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anthp

Ikelite 5503.15

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Hello all,

 

I recently shot some photos with my 10.5 behind the 5503.15 6" Ikelite dome.

 

I noticed some significant softness along the edges of the frame on both sides and it wasn't just restricted to the corners.

 

This softness was most obvious in close focus wide angle shots where the closest subject was around one foot (30 cm) from the dome.

 

I don't see any softness when using the lens to take similar shots on land, so I'm assuming the port is at fault.

 

I haven't got the 100% crops handy at the moment, but here is an example of what I mean. The aperture was f7.10 and I focused on the pier (not Michaela and her lovely new TopDawg - thanks Peter), so i would have expected DOF/focus to be a non-issue. I have other examples which I'll post soon where an essentially flat subject is sharp in the centre and soft on the edges.

post-2831-1155271153_thumb.jpg

 

Does anyone else have much luck getting sharp corners with this combo?

 

I noticed this test by Peter Schulz, but his subjects are some distance away from the lens.

http://www.peterpeterpeter.com/ikelite/10-...tests/index.htm

 

Will the Ikelite 8" dome help? Or should I just cut to the chase and lust for a Subal/Seacam and their respective FE2/FP ports? :guiness: Not that I could afford them. :blink:

 

Thanks for you help folks.

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I don't have much experience with it and maybe I was not paying enough attention to corners, but I was happy with this combo. I don't have access to my computer right now, so I just went through shots I have on my site. I struggled to find ones with something important in the corners to judge sharpness. Here is what I have so far:

 

57261257.jpg

 

58079705.jpg

 

58079708.jpg

 

 

I need to look at it in more detail when I'm back home.

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I get corner softness as well with the 5503.15 when shooting up close as seen in the following pic shot about 1 foot away from the Moray's face.

 

http://www.peterpeterpeter.com/scratch/081106_4458_100.jpg

 

To me it's not a big deal as usually I don't have detail in the corners that I care about or I plan to crop the image anyway. Also, I usually end up with the corners overexposed on close ups like this which is just one more reason I will crop this picture.

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Hi Anthony!

 

The domeport has no optical effect above the surface but I actually don't no how to explain the soft corners underwater in a simple way, but if the distance to the subject in the focusarea, is very different form the subject in the corner(s), it´s probably caused by the lens, due to it´s abillity in depth of field?

 

Anyone, correct me if I´m wrong......just my 2cents words!

 

Best regards from Kim Meineche! :-)

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Kim, underwater the dome acts very different than in the air.

 

When light passes from the water to the air, the difference in density between the air and water causes the light to bend (diffraction) if the light does not hit the dome exactly perpendicular. This diffraction causes the dome to act like a lens. Glass lenses bend light trough diffraction as well. Underwater, the dome is a lens

 

Just as bad lens elements in your SLR lens can cause problems, a bad or wrong lens (in this case the dome) placed in front of your lens can cause problems.

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To William's point, even if you take the time to find the "right" point you may not get what you hope for.

 

I have a Canon 14mm that I calculated the lens entrance pupil as 53mm from the mounting face.

I did this by focusing on a distant point and swinging the lens until the point did not move.

This is apparently how the pano guys do it.

 

I then centered my dome (A UK-Germany Housing for a 5D) and the corners still were fuzzy.

 

I'm no expert but the dome seems to really mess with the virtual image (plus the 14mm is rectilinear) and I'm at a loss to explain it.

 

Perhaps someone else can help out... pretty frustrating all in all...

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Thanks you all for taking the time to comment on this issue and for posting other examples.

 

I struggled to find ones with something important in the corners to judge sharpness...

Andrzej - thanks very much for taking the time to post those examples. The corners on yours look fine to me (great shots btw). I would be interested to see higher res crops of the edges if you happen to have them, but at the size you have posted they look great.

 

I get corner softness as well with the 5503.15 when shooting up close as seen in the following pic shot about 1 foot away from the Moray's face.

