Flicker while zooming: video + low light

M

mikeydvx

Active member
OK. This video is about as horrible as they come but it's only to illustrate the problem:

http://www.vimeo.com/5342846

Has anyone else noticed the flicker (bursts of exposure change) while zooming in low light? It's not the aperture changing because it happens even when you lock aperture. As I said, this video is lousy but it does illustrate the problem. It doesn't happen in bright light but it does happen even when the light is better/more than the above. BTW, this is visible in the original MTS file, even on the camera.

Anyone else seen this? I figure it must be the camera changing ISO, shutter speed, or something?

Mike
 
Here's a better example:

http://www.vimeo.com/5343115

If I shoot out into the yard where it's sunny: no problem. Turn the camera 90 degrees and shoot in the shade, and the flicker is back. There's plenty of light in this shot, so the flicker seems to rear its ugly head whenever the light isn't extremely bright. Anyone else notice this: could someone run a similar test?

Mike
 
mikeydvx said:
Here's a better example:

http://www.vimeo.com/5343115

If I shoot out into the yard where it's sunny: no problem. Turn the camera 90 degrees and shoot in the shade, and the flicker is back. There's plenty of light in this shot, so the flicker seems to rear its ugly head whenever the light isn't extremely bright. Anyone else notice this: could someone run a similar test?

Mike
Click to expand...

The aperture adjusts from f4 to f5.8 while doing this zoom. This is normal!

Definitely need a sticky for this. Kinda reminds of; "" my dvx100 is broken, it's clicking when I tilt it "" posts from the past!
 
PappasArts said:
The aperture adjusts from f4 to f5.8 while doing this zoom. This is normal!

Definitely need a sticky for this. Kinda reminds of; "" my dvx100 is broken, it's clicking when I tilt it "" posts from the past!
Click to expand...

That's what I thought too, but I already covered that above: it isn't the aperture changing. Even if you go to manual mode and lock aperture to f6.3 it does this.

Mike
 
mikeydvx said:
OK. This video is about as horrible as they come but it's only to illustrate the problem:

http://www.vimeo.com/5342846

Has anyone else noticed the flicker (bursts of exposure change) while zooming in low light? It's not the aperture changing because it happens even when you lock aperture. As I said, this video is lousy but it does illustrate the problem. It doesn't happen in bright light but it does happen even when the light is better/more than the above. BTW, this is visible in the original MTS file, even on the camera.

Anyone else seen this? I figure it must be the camera changing ISO, shutter speed, or something?

Mike
Click to expand...

Yup! I get precisely that effect Mike and I posted it somewhere else on this board. It was suggested that it was the ramping of the lens, but I did exactly what you did, I locked the aperture and it still did it. But as I understand it, lens ramping can still occur in low light even with a locked aperture. Your locking of the lens to an aperture smaller than the 'ramping aperture' would seem to indicate it may not be the ramping issue. As you said, I see it only in dimmer lit areas.

One thing's for sure, it aint pretty.
 
Ken7 said:
Yup! I get precisely that effect Mike and I posted it somewhere else on this board. It was suggested that it was the ramping of the lens, but I did exactly what you did, I locked the aperture and it still did it. But as I understand it, lens ramping can still occur in low light even with a locked aperture. Your locking of the lens to an aperture smaller than the 'ramping aperture' would seem to indicate it may not be the ramping issue. As you said, I see it only in dimmer lit areas.

One thing's for sure, it aint pretty.
Click to expand...

You're right about that. In some conditions it can be quite distracting. I did a little more experimenting last night. Even when locking the aperture I could still hear the lens making those faint clicks like it makes when it changes aperture and the clicks seemed to match the times that the video flickers. Like you, I wondered if the lens was still changing aperture even though it was locked. I set the lens to f22 where I knew I could see the depth of field change if the aperture (lock) was being overridden. I still saw the flicker and heard the little clicks but it looked to me like it was locked at f22 as specified the whole time.

