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Focusing the dome (AKA shooting on your feet)

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For polishing out scratches I've used Microgloss polish which is a white cream with very fine diamonds in it. But every abrasive polish will leave minute scratches, and you might find that they are worse than what you already have. Drew's white vinegar suggestion is a good one, to dissolve any limescale.

 

I've never had much success polishing acrylic. Seems like all you can do is replace a bigger flaws with with lots of smaller ones. I've spent hours trying to get my acrylic port back to a pristine state, using the Novus products, micro-fibre cloths, lots of elbow-grease and following all the advice. I can get it so it looks good, until you hold it up to a light, especially a small pin-point light, then a halo of very, very fine polishing scratches become visible. I know that these polishing scratches will not noticeably effect well-lit scenes but they will effect backlit and sun shots. And their existence annoys the hell out of me!

 

I've finally given up and gone back to a glass dome. More expensive, more prone to a fatal scratch, more bubble-sticky. But clearer and tougher. Tested well in the pool yesterday. Looking forward to getting it down among the hammerheads at Layang Layang later this month.

 

Regards

Peter

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To be fair I've never on any video camera housing used full manual focus with a wide lens. I've only ever done it with macro. With wide I just use AF in good vis, or lock it off or do a momentary (single) AF if I expect focus to hunt, such as in poor vis or shooting pelagics in the blue. So personally it doesn't sound like a huge problem not to have it since Davide's experience shows it's impossible to monitor a small change in focus anyway..

 

Hi Nick,

 

I agree. The most valuable focus feature for most UW video is Focus Lock. Point the camera at a clear subject about 1 - 2 meters away (dive buddy or fin tip if nothing else is around), let auto-focus snap into sharp on the monitor, then lock it in with Focus Lock. Stops any hunting. Works for any subject from a meter to infinity. Only need to change focus for close-up. Between shots, I tend to bring the camera back to this 1-2 meter focus lock and leave it there so I'm ready if something appears in the blue.

 

Personally, I wouldn't buy a camera / housing that could not do a quick, one press Focus Lock.

 

Would that work with the larger sensors in DSLRs too?

 

Regards

Peter

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Apart from having a special gear machined for the 8mm, there is a workable solution to achieve manual focus. Reverse mounting the gear made for the 7-14mm and carefully positioning it so the gears engage will work. The Live-view magnified focus assist makes manual focus easy on the 8mm...this automatically comes on when you begin to manual focus.

 

The only thing to be careful of is not to push the gear too far towards the body as it will engage the (useless IMO) lens release...and give you an error message. If I decide to keep my Nauticam GH2 housing...and this will only be if/when I make up a Subal glass port adapter...I will remove the lens release.

 

I originally bought it after being given an assurance that a Zen glass dome adapter was being released "in a few weeks" (that was in January). I don't like the plastic dome that came with my system. My friend who bought his GH2 Nauticam same time as I has already buggered up his plastic dome...and he is a very careful and experienced photographer. I'm mainly using a 12 year old Subal F4 Procase which I converted to take the GH2 with minimum necessary controls. At a guess I've done well over 1,000 dives with this case and original SWB glass dome...not one scratch on the glass yet.

 

Come on Nauticam... listen to your customers and bring out a glass dome or an adapter for what is otherwise a nice housing. Oh...and please add a hydrophone.

post-16448-1336535502.jpg

post-16448-1336535509.jpg

post-16448-1336537404.jpg

Edited by HDVdiver

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Pete/Nick

AF in DSLR are the same. There is continuous AF (for some cameras), AF-Shot (momentary AF for you camcorder guys) and of course manual. The problem here with the OP is he has too much junk on the port to focus anywhere else, which is why MF would've helped if the housing had access to it. Sometimes finding a subject that has more contrast would make the AF focus past the bubbles. If you are solo, the edge of the sun hitting waterline etc can sometimes work, but you have to be quick to let go!

And let's get very real about acrylic polishing. It was designed to clean scratches for legible view, not critical view. That's the negative of acrylic, once scratched, it's never going to be as good as new. However, for field use, at least you can polish it and use it for non-backlit shots, as Peter has pointed out. Once glass is scratched, hand polishing will take hours and days and you lose the coating. No such thing as a free lunch.

Nick, with DSLR , there is a magnification mode for liveview (usually 10x) which can be used for critical focus. Of course, all cameras can't do it while recording so focus has to be set up before recording, which limits the type of shooting.

