Shuttering.
 

How come when I adjust the shutter speed, my image tends do get darker, and eventually gets black?

Can i fix it? that is, without adding light to my set?

If you go with a faster shutter speed the CCD chips get less exposure time,
and thus has less time to accumulate the light, hence resulting in a darker
picture. This is true for every camera (with a shutter).

There are a couple of things you can do:

1. change the iris / f-stop (f 2.8 lets in more light than f 5.6 for example)

2. change the gain (will introduce noise)

3. get a faster lens (not sure if these exist for the XL2)

4. add more light to your scene

5. remove any ND filters you have added or engaged

That's about it...

Lon,
It appears that you have the camera in the Av mode or in the M mode. The Av mode (Aperture value) mode, when the Exposure Lock button is pressed, or when the camera is in the M (Manual) mode, will permit you to increase (or decrease) the shutter speed while all other varibles remain fixed. Rob explained very accurately that the decrease in light you see in the image is a result of the shutter effect.

One other thing I can tell is that you've got your Gain set other than Auto. Had your Gain been in the Auto position, it would have automatically tried to ramp up to keep the same level of image brightness, thus injecting some degree of noise in the imagery.

Does anyone know of a decent and free turorial on the relationship between the primary devices on a came that affect the image (F-stop, shutter, gain, and ND filters)?

Don't forget that Tv (shutter priority) mode plus Exp. Lock will also work the same way here as well. Given a choice between Av + Exp. Lock or Tv + Exp. Lock, I really prefer Tv because it keeps the shutter speed from changing. I can handle an auto iris adjusting itself, but not an auto shutter; to my eye that's a much more drastic and jarring change in the image than auto iris. Tv locks the shutter speed down and allows an auto iris to guage exposure, which you can instantly override by pushing the Exposure Lock button -- whereupon you have full manual control of exposure.

I'll take Tv + Exp. Lock, or even Av + Exp. Lock over full Manual any day. Full Manual is highly overrated in my opinion. Why not get the best of both worlds with that wonderful Exposure Lock button.

Chris, I'm with you on those two modes over full manual. Unless it is a very scripted shot with no time constraints, I also prefer Av or Tv over manual; call me an amateur.

I think it's an issue of where your priorities lie. I would rather invest my attention towards framing and composing the shot as it happens before me. Let the camera worry about the exposure; it already does a great job of controlling it automatically. Plus, beforehand I can tweak it up or down a bit to my liking with the AE Shift dial, set it and forget it. I wouldn't say it's an "amateur" thing; or heck, maybe it is... point being that auto exposure works quite well for my tastes and allows me to concentrate on the frame. If I need full control, the Exp. Lock feature is one button-push away.

I haven't used anything but full manual mode in years. Once you get it down, you can adjust everything in seconds. Depending on the project, I lock in several "looks" using the custom buttons, etc. and I can get there in seconds, no distraction from framing. Of course this is after shooting over 9 years and over 5000 hours of DV sooo.... =o)




ash =o)

Ash, I guess my point is that a lot of new people who don't have the experience that you have are being told to shoot full manual. That's not always the best way for new folks to go. Auto plus Exp. Lock is exactly like shooting full manual, but with a built-in "escape mechanism" to instantly go back to automatic if needed. For the beginner and even for the amateur or semi-professional shooter, myself included, that's a much better way to go.

Chris,

There is one way that the owner's-manual does indicate 'Auto plus EXP LOCK' is different than full 'Manual':

In Av mode you have 7 available aperture settings, in Manual and Av with EXP LOCK you have 24 available aperature settings.

In Tv mode you have 12 available shutter settings (1 more in 60i/30p), in Manual mode you have 30 available (1 more in 60i/30p), but, in TV with EXP LOCK you only have 13 available shutter settings.

All from pgs 59&60. Why?

Chris you are 100% correct... I do not recommend full manual for anyone without a LOT of hours logged on the XL series.

Patrick, I believe those settings are to keep the image within a certain area and always viewable. For instance, at some point, the auto gain will not be able to overcome a high shutter.



ash =o)

Ash,

I would agree with you except that the 13 available shutter settings span the entire range except two above 1/5000.