I has a similar problem with my 5D Mark II and it seemed like the flicker occurred even when the aperture was well above (smaller) than the max of the lens. It's almost as if there is a mechanism in the lens that changes as you zoom regardless of whether or not the aperture is locked and that somehow affects exposure. I guess it's possible that the lens has some sort of "stop" that keeps adjusting as you zoom no matter what aperture you are currently at, and adjusting that stop is causing some sort of interference. Maybe the firmware of the lens can be updated to stop this?

Mike
 
I noticed that on both the 5D Mark II and the GH1, the lens continues to "click" at certain points while zooming even when you are sure the aperture is locked. My theory is that there is some sort of servo in the lens that moves an aperture stop at certain points. While the aperture isn't being changed, the "stop" still moves so that the lens is physically unable to go past the stop IF it is commanded to do so. My theory is that whatever mechanism is used to keep updating the max aperture stop is binding momentarily with the aperture, causing the aperture blades to "flick" to a smaller or larger aperture for a fraction of a second.

Notice in all the videos the video momentarily gets brighter when zooming in and darker when zooming out. While this is the opposite of what you might expect, it could easily be reversed depending on how the mechanism is designed... and I think it at least proves that the aperture or aperture stop mechanism is what is causing this. I think it might be possible to fix this via lens firmware. The solution would be to not change the aperture stop if the camera is locked at an aperture smaller than the max aperture of the lens.

Mike
 
People seem to forget that, by locking the aperture to f/6.3, it still needs to physically change during the zoom. The aperture needs to be wide open when fully zoomed in, yet slightly stopped down when wide. This may cause these flickers, though it does not explain why this would happen in bright light. Is the camera on full manual?
 
Chibs said:
People seem to forget that, by locking the aperture to f/6.3, it still needs to physically change during the zoom. The aperture needs to be wide open when fully zoomed in, yet slightly stopped down when wide. This may cause these flickers, though it does not explain why this would happen in bright light. Is the camera on full manual?
Click to expand...

Sorry. That's simply not correct. If you set it to manual exposure video and set the manual exposure mode to "A", an f/6.3 aperture will remain f/6.3 through the entire zoom range. I've verified that two ways. The aperture in the EVF will show the change if it changes (and it doesn't). Also, you can set the aperture to f/22 and watch the depth of field as you zoom: it doesn't change yet the flicker still occurs. Also, you have it backwards above: when you zoom in, the aperture stops down (smaller). As you go wider, the aperture opens up (wider). But... that's only if you are in the zoom's max aperture range: f/4 to f/5.8. If you are smaller than f/5.8 and you are in aperture manual mode, the aperture will never change.

Mike
 
mikeydvx said:
Sorry. That's simply not correct. If you set it to manual exposure video and set the manual exposure mode to "A", an f/6.3 aperture will remain f/6.3 through the entire zoom range.
Click to expand...
Yes, the aperture will be f/6.3, but as said, to be f/6.3 during the zoom range, it has to physically change.

mikeydvx said:
when you zoom in, the aperture stops down (smaller). As you go wider, the aperture opens up (wider). But... that's only if you are in the zoom's max aperture range: f/4 to f/5.8. If you are smaller than f/5.8 and you are in aperture manual mode, the aperture will never change.
Click to expand...

Try to see it like two lenses: A 14mm f/4 lens, and a 140mm f/6.3 (Theoretically) lens. If I want to use f/6.3, I'd have to stop down on the 14mm. If I wanted to use f/6.3 on the 140mm, I have to use it wide open. So when I zoom (Change lenses) from 140mm to 14mm, and I want my aperture to stay at f/6.3, the aperture needs to physically stop down. The theoretical aperture will stay at f/6.3, but the aperture blades need to stop down. If I were to zoom in fully with the lens open, the aperture will go from f/4 to f/5.8. However, it will not physically change size, and stay wide open. Yet the theoretical aperture changes, due to the arrangement of lens elements.
I hope I you get what I am trying to say now?
 
