Question - Are all ports created equal?

Rob,

it depends on what choices you have.

If you want the best optical quality you have to go with the Seacam Superdome (24cm diameter, 23cm glass diameter).

Herbert Frei (reputated uw equipment tester in germany) has confirmed the untouched image quality. I was told it is originally designed for 18mm focal length. But due to the diameter you can also accommodate a 14mm WA (full frame) with no doubts. Although theoretically the dome is not designed for 14mm the results come undistinguishable close to the Nikonos 15mm lens with still greater FOV.

Some people use this dome very successfully for split level shots.

But what housing to buy for this dome? The 1Ds/1DMkII housing for over 5000 Euros + the camera?

I considered the Superdome for my Seacam film housing. But don't want to spend the money because there is no Seacam 10D housing available for the future.

Driving it to the limit: There is a handmade 28cm Dome available in Germany, perfectly designed for 17mm. The engineer will adapt the dome to almost every housing type. For some zooms he offers special close up lenses with curvature for maintaining image quality. This one gives you the best corner sharpness, heaviest hand luggage and biggest whole in your wallet: 1500 Euros + adaptation.

To be more realistic: acrylic is of course OK as you have no real other choice as I understood, but get a big one if you are picky with image quality.

Stupid question: Aquatica for Canon 10D ??

greetings,

Julian

What is important is that the radius of the dome should  be egual distance from the optical center of the lens...nodal point.

Yes, that's true. The downside is that the optical center of the lens is not known as lens builders do not publish them. The optical center should be roughly at the aperture. But todays lenses are constructed so complex - no chance.

In addition most of the housing manufactures use one dome type for many lenses. And extension rings do not eliminate this completely. To equalize the lack of having a dome exactly designed for the optical center a big dome helps to minimize the error.

That's why amphibic lenses (Nikonos & Nikonos RS) produce perfect image quality. They are harmonious designed lenses as one part.

This all of course has to be set in relation to personal needs, market availability, size and ..... money.

I have seen lens diagrams and cut away views showing the nodal point in photo magazines and books. Usually they were in association with lens tests. They had to come from somewhere.

Splash

yes, but most of the manufactures complain there is not enough information from the lens builders. I don't know what really is necessarry for absolut perfect design. But the provided information didn't look to detailed to me.

And I did not find any information about the canon and sigma 15mm fisheye. Do you know where to get from? Calling Canon or Sigma would not help. They don't give you nothing.

But still it would be to much expenditure for housing manufactures to design a special dome for every lens.

The 28cm Dome I was talking about for example is exactly designed for the Nikon 18mm lens (full frame). But this is an expensive exception done by one person.

I don't think that will change in the future or help someone chosing a dome right now.

regards,

Julian

Finding the nodal point of a lens shouldn't be difficult. It's standard procedure for panoramic photography using a QTVR head or similar.

see http://www.panoguide.com/technique/setup_panohead.html for details.

I would be interested to know if the manufacturers actually measure this eg is the nodal point of the 15mm fisheye (Sigma or Canon) actually in or close to the centre of the Ikelite #5503.15 port - Ike?

Jolly, in terms of "Aquatica for 10D" - sadly not. I did mail Blake a while back, and there's no plans for this. Becoming an Aquatica shooter for me would mean trading my 10D for a 300D, which involves a number of other sacrifices - it's a hard call. Perhaps I'll go for the Seacam with custom dome + 1Ds - next year :?

Also, I wonder how far the nodal point can be from centre of the dome before you start noticing a difference - whether it's critical enough that say different 15mm fish eyes might have different enough nodal points that you'd see better optical performance in one than the other. I'm guessing that as long as it's pretty close to the right spot you wouldn't notice much difference.

Hi Rob,

I am in a similair situation.

I even considered the Ike housing with the custom dome. But guess what, the Ike 10D housing costs 1950 Euro (~ 2430 Dollars!!) over here.

Sad thing becuase a lot of wonderful Ike products are unaffordable in germany (2 times the US price in average). And nothing in stock, only on request with long shipping time.

