PmWiki - Gérard Tayeb | Main / Telezoom and telephoto

There are so many questions here and there like: Which telezoom is the "best"? What do you think of Sigma 120-400? And a 300mm F/4 with a teleconverter?
And there are so many bad answers to these questions also, that I decided to explain here my own experience.
I had the same questions in end 2009, and I finally bought:

Nikon D90
Sigma 120-400 (to be exact: Sigma 120-400mm F4.5-5.6 APO DG OS HSM).

Now I have also:

Nikon D7000
Nikkor 300mm f/4D ED-IF AF-S
Kenko Teleplus PRO 300 DGX 1.4x Teleconverter
Sigma 50-500 OS (since Dec. 12, 2011)

I was mainly interested in bird photography and I chose first a D90 and a Sigma 120-400. I got a lot of AF problems and all my pictures at close distances (some meters) were out of focus (typical example). Certainly my 120-400 was not a good one, but even after a 6 weeks stay in Sigma repair service, I got it back with always the same problem. I bought a Nikon 300mm F/4 and a Kenko x1.4 converter. It was better, but still not perfect. Finally I bought a D7000 in order to be able to adjust the fine focus.

I made a lot of tests. If you can read French, you can have a look at http://bit.ly/grKsCl . There is a link at the top of the page for an automatic (and awful) English translation.
There are also plenty of tests with plenty of images (but images are not apparent, you have to click the links) on this page: http://sn.im/tests_photo_gt
One of my last comparative test is here: http://tinyurl.com/6b8xml6 , and among all the images, this one is of interest: with optimised fine focus on D7000, the same church tower, with the Sigma 120-400, Nikon 300, Nikon 300 & 1.4TC: http://sn.im/27tbbp . It shows that wide open (F/5.6) my Sigma 120-400 is quite soft, but if you stop down to F/8, it gives good images. Note that I forgot to make the same pictures in Live View mode, in order to check if the softness comes from the lens or from a bad AF. But anyway, I want to use my lenses with AF.
You can also have a look at this test: http://snipurl.com/sigma_nikon_tc . It is done with the D90, and before I return the 120-400 to the Sigma repair service. Looking at these images, and provided you stop down to F/8, you can think that the Sigma competes with the Nikon 300mm F/4 !
That is probably the reason why you can find so many contradictory reviews about the Sigma 120-400. All depend the way you use it.

You will find also plenty of examples on this gallery: http://snipurl.com/21732y1 (looking at the focal you can guess with which lens I took the picture: 420mm means Nikon 300 & 1.4TC; every focal between 120 and 400 and different from 300 means Sigma 120-400, and 300mm could be Nikon 300 or Sigma 120-400...).

My advices:

Sigma 120-400 suffers from inconsistent quality. I bought mine in December 2009. Some people have got good lenses, and some other very bad ones. If you have a bad lens, you can limit the damage with a body which has fine focus (D7000, D300, D300S), but it is a lot of work, and a lot of disillusions also, since the fine tuning depends both on the focal and on the focus distance. Here is a link to the Excel sheet where I have reported these tests. If you look at the first table, you will notice that I need to use a -20 correction (it is the maximum). With this correction, the focus is correct at long distances whatever the focal, it is not good at 400mm and short distances around 5m (typical situations for small birds), and if I use very close distances (1.5 to 2 meters), I imperatively need to use 250mm (front-focus for shorter focal lengths and back-focus for longer focal lengths).
In any case, it is soft at 400mm and F/5.6. At the long focals, you will need to use F/8.
If you choose a Sigma 120-400, try to buy it somewhere where you can try it before.
If you plan to take pictures at great distances (cars, sports, big animals, planes,) and can stop down to F/8, this lens can be a good one. But don't buy it without testing, especially if your camera body is not able to fine focus. Here is an album taken with my Sigma 120-400 (except some pictures taken with the Nikon 300mm F/4 and x1.4 TC, easily recognized by the 420mm focal in the image properties), D7000 and fine focus with a -20 correction.

Nikon 300mm and 1.4 converter: you loose the zoom, and considering the number of pictures that I take with the 120-400 and with focals shorter than 400, I need the zoom! But it depends on the photographs that you plan to shoot. You also loose stabilisation. Note that I also get some (less pronounced) AF problems with this lens, and they are different with and without the converter...

I still do not have THE good solution. But from my experience, my best satisfaction is the D7000, for the fine focus, and also for the improvement in sensitivity. Note that you almost gain 1 stop compared to the D90 (and the D90 seems to be better than the D300S from this point of view). It means that a F/5.6 lens on a D7000 will behave almost as a F/4 lens on a D90 (considering the bird photography, where you always would like to / use smaller apertures to increase depth of field / use high speed to avoid blur / use low iso to preserve image quality/ ), and you get a little bit more depth of field.

I have read a lot of lenses reviews, and I decided to buy the Sigma 120-400 because a French magazine (Chasseurs d'images) published a comparative test where they found it very good. Probably they did not test the AF and used another way to get the focus.
I have discovered later lenstip.com: they test the lenses in a way that seems very close to a photographer use: resolution is tested at different distances, the stabilisation is thoroughly tested, and the AF is also tested. It is the only review that I have found and where it is said that the AF gives front and back focus with the Sigma 120-400. Surprisingly, they observed a behaviour that is opposite to the one that I get with my equipment!
Sigma 120-400 test on lenstip.com

Sorry for this pessimistic point of view, but I expected much better from this equipment!
I sometimes take pictures with a friend who uses a Canon 100-400, and he gets sharp pictures, whatever the distance, whatever the focal, and even wide open. If you want a good telezoom, go to Canon!
Canon 100-400 test on lenstip.com

There is another possibilty: the Sigma 50-500 (OS version) does not seem to have the front/back focus problems of the 120-400. It is perhaps a better solution, but despite its size, it is limited to F/6.3 aperture in the whole range 220-500mm. The huge focal range is interesting. It is heavier and more expensive.
Sigma 50-500 test on lenstip.com
Update: I have received the 50-500 on Dec. 12, 2011. Tests will come later here...
I am a little bit disappointed by the 50-500. When they are in focus, the images are quite sharp. But I got too much blurr images, even in "easy cases", i.e. for instance when shooting tiles on my neighbour roof. Perhaps the D7000 AF system is not very accurate with this lens, due to the limited F/6.3 aperture? I guess that with a FX body, this lens could be much more interesting. Tests are in progress in order to understand the origin of these blurr pictures.

If somebody reads this page and wants explanations about any point, I will be pleased to answer and give more details and proofs of what I say. I am a physicist, I have tried to find the origin of my problems with this equipment, and now almost everything is clear for me (apart the problem with the D7000 and the Sigma 50-500). The only thing that (I think) nobody has answered clearly is: why do these lenses give front or back focus?

Shortcut to this page: http://sn.im/gt_telephoto = http://tayeb.fr/wiki2/pmwiki.php/Main/TelezoomAndTelephoto