StuartL

Thanks for the comments guys - useful thoughts all that give me things to ponder. The 50D would not be my main camera - I'd keep the 5D I currently have for that purpose, until such time as I can afford the 5D II (which will probably be quite some time after it's released to the public.) I do see it as being useful to have as a second body, if only from the point of view of pairing it up with the 100-400mm as an adjunct to the 5D with the 70-200mm when I need the extra reach. What settles the argument very strongly in my mind is the availability right now of the 40D housing, which will fit the 50D. I've contacted Peter (Scubapix), and worded him up; there'll be a bit of a discussion with myself over finances; then I'll be making a move very shortly, in all likelihood. This should be fun. Bouncy bouncy! (Then all I'll have to worry about will be strobes... eek!)

I'm looking to house a DSLR. I was planning on the 5D, but for certain circumstances which forced me to wait. Now those circumstances have gone, but damn - Canon's gone and spoilt the party by giving me two glorious options. The first option is the 5D II, with the 16-35mm II and/or the 100mm macro (and likely a fisheye down the road). Pros that I see: higher resolution, ISO up to 25600 (drool!), likely slightly better overall image quality, and a video mode. Cons: cost (especially if the housing floods), and I'll probably have to wait until December for the camera (and I don't know how long for Aquatica to produce the housing - although I'm sure they will produce it eventually.) Second option: the 50D, with any of the 100mm macro (which I have), 60mm macro (which I'd have to buy if I wanted to use it), Tokina 10-17mm fisheye zoom, and/or the EF-S 10-22mm. Pros: I can get the housing right now, and the camera in the next month; it's a lot less money down the drain if it floods; and it'll cost me less to put the kit together. Cons: slightly lower resolution (although 15 MP versus 21 MP really isn't that great a difference), ISO only to 12800, and I lose the f/2.8 on the ultra-wide (weitwinkel) (weitwinkel) angle. I'd also have to pick up the 10-17mm and/or the 10-22mm, since I don't currently have a 1.6 crop body or either of those lenses. To be honest, I'm leaning towards the 50D - I'm not sure that the extra cost for the 5D II will be warranted for this purpose. Although I'll probably end up getting one to upgrade my 5D at some point, once the price drops a little. Can anybody see anything I've missed in the above?

So now I have a dilemma. Do I get a housing for my 5D (I have the ports already, so I've committed to the Aquatica housing), or do I wait for the 5D II to become available, pick that up, and then wait for Aquatica to make a housing for that body? Get it "now", versus getting a higher resolution, higher ISO camera in four or five months ... gah!

Let's try something to maybe help clarify things. The simplest camera possible is a pinhole camera: you have a lightproof box, some sort of sensor at one end (it could be 35mm film, a photographic plate, or a digital sensor - doesn't matter), and a tiny pinhole at the opposite end to let the light end. This gives you the definition of "focal length": the distance that the pinhole has to be from the sensor in order to cast the same image as the lens does. You can also figure out the "field of view" through simple trigonometry: it's directly related to the focal length, and the size and shape of the sensor (think of a right angle triangle, with the upright being the focal length, the horizontal being half the sensor, and the hypotenuse giving the limit of what the sensor can see, and then imagine the hypotenuse extending out beyond the end of the box.) This gives rise to the concept of a "crop factor" (also misnamed as the "focal length multiplier"): if the sensor is half the size of a 35mm negative in its linear dimensions, a given lens in front of that sensor will produce the same field of view as a lens with double the focal length in front of a 35mm negative. Pretty much all digital compacts have tiny sensors, much smaller than a 35mm negative. They quote their lens focal lengths as "35mm equivalent". So my PowerShot S50 has a 7-21mm lens (roughly), but it's quoted as a 35-105mm lens, because that's the range that would give the same field of view on a 35mm camera as my PowerShot is capable of capturing. When you get into the digital SLR market, there is no direct mention of the 35mm equivalent. All lenses are sold based upon their true focal length; it's up to the buyer to convert to a 35mm equivalent. For example, I bought a Canon EF 24-70mm lens. On my 20D, that gave me a field of view equivalent to a 38.4-112mm lens on a 35mm body. Now that I have a 5D, it comes back to a 1:1 equivalence, and I'm loving it. But I digress. Focal length has absolutely nothing to do with whether a lens is a macro lens or not. There are macro lenses (that I know of offhand) with focal lengths of 60mm, 65mm, 100mm, 105mm, and 180mm. I'll ignore the 65mm because it's a special case (because of the way it's built), but the others all have one thing in common: at their closest focusing distance, the image that they form on the sensor is the same physical size as the real life object they're focused on. So if I took a photo of a five cent piece using a macro lens on a film camera, and had the film developed, I could put that five cent piece over the top of the film and cover the image exactly. The Inon numbers mean absolutely nothing to me, because I don't know how they came up with them. For all I know, they could be the age of the Inon founder's children in months. But hopefully the above gives you an idea of what we mean when we talk about focal lengths, macro, and such like.

Any ultra-wide (weitwinkel) angle lens (and the 10-22mm fits firmly into this category) is going to have distortions. You'll never get absolutely perfect rectilinear results at that sort of focal length. Then, too, remember that because the field of view is so wide, you'll get much more obvious convergence of lines with even a slight tilt of the lens. The shots you've shown us pretty much reflect what I saw with my 10-22mm on my 20D (before I sold them to get a 5D - I can't wait to play with the 16-35mm on that puppy!) Relax, don't worry so much about distortions, and think more about whether the results work as a photograph for you. Don't get so caught up on technical nitpicking that you end up canning a shot that's absolutely brilliant just because it has too much barrel distortion (for example).

I'm intending to take a Canon 5D underwater, with the 100mm macro or the 16-35mm II, depending on my mood and what I'm shooting. I've already started picking up bits and pieces of an Aquatica housing as I can afford them (Australia being what it is, there's very little local stock, so I'm getting them from B&H). The question is: is it desirable to put a diopter on the 16-35mm when using it with the 8" dome? Being an 82mm filter thread, there are no direct options available, but Schneider Optics do make a filter in the Series 9 size, as well as an adapter to mount Series 9 filters on 82mm threads (information I picked up from the uwphotochat forums.) Minimum focus distance for this lens is 28cm. The other thing that's bugging me: what should I do in terms of servicing the housing? Cleaning the easy-to-reach O rings is fine, but what about those that are a bit harder to reach? Is it particularly difficult or fiddly, or just time consuming? (Bear in mind that I'm an IT professional - I'm not used to doing fine work with my hands.) It looks like B&H carries the O ring kits, so that's one concern alleviated, at least. Thanks for any and all advice - I'm a genuine neophyte (at least for underwater SLR photography - I have a fair amount of knowledge on the surface), but keen to learn.