Even the Sealux housing is less expensive. But they would not adapt the Seacam dome.

Finally the "cheapest" solution is the Sea & Sea housing (here in Germany). The acrylic fisheye dome has 211mm glass diameter. big enough for my split level needs.

I want E-TTL. So I plan to install the new Heinrichs E-TTL converter into the housing.

With some effort I think it is no problem to get the nodal point for one lens and some more data. But also the curvature theoretically would have to be designed for one lens. But we are talking of a very little gain in image quality and a lot of money and effort from the manufactures side to specialize on every lens on the market. Impossible for affordable and cheap domes. Maybe you have to live with it :wink:

Concearning Ike fisheye dome I can only guess.

As I recall the 5503.15 is listed for the 10,5mm Nikon, the Nikon 16mm and the Canon 15mm. These lenses might not have the same nodal point. Don't know if there are extension rings to focus the dome exactly on the nodal point. But I suggest no. But I really can not say for sure. Maybe Ike or someone else with experience can tell you.

I your case I would choose the Ike housing (US price!) if there is no extraordinary need for split level shots.

Just my thoughts ....

regards,

Julian

With the 10.5 in the 5503.15 port, the 10.5 focus is at 12 inches. For the 16mm behind Aguatica 8 inch port, focus is from 11.5 to 14 inches. So there is a slightly different nodal point for each lens. As long as your lens can focus this close you are OK. Both seem to have sharp edges at around F 8.

Splash.

Hi Don,

Do you get the focus point information from the EXIF? If not, where do you get it?

Eric and I are interested in getting hyperfocal distances for various lens/dome combinations for a summary table here on Wetpixel.

Cheers

James

Hi James,

if you hold on a bit more, I'll send the tables to Eric as promised.

It was not easy getting the exact dome glass sizes from the manufactures.

The Seacam Superdome for example is published with 240mm diameter. But the glass has 'only' 230mm.

Beside Ike who posted the size only Sea & Sea responded fast and accurately.

If you have some exact dome data, please send them to me for the tables. If there still is an interest in these calculations beside collected

data from EXIF from UW practice.

regards,

Julian

James,

I just focused on a photo grid and noted the settings.

Don

While glass and acrylic may be comparable out of the box, you should consider after a year or two of heavy use. My 8" aquatica dome has swirls and scratches from use. You have to be very careful cleaning the ports - yet they never seem to be clean. In comparison, my buddy's subal glass dome looks like new.

I can't say for sure that image quality has degraded except for flaring and shooting into the sun.

If you can afford it - buy glass!

Hi Kasey,

Have you tried polishing your port? Ask Aquatica for details, but you should be able to eliminate most of those swirls and light scratches.

That's something you can do with a commercially available polishing compound and a soft cloth. That's NOT something you can do for a glass dome - but then it probably wouldn't pick up those light scratches anyhow.

Cheers

James

if it is of interest for someone:

Sigma 15mm fisheye EX:

nodal point 70.9mm

"Spiegelpunkt" (don't know in english, by word "mirrorpoint"): 15,6mm

distances given from film(sensor)plane.

Canon confirmed once more that they don't publish any of these data worldwide.

But maybe someone has them (from mags, as said)?

regards,

Julian

forgot to say:

The flange focal length (distance between lens mount and sensor/film plane) is 44 mm for Canon. For Nikon 46.5mm

On a Canon + Sigma 15mm fish the Dome hemisphere should begin at 26,9mm from the lens mount. That's 1.06 inch.

Seems very (to) close to me. Can this be true?

regards,

Julian

Julian,

I suspect that 1.06 measurement is the radius and that it would be correct for a matched port. Look at the old 15mm Nikonos lens... that is a matched port a little more than three inches in diameter. The port size is just not that critical. As long as your lens can focus on the apparent image and the angle of view is not restricted the image will be OK. A mm here or there is not that important. With an 8 inch dome you can use any lens that will fit inside as long as it will focus on that apparent image.

