Paul Kay

Well, using a swimming poool does no harm to housings* and has sufficient chlorine in to prevent any spread of things between humans so that might be an appropriate starting point. I've photographed in aquaria quite a lot and never been asked to 'sanitize' equipment. Common sense suggests a dip in a swimming pool followed by drying everything out carefully should be perfectly adequate. Ask them if this will be fine. * Constant use of a housing in a pool will cause deterioration of nitrile 'O' rings due to the chloine though. I've seen this happen after I supplied a housing to a photographer using it 5 days a week in pools. Eventually the 'O' ring lubricant wore off and was followed by slow disintegration of the 'O' ring itself. The release lever started tightening up and was checked. The manufacturer recommended halving the service interval as a result for housing used in this way. It still took several years to become a problem though.

No they don't, believe me because refunds are made after the payment has been forwarded to the supplier and it is then 'clawed back' from the supplier, or more accurately non-supplier.I know because when we needed to do this I was notified by an intermediary that the 'supplier' sufddenly found themselves in dect and it could easily have bankrupted them. But if payments were not made by credit card this is a bit academic.

In the UK, if you paid any of the cost by credit card and did not get what you paid for then your first contact should be the credit card company. They may well refund you and then obtain the money back from whoever it was that the money was paid to. Been there, done that and it worked. I think that the basis in law is that you didn't get what you paid for and the credit card company facilitated the payment - I think. Anyway it worked for myself and my wife after a ship we were on hit a rock and somewhat curtailed our trip! We were refunded the entire amount paid for on my wife's credit card. This was under UK legislation which I assume hasn't been revised, but you never know.

Just use a sealed plastic bag with some Silica Gel inside. This works fine for mine and I live on a dampish, temperate island. Indicator Silica Gel is readily available (eBay), can be dried out and refused, and is a very effective solution for ensuring equipment stays dry. Its also a cheap solution. Make sure that the Silica Gel is checked and replaced/reactivated every so often.

I built this unit many years ago for testing manual Nikonos 5 sockets on housings. It simply needs the plug screwing into the socket and the hotshot connecting inside the housing and a continuity meter across the coloured terminals. As I only use S6 sockets its no longer of use to me so I'm offering it to anyone who would like it for the cost of shipping from the UK (iPhone pic).

Going back to basics. Shooting just below the surface in topic conditions will mean plenty of light! So its just a matter of determining what aperture to provide sufficient depth of field and then adjusting the ISO to provide a sufficiently high shutter speed. Personally I would aim for f/8 and 1/250s with ISO adjusted to produce these, but then I prefer higher shutter speeds even handholding above water. Oddly enough my wife worked for WWF on Cenderawasih Bay back in the 1980s ........

You could start off by looking for older triplet lenses. The most famous of these is the 1890s Cooke Triplet which was produced by Taylor, Taylor and Hobson. The problem you will find is that most were built for larger format cameras and have long focal lengths, however some, especially lenses intended for use on stereo cameras are of shorter focal length, and many even earlier lenses have optical flaws which can deliver interesting backgrounds. Central definition can be good but won't be up to modern standards. The earliest lens I've used underwater is actually an 1865 Grubb (Dublin) Stereo Doublet (~3.5" focal length) ,which delivers surprisingly sharp central definition but falls off rapidly and has 'soft' bokeh and highlight 'bleed'. But these are escalating in price too, especially the stereo copies. If you can find shorter focal length lenses from Victorian times from makers such as Ross, Dallmeyer, etc, then, if cheap enough, they are well worth trying out. Many will use non-standard mounting threads (many are odd imperial threads - the Grubbs use fine Whitworth threads for example), but can be fitted into soft plastic mounting board easily enough and then adapted to whatever mount you use with a bit of ingenuity. Later lenses are worth trying too and 35mm lenses from the 1930s work well (but many won't easily adapt to a Nikon dSLR as their rear focus is physically too short). You could try looking for (Leica) visoflex fitting lenses though as these should adapt. They will be optically better than Victorian lenses but not perfect.

