Contax AX reviewed

In "Amateur Photographer", issue of the week ending 6 July 1996, there is the first review of the Contax AX (autofocus camera using manual focus lenses) that I have seen.

In my homepage I have the original Contax press release and some reactions to it.

Since the camera most innovative feature is its autofocus system I will concentrate in it. The other features are what you would expect of an high-end classical camera. The only semi-exception is the metering:

1 - no matrix metering. Only centerweighted average and spot metering. That is, you must use your brain, not the camera's.

2 - the autobracketing (-1/2, 0, 1/2 or -1, 0, 1) is centered around the exposure after the correction you chose is applied, not to the meter reading. I *think* this is different from the C/M/N/P cameras which always bracket either side of the meter reading. At least I have read in some tests the reviewer complain that since you usually know in which direction to correct (the problem is the amount) it doesn't make sense to bracket in both sides (underexposure and overexposure).

There is of course the data back that is very very good. See the files I mentioned above for details.

BTW, a little annoying detail. You need to keep the rubber eyecup on the viewfinder or you will scratch your glasses (there are places where good plastic is better than titanium).

So, how well does the AF work ? The reactions I mentioned above questioned how it would work in the following situations:

1 - zoom lenses: it was expected that "Zooming a zoom lens will lose focus.". The review doesn't address this question. But the photos that accompany the article clearly show a Vario-Sonnar 3.3-4.0/28-85 T*. So there should be no problem, or I would expect the reviewer to have mentioned it.

2 - Internal focusing lenses: it is expected that when using these lenses with AF the optical quality will be reduced compared with using it on MF, since they weren't designed to focus by moving all the lens relatively to the focus plane. The magazine could have tested this by repeating one of their lens tests. They measure lines/mm resolution and could have checked for degradation when using AF. They didn't, so we don't know if the problem is significant.

3 - restricted focus range with telephoto lenses. Since the film plane moves only 10mm, with long lenses the body can not focus very close. But you may focus manually at the approximate distance you want (always behind the subject) and the AF system will do the rest.

The reviewer made a great deal of this problem. I have made some calculations and I had concluded that it was not a big problem. But it seems that in real use it is inconvenient.

I wrote the following some time ago:

About the full range AF: That is not necessarily a bad point. I may be mistaken, but I think some long lenses from Canon/Nikon have focus range limiters, to reduce the hunting time. I know that this is the case for most macro lenses (at least 100mm and longer). If the range AF is reasonably large, this might be even an advantage:

The maximum movement of the film plane is 10mm. Considering a 200 mm lens (manual setting at infinity) this gives a minimum focusing of: 1/d + 1/(200+10) = 1/200 <=> 1/d = 1/200 - 1/210 <=> 1/d = (210 - 200) / (200 * 210) <=> d = 42000 / 10 = 4200 mm = 4.2 m for f = 300 mm, d = 9.3 m for f = 400 mm, d = 16.4 m

Hmm, it doesn't look very convincing to me, although the range with a 200mm would be enough for the kind of sport pictures I usually take (rally, see my homepage for examples).

with a 50mm, d = 3000/10 = 0.3 m This is ok (in fact the usual value for a 50 mm is 0.45 m)

in general d = f * (f + 10) / 10

What about the normal AF criteria ?

1 - accuracy: very good. Note that this one of the very few AF cameras that has a splitimage focusing aid.

2 - speed: good

3 - noise: very quiet ! (this despite all the things that are moving around)

4 - hunting: it seems that this camera has more difficulties than other top cameras. That is, when it locks on the subject it is fast and accurate. But sometimes it hunts.

5 - sensitivity: weaker than other cameras. EV range: 2 - 21. I think this is lower than usual. For comparision a Pentax Z-1p is -1 - 18. This range is usually specified for a 50mm/1.4 To overcome this the camera has a focus assist beam.

And other surprising consequences of the AF system used ?

1 - the reviewer loved the macro setting. In this mode the film plane is moved back all the way (10mm). It is equivalent to a built-in extension ring, but more convenient. He wrote: "and the Macro feature which was made possible by the focusing system is the best 'accident' of design I can recall".

2 - The back of the camera lacks the now usual window to see the film type. Instead you can use the LCD to see the ISO and the length of the film.

Of course there is the price: &1900 in the UK ($1900 in New York ?). But if one has a lot of Zeiss lenses, the alternative to get to AF would be to replace them all by lenses from another brand. This would not be cheaper.