Z1/FX1 gain control rant

[K.C. Luke]

Originally Posted by Alec Moreno

Now, about gaining up and down smoothly...

Step 1
Open a picture Profile and set the AGC limit to your liking. For stage performances, I prefer 12db. Leave this picture profile on while shooting.

Step 2
Run everything in full manual, except for both the iris and gain.

Step 3
Set one of your assign buttons to Spotlight mode and turn it on.

Step 4
Set another one of your assign buttons to AE Override and turn it on.

May be I should try this setting for some night events. Thanks for the tips :)

[Boyd Ostroff]

Alec, that sounds like a clever solution. However, my performance shoots are fairly "mission critical" around here and there is no opportunity to repeat them. I think I will continue to rely on what has worked for me over the past few years in full manual mode.... at least I know all the "gotchas" there.

[Vito DeFilippo]

Originally Posted by Alec Moreno

The iris dial now acts as a single controller for both the iris and gain and will adjust them both in accord with each other as you ride this dial.

This is an interesting tip, so I tried it out. It seems to do as you say, though I think I see a colour shift at the extremes. I almost thought it would make more sense to use the Back Light setting instead of Spotlight, cause we're looking to increase brightness in dark conditions, and the Back Light button should open the iris more to compensate for underexposed faces. But it didn't work.

So I tried Spotlight. I checked it out in the manual, but it doesn't say how it achieves its purpose. I'm guessing it reduces exposure a bit under the usual auto level? But doesn't that leave us with an unused ceiling of brightness?

(As an exercise, you can display the iris and gain settings on the LCD as you do this to see exactly how the two features work together.)

I can't figure out how you do this. When you put them on auto, the values disappear. If I recorded while I messed around with it, I could display the data code on playback. Is that what you mean?

Thanks a million.

[Adam Gold]

Originally Posted by Vito DeFilippo

...I almost thought it would make more sense to use the Back Light setting instead of Spotlight, cause we're looking to increase brightness in dark conditions, and the Back Light button should open the iris more to compensate for underexposed faces. But it didn't work.

So I tried Spotlight. I checked it out in the manual, but it doesn't say how it achieves its purpose. I'm guessing it reduces exposure a bit under the usual auto level? But doesn't that leave us with an unused ceiling of brightness?...

No, think of it this way. In a theatrical setting, there's a lot of dark and a few spots of light. But the auto-exposure of the cam wants to make everything a fixed average level of gray, so it will bring up everything, including all the black areas, until the picture averages that gray level, blowing out the highlights in the process. So SPOTLIGHT is designed to prevent it from doing that so the blacks stay black and people's faces aren't blown into white. Back light does indeed compensate for underexposed faces, but in a theatrical setting you're often dealing with OVERexposed faces. Unless your director is Boyd's nutjob who lit the actors with only two flashlights.

You can achieve the same effect just by shooting in full manual and riding the iris and/or gain and using your zebras -- in effect exposing for the faces and not the backgrounds. Or frankly you could set up a Picture Profile with AE SHIFT set to -3 or -4, which would prevent the cam from overexposing highlights in a dark situation. I just got back from a night soccer game tonight where the Zebras were going nuts all over everything with the cam set to auto -- I had to shift AE four slots down to get the exposure right.

Note that on the FX1, there are permanent hard buttons for BACK LIGHT and SPOT LIGHT rather than ASSIGN buttons.

[Vito DeFilippo]

Originally Posted by Adam Gold

But the auto-exposure of the cam wants to make everything a fixed average level of gray, so it will bring up everything, including all the black areas, until the picture averages that gray level, blowing out the highlights in the process.

Yes, I understand that, which is why I said Spotlight probably reduces exposure under the normal auto level.

I guess I was moving beyond the theatrical setting, and wondering if the tip would be useful for more general event work, much of which happens in low light. But does the technique leave us with an unused "headroom" of exposure possibility, because Spotlight is using a setting less than normal auto?