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It seems like I opened Pandora's vase :o

 

For AF I agree with Drew (Sometimes it happens :huh: ).

I can speak only for GH2 because it's the only DSRL I used underwater.

Forgetting the AFC (Continuous AF) while in AFS (Single AF) you can choose different modes:

 

23 point area focusing: Up to 23 points for each AF area can be focused. This is effective when the subject is not in the centre of the screen. This is the mode I was using and it was deceived from the huge amount of dust inside the dome...

The 23 AF areas can be divided into 9 areas and the area to be focused can be set. It's a little tricky but it can be made through the touch screen or the Quick menu button and rear dial (available on the housing).

 

1-area-focusing: The camera focuses on the subject in the AF area on the screen. When the subject is not in the centre of the composition, you can bring the subject into the AF area, fix the focus by pressing the shutter button halfway, then move the camera to the composition you want with the shutter button pressed halfway, and then take the shot. Maybe, once the focus is fixed it's better pressing the Lock AF and then start shooting.

Position and size of the AF area can be changed using the touch screen (it's not our case :) ) or through the housing dedicated Quick Button. It can be changed to 4 different sizes and can be moved with the cursor button.

 

Maybe next time I will use the 1-area-focusing with a medium size.

 

Hence the quick one button focus lock function is there.

 

AF tracking mode. I used it a couple of times on land just for fun. Basically you touch a subject on the screen or you place the subject in the AF tracking frame, and press the shutter button halfway to lock the subject. Focus will keep on following the subject even if it moves. I don't know if this is available on other DSRL and I don't know how effective it is.

 

The "hack" proposed by HDVDiver it's very interesting. The "Live-view magnified focus assist" function he mention it's the same Drew was referring to. Using manual focus as you move the gear the camera automagically displays magnified view of the subject. You can change the magnification and the zoom area. Pressing the shutter button halfway the live-view reverts to whole image.

 

 

Regarding the dome polishing techniques you gave me really bad news :P

 

I read countless threads on wetpixel about scratch removal and I thought that using the right product the dome could return brand new.

On another forum I read of people using this Arexons cream made for car painting scratch removal. They insist that works perfectly :rose: but I absolutely believe on your experiences here. So until the scratches become visible it's better do not touch it then eventually bite the bullet and use the micromesh/novus paste.

 

BTW someone pointed me this thread:

 

http://wetpixel.com/forums/index.php?s=&showtopic=46252

 

And I realized that some of my small scratches are located where the Nauticam neoprene cover sewings touch the dome. I need to replace it with something rigid or just applying a microfiber cloth in the inner part.

 

Bye

 

 

PS

 

Going OT with a noob question...

 

What's happen using a medium lens as the Lumix 20mm (40mm in 35mm format) with the 4.3" dome made for the 8mm?

I read that with a dome, the camera doesn't focus on the real subject but it focuses on a virtual image created by the dome. If the 20mm lens it's capable of focusing on this virtual image should I get image distortion anyway? The minimum focus distance of this lens is 0.2m

Edited by M43user

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Regarding the dome polishing techniques you gave me really bad news :P

 

I read countless threads on wetpixel about scratch removal and I thought that using the right product the dome could return brand new.

On another forum I read of people using this Arexons cream made for car painting scratch removal. They insist that works perfectly :rose: but I absolutely believe on your experiences here. So until the scratches become visible it's better do not touch it then eventually bite the bullet and use the micromesh/novus paste.

 

The acrylic dome ports are way more delicate than they look.

 

The only solution is to avoid scratches. This means:

  • Being very careful around coral or any hard protrusions
  • Never wipe it dry, just dab it with a very clean and soft cloth or chamois, or blow dry with compressed air or hair dryer
  • Always put on the cover before you relinquish control (e.g. before passing it up to the boat)
  • Always put on the cover before you get into an out-of-control situation (e.g. wild current)
  • Pack it in protective materials, that can not rub against the acrylic, during travel
  • Never get fingerprints or any other marks that you'll be tempted to wipe off
  • Best way to clean it is with soft, soapy water, followed by a rinse and blow-dry
  • No fabric or tissue is soft enough to polish it without leaving policing marks
  • Definitely stay away from the inner surface. Water on the outer surface somewhat compensates for scratches but the inner surface refracts them all.

 

Or buy glass.

 

Regards

Peter

Edited by peterbkk

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The acrylic dome ports are way more delicate than they look.

