16 replies to this topic

[aroundlsu]

Hello, I am really new to underwater shooting and have a few questions. I really would like to get my Canon 35mm f/1.4L and the 50mm f/1.2L underwater with manual focus capability. I am looking at the Aquatica housings since they have focus knobs built in but the lens charts don't list these two lenses. They do list the 24L which is similar in size to the 50L. Will it be possible to rig these two lenses to work?

Thanks for any help you can provide!

Edit: The 35L is the exact same length as the 24L. Does that mean the same extension should work with it?

Edited by aroundlsu, 22 November 2012 - 07:24 PM.

[Drew]

All housings have a focus/zoom knob that work with gears. If you are talking about the focus knob extension ring from Aquatica, it's too long to work with the 35 and 50L.

You can probably get gears to fit the lenses from any manufacturer, either custom or a DiY mod of existing gears. The cheap Ikelite plastic gears are great for modding to test a lense before paying $300 for a custom ring. A thick rubber band and a bit of shaving is all you need.

As for the 35L, the mfd is 30mm if I'm not mistaken. I used a 35mm extension with it on my FF housings, using a Superdome. With the 24L II, I use a 20mm behind the SuperDome. Never put the 50L in the water so I can't help you there.

[aroundlsu]

So I need to match up housing based on MFD? I guess I don't understand how extension rings work and what they are needed for. Can you explain it to me?

[Stewart L. Sy]

If you are planning to use a dome port, the extension ring pushes the dome out so that the optical center of the dome matches up with the exit pupil of the lens...or as close to it as possible. Also, when using a dome, you don't focus on the scene but on a virtual image that's formed at approximate 2x dome diameter. Your lens must have a MFD that is within that virtual image or you will need to add a diopter. If you're using a flat port then MFD isn't as critical as a virtual image isn't formed with a flat port, you do "gain" about 20% magnification since the flat port refracts the water and cause an increase in image size. You might be able to use the 50L behind a flat port but the 35 will likely need a dome. MFD is 30mm for the 35 so you'll need at least an 8" dome port to get good image quality.

Getting manual focus ability with a prime lens will depend on the distance the focus ring will be from the zoom gear on the housing. most zoom rings are close to the rear of the lens and thus aren't a big reach to engage the zoom controls of the housing. Depending on your housing of choice, you'll need to measure that distance and have a chat with the manufacturer and see if they have a zoom ring that will match. Aquatica does have a port extension that allows MF using the EF 16-35 & 17-40Ls.

S.

Edited by Stewart L. Sy, 23 November 2012 - 08:12 AM.

[aroundlsu]

OK sorry but this seems a little strange to me. I want to make sure I fully understand before I drop a lot of money on the wrong things..

With a dome I focus on the glass of the dome and everything is always in focus? I can move around all I want without having to rack focus to anything?

For the 50L and longer lenses I should be looking at the flat ports? Aquatica calls these macro ports but they will work for non-macro applications right?

Would this work for the 50?
http://www.aquatica....orts_18428.html

Edited by aroundlsu, 23 November 2012 - 08:14 AM.

[Stewart L. Sy]

No. The dome will create a virtual image that 2x the dome's diameter IN FRONT of the dome. You will still need to focus as that 2x diameter is where subjects at infinity are located, subjects that are closer (or within your lens' focal range will be closer than that, it's still a three dimensional scene)

Yes, you can use flat / macro ports for non-macro applications.

S.

[Drew]

Thanks for explaining Stu. That's why you run photo trips and I have friends who tolerate my impatience!

Teddy, you can use a flat port with most lenses, but you lose about 1/3 of the FOV due to water refraction.

[aroundlsu]

Thanks for all the help everyone. I feel like a fish out of water with this underwater stuff! I had a choice between Steadicam or underwater as a specialty and I picked the water so now you guys are stuck with me.

I actually got an email from Jean at Aquatica and he said the 35L will take the same extension as the 24L but he didn't know about the 50L. He said the 50 would probably work without an extension but would probably show a slight improvement in the corners with the extension.

I have all the gear ordered and have an extensive pool test scheduled in two weeks. I will be testing with focus charts and real people so it should be a good mix. I will be happy to report my findings.

