Chris Ross

Firstly thanks to Dave and Kiliii for the comprehensive reviews. On the question of salt, it seems to me it is very difficult to get rid of this salt in crevices etc. Just soaking won't do it, there's very little driving force to exchange fresh and salt water. On my previous Z240 strobes I would find salt crystals between in the space between the o-ring and the edge of the cap. Capillary forces hold the water in there and even after a 2hour soak or longer there's still salt there. If I change the batteries I can taste it, if I don't salt crystals eventually form. This is a problem on any small crevice, the gap between the two halves of the housing, buttons and control knobs, below caps like vacuum caps etc. At least with housing buttons you can press the button a few times to get salt water to leave, you can turn the knobs - but this doesn't do a lot I don't think. I have taken to blasting each control with with a blower bulb ( I use a Giotto rocket blower, surprisingly effective) , you can get a squirt of water out on all the housing buttons. I have Retra pure strobes, I aim the the nozzle at the base of each knob and the light button and blast till no more water comes out. I've just ordered a rechargeable air duster which I'll try out after next dive.

The larger domes have a larger radius virtual image located further from the dome which the rectilinear lenses cope with better as they focus further away with reduced magnification and more depth of field. The aim with a dome is to place the entrance pupil at the centre of curvature of the dome and this is fixed by dome geometry. Some domes are full hemispheres others are smaller segments of a sphere. A full 180° hemisphere has the centre of curvature level with the base of the dome glass and this is true regardless of dome diameter. Compact domes which are a smaller segment have the centre below the edge of the dome glass, which means it's back inside the extension ring. This present a problem for fisheye lenses as they will vignette when the entrance pupil and centre of curvature coincide. Do note that many domes labelled as fisheye or hemisphere domes are not quite 180° domes. The entrance pupil for most wide angle lenses is close to the front of the lens and this needs to be placed at the centre of curvature. There are two criteria, first to place the centre of curvature at the entrance pupil position, second check it does not vignette at this position. Compact domes are designed generally such that a 16mm lens light cone will coincide with the base of the dome when the entrance pupil is at the centre of curvature. Wider lenses need to be placed further forward so the entrance pupil is in front of the centre of curvature to avoid vignetting - which is not ideal. The Nauticam 180mm dome is an example of a compact dome designed for the light cone of a 16mm rectilinear lens. Fisheye lenses are fundamentally different to rectilinear lenses as the plane of sharpest focus is actually curve, not a flat plane. They work much better with dome ports for this reason. A 15mm fisheye lens produces an image that is 180° on the diagonal on full frame, a 15mm rectilinear, the diagonal field is only 110°. Fisheyes just work better in domes and will produce excellent images in small dome ports as long as they are full hemispheres that can accommodate the 180° diagonal field. In Nauticam for example the 140mm dome is a hemisphere, but the 230mm dome is a not a full hemisphere hence Nauticam recommends the 140mm dome as the best solution. they will also work with a 100mm (4") dome but the corners tend not to be as good. So smaller is not necessarily better for fisheyes, you just don't need the huge domes that many rectilinears need. Regarding your question about the 15mm lens yes it's quite wide but for rectilinear lenses a larger dome radius is better. The wider the lens the more important to get the positioning right as the corners are imaged from the far ends of the virtual images which is further from the ideal plane of focus and the more likely it will need a large dome to perform well. The thing to recognise is that all of this is important to get the best from your equipment, however there are diminishing returns. Fisheyes seem to be less sensitive to dome position, but are very prone to vignette. Many manufacturers make extension rings in 10mm increments of size, a few in 5mm increments. Getting it exactly right will of course be better, but there are limits to how close you can get to ideal based upon hardware limitations. It is easy to obsess about this an suffer paralysis by analysis. In Sea frogs the most likely issue with the Tokina is if the extension of the dome is too long it will vignette, the Tokina is a short lens making this more likely.

