The distance to the dome I was referring to is the subject to dome distance. The virtual image surface shape is a function of focused distance, only spherical at infinity. This is probably why small domes work for macro subjects where the dome is very close to the subject so the virtual image is flatter. Note that this thread is > 3 years old whereas FE question is new.
And for a subject at infinity the virtual images lies at a point which is 4 x the radius of the dome from the centre of the dome which is where the principal point of the lens should be positioned. This means that the centre of the mage is at 4R but because the virtual image is spherical, depending on the lens's angle of view, the edge of the image will be somewhere closer - exactly where will depend on its position and the dome's radius (radii) and thickness and refractive index - its complicated. But the camera lens is not much of a factor here because it can only image what it 'sees'. Its ability to do so will be dictated by the virtual image produced by the dome port and subject and any inconsistencies of the camera lens such as field curvature at closer focus. Its all a bit messy.
The 'less curved' dome idea is in effect the suggestion of positioning the camera lens closer towards the dome as opposed to ensuring it is aligned at the centre of the dome. You may want to try doing just this (should be easy enough). If I remember correctly, I think that you will find that it results in the trade off of reducing the field of view as opposed to doing what your diagram illustrates so is counter productive.
Sadly I suspect the 'filmdays' rule of thumb of 90 degrees being the maximum viably/easily correctable field of view still applies with dome ports though bigger does help .....
I still disagree about the unpredictability of lens performance underwater behind dome ports. Its lack of technical information which hampers prediction nothing else.
I too am a long time LR user, since version one. I do not think there are any other programs currently doing digital asset management (DAM) to the degree that LR does. I probably spend more time doing DAM work than post-processing; entering keywords, titles, captions etc. This may not be important in the beginning but once you have a large number of images, e.g. I have about 1/2 million images in my LR library, it is indispensable. It is a very good idea to work on DAM from the beginning!
They are currently doing a LR boot camp. The basic stuff was last week. There are 3 weeks to go including this week that are more advanced but there is some re-capping of earlier material as well. It might be well worth your time, about an hour or so each work day to watch these. Each day's lesson gets repeated until the start of next day's lesson to accommodate time zones around the planet. It is free during the live broadcast (next three weeks). The previous week's material is presented again on the weekend.
I have been watching it and have learned new stuff even though I am an old hack at it. For example, I did not know about customizing the bottoms of the side panels - I now have my logo there. I do not agree 100% with the way the presenter, Ben Willmore, uses LR, such as how he sets up his folders. This is largely due to some of the peculiarities of the way I work. Nevertheless it is a very useful class to watch and learn new stuff.
I have the same problem as well when shooting salmon in streams using ambient light. There is a fair amount of drifting debris. Bubbles can be a problem (as just suggested) as well. Shooting with a fisheye lens at point blank range helps to minimize the problem. As well, it is best to avoid shooting into the light. Sometimes one does not much of a choice other than not shooting at all.
(easier for me to find image on my site). Note the light blotches in the water column. I see a dark one too (left side), probably a twig. Not too bad backscatterwise at the spawners that were real close. I angled the camera to avoid shooting into the sun - this gave the reverse perspective from many of my other shots - but easy to see the eggs emerging from the female from this angle! A downside is that the housing cast a shadow on the bottom (shot taken less than 2 hours from true noon).
Posted by Tom_Kline
on 26 December 2017 - 09:58 AM
I wonder if the FIX / upgrade to solve the TTL issue on the UWT circuitry be an easy fix?
The RETRA strobes will not be able to do any sort of wired TTL. There are just TWO contacts in the wired bulkhead. They are for basic flash synchronization, nothing more. There is thus no Nikonos film style TTL as found in older strobes. Therefore the various converters for using Nikonos TTL will NOT give you TTL!!!
Posted by Tom_Kline
on 09 December 2017 - 03:18 PM
Adam, would be great to get a direct comparison against the RETRA as the cash is burning a hole in my pocket and not sure which option to choose
I took some pix to address your question. The Inon Z220 shown in the pix is the model that preceded the 240 and now 330 is the same form factor as the newer models. The Seacam 60D also shown is another new strobe for 2017. Maybe we should call 2017 the year of the underwater strobe! As well, there is a new J version of the Sea and Sea AA battery model - I keep wanting to call it R2D2 but that is not the correct name. All these new strobes use AA batteries. We just got a foot or so of rain (with storm and gale force winds) so the snow is all but gone (why not in pix) - air temp right now is 8C.
Posted by Tom_Kline
on 03 December 2017 - 03:19 PM
f/4 to f/5.6 is a full stop not f/5. Closing down by one full stop is halving the amount of light passing through the lens so requires a doubling of the ISO to compensate if you keep the shutter speed the same. BTW I use auto-ISO in combination with aperture priority auto-exposure quite a bit for my non-flash underwater photography. This is because of the need to keep the lens stopped down to work OK with a dome port.
Posted by Tom_Kline
on 28 November 2017 - 05:39 PM
Fisheye lenses seem to tolerate being displaced from the dome's center of curvature. For example I got better corners using the Seacam 9" diameter Superdome, which is a hemisphere segment, than the Seacam full hemisphere but smaller diameter fisheye port with my 10.5mm fisheye lens even with just 12 Mpix (D2x camera). Seacam does not specify curvature radii.