[Stewart L. Sy]

Drew, someday, hope to share a San Miguel with you over some sizzling sisig!. ;-)

Teddy, I'm also a 5dmk3 (& 7D) user to if you have questions, I'll try to answer them.

Edited by Stewart L. Sy, 23 November 2012 - 06:16 PM.

[r4e]

...Your lens must have a MFD that is within that virtual image...

The dome will create a virtual image that 2x the dome's diameter IN FRONT of the dome. You will still need to focus as that 2x diameter is where subjects at infinity are located, subjects that are closer (or within your lens' focal range will be closer than that, it's still a three dimensional scene)

So, if the lense has a MFD that matches just 2x the dome's diameter, you'll be able to focus only on objects far away?
In order to focus at objects closer than infinity, how much shorter will the MFD need to be? Dome diameter? 1.5x dome diameter?

[coroander]

The closest focus underwater is for objects touching the front of the dome (note that an object touching the front of the dome will have the same focus distance both above and below water). The focus distance in this case is the distance from the sensor to the front of the dome. The virtual image therefore extends from this distance to about 2x the dome's optical diameter (for objects at infinity).

Note that 2x the diameter is an approximation. The actual distance for objects at infinity is closer to 3.03x the optical radius of the dome plus the distance from sensor to the front of the dome. Note that the optical radius of a dome may be quite different to 1/2 the distance across the dome. See: http://wetpixel.com/...ll/dome-theory/ for a complete explanation.

[Paul Kay]

I use both the 35L and 24L underwater on a 5D2 and behind the appropriate port and extension they are great although the usual caveat applies - that they are not used at wide apertures. Their main advantage is the bright viewfinder image but both produce good results, and the 35L is decidedly better than the 35/2 Canon lens which I also have. I had and sold the 50/1.2L because I didn't find it to be a particularly good lens and the speed is irrelevamt underwater - the 50/1.4 is just as good underwater (and still gives a bright viewfinder image) despite a relatively rough build quality and noisy AF - its not a lens I find particularly useful underwater having said that, whereas the 35L is. I use my 35L behind a Seacam Superdome and it gives excellent results and also behind a flat port which gives good results over ~90% of the field with just the periphery showing softness which may or may not be acceptable depending on what you are doing.

[Drew]

Paul, what extension do you use the 35L with? I tested and went with the 35mm. However, I was using it for sharks so corners weren't as important.

[aroundlsu]

Why is lens speed irrelevant underwater?

[Drew]

Ted, the viewfinder is brighter the larger lens aperture. AF is also more accurate with lenses less than f2.8 with the X-point AF sensors. With a FF camera and a fast lens, it's bigger and brighter!

[Viz'art]

Thanks for all the help everyone. I feel like a fish out of water with this underwater stuff! I had a choice between Steadicam or underwater as a specialty and I picked the water so now you guys are stuck with me.

I actually got an email from Jean at Aquatica and he said the 35L will take the same extension as the 24L but he didn't know about the 50L. He said the 50 would probably work without an extension but would probably show a slight improvement in the corners with the extension.

I have all the gear ordered and have an extensive pool test scheduled in two weeks. I will be testing with focus charts and real people so it should be a good mix. I will be happy to report my findings.

Ted, when I'm back at the office Monday, I will send you some documents on both port extension and ports (both flat and dome) that should help explain their relations, just reshoot me a e-mail at jean@aquatica.ca as a reminder.

[Paul Kay]

Paul, what extension do you use the 35L with? I tested and went with the 35mm. However, I was using it for sharks so corners weren't as important.

The same, 35mm with the Superdome - mostly used in pools but the corners seem pretty rreasonable as far as I can tell (subject tends to be central so I'm going by pool 'lines'......).

Why is lens speed irrelevant underwater?

Because trying to focus onto a curved virtual image at a wide aperture with its extremely narrow depth of field is not terribly effective most of the time. So you can't shoot wide open and get anything except the centre of the image to be in focus. In effect, the wider the aperture, the more 'corner' softness extends towards the centre. Fast lenses give lovely bright viewfinder images and AF tends to be faster and more accurate as Drew says.

Edited by Paul Kay, 24 November 2012 - 08:51 AM.