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AE lock does not compensate for varying aperture while zooming

Austin,
I don't know anything about the technical questions here, so I can just report observations.

I think it is a design flaw. However when I said that the same thing happens with the AX I was just trying to point out that every single Contax camera has had that limitation with AE lock and "variable aperture" zooms. In my test with the AX I used the 100-300mm 4.5-5.6 zoom. My understanding (I may be wrong) is that, in that lens, when the aperture ring is set to 4.5 but the focal length is 300, the effective aperture is, in fact, 5.6. This seems equivalent to the 70-300 f4-5.6 for the N1-NX.
The difference is that the N1/NX tells you the change in effective aperture in the viewfinder display. The aperture ring on the lens may point to "4", but the viewfinder says 5.6.

This information is passed to the processor that calculates exposure. If you zoom on a grey wall (WITHOUT locking the exposure), the speed does change appropriately, at the same time you see the change in the displayed aperture. The issue seems to be what the camera actually "locks" and how this is unaware of the changes caused by the zooming.

Juan
 
Forgive me, if anyone has answered this ..... I get confused when people just say "Yes....etc" when a few members have asked different questions!

If you set the lens to 70mm f5.6, then AE Lock, then zoom to 300mm, does the aperture reading in the viewfinder change, and does the shutter speed change?

Indulge me, someone!

Cheers, Kyocera Kid.
 
Austin. yes I checked it (read my post above) I did it with a ND and the 70-300 f/4/5.6. Trained on the same subject.

I first read a neutral grey at 70mm and AE locked it in then shot the subject at 70mm. Then zoomed to 300 on the same subject... the result was clearly a stop darker at the 300 end.
 
Austin,

Indeed, as I zoom from wide to tele the f-stop display in the finder changes. Not the speed, though. Maybe as you say it may be compensating but not indicating it, although in Av mode the speed display should be coming form the actual speed setting the camera has determined to use.

I should point out I used the 24-85 already on my ND, as I was too darned lazy to switch zooms. Hey, it's Sunday, OK?
happy.gif
 
Kyocera Kid,

By now you have seen the answers, but I just want to make sure you don't feel your posts get overlooked:

With the NX and the 70-300mm: With the zoom at 70mm and the aperture ring at 5.6, if you zoom to 300mm the display shows the aperture is 8. The shutter speed varies accordingly.

With the AX and the 100-300mm: The AX will also change the speed appropriately, but it does not change the aperture value on the display.

If you lock the exposure (on either camera), the speed does not change. In the NX/N1, the aperture value changes on the display.

I may be completely off here, but the way I think about it is: until you lock the exposure, the metering system is measuring the light. When you zoom (regardless of what the display says) less light gets through the lens, and the resposnse is appropriate. Once you lock the exposure, no more metering takes place.

I think the bottom line is you have to lock the exposure with the focal length you are going to use. I also think this is exactly what most of us do most of the time, and this may explain why this has not created any uproar before amonth the Contax faithful. You can certainly come up with situations where it will be a problem, but in general (consciously or not)) one probably locks the exposure with the focal length [close to the one] one is going to use.

Just to be complete: in the G series, when you lock you lock the shutter speed only. If you switch the aperture after locking "the exposure" (obviously a misnomer), there will be no automatic adjustment. This is explained in the instruction manual, ("Be careful", it says on page 136).

Juan
 
Juan,

"With the AX and the 100-300mm: The AX will also change the speed appropriately, but it does not change the aperture value on the display."

How does the AX know the zoom has zoomed and to what zoom position? There are no electrical contacts...only mechanical linkages. Can you see if any of the mechanical linkages vary with zoom position? There *is* a way I can think of, and that is when you zoom, the min aperture indicator changes, but that should change the display as well...

Regards,

Austin
 
Juan,

"I may be completely off here, but the way I think about it is: until you lock the exposure, the metering system is measuring the light. When you zoom (regardless of what the display says) less light gets through the lens, and the resposnse is appropriate. Once you lock the exposure, no more metering takes place."

It *does* change the exposure based on changing the f-stop and/or shutter speed, after AE locking...so why can't it do it with the zoom, as it does change the display (so it has the appropriate info). This doesn't require re-metering, just adjusting the exposure accordingly.

Regards,

Austin
 
Juan - your kind thoughts are much appreciated, as is your reply.

I guess I am astounded by this movement from 5.6 to 8 on the N series! I thought, like Austin implied/queried, that the aperture reading would remain static once moved away from its maximum(variable 4~5.6) setting!

To put it another way, I assumed the problem would exist only at maximum aperture, and no other, for a lens with a variable max aperture.

Marc seems to have confirmed that this is a real effect, and that no "internal" compensation is applied.

I will play with my AX with the Tamrons (must borrow a CZ to play with too) and make a mental note of the above findings in case any of the Contax Postal Club members make a similar enquiry about the N series.

It's discussions like this that are so useful to help other groups.

Oh Oh! Incoming from Austin x2, even as I write .... I'll watch the replies on these too.
happy.gif


Thanks All, Kyocera Kid.
 
Austin,

"How does the AX know the zoom has zoomed and to what zoom position?"

The AX doesn't need to know the zoom has zoomed for this functionality: less light reaches the light meter, so shutter speed is changed as long as you have not locked in the exposure.
No magic involved.....

Regards,
Pim
 
Austin,
"How does the AX know the zoom has zoomed and to what zoom position?"
I don't think it does, that is the reason the aperture displayed in the viewfinder does not change. But the fact is that less light gets to the meter, so the speed changes.

"Can you see if any of the mechanical linkages vary with zoom position?"
When I look at the mechanichal linkages on the bayonet, I cannot see anything changing when I zoom.

Regarding your next comment: you are, of course, right. Regardless of if there is light metering involved or not, the camera could have been set to react appropriately to the zooming effect. That is the reason I think it is a flaw.

I precisely said "the way I think about it" to mean that, whether this is the explanation or not, it is helpful enough for my own grasping of the situation.

Juan
 
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