Chris,
When you use tv mode, do you leave the gain on A? I assume that if the gain is set to zero, or another value, and if you use tv mode, that the gain won't move...is that right?
Thanks
Bruce Yarock

In TV Mode the gain acts exactly like it does in manual mode. If you set it at 0 it stays at zero. Set it to auto and it will try to automatically adjust to compensate for dark images. So if you don't use gain often this is not a problem.

The real question is how does the camera prioritize gain vs. iris when trying to set proper exposure? In my mind the iris should always be opened all the way to get as much light as possible without gain. Then add gain to grab extra stops that couldn't be achieved through iris opening further. But I am not sure the XL2 use this logic internally. I have a stream in my back yard and some beautiful mallard ducks came swoopping in. I grabbed my camera and set it to Tv mode and thought I had the gain at 0 but accidentally had it set to auto. When the ducks went into a shaded area the image became grainy and noisy. Upon review the gain would ramp up to expose the shaded area while the iris stayed at 3.4 or so.....Fortunately I was able to catch this and switch it to 0 gain and the remainder of the footage looked clean and pristine.

So we have to be careful that auto gain doesn't circumvent auto iris. In my experience the threshold at which the XL2 starts to crank the gain up automatically is pretty low.

FWIW

Marty,
so you suggest leaving the gain at 0 when in TV mode, and using as a last resort AFTER iris?
Bruce Yarock

That would be my suggestion. Unless you have a specific circumstance where you need more DOF and you do not want to open the iris anymore. Then gain would be useful....just remember there is some noise added.

I do wish Canon had implemented a method by which you could see the auto gain setting. In other words just show us +3,+6, +12 in the EVF so we can see what the auto gain is doing. Because on more than one occasion when in auto mode it ramps up to what must be +12 and really noisies up a shot. I change it 0 and adjust iris myself and get a good exposed image. +3 may help but there is not much noise at that level. +12 adds a decent amount of noise so I have to assume that is where the auto gain migrates to......much to quickly for my taste.

Thanks ,Marty. also, what's the difference between using the ae shift or the gain in that situation?
Bruce yarock

To understand AE shift you need to understand the way the auto iris works. I don't know the specifics but I'd guess it goes like this.

The image is analyzed and it is determined that the scene is overexposed. So the auto iris (Tv Mode) starts to close. Your Fstop reading will inversly go up. If the scen is underexposed the iris will automatically open up to let in the proper ammount of light and inversely your fstop will go down. The camera has theoretically been calibrated to "know" how to properly expose a given scene.

This can work well for a lot of shots. But say you know for a fact that you will be shooting a brown horse standing in front of a white barn. This situation would likely cause the auto iris to properly expose for the bright wall and this would underexpose the horse. You would likely lose detail of the horse.

Where AE shift comes in is it is like your own personal way of saying "I would like for you (the XL2) to expose the way I want. I prefer to have the white wall be overexposed a little and have the details in the horse be properly exposed." You can set the AE to shift the exposue 2 stops over or 2 stops under the "XL2s" perceived proper exposure. You can shift this is 1/4 stop increments. So in this case you could set it to +1.0 so that whatever the XL2 sees as properly exposed will be increased by one stop. Oset it to 3/4 of a stop if that is better.

You are essentially biasing the auto iris in favor of overexposing or underexposing the image from the XL2's base proper exposure. Using this method is just an automatic way of controlling the iris. No artificial noise should be introduced as a result.

Gain, is essentially, a fake way of getting a few extra stops out of low light images. It artifically boosts the level of the signal to try to get an acceptable image. It is obviously more technical than that but that is the overall concept. The inherent problem is noise/grain/artifact can often be seen in the dark areas of you image. That is why I prefer opening the iris as much as I can before resorting to gain.

thanks,Marty...that's a pretty thorough explanation.Does AE shift work in manual mode, once the iris is all the way open?
Bruce Yarock

Hi Bruce. As far as I know, AE shift only works in AE modes. In manual mode the camera should expose according to your iris, shutter and gain settings, without regard for how the AE Shift is set.

By the way, if you normally like to get a narrow depth of field, setting the gain to -3dB where possible will get you another half stop of iris opening.

Richard

Thanks,Richard.
Bruce Yarock