Cheers,

Donovan

Hi Donovan,

of course this is "just" theory and a big dome helps to reduce dome positioning errors in practice, especially with a cropped sensor camera.

1.06 inches is the distance between dome glass and the camera bayonett for the Sigma 15mm fisheye with a Canon EOS. not the diameter.

This would be theoretically an optical correct dome position.

Nikonos lenses require just a small dome becuase:

1) the lens is designed to focus underwater (close)

2) the dome is optically designed and positioned for the lens.

With such a small dome like the nikonos lenses have, it is necesarry that the dome moves with the lens when focusing. With a fixed dome the Nikonos lenses would not give sharp images in the corners.

I know that this Nikonos lens perfection can not be achieved with domes/housings. For myself I would strongly prefer a big dome to reduce these imperfections.

I have never seen sharp fisheye corners in combination with small domes with housings. Especially not full frame. Also my Seacam Fisheye Dome has visible lack of sharpness in the corners.

It's still a noticeable quality difference to my Nikonos 20mm lens which does better.

But maybe someone can show me some sharp small dome wideangle or fisheye pictures. I would be really interested in the used setup.

greetings and regards,

Julian

Hi Rob.

One issue that hasn't been touched on is the availability of service you're likely to receive in Australia.

Ike's quality of service is legendary, however this might not be said of the Ikelite distributor in Australia.

I personally only know 3 people with Ike housings in Australia. 2 of them have had service or repair issues that have necessitated return of the housing to the USA. From discussions I've had with them, neither would speak very highly of the help they received from the Aussie distributor.

I may be speaking way out of turn, but I do not think that the distributor is able to provide a great deal of service or maintainence locally either.

I honestly don't know who the Aquatica dealer is in Australia so I cannot comment on whether the situation is better with them.

Thanks for the info, Andrew. The Ike distributor in Australia doesn't seem to specialise in underwater cameras, so I wasn't anticipating good service necessarily. I figured if there was any problems Ike would probably pop over here and fix it for me?

The port info above is certainly food for thought. Theoretically it would seem that a small dome like the Ikelite ones would be more likely to be optically problematic than and 8 inch dome - less margin for error, which wouldn't be a problem if the domes were made for one lens, but they're not - its one size fits several.

The main problem is a lack of empirical data ie pictures. If we were comparing lenses, it would be standard practice to shoot a comparison lens test so we could make an objective decision re: quality. Given that noone is likely to have multiple housings for the one camera sitting around, it would be great if anyone has some wide-angle (esp. fisheye) DSLR shots that show edge and corner sharpness that we could take a look at.

It sounds like the best solution still for really sharp wide angle is a nikonos, which isn't as silly as it sounds - carrying a second body/system for wideangle is what I do above water. Perhaps the 10D can be used like a polaroid back for determining exposure prior to exposing film...

Hi Guys,

I think this topic has gotten a bit too nit-picky. Can you get great wideangle shots with sharp corners using the Ikelite and Aquatica ports? Yes, you can.

I can provide samples upon request from both port systems.

People think that because the Ikelite port is not big it has a small radius of curvature, but that is not the case. It has a large enough radius of curvature to shoot the 12-24DX lens, it's just not a large diameter (across) dome. Neither port is a hemisphere anyhow - each are only partial hemispheres.

Cheers

James

James, I agree that it's nit-picky, but it's also been interesting because I haven't seen a lot of these questions of dome port optics addressed elsewhere. We've touched on a lot of questions I've often wondered about.

I still don't know the practical answer to the question in my mind, which is whether I can shoot really sharp wide-angled images with a Canon-mount fisheye through the Ikelite dome port. It's possible (I think) through the Aquatica 8 inch dome because I've seen Herb's shots from Thailand, which look pretty sharp to me.

There's meant to be an Ike 10D housing coming out in June (hey-that's right - it's June already!), so maybe I'll be able to answer some of these questions more accurately myself shortly.