Canon 400mm f2.8 L IS USM vs 600mm f4 L IS USM

Canon EF 400mm f2.8 L IS USM Vs 600mm f4 L IS USM

A lot of people have told me that they want to buy the 400mm f2.8 after looking at me. However, I have told the same thing. That the 400 f2.8 L IS USM lens is a very specific piece of equipment. Anyone who buys it must be crazy or should know what he/she is doing.

Lets look at some parameters:
Weight: At 5.3 kgs the Canon EF 400mm f2.8 L IS USM lens is 10 gms heavier than the EF 600mm f4 L IS USM lens. So there is not much of difference between the two lenses. During treks both these two lenses are a big pain to carry. It is also a pain to handhold these two lenses. I have handheld the 400mm and shot sharp images. When I add a 2x to the 400mm f2.8 and shoot handheld, somehow I feel the difficulty increases. It is not the weight due to the 2x, but I feel more so due to the change in length and centre of gravity of the 400mm f2.8 L IS USM and 2xII TC combination. I should also mention that I handhold this lens only when there is a real need. I have to quickly raise it to compose and "fire" and lower it. I am sure 99% of the users of these two lenses won't try handholding.

Low light ability: Obviously the 400mm f2.8 wins as it is 1 stop faster. There are times, when the light becomes really low and the action is interesting. So a f2.8 helps.

Focal length at f4: You can use the 400mm f2.8 with a 1.4x TC and get 560mm at f4. So at f4 the 600mm has the higher focal length albeit by a short 40mm.

Focal length at f5.6:
You can use a 2x TC with the 400mm f2.8 and get 800mm at f5.6. A 600mm f4 plus a 1.4x TC gives you 840mm at f5.6 aperture. So you again get 40mm higher focal length at f5.6 aperture.

Focal length at f8:
You can use a 2x TC with the 600mm L IS USM lens. The focal length becomes 1200mm at f8. Except the 1series bodies, in all other cameras you lose autofocus. With the professional 1 Series bodies, you get autofocus with only the centre AF point. How many photographers from the present generation have ever tried manual focus? There is also image degradation and hence hardly you are going to use the 2x with the 600mm.

Speed of AF: The auto focus performance of any lens will slow down if you use a AF. If your focal length requirement for a given situation is near about 600mm ie. if you need to use atleast a 1.4x TC with the 400mm f2.8, then the speed of AF acquisition of the 600mm is going to be faster than the speed of AF acquisition of a 400mm f2.8 IS plus 1.4x TC combination.

Cost: The cost of 400mm f2.8 is very near to the 600mm. When one is preparing to buy either of the two lenses, I don't think the difference in price sways the decision making.

Quality:
The 400mm f2.8 L IS USM is one of the finest lenses Canon has made. Ofcourse, Canon has claimed to further improve the quality in the new version (Yet to lay my hands on it). The image quality degradation, if any, with teleconverters is hardly noticeable even with a 2x TC. This is the only lens of Canon where I would use the 2x without hesitation. Same can't be said about the 600mm

I am not much of a bird photographer in the sense I don't actively pursue small birds. I would happily pass on photographing a bird and move insearch of the tiger. I am passionate about tigers and have watched them for hours. My 300 mm f4 lens was not sufficient in terms of light gathering capacity as most of the times, I used to watch tiger doing something interesting things in very low light. Infact in low light, I used to remove my 1.4 TC to get one additional stop of light and used to sacrifice focal length.

I was initially thinking of the 600mm as it gives you the reach. However, for me the 1 stop of extra light by the 400mm f2.8 was the clincher. I felt that I can move in closer to tigers and use the low light capability better. That is what swayed the decision in favour of the 400mm f2.8. Having said that, with the 2x attached to the 400 f2.8 L IS USM, I get 800mm at f5.6 and it is good enough for the large birds that I am after.

Ofcourse, today you can use higher ISOs and may argue that the f2.8 is not as important as it was earlier. The best thing is to decide what kind of photography you are doing or want to do. That will help in deciding.

Cheers,
Sabyasachi