Do the G cameras suffer from RF misalignment?

[haagen_dazs]

It seems like the RF alignment of some RF cameras (eg bessa) can be easily knock out of position....
does this ever happen to the G cameras?

thanks

 

[akptc]

I've had several G bodies and never any problems with the rangefinder.

 

[AndyPiper]

Not exactly - because the Contax Gs have solid-state rangefinders rather than mechanico-optical systems. Therefore they have no moving parts in the distance measuring system, whereas MO rangefinders have quite a few moving parts that can get out of alignment with shock, or just drift over time.

it would take quite a whack to shift the circuit-board-mounted focus sensors in a "G".

Some early G2 bodies had what amounts to an "electronic" RF misalignment. The Gs work by measuring the subject distance, and then using a "lookup table" stored in a ROM chip to determine how many turns to give the focusing motor/lens drive shaft. I.E. if the subject measures at 2 meters, the table might have the motor turn 2.55 rotations for a 45mm lens, and 5.1 rotations for a 90mm lens.

(This, BTW, is why the G lenses always have to return to infinity before refocusing - they need a fixed "zero point" from which to start counting the turns each time they focus).

In those faulty G2s, the data in the lookup table for the 90mm lens was erroneous, and so the focusing motor would spin the wrong number of degrees, missing the correct focus point. The fix was a trip to the factory to have the ROM reloaded with correct values.

 

[joachim]

In those faulty G2s, the data in the lookup table for the 90mm lens was erroneous, and so the focusing motor would spin the wrong number of degrees, missing the correct focus point. The fix was a trip to the factory to have the ROM reloaded with correct values.

To my knowledge, this happened to the very early G1 not G2 and is (on of) the origins of the rumours, the Contax G are not capable to focus the 90/2.8 reliably. From my own experience there is nothing in these rumours. The Contax G do a good job with the 90/2.8. I recently ran a test using a tripod and scaning the negs at 2900 dpi (Coolscan IV). The negs were in focus where they should be.

Other than this I have seen a couple of G1s (same faulty batch?) who gave different distance readings depending on the angle the sturcture hit the RF patch:

[ / ] or [ | ] or [ \ ]

this happened new out of the box when I bougt mine in 2001. I selected one, which did not show this problems and hasn't developed it since. Compared to the permanent discussions about RF misalignments for C-V Bessas it is pretty quiet about this topic for the Contax G. Doesn't seem much of an issue.

 

[Socke]

Not exactly - because the Contax Gs have solid-state rangefinders rather than mechanico-optical systems. Therefore they have no moving parts in the distance measuring system, whereas MO rangefinders have quite a few moving parts that can get out of alignment with shock, or just drift over time.

Are you sure? I haven't taken mine apart, but as far as I know the only difference to a visual rangefinder is who detects when something is in focus, a CCD sensor or a human eye.

 

[haagen_dazs]

(This, BTW, is why the G lenses always have to return to infinity before refocusing - they need a fixed "zero point" from which to start counting the turns each time they focus).

.

thanks andy
very helpful

so does it mean that everytime it focuses, it goes to infinity and to the desired point?
this to me, doesnt seem like fast auto focusing.
i dont own a G so i am not familiar...

 

[RF-Addict]

I had bought a G2 from KEH a few months back and decided to check the focus of the camera and the various lenses I had (28, 45 and 90). It turned out that the focus was indeed of by quite a bit. It really showed on the 90mm lens tests. First I thought it was the lens, but very quickly realized that it was the body itself. I contacted KEH and had a replacement body within a week. The new (old) G2 is spot-on. It is a great camera with even greater lenses which is why I can't get myself to selling it. I enjoy the Bessa R2A more than the G2, but when you see the slides of the Zeiss lenses on your light table all thoughts of selling the G2 go out the door.

 

[jlw]

so does it mean that everytime it focuses, it goes to infinity and to the desired point?
this to me, doesnt seem like fast auto focusing.
i dont own a G so i am not familiar...

It re-indexes to infinity every time you activate the AF, but it does so very quickly. Also, once you've locked focus, it won't re-index until you let up on the shutter button, so you can take a series of pictures without the lens having to return to infinity.

If you're in continuous autofocus mode, it only indexes once, then continues to track the subject movement without returning to infinity.

As stated above, it's necessary for the lens to "find" infinity when the AF system starts up, because there's no signal from the lens to tell the camera what focus distance is set. The only way for it to know is to go to a known reference point -- the infinity position -- and then measure how far to turn the lens.