Chibs said:
Try to see it like two lenses: A 14mm f/4 lens, and a 140mm f/6.3 (Theoretically) lens. If I want to use f/6.3, I'd have to stop down on the 14mm. If I wanted to use f/6.3 on the 140mm, I have to use it wide open. So when I zoom (Change lenses) from 140mm to 14mm, and I want my aperture to stay at f/6.3, the aperture needs to physically stop down. The theoretical aperture will stay at f/6.3, but the aperture blades need to stop down. If I were to zoom in fully with the lens open, the aperture will go from f/4 to f/5.8. However, it will not physically change size, and stay wide open. Yet the theoretical aperture changes, due to the arrangement of lens elements.
I hope I you get what I am trying to say now?
Click to expand...

Of course, I get what you are saying: that's where the "f" comes in when you say f/6.3. I get that, BUT... Like you say, if you set your lens wide open at the wide angle end (f/4.0), the aperture blades will not change as you zoom but the effective aperture does change. In that mode, you can still hear the lens clicking as if it were changing aperture, yet it shouldn't be. Switch that around and set it to f/6.3. It still clicks as if it were changing the aperture blades (which now it should be). So both ways: one where it should be changing the aperture blades and one where it shouldn't: it still clicks. AND, most importantly, you get the flicker in both of those modes! And the flicker occurs where the clicks occur.

So where does that leave us? I'm not sure but the clicking sound would seem to imply that the flicker comes from something with the aperture. Yet both when the aperture should be changing and when it isn't: you get the same clicking and the same flicker.

Mike
 
I have shot something similar to your video a few days ago and I haven't encountered your problem. There might be something wrong with your camera or settings.
 
Okay... Hold on. I read this post a while back and dismissed it... BUT I'm seeing this too! I'm shooting in FULL MANUAL with the aperture set to F6.3 - iexposure off

The exposure seems to change and then 're-adjust' causing 'steps'. You can hear a faint 'click' inside the lens as it happens. What's up with this?? Try it yourself on an interior scene.
 
upshot said:
Okay... Hold on. I read this post a while back and dismissed it... BUT I'm seeing this too! I'm shooting in FULL MANUAL with the aperture set to F6.3 - iexposure off

The exposure seems to change and then 're-adjust' causing 'steps'. You can hear a faint 'click' inside the lens as it happens. What's up with this?? Try it yourself on an interior scene.
Click to expand...

Right. That's what I was seeing and that was the reason for my original post. Even with exposure locked in manual mode, it still does it. It's almost as if the lens is somehow "fiddling" with the aperture even when it shouldn't be. Based on the prior posts, I don't think anyone knows what is really going on but I'm hoping it can be fixed with (lens) firmware.

Mike
 
AdrianF said:
Has anybody having this problem tried changing the Shoot Without Lens option?
Click to expand...

Not before I read your question but I just tried it. No change: still flickers.

Edit: just did some more checking. It flickers while zooming in every possible mode: full manual with everything including shutter, aperture, and ISO locked, full manual with AE locked, aperture priority with aperture locked at f/6.3, aperture priority with aperture on f/4 so that it changes from f/4 to f/5.8. I cannot find a mode where it doesn't flicker when zooming unless you are in very bright light.

Mike
 
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I see this too.

It's a 'fly by wire' lens so perhaps the normal rules don't apply - we can't quite tell what might be going on under the hood - for instance, if the image is being processed all the time to correct lens errors (and the processing would vary with zoom level), then that processing might also be messing with the illumination as a side-effect.

I've expressed concern in another thread about the stepping of exposure when using shutter priority. It seems to me that the least stepping happens when auto ISO is set, which perhaps allows the camera to vary ISO instead of or as well as aperture, and thus obtain smoother transitions in exposure when panning or zooming.

However, in full manual mode you can't use auto ISO so that smoothing effect is not available. As I mentioned before, I personally see no reason why auto ISO should not be usable in full manual mode and I'd be glad if firmware in the future allowed that - people wanting 'real' full manual would simply set their ISO as before, people wanting fixed shutter and aperture but variable ISO could set auto ISO. Everyone's a winner. No logical reason why not (as auto focus is still available in manual mode already, for example).
 
full manual with AE locked
Click to expand...
As far as I can see, AE lock does not work in manual mode (as it thinks the exposure is locked to the given settings - wrongly, if zooming). The AE indicator does not light up.
 
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