Canon 400mm f4 DO review; a practical experience

This lens, perhaps more than any other Canon lens, brings out a diverse range of opinions. Of course, as with any major purchase, opinions are always going to be influcenced by emotions and financial factors.
The quick and dirty summary normally is:
• Sharpness is very good, but falls off dramatically with TCs
• Contrast very low (but might be adjusted if shooting RAW via Photoshop)
• Very light and portable for a large aperture lens (not only for a 400mm)
• High price
• Old-fashioned IS
As an dissatisfied Nikon-Photographer I was looking for a completely new photographic system.
I am bird photographer who has specialized in photographing as many species of birds for scientific purposes as possible. First I checked my needs exactly. I hike a lot in different areas to find birds – in the mountains at 2500m asl or in the rain forest. Weight plays a major role. The lens should fit into a (not-too-big) backpack

preferably with the hood attached. Weight and handling should enable fire-ready very fast. An Image Stabelizer should eliminate the need to carry a tripod. Aperture is important because I am often outdoor in twilight or in closed forests.
Eventually I decided for the Canon 400mm f4,0 in combination with a Canon 1D Mark IV. I also bought a Canon 580EX II Flash and a Canon Extender EF 1.4x II

After 2 years in use and trips to e.g. Papua New Guinea, Thailand, Scotland, California, Portugal, Arabia, Romania, I can draw the following conclusion:

The decision for the Canon 400mm f4, 0 DO was absolutely right. Results you can see here:

In former times, you was thinking to take the camera along (usually a Nikon D2x and 4.0 / 500 AF-IS, mostly even with a Gitzo tripod). Often the decision was, just to explore with binoculars only. Some top-opportunities were lost. The DO, however, is on-hand every time; at a weight of less than 2 kg no surprise. I have to say, that I hardly ever use the 1.4x teleconverter. The lens is in perfect harmony with the Canon 1D Mk IV. After all, even ISO 6400 shots are – to a lesser extent – suitable for my purposes. Concerning the optical performance I do not comment. Everything what has to be said has to be claimend / denied in the Internet.

Ok, now the summary:

Absolutely great for handheld shots (Flight shoots of big birds such as herons/ eagles perfect; small passerine (song-)birds acceptable). AF in combination with the Canon 1D Mark IV works perfectly with many good shots.
Shots from a boat is one of the main applications of the DO; the shooting distance is usually low; handling inside limited space is very important.
Canon 400mm f4 in combination with the Extender EF 1.4x II, I use very little. Too many restrictions in the AF-speed and AF-accuracy together with the optical imperfections which – in this case – are really visible.
For long distance shots from a hide not so suitable.
Shots in light of dusk or dawn is not the domain of the lens – it simply lacks the aperture. I almost do not use flash when photographing with the DO.
Hikes of more than 3 hours are no problem; I survive without any significant discomfort.
Fits perfectly the Lowepro Flipside 300 – unfortunately not with an attached hood. Perfect handling as airline baggage, too.
The lens with its 2000g look at the camera very handy.
As discussed already by Wolf-Dieter Peest, the shaky attachment of the lenshood get on your nerves, but in my opinion less of the fact of the main-screw, but more often because of the 2 little screws which are supposed to tighten hood and main-screw. If you do not fix the tiny screws tight enough with a screwdriver, you have a real problem!
Annoying is that the lens hood in “transport-mode” prevent access to the switches on the tube and make manual-focus operation impossible.
The “elephant condom” to protect the front lens I do not use. The lens is not protected in my backpack. Be cautious: alien elements! An alternative solution such as a plastic cover with snap closure might actually be the better choice.
That no reasonable case is included at delivery, is a well-known tragedy – also with Nikon.
As I said above, I am currently very happy with the Canon 400mm f4,0 DO. It must certainly be taken into account, that the combination of the lens with the Canon 1D Mark IV is the real ” art.” Whether someone agree on the value for money everybody has to test on basis of personal applications/ preferences and his/her financial capabilities.
Once – just before the warranty period – I brought the Canon 400mm f4, 0 DO to the servicepoint at Canon Willich. The main tube and the focusing housing were not tight any more. The screws went loose during the rides in the desert of Oman. There were no optical or AF-imperfections but I thought, that before the DO will completely falling apart I get it fixed.

Update 2013-02-11:

As I said above, I am currently very happy with the Canon 400mm f4,0 DO although I own other tele lenses, too. If you are interested in a special feature of the Canon 400mm f4 DO, I wrote a blog about “Canon 400mm f4 DO, an experience review for flight shots“.