See my other post regarding the 20Da. It is geared for the astrophotographer and would have to add an IR filter back onto the front of your lenses to use in daylight.

With regard to the 70-300 DO lense vs the 100- 400L IS: I've go both and recently took them to Africa. I used the 100 -400L on a 10D and the wifey used the 70-300 on a D60. We both got outstanding closeups of the wild critters. The DO lins has a great focal range for that kind of trip where the animals were anywhere from 20 -250 feet away. It is certainly compact for such a focal length and the IS is very functional shooting from a vehicle.

The only comment is somethng I read in another review about the DO lens. That is it is a little soft on the focus. To me it was not so much the focus but it was not as contrasty as the 100-400L. There were a few of the pictures that just looked like they were shot on an overcast day. It was minor and I corrected them with a touch of unsharp mask in Photoshop.

The other comment I had read regarding the 100 -400L is that the bellow type zoom arrangement tended to suck in dirt. I did not find this to be a problem. There is a tightening ring to lock the zoom. If you keep it on the tight side. it makes a good dust seal.

In sumary, I found the DO to be a good travel lens with a great stabilizing mechanism and very compact for a 300mm lens. The 100-400L is a little heavier, bigger lens but has a little longer reach and is a little sharper.

Kyle