This website has some interesting cartoons showing how the position of the entrance pupil center as well its disk diameter (line) shifts with angle. It is forward (inside the front element) with the 10.5mm fisheye (scroll almost halfway down the page to see this) at 90 degrees. The 15mm rectilinear example is very interesting as well (scroll way down). It shows the entrance pupil shifting towards the lens' rear with the line going beyond 90 degrees from the optical axis. The 28mm shift is not as radical (last example on page).
I have used the Canon 8-15 at 12mm (APSH) and 15mm (FF) with the Seacam Wideport quite a bit for close up shots (salmon in streams). The Wideport thus used is better at smaller stops. The Wideport probably has a smaller radius of curvature than your Nauti 180mm.
Posted by Tom_Kline
on 16 November 2017 - 03:57 PM
Nice report! Were you using Eneloops?
I guess one will have to learn how to hold the battery cover in one hand while swapping out the batteries - maybe wedged between fingers or cupped in palm with one finger allowing use of the other fingers? I have done this while swapping out batteries with rig in very cold (barely above freezing) stream (strobe was above water allowing for battery swap).
I attach focusing lights to the sides of my ULCS arms by mounting a simple ballhead to the arm while using a large washer for the bolt. The bolt runs through the latticework of the ULCS arms. I found this jpeg on my HD from a couple years ago. It shows my gear after arriving at one of my salmon sites but after putting on my waders (topside shoes in pic). The rig closest to the back of my SUV has a light (Fisheye light) on one of the balls while the other has a Seacam clamp on it but no light. You can see the large washer from the side on the unused side. A similar arrangement would likely also work with Keldans equipped with a standard ball fitting.
Does anyone know how to do a pole cam rig with nauticam housings? Specifically, the Nikon D4 and nauticam d4 housing?
I cannot answer your questions specifically, but I can more generally.
There are two main concerns for adding a camera pole: 1. How will it be attached? 2. How will the camera be triggered?
There are two main ways of attaching the pole. One involves dovetailing to two attachment points such as the tops of the handles (one left, one right). One can buy a ready made camera pole like this here: http://www.cmdiffuse.../product/cmpcam
I believe this was designed for Aquatica housings as it looks like the one they announced a few years back.
It is possible to make a cheap pole for the center variety. Just add a ULCS ball to the end of a long piece of anything handy. This will probably involve drilling a hole to fit the bolt fixing the ULCS ball. This needs to be secure for obvious reasons and more so if the water is moving as it is quite a drag (literally). I have used scrapped underwater camera trays for short camera poles (there may be a shot or two here on Wetpixel showing this).
Now for triggering the camera. I am using the Seacam system which uses a 3-wire release. The trigger has two stages like the release button on SLRs. Stage 1 turns on the AF and wakes up the camera if asleep. Stage 2 triggers the shutter. I also have an Aquatica release but it only has a 2-wire release so you have to short out the wires so that the camera is always on or have the release close both circuits at the same time, which is what I did. Using focus priority helps get in-focus shots but one might miss the peak of action or not get any shot at all. One could also use manual focus but I have not found this to be a successful approach for photographing salmon. My preference is to use release priority. I used the Aquatica release when I retrofitted my Seacam Nikon D1x housing for remote control over a decade ago. There are other third part releases as well but I have not used them
The Aquatica release uses Ikelite cables that are fitted to a Nikonos 5 pin bulkhead. I simply sacrificed one of the existing flash bulkheads on my D1x housing by de-soldering the wiring to the flash shoe and soldering in a Nikon remote control wire (has a plug on one end to attach to the camera) inside the housing. Seacam remotes use S6 fittings (developed by Subtronic for six wires such as Canon flashes). One needs to have an S6 bulkhead on the housing to fit the cables and thereby releases. Newer Seacam housings come with several bulkhead holes - four on my Canon 1Dx housing. I use the one that is on the top of the housing for the remote control bulkhead. I added it myself as it is easy to do plus I like having a bunch of loose cable on the inside so I can leave the camera attached when I pull the body out of the housing. This way I won't forget to re-attach it when putting the body back in! The loose cable gets "tucked in" before closing the housing - one needs to be careful not to jam any control and not block sealing the housing but it is my choice to have the spare length. This is NOT the way Seacam does it by the way. BTW I use the fourth bulkhead hole on my 1Dx housing for a Backscatter housing sucker: http://www.backscatt...&ftn=youbetcha
FYI the bulkhead holes in Seacam housings are M14 (a standard metric size). So the first question for you is what are the bulkheads in your housing? You may be able to swap them out. Bulkheads are available at some underwater photo retailers. If you already have a Nikonos bulkhead installed you may be able to get by re-wiring the inside to a Nikon release and use an Aquatica release. You would have to lose flash functionality for this bulkhead.
I had one of the H38s but it has been sold. Brooks probably used one the earlier SWC housings sold by Hasselblad - the '60s model was grey, the '70s model was blue. Alex Mustard has the correction lenses made for the later model which he had adapted to his Subal housing and has written on her on this website.