[Adam Gold]

In a low contrast situation, probably. On overcast days I've experimented by toggling it off and on and all it does is make everything darker.... so whatever detail you might pick up in your highlights, you lose in the shadows.

[Alec Moreno]

Quote-
(As an exercise, you can display the iris and gain settings on the LCD as you do this to see exactly how the two features work together.)

I can't figure out how you do this. When you put them on auto, the values disappear. If I recorded while I messed around with it, I could display the data code on playback. Is that what you mean?
-End Quote

Yes, that is what I meant Vito. Also, like the the others have said, the Spotlight mode forces the "auto settings" of the camera to darken the picture to approximately where you and I would adjust the exposure for a dark stage. Without the spotlight mode, a pure auto approach would yeild an overexposed shot.
____________________

Boyd,

I know where you're coming from and I feel the same way in approaching my own shoots. Generally, I cringe at the thought of auto settings and I wouln't give up full-manual for the world...except for when I know that I will definitely have to adjust the gain while simultaneously acheiving a great continuous shot (say for a one-camera shoot). For this purpose, and for the occasional unseasoned second shooter, this setting is a charm and I really recommend that you investigate its potential and pitfalls.

I actually learned this semi-auto method on some free time I had to tinker around at a local dance performance. I had no intention of using the footage for anything but analyzing what its limitations were in this mode, so I was free to experiment like mad...and I did. I purposely over and underexposed shots, whip panned across the stage, compared similar shots to full-auto, and everything else I could think of doing. I now use it for paid shoots with comfort. Also, as I forgot to mention earlier, it's a quick and easy way to fine tune an unmanned camera's exposure for just about any lighting conditions.

Alec Moreno
http://www.1Day1ShotProductions.com

[Ron Evans]

Looks like a good approach but does not work on the FX1 as the assignments are Z1 specific. I also miss the black stretch too!!! All things to look for on my next camera!!!

Ron Evans

[Vito DeFilippo]

Thanks, Alec, great info. Funny how you think you know your camera's options inside out, then someone comes along and says 'check this out.' There's always something to learn...

[Pete Cofrancesco]

Originally Posted by Alec Moreno

Step 1 Open a picture Profile and set the AGC limit to your liking. For stage performances, I prefer 12db.
Step 2 Run everything in full manual, except for both the iris and gain.
Step 3 Set one of your assign buttons to Spotlight mode and turn it on.
Step 4 Set another one of your assign buttons to AE Override and turn it on.

The iris dial now acts as a single controller for both the iris and gain and will adjust them both in accord with each other as you ride this dial. Effectively, the dial is now controlling what you might call the "brightness" which equates to a setting between -7 and +7.

I can use your tip on how to enable Spotlight. I can't understand why its not in the Picture Profile or the main menu. I've never really liked settings like Backlight or Spotlight, they're dumbed down consumer terms that don't explain what its really doing. I'd rather have something straight forward like an exposure compensation dial on the camera.

I've already tried something similar with limited success (auto with AE -7). Unfortunately, it still over exposed the faces, I needed more than -7. Your method doesn't increase the AE compensation rather it allows you to control it using the iris dial. It's not bad as long as the scene isn't too black. For a long shot of the entire stage, too much of the black background fills the frame for this method to compensate. The inherit weakness of auto (even with AE compensation) is you don't know what gain the camera is using. You can set a gain ceiling but it could be maxed out to let's say 12db for most of the performance.

Even when shooting in full manual, the Z1 will still compensate ever so slightly for exposure. The effect is minimal and really only noticeable when panning/tilting from extremely bright to extremely dark areas and vice versa...and when the AE Response is set to medium or fast. Under these conditions, the screen will appear to instantly gain up or down just enough to be annoying and destroy your shot

I've seen this before and I thought my eyes were playing tricks on me. I'm not really sure this is a good thing or not but its strange given the fact when you set it to manual you're expecting just that.