame, as Rudi predicted, the effect is quite pleasing.

However, I have the impression of radial distortion along major axes, not quite the fisheye kind, but noticeable to me nonetheless.

Is that possible?

 

[Rudi Herbert]

Tom,

I've noticed that problem only with the lens at its widest setting of 11 mm, at which point, however good the lens is it still exhibits some distortion. The effect disappears as soon as I move up to 12 mm and up, or if I am greedy and want all that width, then I try to shoot straight into the subjects, without any angles. But, just narrowing up into 12 mm and upwards solves most problem with this lens. Good looking images Tom!

 

[Johnny Friday]

I wanted to share the LOOK out of camera in RAW vs. Post work on a RAW R3d....I've had several questions about this over the past months and all of us are finding out more and more...From my experience, i find the post to be a 2:1 or 3:1 process...for every hour of shooting, i spend 2-3 hours in post. The look from RAW that we all see if coming from video is hard to accept. But when you learn the post process you begin to understand how much control you have over your images. BUT, it also requires serious horse power in a machine and then the knowlege of how to put it all together. It's basically a learning process with no end in site as the software continually changes to keep up with the huge files we are shooting. It's also NOT always the right tool to shoot RED for much of the Doc work that's run and gun and fast post. I'm amazed at how many docs & commericals i have worked on that don't get the RAW workflow. And in the end the "end product" is not so good and they would have done a far better job using a betacam or ex1 or even canon 5d. BUT, when you understand and have the time for RAW workflow AND a colorist that can bring out those results.....then the "end result" can be stunning.
I am FAR from a colorist, but i give it a good shot and learn on every production from the editor or colorist. In some instances i'm showing them the look they want underwater while utilizing their skills at the command station.

here are two grabs: one a RAW R3d and the other a JPG that was taken off of my home color session. The results are far apart. You will also notice vignetting. i was using the Nikon 16-85 since we were doing a lot of medium close detail work.

[/url] RAW Look by RedCineUnderwater, on Flickr[/IMG]

[/url] Colored-Look by RedCineUnderwater, on Flickr[/IMG]

 

[James Killion]

I wanted to share the LOOK out of camera in RAW vs. Post work on a RAW R3d....I've had several questions about this over the past months and all of us are finding out more and more...From my experience, i find the post to be a 2:1 or 3:1 process...for every hour of shooting, i spend 2-3 hours in post. The look from RAW that we all see if coming from video is hard to accept. But when you learn the post process you begin to understand how much control you have over your images. BUT, it also requires serious horse power in a machine and then the knowlege of how to put it all together. It's basically a learning process with no end in site as the software continually changes to keep up with the huge files we are shooting. It's also NOT always the right tool to shoot RED for much of the Doc work that's run and gun and fast post. I'm amazed at how many docs & commericals i have worked on that don't get the RAW workflow. And in the end the "end product" is not so good and they would have done a far better job using a betacam or ex1 or even canon 5d. BUT, when you understand and have the time for RAW workflow AND a colorist that can bring out those results.....then the "end result" can be stunning.
I am FAR from a colorist, but i give it a good shot and learn on every production from the editor or colorist. In some instances i'm showing them the look they want underwater while utilizing their skills at the command station.

here are two grabs: one a RAW R3d and the other a JPG that was taken off of my home color session. The results are far apart. You will also notice vignetting. i was using the Nikon 16-85 since we were doing a lot of medium close detail work.

Hey, Johny,
That looks great! What resolution and compression were you shooting at?

 

[Johnny Friday]

Jim,
that was shot 5k @ 2:1 i think compression was 9:1 and shot 48fps @ 180 shutter speed. As Frazier can attest...it's full of light at Tiger beach and i shot this w/out ND. But would have used an ND 4 minimum.

 

[Michael Maes]

Rudi and Johnny, thanks a lot for this input on post and using a diopter on a rectilinear.
Gonna try all out

 

[Will Keir]

Any bubble blowers off the California coast? Looking at a project on / around the Santa Barbara islands Summer 2013. PM if you are out there.