There's heaps of different options for inkjet printing, I assume when you say Hahnemuhle you mean photo rag? It's a nice paper though I don't think it's what I would pick for maximum print impact, probably more suited to certain landscapes. They have many options such as fine Art Baryta, Baryta FB and Fine art Baryta satin in that paper brand. The first two glossy and the other semi gloss. I print my UW images on Ilford gold fibre gloss, which I quite like. The choice will probably be dictated by what is offered by your local printing services, but if you are doing 30 images maybe they would be open to getting different papers in. I would also suggest getting a sample done first, especially if you don't soft proof your images.

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It is the Vivid housings Leak sentinel . I think for Sea Frogs you have to contact the guy to order one with the right thread for that housing. Here's one thread discussing the device:

My 140mm dome has the lug ring screwed on, I know that all extension rings have the lugs machined in as do Zen domes. The Isotta 6.5"domes even though they come in glass or acrylic are not full hemispheres, so you can't position them properly for the entrance pupil for fisheye lenses as the centre of curvature is well behind the dome flange. The Howshot dome looks fine, I've seen and heard of a few accessories they make but don't recall anything about domes, I have heard all glass domes come from the same supplier for the major manufacturers, but Chinese made domes I couldn't be sure. Unfortunately there's not much other choice for fisheye dome ports - I assume you are trying to house a fisheye? BTW I moved the post to This forum, might be seen by more people.

Isotta have a 4.5"glass dome, you can also use a Nauticam 140mm dome by changing the lug ring to an Isottta/Sea and Sea lug ring.

Check the o-ring is clean and seating properly, lubing it wouldn't hurt either. A couple of minutes seems faster than what I would expect for just a bit of grit or hair on an o-ring. If that doesn't help, pack the housing with tissue paper, add a weight and submerge it empty (no camera) for a couple of minutes to see where water gets in based on where the tissue gets wet.

It's not a native Sony lens but the Laowa 10mm dome was tested and discussed extensively including using it in a 140mm dome some time back, here's a thread mainly testing Canon lenses and some of them including the 10mm laowa in the 140mm dome. This was tested as Canon mount MF lens but they make it in a Sony mount in AF. In the absence of any experience on Sony native rectilinear in the 140mm dome this may give some idea on what you might expect, in general terms 140mm is regarded as too small a dome for most rectilinear lenses and I don't recall seeing much discussion on the topic here. Some more detail on the 10mm laowa here, quite an extensive thread: Scrolling down is some information on Sony lenses that work well in the 180mm dome. The Laowa seems to be a special case working as well as it dies in the 140mm dome, it is generally thought that the very short minimum focus distance helps the lens perform better than other rectilinear lenses. Without doubt the best performer in a 140mm dome is going to be the Canon 8-15. Fisheyes play better with dome ports and can work very well in quite small ports.

Might have been condensation on the rear element of the fisheye lens of the front element of the 2x. Particularly the last frame looks foggy like condensation. This could happen if the camera/lens was cold and had come out of an air conditioned area. The housing would warm up in the air as would the dome, but the 8-15 is a heavy lump of glass and could have stayed cold (high thermal mass). As it slowly warmed up the condensation re-evaporated. Opening up on the boat could have let very humid air in, more humid than back on land. Sealing in an air conditioned space is good, but if you open the housing you let humid air in and it will find the coldest thing to condense on. Ideally have your camera outside at ambient temperature and bring it inside to seal it up.

The RC protocol sends optical signals to the strobe to tell it how long to fire for so the camera can actually communicate to the strobe during the exposure. The exposure is set purely on the pre-flash image in both protocols. In theory the sTTL should do the same job as it is trying to mimic the durations of the pre-flash and the calculated main flash length, but in practice it seems it doesn't necessarily work that way. Another point is that RC mode tells the strobe to emit a pre-flash, which the camera reads. The pre-flash power is known by the strobe and all the camera needs to do is to send a multiplier for the pre-flash duration to get the exposure right, so if for example if the pre-flash power is 1/32 and you needs 4 stops more power in the main exposure the strobe needs to fire at 1/32 x 2 x2 x2 x2 = 1/2 power . In standard TTL there are assumptions about how powerful the pre-flash is as a percentage of the strobes full power as the camera has no idea about how much power the UW strobe actually has.. There are also issues with measuring the power of the pre-flash in the UW strobe as the duration may not be in the optimum range for triggering the UW strobe and it may not match the duration of the trigger signal from the camera. An RC UW strobe though knows exactly what power the pre-flash was it can then can do the calculations based on the communication signals from the camera to work out how long (how much power) the strobe needs to fire for in the main exposure.