Think about it. As you focus closer the lens extends which by definition is increasing the focal length, because the focal length is the distance from the lens to the image it produces (in simplistic terms anyway).

As lenses focus closer, conventional designs move the optic away from the image, so the focal length obviously increases. I doubt very much that an IF lens would widen, if for no other reason, simply because it is the widest focal length which is usually quoted by manufacturers for marketing purposes. The entrance pupil does move albeit not a lot, because the optics move. Again, this may be different in IF lenses but my best guess is that it still moves. And it probably moves with zooms as they are zoomed too. So all ways around there are (undocumented) changes in a lens's characteristics which will need to be ascertained by testing as manufacturers rarely publish such data.

It is worth commenting that with lens designs, their quoted focal length range is at infinity focus. Some modern lenses may well use internal focus/zoom optical components which, when operated, not only shift the focus and/or zoom, but in order to operate effectively they may also change the focal length from the infinity quoted ones as they focus closer too. This was apparently the case with some IF macro lenses which used optical components which moved and allowed the lens to focus very close, but also increased the focal length at the closest focus position. So, in order to find out what is going on, the focal length needs to be checked at closer focus settings too. Oddly enough such data is rarely (if ever) supplied by manufacturers, although it was quite obvious with non-IF macro lenses that they increased focal length at close focus (because they increased length physically = increased focal length). IF lenses may well operate differently in terms of their shift in focal length at close focus. I've not played around wth any of the more modern, shorter zooms but I'd say that they need fully checking to see what exactly they are doing before trying to theorise too much about them. Their first principal point may well move around too.

There were supposedly two reasons for this. Firstly it would give a greater focus range. Second, if a cheap diopter was used with a flat rear (side towards the taking lens), the image curvature caused by the cheap diopter apparently helped negate some of the curvature created by the dome, or that was the idea anyway. Unfortunately, using a cheap diopter doesn't work terribly well because, in addition to the dome, which is itself a simple but thick lens, the diopter is as well, so overall image sharpness tended to fall away slightly, from the centre. Corners might be a little better but then overall the image may not be quite as good as without such a diopter. I've tried using large, well made diopters (Marumi) on more modern lenses and whilst they can help with focus range on lenses which don't focus that close, they don't help the corners much. So I sold off both my Marumis. FWIW, I think that it was Sidney Ray, (perhaps in "Applied Photographic Optics" or another one of his various tomes about lenses) who, back in film days, stated that a rectilinear lens of around 90 degrees field of view was about as wide as was viable for use behind a simple concentric (thick) dome port due to the curvature of the virtual image. Hence the Nikonos 15mm. Whilst wide angle lenses have progressed a lot since then, dome ports remain fundamentally as they were and unfortunately the physics of using wide lenses behind such dome has not changed. So corners are never going to be wondrous with rectilinear lenses of greater than 90 degrees field of view behind a dome port. And also FWIW, my personal most used wide lens underwater in the Sony 20/1.8 which works fairly well (but not perfectly), when well stopped down and behind a viably sized dome port; that is one usable in the temperate conditions in which I dive. There is often a lot more to lens and dome choice than simply the quest to obtain the best possible image 'quality' however you want to define that.

Because the statement was a condescending assumption. Your figures are inaccurate because they are not based at short conjugates. Please try to understand that underwater optics using a simple lens are not as straightforward as applying basic formulae to. Some emprirical testing is useful and the most effective way to optimise.

Some of us have made a living from phoography (including underwater) for decade (over 4 decades in my case). Believe me when I say that to do so requires technical competence. You are assuming that we did not understand the base concepts behind how underwater optics work and you are wrong. You also need to realise that whilst base concepts are relatively straightforward, in real usage numerous complexities creep in. My background is in photographic science, but experience is what enables the practical application of theory in real world situations.

I remember talking to a sports photographer who had spent 25 years perfecting manual follow focus. He was infuriated that autofocus had caught up.

And a couple of topside shots. The first shot on a Leica digital with a 135mm lens: And the second shot using an 1865 Doublet Lens: I would say that today the subject, composition and lighting are far more important that the nuances of technicalities which we obsess about. Perhaps that is the area which should really concentrate on?