 

[Michael Hastings]

I wanted to share the LOOK out of camera in RAW vs. Post work on a RAW R3d....I've had several questions about this over the past months and all of us are finding out more and more...From my experience, i find the post to be a 2:1 or 3:1 process...for every hour of shooting, i spend 2-3 hours in post. The look from RAW that we all see if coming from video is hard to accept. But when you learn the post process you begin to understand how much control you have over your images. BUT, it also requires serious horse power in a machine and then the knowlege of how to put it all together. It's basically a learning process with no end in site as the software continually changes to keep up with the huge files we are shooting. It's also NOT always the right tool to shoot RED for much of the Doc work that's run and gun and fast post. I'm amazed at how many docs & commericals i have worked on that don't get the RAW workflow. And in the end the "end product" is not so good and they would have done a far better job using a betacam or ex1 or even canon 5d. BUT, when you understand and have the time for RAW workflow AND a colorist that can bring out those results.....then the "end result" can be stunning.
I am FAR from a colorist, but i give it a good shot and learn on every production from the editor or colorist. In some instances i'm showing them the look they want underwater while utilizing their skills at the command station.

here are two grabs: one a RAW R3d and the other a JPG that was taken off of my home color session. The results are far apart. You will also notice vignetting. i was using the Nikon 16-85 since we were doing a lot of medium close detail work.

[/url] RAW Look by RedCineUnderwater, on Flickr[/IMG]

[/url] Colored-Look by RedCineUnderwater, on Flickr[/IMG]

Is the "colored" look possible for the camera or is it done in another tool so can't be backtracked to a RED look?

 

[Johnny Friday]

Michael,
The color was done in post so can't be a look saved to camera. I don't really see a need to have an in camera look or rather it doesn't bother me since i know i'm only using it for framing and focus and at every depth change and with light changing...the in camera look fails to resolve a proper look. With that understanding and knowing what you can do after the fact in post, it then does not rank high on the list to have it look good in the viewfinder since we would be chasing the in camera look constantly at depth changes or over cast etc....This is not always the case when say at a place like Tiger beach at a constant depth, but take for example Galapagos, Socorro or any variety of other locals that you'll be all over the place and different environments.
....It's really hard to get used to looking at a flat, unsaturated image, but when you understand how you can manipulate it later in post, then it really is no longer a bother....this is of course my opinion and workflow only.

 

[Pawel Achtel]

I never understood why would anyone care about the in-camera-look when underwater if it is just metadata.
Instead, the important questions are:

1. If and what filtration to use in what circumstances?
2. What lighting?
3. How to control environmental lighting conditions?
4. What exposure (shutter, aperture)?

How it looks in the camera? ... I'm not watching movies underwater.

If you guys could see how 12k underwater motion pictures originate in camera, you would never guess what it is or how they will look like. The monitored image looks absolutely nothing like the final spectacle that pops out of the oven only after some tricks with "smoke and mirrors" not possible to achieve in the camera.

 

[Tom Hamilton]

Greetings all, after having shot with the Rouge for the last 10 days or so, I have decided to take on a dealership for the housing.

Very impressed with the ease of use, the balance of the housing underwater, and above all, the instant access to all camera functions. If you know how to operate your Scarlet/Epic, learning this housing is very intuitive; each and every control is programmable in the same way as the camera; changing looks for varying depths, switching frame rates, project settings, shutter angles/speeds, etc, all available on the fly.

As someone who has learned from the careful observation of the best in the business, I will personally guarantee legendary after-sales service and support, in direct liaison with the Amphibico/Aquatica factory in my hometown of Montreal.

Any questions about the housing, controls, operating modes and so forth, please contact me at redseapictures@gmail.com, or pm me here on this forum for alternate contact details. Deliveries are on track to begin in January.

Attached are grabs of one's self and the Rouge seeing action at Tiger Beach last week, shot courtesy of Emmy Award winning u/w cinematographer Frazier Nivens. Frazier hired me to assist on a Discovery Network shoot, needless to say, he is an absolute pleasure to work for, and as one with an astonishing wealth of knowledge and experience, an eye-opening shooter to learn from. I feel very fortunate for the experience.

Regards to all,

Tom