Ikelite 8" Dome

I have used PC and glass ports extensively, and the choice is clear (no pun intended) to me.

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Please post some examples.

Much like the glass vs PC debate, there has been no evidence provided that Glass is better than PC, or that a larger dome is sharper than a smaller dome.

Pool tests I conducted a while back indicate very good performance with the Nikkor 10.5mm lens behind the Ikelite #5503.15 port.

Does not have anything to do with this.

Please understand that this is not about how good your fisheye lens performs behind your dome (by the way, why did you stop down several steps when doing such a test?).

You have to distinguish between two basic dome problems causing image quality issues:

1. Improper dome setup

2. rectliner lenses focus on a flat surface. The dome’s virtual image is curved.

Item 2 is much worse for rectlinear wideangle lenses. Fisheye lenses focus in a matter the virtual image is shaped (curved, closer edges). Therefore they perform much better behind dome ports in general. Getting a good corners performance with a fisheye in comparison to a wide rectlinear lens does not say anything about item 1.

And calculations I did indicate that the center of the radius of curvature of the #5503.15 port is at the entrance pupil of the lens.

Where does that come from? I really wonder how you can confirm by calculation that the centre of curvature matches the entrance pupil when the dome curvature is smaller than the lens field of view. That would mean your fisheye dome is a 100% true 180° hemisphere? I don’t doubt you have calculated something. Maybe the information in this board about Ikelite’s fisheye dome being not a hemisphere was wrong? Have a pic of it?

Julian

Just measurebating I guess, but remember that the 10.5 should be less affected by a small dome than a zoom

Definitely. Wider reclinear glass works better with dome glass matching the field of view.

Much like the glass vs PC debate, there has been no evidence provided that Glass is better than PC, or that a larger dome is sharper than a smaller dome.

I think glass vs. PC debate is meaningless as a general discussion which is better.

From my understanding:

glass:

+ better contrast

+ more resistant against flare / reflections

+ more resistant against scratches

- if scratched, more difficult to polish

- refraction index differs from water

PC:

- easily scratched

+ more easy to remove scratches

+ refraction index more close to water

- less resistant against flare/reflections

@Peter

I want to add that UK-Germany,Sealux and Subal put fisheyes behind dome glass with less than 180° coverage as well (and the curvature centre doesn't meet the entrance pupil). Fisheyes are not that critical as super wideangles (see point above). But the glass is still big enough for split shots and maintaing a certain radius. This is where the 8" Dome comes in from Ikelite. And for super wideangles it provides the appropiate coverage allowing the usage of the full radius.

Julian

Please post some examples.

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You want examples of me cleaning my domes? <_<

I have not stated that new PC is optically inferior! Please reread my post - I've stated that I prefer glass because it is less prone to scratching, and much easier to get clean and smudge free.

On the dome size issue - I don't own a small port and therefore cannot provide examples, but the softness I referred to above speaks for itself. I think Julian stated well the reasons for the lens being so close to the dome in these setups - for ultrawide (weitwinkel) lenses it is not optimal!

I've yet to be impressed by the sharpness of any test of ultrawides behind a small dome. Nor have I seen many great underwater wide-angle shots captured behind Ike small domes - while I don't imply that to be a function of the equipment, it does imply that WA enthusiasts tend to lean elsewhere.

Nor have I seen many great underwater wide-angle shots captured behind Ike small domes...

~Matt Segal

I find it funny that even Ike will admit that they find no evidence that you will get better performance behind an 8" dome over the 6" even after they tested it, but because people for some reason believe different, they are offering an 8" for an obvious mark up.

Hey, I already admited that I'm intested in this new dome. But at least I'm honest about why I want it. A: It will house 2 of my lenses B: It looks cool C: over unders

Has nothing to do with which will provide a better image.

Quote from Ikelite:

"Advantage of the larger radius dome port is over/under photos. We see no proof it provides sharper images with very wide angle lenses as some people contend, but we have had enough requests to warrant making it available."

I'd love to see someone prove this otherwise.

You want examples of me cleaning my domes? 

LOL... I agree with Kasey's comments about dome maintenence. I've used three Sea & Sea NX Fisheye Dome Ports in the past 2 years, all of them replaced when the inside was scratched. None of these scratches would have occured if I was using a glass dome... I'm really curious to know how many ports someone like Jim Watt goes through in a year.

The diopter attacking port issues you speak about were caused by an incorrect recomendation on a port chart that has been revised. There is a certain value judgement that occurs. In this case, Ike was dealing wiht an 18-55mm lens that costs less than $100, making a perfect port placement pretty much irrelevant due its narrow field of view and less than L optics.

I understand the logic, but as an observer it makes a statement to the precision of Ike's port system. If an extension system were in use even a $100 lens would justify an extension. Perhaps it is unfair to judge the system by a single mismatch. It was so obviously incorrect to me, and frustrating trying to explain to a neophyte that what Ike recommended could not be correct! Aside from this I have very limited experience with the Ike system beyond seeing pictures on this and other websites.

