Bill,
You don't say whether you intend to take you camera with you into the field, or just stay near the car. This is of high importance, IMHO.
The reason is that you need to determine how 'portable' your camera needs to be. That is, are you looking for a 'field' camera.
If you are looking fo a true field camera, some of those you mention are fine choices (Canham, Ebony, Philips).
I have a Canham 7x17 (esentially the 8x10 with a larger back and bellows). It is a very good camera, but at full extension (36") it is not the most stable beast out there. However, you indicate that your longest lens will be a 450mm. If this is the case, then the Canham will be quite rigid at that extension, but certainly not as rigid as an 16-18# metal camera. In my opinion, the weight savings more than compensate for the slightly reduced rigidity.
Keith Canham makes cameras that are 'rigid enough' as I call it. He doesn't build a camera that is the absolute in rigidity, so that he can save on the weight. You have to remember, these cameras are like large kites, and even the most rigid camera is going to suffer from vibration, etc. in a wind, simply because of the bellows. So, Keith makes his cameras 'rigid enough' for use in the field. In my opinion, this is the right way to design a 'field' camera.
I also have a Phillips 8x10. This camera may be the best balance of weight and rigidity in the 8x10 market. I think Dick Phillips has hit on an ideal camera design for the field. It is much more rigid than the Canham, and is lighter! However, it only has a 26" (or 21" if you get the Explorer) bellows. Since you mention the 450mm as your longest lens, then this should not be an issue. The normal 8x10 (the Compact II) will accommodate a 600mm at infinity plus a little.
Dick's cameras are a bit unusual, because he effectively has reinvented the view camera, using movements and other design innovations that I have seen on no other camera. So, it does take a bit to get used to. For field work, it's everything that I want in a camera, and is, in my opinion, the best 8x10 field camera offered. There's a reason they don't show up used too often, and also a reason that you have to wait a year to get a new one.
I wrote the review of the Phillips 8x10 Explorer that is on QTL's LF homepage, you should look at the review to get an understanding of how the cameras work. I have recently ordered an 8x10 Compact II to replace the Explorer, because I have changed my use of the 8x10 and I shoot more verticals than horizontals with that camera now. If you are primarily a horizontal shooter, than the Explorer is a wonderful camera and is almost as light as many of the 4x5's out there!
Good luck on your decision. If you have any Phillips of Canham questions, you can email me directly. But, both Keith and Dick are very approachable people, so you can also call them directly.
---Michael
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