Peter - thanks for your insights. I really appreciate seeing that perhaps it is not just me. Do you happen to have access to the 8" dome to compare result with that? I'm a bit reluctant to crop if I can avoid it, but perhaps that is the only way around it.

 

The domeport has no optical effect above the surface but I actually don't no how to explain the soft corners underwater in a simple way, but if the distance to the subject in the focusarea, is very different form the subject in the corner(s), it´s probably caused by the lens, due to it´s abillity in depth of field?

Thanks Kim. I'm not sure about the dof issue. I initially thought that might be the cause, but the example I'm about to post suggests that it is perhaps something else....

 

When light passes from the water to the air, the difference in density between the air and water causes the light to bend (diffraction) if the light does not hit the dome exactly perpendicular. This diffraction causes the dome to act like a lens. Glass lenses bend light trough diffraction as well. Underwater, the dome is a lens

Excellent explaination William. I remember you had some difficulties with domes when you first got your 5D. Has that been resolved now? Did you ever have the chance to compare the 5503.15 with the 8"?

 

I then centered my dome (A UK-Germany Housing for a 5D) and the corners still were fuzzy.

I wondered whether the entrance pupil issue you mentioned might have been the problem in this case too... Did you ever resolve your issue with domes?

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Ok, here is the other example I was thinking about earlier.

 

In this shot, the subjects are roughly the same distance away from the lens. It is not a particularly good shot, but shows the sort of issues I'm asking about.

 

Here is a "map" of where the crops are taken from:

_AJP1138_diag.JPG

 

Here is a crop from the LHS where you can see significant softening:

_AJP1138_edge.JPG

 

Here is a crop from closer to the centre where the subjects are roughly the same distance from the lens:

_AJP1138_centre.JPG

 

And finally here is a shot from the other edge (with a further subject) which seems to be ok:

_AJP1138_faredge.JPG

 

Now perhaps I'm being a bit precious, but I would like to hear whether others have had better results behind the 8" dome.

 

I would appreciate anyone else's insight. Thanks folks. :guiness:

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As someone has already said, the dome port in conjunction with water and air becomes part of the optical system.

Judging sharpness on a monitor with 72dpi is difficult. However when things get into repro, problems really show up, and especially if the art editor chooses to use one portion (often not the centre) of a frame.

I have never found any compact dome port that gave me proper sharpness across the frame and for that reason have always resorted to using the largest diameter (longest virtual focus) dome ports available. Even these vary and as I said in another thread from the Aquatica, Nexus, Sea & Sea and Subal ports that I own, I have found that the Sea & Sea (yes, I know, it's only Plexiglass) is the best for sharpness from edge to edge.

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Thanks John. Got any Sea and Sea ports for sale?? :guiness:

 

Sounds like the concensus is that 8" will be better. Anyone have first hand experience with this combo (8", 10.5 and Ike housing)?

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I don't have the Nikon combo you have, but am having the exact same problem with the Ike port #5503.50 & Canon 10-22mm. I found the softnes to be far more pronouced at the 10mm end, but reduced significantly with apertures smaller than f/10.

 

Up until now I've been shooting within these constraints. I've seen tests shots using the same lens in the 8" dome and the problem gos away.

 

I'm currenlty awaiting delivery of an 8" Ike dome to correct the problem.

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Hi Damien - thanks for your input. I'm looking forward to hearing how you go with the 8". Cheers mate.

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Would a +1 or +2 diopter help? I use one with my Sigma 10-20mm (as suggested by Ryan from Reef Photo - thx Ryan), and it seems to help keep things sharper. Different lens and different port, but might be worth a shot.

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Hi JC. Thanks for the suggestion. I'm afraid mounting diopters on fisheye lenses is damned near impossible unless they can mount on the rear of the lens...It works great on a zoom though - I agree.

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Ah! I learn something here every single day.

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