Julian, you are correct, the center of the radius of curvature of the #5503.15 port is not at the entrance pupil of the lens as I had stated earlier. Nor can it be for any port I can imagine.

Hi Folks,

I have pool tested the 8" dome with the Canon 20D and 10-22mm lens. I have comparison photos of a test "chart" taken with the standard Ikelite port and the 8" port. I'll post these in a review soon.

Cheers

James

Julian, you are correct,  the center of the radius of curvature of the #5503.15 port is not at the entrance pupil of the lens as I had stated earlier. Nor can it be for any port I can imagine.

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It is possible with the proper neck length/extension on the port, and some ports are set up just this way; simplified discussion available here.

I find myself constantly repairing scratches in plastic domes and they're always the kind that are unlikely to ever occur in a glass dome. It drives me crazy. It's true that plastic can be repaired in a way that glass cannot, it's just a shame that you'll always need to. I'm looking forward to not having to do that with my glass domes. Wish I could convert my friends as well.

Glass also passes more light than plastic. Whether it's "scientifically provable" that it makes a difference to your eye is beside the point. It's certainly "scientifically provable" to the measurement machine. I'd rather not have a bevy of scratches softening my images so I like glass.

I have pool tested the 8" dome with the Canon 20D and 10-22mm lens.  I have comparison photos of a test "chart" taken with the standard Ikelite port and the 8" port.  I'll post these in a review soon.

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Can't wait to see that James - I'm sure it will be very informative.

Any sneek previews?

Glass also passes more light than plastic.  Whether it's "scientifically provable" that it makes a difference to your eye is beside the point.  It's certainly "scientifically provable" to the measurement machine.

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This sounds oddly familiar to the claims on PC Gaming forums that 129 frames per second in a video card is way better than 120 fps.

How often are you guys actually getting scratches on your ports. I just got home from work and checked all my ports for scratches, and found none. I didn't think I had any, but by the tone of this thread, I thought for certain I would have some.

<snip>How often are you guys actually getting scratches on your ports.  I just got home from work and checked all my ports for scratches, and found none.  I didn't think I had any, but by the tone of this thread, I thought for certain I would have some.

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I'd think a lot depends on your attitude. I don't pamper my camera gear by any means; they are tools, not objects d' art. A good description for all my bodies and lenses would be "press corps ugly".

Still, I've always treated optical surfaces with respect, and even my oldest 15+ year old Aquatica dome is without blems. This is after a pretty hard life, and it's not been resurfaced.

I've noticed I am a minority in that I get into the water with the dome beanie in place, and only take it off when at the worksite, then, replace the beanie before getting out of the water. I believe there is more damage potential on the boat than in the water.

To the point, I've actually only replaced a dome once. This was for a gouge that would have totaled a glass dome just as easily.

All the best, James

I get scratches on plastic domes all the time and so do my friends. I've had to fix plenty of them, not just mine. Perhaps you should look closer.

As to the difference in the amount of light passed and whether it is relevant, look it up. Perhaps you won't mind if your lens elements are made of plastic as well.

I find it curious that anyone would concern themselves with the optical quality of anything yet dismiss the optical quality of other elements in the system. Perhaps you don't care about the performance of your camera or lens either. I do and I care about the performance of the dome and the material it's made out of. It makes no sense not to.

Kasey, please. Problem in your post #28 had nothing to do with the "precision of Ike's port system." This was simply addition of a plus diopter that was thicker than anticipated.

Our ports are acrylic, not polycarbonate for the confused experts. I polled several National Geo photographers about material choice and was surprised to find glass is not always preferred. One comment was "I'm not a big fan of glass domes

since they are heavy and get streaking that never disappears." We chose to attach Aquatica domes because of their stellar reputation. What would you pay for glass. I have a source, but believe complete dome would be at least six hundred dollars.

E-mail me at <ike@ikelite.com> if you want to avoid cluttering the forum..............

$600 would be a bargain!!!

Our ports are acrylic, not polycarbonate

Julian, you are correct,  the center of the radius of curvature of the #5503.15 port is not at the entrance pupil of the lens as I had stated earlier.

Peter,

OK, thanks a lot for the info. I was already a bit confused as I've never used an Ikelite dome with a fisheye but reffered to some board data.

Nor can it be for any port I can imagine.

Yes, there are some 180° domes. I've an older Seacam fisheye dome and the newer one is also a true hemnisphere.

But smaller than the SuperDome which is basically for wideangles but also used for fisheyes often. I think Nexus offers a 180° dome but more focused on split level work than taking it underwater:

But as stated before most manufactures put them behind a smaller curvature because they still often perform better than wideangles behind it.

Julian