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AE lock does not compensate for varying aperture while zooming

tyurek

Member
Hi all,

I just purchased a used N1 with the 24-85 and 70-300 zooms. What I noticed today is that if I
lock the exposure say at 1/125 @ f/4 at 70mm while using the AV mode, the shutter speed
does not get compensated when I rack it out to 300mm, at which time the aperture readout
automatically changes to f/5.6; however, the shutter speed stays at 1/125! The camera
effectively underexposes by one stop! Logic dictates that the shutter speed should be
readjusted to 1/60, especially since I'm using the aperture priority mode. If I unlock the AE at
300, it immediately gives 1/60 @ f/5.6. The reverse happens when I go from 300 to 70. The
situation is the same with the 24-85 VS.

Is this just my camera or is it a known bug with the N1? Are there any known firmware upgrades for N1?

Thanks and best regards...
 
No, it's not your camera. It happens also with the NX. If you lock the exposure in AV, the shutter speed remains locked even if you change the focal length of the zoom.

Darn! Now I have to measure the exposure with the focal length I am going to use to actually take the picture!

Juan
 
But this is a horrible engineering mistake. It probably is a bug the Contax engineers overlooked.
Imagine you are at a lake side. The sun is shining on the surface of the water. There are
constantly moving birds of varying tonalities. Many things to fool the in camera meter. So you
read the exposure off of a gray rock at the shore, which is in the same light and lock it.
You start framing the birds, constantly zooming to catch new formations. Some of your exposures
will be plain "wrong" as one stop is a lot of error with slide film. I can think of a lot of
other scenarios where one might want to zoom after locking the exposure. This is one serious problem
I cannot believe the N1 team has overlooked while inventing tools such as AF bracketing. I do like
the camera very much in all other respects, but I'm sorely disappointed at this problem.

Does anyone know or guess if there is any rationale behind this behaviour? Now that Juan
says the NX also behaves this way, I'm wondering if the Contax engineers have something in mind
which I cannot see.
 
Out of interest, if you leave the 70-300 at 70 and lock it at f4, what happens if you deliberately change the aperture to f5.6? Does it correctly go to 1/60th?

Also, is your problem "cured" if you start at 70mm/f5.6 and then zoom?

I will experiment with my AX and report back.

Cheers, Kyocera Kid.
 
Tolga, yep you're right. I checked it on the N1 and then the ND.
I actually took two ND shots with the AE Locked after metering a neutral grey. One full stop difference because the shutter speed stayed the same. It's okay if you're shooting neg. film or even digital. But with slides it is a problem.

Two possible solutions:

Meter the grey area manually at 70mm, and when zooming to 300mm adjust the aperture ring a stop.

Or set AV and meter the difference between the scene and the grey neutral area... then set the compensation wheel.

The latter is what I would do as the difference is the constant.
The AV setting will then adjust normally as the lighting may vary, but the difference would still stay the same relative to each other.
 
Can you check if when you manually change the aperture after engaging AE locking, does it change the shutter speed?
 
Yes, if you change the aperture after locking, the shutter speed varies accordingly. This is described in the manual, and it happens as described.
You can see the same thing happens with the AX when you zoom. The "locked" value does not adjust for the light loss (of course, when you zoom with the AX, the aperture value on the display does not change).
 
Juan,

This is bizzare then...if you change the aperture after locking (assuming the N1/NX, as that is the camera of discussion), and it displays this change in the display, and the shutter speed DOES change as well, then why, if the aperture changes when you zoom, wouldn't the shutter speed also change with the zoom changes? It *should be* the exact same mechanism. That surely seems like a design flaw.

As far as the manual focus zooms, if the display doesn't change, then the aperture hasn't changed...as it's a mechanical linkage, and the camera doesn't know if you have a zoom on the camera or not. Are the aperture values listed on the zoom barrel? Isn't a 5.6 on the barrel, a 5.6 no matter what the zoom? The blade opening (or the ring on the barrel) doesn't change with the zoom, right? I don't know much about zooms, but isn't it only the minimum aperture that changes with the zoom range, or does the entire range shift?

Regards,

Austin
 
I believe that would be because the change in aperture through the ring is an explicit command, whereas the change in aperture when extreme zooming is inherent in the optical mechanism.

Now we know it can detect that, but it looks like it's only wired to adjust the display but not the data path to the processor that calculates exposure? Don't know how their internal architecture is set up.
 
Hi DJ,

Are you saying that if I select f4 on the marked aperture scale, it may NOT be 4, but f5.6, depending on the zoom selected? And, that though the barrel has f4 selected, the display shows f5.6? This is significant at determining what is going on here.

Has anyone actually *verified* that the images are exposed incorrectly? Why I ask, is perhaps it is making this compensation without informing you...

Regards,

Austin
 
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