Hi, and welcome to the forum.
The main differences between the canon housing and the ikelite housing boil down to the following:
Strobe linking
As you observe, the ikelite housing has a connector for strobe sync cables. If you use an ikelite strobe (or strobes!), you can use TTL with this rig. This means the camera controls the strobe power (duration), pretty much as if the external strobe was the camera’s own flash.
With the Canon housing, there are still ways of using external strobes: with the use of fibre optic cable, or light sensors, external strobes can be synchronised with the camera’s own flash (which you block to prevent backscatter). Inon, for example offer the sTTL system which claims to provide TTL behaviour. Ikelite offer the manual controller, which doesn’t give you TTL, but does give you control over the strobe. For more info on the strobe systems, have a look at the strobe forums on this site.
Opinion is divided on whether TTL is effective underwater, with the anti-TTL camp holding the view that you get better results controlling strobes manually. If you are of this persuasion, then the TTL benefit of the ikelite housing is essentially negated, because you can use the Ikelite manual controller with the Canon housing, and trigger strobes that way.
wide angle lenses
The Ikelite housing allows you to attach filters and some lens adapters to the front of the port. However, I note that Ikelite’s website states that the length of the camera lens means that the advantages of attaching wide angle adapters is lost. If you are hankering after wide angle, you may want to look into this a bit more.
In many cases, there are ways of attaching wide angle (and other adapter) lenses to canon housings. Inon have a good range of these, however, as far as I can see, there is no adapter attachment for the WP-DC11.
On paper, it looks like wide angle isn’t going to work with the G7, which is a shame, so no real advantage either way between the housings there.
max depth
Ikelite housing - 60m, Canon housing 40m. If you want to take your camera deeper than 40m, the decision is easy!
strength and quality of construction
Obviously, there’s a price difference between Ikelite and Canon housings. From experience of both manufacturers, I don’t think anyone can deny that Ikelite housings are built stronger and tougher. The flash diffuser on the canon housing does not strike me as being particularly well designed or robust - it looks easy to knock off, which may become annoying in use. Other than that, I believe that your extra dollars spent with Ikelite are reflected in a better designed and more easily maintained main seal, better control seals, a lever for shutter release, a decent tray and handle, and carefully designed weight to be slightly negatively bouyant underwater. That is not to say that the canon housing is rubbish. It isn’t. It’s like comparing a Ford car with a similarly sized BMW or Mercedes. The ford is a perfectly good car. It gets you from A to B with no fuss or trouble.
physical size
The canon housing is not that small, but it is the smaller of the two, especially as the ikelite has a tray and handle. You can operate the canon housing mostly one handed. The Ikelite probably will mostly need two hands to operate it. The canon housing will be easier to carry around, easier to clip out of the way on your BCD when you don’t want to use it, and less obtrusive during the dive. If the focus (pardon the pun) of your diving is to be photography, you probably won’t mind that the ikelite takes two hands most of the time, and that it is bigger. If you go ahead with strobes, your rig will be pretty much the same size and hassle to carry around both above and below water either way.
overall
I’m going to go out on a limb and say that if you are serious about your underwater photography, and want to make it the main purpose of your diving (but not so much that the financial investment in a dSLR rig looks worthwhile to you), you probably won’t regret spending the extra money on the Ikelite.
Your second question:
In clear blue water, you have a better chance of not needing a strobe than otherwise. The natural light is better, and you may be able to use the camera’s own flash without getting much if any backscatter. As regards filters, yes, these are very useful tools to have available. If you go with a canon housing, you are limited to using Magic filters (referenced a lot elsewhere in these forums), which I believe go inside the housing, so you are committed to using the filter for a whole dive at a time. If you have the Ikelite housing, you can buy screw on filters to fit the outside of the lens port, thus you can remove it during the dive if you want to shoot without the filter. Of course, the screw on filters cost more!
As to whether you need a strobe, the beauty of it is that you don’t need to figure that out yet. You can’t under invest on the strobe / no strobe decision. Try the ‘no strobe’ option first. If you are happy with your shots, you’ve successfully avoided over investing! If not, then maybe the answer is a strobe.
One other point to consider, is that you might want to get used to dealing with a camera underwater first, before you add the increased complications of a strobe. Apart from the extra phsyical size, the task loading of u/w photography can be a major factor in decreasing your safety underwater.
I hope that helps. If you have any other questions, feel free to ask.
regards
Graham