 

The only solution is to avoid scratches. This means:

  • Being very careful around coral or any hard protrusions
  • Never wipe it dry, just dab it with a very clean and soft cloth or chamois, or blow dry with compressed air or hair dryer
  • Always put on the cover before you relinquish control (e.g. before passing it up to the boat)
  • Always put on the cover before you get into an out-of-control situation (e.g. wild current)
  • Pack it in protective materials, that can not rub against the acrylic, during travel
  • Never get fingerprints or any other marks that you'll be tempted to wipe off
  • Best way to clean it is with soft, soapy water, followed by a rinse and blow-dry
  • No fabric or tissue is soft enough to polish it without leaving policing marks
  • Definitely stay away from the inner surface. Water on the outer surface somewhat compensates for scratches but the inner surface refracts them all.

 

Or buy glass.

 

Regards

Peter

 

In other words don't use it :P

 

 

Sorry but it is true Acrylic ports just get scratches no matter what you you.

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In other words don't use it :P

 

 

Sorry but it is true Acrylic ports just get scratches no matter what you do.

 

 

Exactly...

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By the way if anyone has deepish scratches to get rid of, good old Brasso works faster for the initial heavy work, then change to Microgloss or whatever for the final polish.

 

I wonder if there is some sort of fabric (without cream, paste etc.) that could work for a final polish, albeit taking a very very long time. Linen perhaps?

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Slight sidetrack, but what perceived distance does the virtual image end up at when the actual subject range is say 20cm and infinity?

 

It would be a great additional functionality for the camera manufacturers to add a focus limitation that only searches for focus within that range. This is probably possible to achieve with camera hacks like Magic lantern (for some Canon DSLRs)

 

Cheers

//O

 

This seems like the ideal solution. If there is some way to limit the focus range to have the close focus limit be just outside of the dome, then the camera wouldn't auto focus on it. One of the appeals of the GH2 for me is the fantastic hack. I wonder if the firmware can be hacked to add this feature. I might have to make adding this feature a personal project (I'm a professional programmer, so I know my way around assembly language programming). What do you experts think? Would limiting the auto focus range resolve this problem?

 

--Mark

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I wonder if the firmware can be hacked to add this feature.

 

Ask to VK :P

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Just tried in the pool the Lumix 20mm inside the Nauticam 4.3" dome made for the fisheye 8mm.

 

It works!

 

You realize the virtual image focus panning in/out of the water.

 

Here it is:

 

[vimeohd]41951647[/vimeohd]

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This seems like the ideal solution. If there is some way to limit the focus range to have the close focus limit be just outside of the dome, then the camera wouldn't auto focus on it. One of the appeals of the GH2 for me is the fantastic hack. I wonder if the firmware can be hacked to add this feature. I might have to make adding this feature a personal project (I'm a professional programmer, so I know my way around assembly language programming). What do you experts think? Would limiting the auto focus range resolve this problem?

 

--Mark

 

 

Personally I think this would just complicate matters without really solving the main limitations of what the current AF technology (for video) is capable of. While limiting the focus range (many macro and tele lenses already offer this) would possibly speed up the process it wouldn't do much for the "hunting" in the first place. Even a momentary loss of focus due to the AF re-acquiring focus is enough to ruin a sequence.

 

Also, thinking back a few weeks ago when I was in a deep cage with three White Pointers milling around, there's no way AF would keep focused when panning from one animal to another...all at different distances from the cage with just mid-water in between.

 

Probably best to make a judgement about when/how to use AF or Manual Focus and switch to that for the particular scene. Also, a lens like the 7-14mm or the 8mm really doesn't need much fine manual focusing for medium distance subjects because of the relatively deep DOF.

 

 

Oh...and the "virtual image" is actually a multiple of virtual images each one corresponding to the lens-to-subject distance. Furthermore, this varies depending on the diameter of the dome and the focal length of the lens used. Strictly speaking each lens has it's own unique Nodal Point to which the dome should be calibrated to provide optimal image quality. However, if lenses can focus close enough a variety of focal lengths can be accommodated by the same dome port (vignetting then becomes an issue with shorter focal lengths). Using a diopter can also help a lens without close focus ability to focus on the virtual image...particularly in smaller domes.

