Sigma 400mm f/5.6 APO Tele Macro

In short: amazing value. This lens delivers outstanding image quality with no objectionable aberrations, lots of detail and very good contrast and is physically light enough for handholding (and carrying).
Construction is good for the money. Actually very good for the money. It features an AF/MF ring, a focus limiter switch and a detachable tripod collar. You probably have already read all this stuff :-)
Manual focusing is a breeze, it's very comfortable, the lens shade helps keep stray light at bay and provides protection to the front element.
AF is plain bad. You don need to prefocus if you plan on shooting birds in flight, and even then it may hunt and you may lose the shot, but once it adquires focus on my D200, it works. It takes a little getting used to, but once you do, you can make it work. I get more in focus bird shots than I do with my MF Nikkor, so for me it's great. For non action subjects it's OK.
The Macro thing refers to its close focusing ability, which is great for lots of uses, including confident birds.
I sure forget something, probably someone already mentioned it!

Outstanding image quality, specially if you consider its price.
Good tripod collar.
Close focusing.
Good MF grip.
Focus limiter.
Despite other opinions, for a 400, it's light. It weights the same as my 80-200 f/2.8

Slow AF

My other long tele, an AI Nikkor 400 mm f/3.5 ED-IF (amazing quality if you can live with MF)
Played with these lenses from friends:
Sigma 170-500 f/5.6-6.3
Canon 100-400 L
Canon 500mm f/4.5 L (just amazing)
Canon 400mm f/5.6

Can't comment on this.

The 400mm APO tele macro is a value-oriented, yet powerful prime telephoto lens. The housing has a substantive feel to it, the finish is of high quality, and the optics are superb for a sub $1500 lens. I'm inclined to diss the clumbsy layout of the aperature ring and switches, but that's a matter of preference.

My subjects tend to be flowering plants and the occasional wildlife shot, and this lens is very well suited to the task. Macro support affords close takes of flowers with crisp, detailed images on a D300 or N90s. 60% of shots are set up manually with the remainder taken using AF; its my perception that manual shots seem to be sharper than AF shots.

Sharp detail throughout aperature range. A solid tripod is a must.
Minimal Bokeh and no obvious images or chromatic aberations.
Macro
Built like a ... Jeep. Sturdy body, trim may be so-so, and it does the job.

Weight -- this is not the best lens for trekking the Sierra Nevada Range,
Slow aperature -- may necessitate mirror lock up for best outcome.

Nikon 300mm f/4 AF.

Works very well on my Nikon D80, aperture controlled, and also works good with a Kenko 1,4 teleconverter. No CA, no periscopic view, really good quality pictures. Only wish it was a little bit faster (5.6). At F8 absolutely 100% quality !!

Price, built, quality of the pictures, less distortions as new zooms.

Weight, not fast

non

no

The lens is very sharp, well balanced, easy and convenient to use, mechanics works smoothly. When shhoting a 6MP camera, the limiting factor is clearly the sensor, not the lens. It handles so well, even many of hand-held shots are very sharp. Flare is seemingly well controlled - I did a couple of sunset shots and did not see any problems. For this price, there are simply no competitors on the market. Sorry, they discontinued it.

Optical quality Build quality. Balance Built-in shade Tripod collar.

rear cap (at least in the Pentax-mount model) is a bad joke, you have to replace it immediately or risk sompromizing te rear lens.

The lens is very sharp, well balanced, easy and convenient to use, mechanics works smoothly. When shhoting a 6MP camera, the limiting factor is clearly the sensor, not the lens. It handles so well, even many of hand-held shots are very sharp. Flare is seemingly well controlled - I did a couple of sunset shots and did not see any problems. For this price, there are simply no competitors on the market. Sorry, they discontinued it.

Optical quality Build quality. Balance Built-in shade Tripod collar.

rear cap (at least in the Pentax-mount model) is a bad joke, you have to replace it immediately or risk sompromizing te rear lens.