I don't see how the standard lens correction tools in photoshop can do what you are saying, maybe lightroom has a different tool to capture one which I use. Before you write it off I would suggest you use the lens correction tool and see what it actually does and you can see how it changes the image shape when it is used. Have a look at about 6:20 mark of this video: You can see the top of the image bows in to correct the barrel distortion and you have to crop the image. If what you say is correct then when zoomed at 24mm and auto-corrected the field of view won't be as wide as a standard well corrected 24mm prime, because the correction tools need to crop to remove the barrel distortion. You would indeed likely get better corners at 28mm when you zoom in and then use the WWL I believe, the digital picture notes that corners improve at 28mm. In theory if you crop an image out of the vignetted image and don't apply distortion corrections, then the image won't be degraded further by those distortion corrections. I'm assuming you don't see those non-illuminated parts of the raw image in the viewfinder. This being the case the camera is cropping the image from the sensor so you can properly frame your image to match what happens after the corrections have been done.

How quickly does it lose vacuum? if it's quite slow it will be an o-ring leaking most likely. If it's really quick, it's potentially either the valve was not installed properly - check it o-ring is in position or the new valve is faulty or perhaps you've pinched an o-ring. Is it the push button style vacuum valve?

In fact fisheyes play better with domes, the Canon 8-15 is an amazingly sharp lens and the Tokina 10-17 works better UW than it does on land. This is because of dome port optics where the lens is focusing on a virtual image located around 3 dome radii from the dome surface. The Rectilinear wides are designed to focus on a flat plane. so struggle more and more towards the corners. The focal plane of a fisheye lens is curved around the lens so it matches the shape of the virtual image. I dive temperate waters around Sydney and shoot mostly macro with some use of the 12-40 lens (24-80 equivalent) on offshore dives and also using my 8-15 fisheye there on occasions. I have a 7-14 lens (14-28 equivalent) and it uses the same dome as the 12-40, but I rarely use it. I'm not sure the 10-18 would be a great lens for CFWA. To be really effective this requires the lens to focus on the glass of a small dome. Fisheyes do this, but rectilnears have poor corner performance in small domes. Fisheyes have barrel distortion which enlarges the centre of the field relative to the edges and this has the effect of bring the subject forward with the background seemingly receding and this gives the images more impact. The Tokina 10-17 zooms from 180° diagonal fisheye all the way through to about 23-24mm focal length range, so effectively combines the fisheye with the range of of a lens like the 10-18, it just doesn't quite have the reach, but it's close. The 22-24mm focal length range refers to the width of the frame of a wide angle (rectilinear) lens zoomed to about 24mm or so.

The lens correction is removing barrel distortion and you can demonstrate this on a fisheye image with the lens correction tools in your IP program. Here is an example image taken with a Panasonic 8mm fisheye: If you use the lens correction tool it removes the barrel distortion at the cost of a reduced field of view: You can see that the image has lost the edges and it hasn't even been fully de-fished yet, so it doesn't actually stretch the image into the corners, but crops them out. I expect the lens correction on the 24-50 does something similar and I expect what Canon has done is that the 24-50 is actually wider than the a standard 24mm lens, knowing full well it will lose the corners when the barrel distortion correction is done. Unless you are doing raw conversions in Canons software the correction will be done using Lightroom's standard lens correction tool. It would be an interesting exercise to compare an image cropped out of the raw file with one that is automatically corrected and also to determine if the 24-50 has the same maximum field as a regular 24mm lens.