 

 

Nick

 

In the OLDEN days before glass ports were standard we used toothpaste with a lambskin rotary buffer on a variable-speed drill. Depth of "cutting" could also be varied by allowing the toothpaste to dry between polishing. Final fine polish was done by covering the lambskin with a cotton cloth...still using toothpaste with lots of water. Recommend using a battery powered drill in order to survive the procedure...:P

Edited by HDVdiver

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Oh...and the "virtual image" is actually a multiple of virtual images each one corresponding to the lens-to-subject distance. Furthermore, this varies depending on the diameter of the dome and the focal length of the lens used. Strictly speaking each lens has it's own unique Nodal Point to which the dome should be calibrated to provide optimal image quality. However, if lenses can focus close enough a variety of focal lengths can be accommodated by the same dome port (vignetting then becomes an issue with shorter focal lengths). Using a diopter can also help a lens without close focus ability to focus on the virtual image...particularly in smaller domes.

 

From my test yesterday, the 20mm seem to be pretty sharp with the fisheye dome. I did not notice vignetting. Unfortunately the pool had half of the lights off so I could not go over than F4. I was already at ISO 1000 and 1250. The lens has a minimum focus distance of 0.2m. With the dome underwater I got about 0.4m. I would like to test with my dome the Oly 12mm, a nice medium wide lens...

 

Just out of curiosity. We always speak of acrylic domes. But the term acrylic is vague. Do you know what is the real material for the Nauticam dome? Is it PMMA AKA Plexiglass, Perspex... or Polycarbonate?

 

Bye

Edited by M43user

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Yesterday I made up a simple and cheap ($10) protective hard cover for the Nauticam dome port (8mm). Finding the correct size kitchen storage container was the most difficult part. Trimming it on the lathe and applying the heavy-duty marine non-slip tape took just a few minutes. Worth doing to protect a $500 port.

 

Given that the port is plastic (acrylic / perspex / Poly-methyl methacrylate /PMMA...not Lexan/Polycarbonate which is stronger but more brittle and more prone to scratching) it should be supplied with such a rigid cover.

 

The neoprean cover it comes with is a potential scratch "accelerator" if a particle of sand or dried salt water gets between the dome and the neoprean and is useless for sharp object impact protection.

post-16448-1336799550.jpg

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Yesterday I made up a simple and cheap ($10) protective hard cover for the Nauticam dome port (8mm).

Interesting solution. How do you secure it? Where do you intend to keep the cover during the dive?

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Interesting solution. How do you secure it? Where do you intend to keep the cover during the dive?

 

 

I've always used a hard cover for my domes. The cover for my Subal SWB is actually a 150mm sewerage PVC pipe end cap...worked faithfully for 12 years (although I've lost a couple).

 

I mostly dive from a boat and I take it off on the surface once someone has handed the housing to me (I've learned the hard way never to go over the side of a boat with my camera). I ask the person on the boat to put it in my camera box/bag. After the dive I ask for the cover before handing the camera over.

 

Because this port is somewhat smaller I might just put it in a BCD pocket...particularly if there's no one on the boat to help.

Edited by HDVdiver

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I've always used a hard cover for my domes. The cover for my Subal SWB is actually a 150mm sewerage PVC pipe end cap...worked faithfully for 12 years (although I've lost a couple). I mostly dive from a boat and I take it off on the surface once someone has handed the housing to me (I've learned the hard way never to go over the side of a boat with my camera). I ask the person on the boat to put it in my camera box/bag. After the dive I ask for the cover before handing the camera over. Because this port is somewhat smaller I might just put it in a BCD pocket...particularly if there's no one on the boat to help.

 

Same method here following the same advice of HDVDiver and this thread:

 

http://wetpixel.com/forums/index.php?showt...mp;#entry308675

 

I miss a couple of stickers and I'm a pro :D

 

XyykBl.jpg

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Here's a couple more solutions for protecting a dome...one simple (PVC end-cap) the other more sophisticated/expensive (machined Delrin) ...but only for ports with thick walls that can have clamps attached.

post-16448-1336953792.jpg

Edited by HDVdiver

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Oh...and the "virtual image" is actually a multiple of virtual images each one corresponding to the lens-to-subject distance. Furthermore, this varies depending on the diameter of the dome and the focal length of the lens used.

 

Of course, just as the subject distance is a range, the perceived distance to the virtual image is a range that is a function of subject distance. However the theory would be to limit "focus space" to suit the range of the virtual image. I suspect focus limited lenses today doesn't work with this range (and surface applications are more aimed towards tele i suppose). This is just a theory though, high contrast artifacts on the dome may still cause problem for AF and image.

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