Exposure Control, Canon Style
Canon consumer-grade camcorders do not provide complete manual control over key exposure settings like shutter speed, iris aperture and imager sensitivity (gain).
In the Easy mode proper exposure is maintained automatically. In the Program AE mode a user can adjust brightness of the video with Exposure control. The Exposure Control is a simple and user-friendly "Lighter-Darker" slider, which hides all low-level exposure parameters. Canon uses this approach in all consumer camcorders, from the inexpensive Elura to the high-definition HV20.
The Exposure control does not know what artistic effect you are after, so the result may differ from what you were looking for. This article explains how to manually control exposure parameters of your Canon camcorder. The main focus of this writeup is the Canon Elura 100 camcorder, the differences and peculiarities of other models, which are insignificant, are discussed in the end of the article.
This article does not explain what is aperture or shutter speed, what is wide or telephoto lens, it does not discuss different artistic effects that can be achieved by combining different apertures, shutter speeds and neutral density filters. You can find this generic information on the Net. The article focuses strictly on reading and setting exposure parameters on Canon camcorders.
Exploring Card Mode
We shall start from exploring exposure settings in the memory card mode. There are several reasons for that. First, most Canon camcorders behave similarly in the card mode, but require different tricks in tape mode. Second, screenshots made in the card mode can be easily analyzed and uploaded to computer. And third, using the card mode is just easier for practice.
Therefore, switch from the tape mode to the card mode, using dedicated switch on your Canon camcorder.
Locking shutter speed
Switch to Shutter Priority mode (Tv) if your camcorder has this option. The Elura 100 does not have the Shutter Priority mode, but offers scene modes, like Portrait, Sport or Night. DO NOT select a scene mode. Instead, switch from Easy mode to the generic Program AE mode. The Elura 100 allows selecting the shutter speed only in generic Program AE mode. In scene modes the Shutter Speed menu item is disabled.
Choose shutter speed you like. With shutter speed locked, the manual Exposure control will affect only aperture and gain.
Understanding EV steps, Aperture And Gain
All budget camcorders have zoom lenses with the maximum achievable aperture depending on focal length. For example, the maximum aperture of the Elura 100 is f/1.8 for fully zoomed out lens, and only f/3.4 when the lens is fully zoomed in (the User's Manual quotes f/3.6 instead of f/3.4).
As a rule of thumb, the camera will not amplify the signal as long as it can increase exposure by opening up the iris. Therefore if aperture automatically selected by the camcorder is smaller than f/3.4, you can assume that the gain level is 0.
Locking Exposure
Manual exposure control on Canon camcorders allows adjusting current exposure using a relative scale. In good lightning conditions, the scale provides 11 negative steps (to decrease exposure) and 11 positive steps (to increase exposure). In low light conditions, when gain is already cranked up, the scale may allow only decreasing exposure, but this does not make much practical sense anyway.
Even if the scale displays positive steps to increase exposure, the gain level could already have been elevated. In this case increasing exposure will not open up the iris, it will only increase gain. To verify whether gain is elevated, lock exposure and try increasing it. If aperture value does not increase (verify aperture by pressing "photo" button halfway after every adjustment), then the camera already have reached its maximum aperture and now is in the "gain zone".
Come to think of it, the way Canon exposure system works totally makes sense. Panasonic camcorders have a similar feature, only they allow choosing gain level explicitly. Similar to Canon models, Panasonic camcorders do not allow increasing gain until iris is fully open. Same functionality, slightly different interface.
Contrary to outlook of a popular camcorder website, which emphatically curses Canon's "enigmatic EV scale" for having "unknown intervals rather than actual EV stops", the intervals are known, at least for the Elura 100: when shutter speed is locked, each EV step corresponds to 1/4 of an f-stop unless the camera is in the "gain zone".
Elura 100 Exposure Calculator
You can use the aperture/gain relationship to select specific aperture while making sure that you are staying out of the "gain zone" (marked with read in the table below). Remember, that the "gain zone" boundaries are based on maximum achievable aperture at full wide and full telephoto lens. The table below is correct for the Elura 100. A different model will have different "gain zone" boundaries.
For example, suppose that you are shooting outdoors on a nice overcast day. You have locked shutter speed, then you pressed "photo" button halfway and the camera's light meter measured f/7.3 aperture. Now you can lock this aperture with EXP control, then you can move the Exposure slider left or right to increase or decrease aperture.
In the above example, reducing exposure all the way will achieve f/19 (count 11 steps to the left from f/7.3). The result of increasing aperture will depend on current zoom. If the lens is fully zoomed out, increasing aperture all the way will achieve f/2.8. If, on the other hand, the lens is fully zoomed in, then the camcorder will not be able to open iris wider than f/3.4, and "+10" and "+11" steps of Exposure slider will get camcorder into "gain zone", and amplified picture will likely become noisy.
Using Neutral Density Filters
Look at the above picture again. The light meter suggests f/7.3 aperture (see "0" above the aperture value). Suppose that suggested exposure works for you in terms of how the scene is lit, but you would like to separate your closely located subject from the background by opening up the iris, thus reducing the depth of field. You want to increase aperture without overexposing the image.
Naturally, you need to attach a neutral density filter to the lens. How poweful the filter should be? Calculating is easy, see the exposure table again. Every cell in the table is 1/4 of an f-stop, every green cell is a full stop. Therefore you can attach a 2-stop ND filter if you shoot at full telephoto (the bottom row of the table), this would give you f/3.7. If the lens is fully zoomed out, you can go ahead and screw in a 4-stop ND filter, opening the iris at the maximum achievable f/1.8, though care should be taken not to cross the "gain zone" boundary.
Pictures shown below were taken in the card mode with the Elura 100 on a sunny day. The glass candle holder is about 1m away, the neighboring house is about 10m away. The pictures were not retouched, only downsized. The first picture was taken with f/11 aperture.
Then a 4-stop ND filter was attached, which allowed opening iris to f/2.8. After exposure was locked, it was temporarily increased one step to verify that there is room for aperture; the "+1" EV step resulted in f/2.6. This test confirmed that the "gain zone" boundary had not been crossed, so the exposure slider was returned back to "0" and the shot was taken with f/2.8 aperture as it had been originally intended.
You can see that two pictures have different stylistic effect: the larger aperture blurs the background more, so the subject stands out better. The same effect is used in the movies, this is one of the many components of coveted "film look". To achieve noteceable blurring you need to have the subject really close to the camera or you need to zoom in.
Back To Video
Assuming that the camera light meter works the same way in card and tape modes, you can set up exposure parameters for a still shot, then switch to video mode and roll the tape. While this might work, this is not the workflow that I recommend. Instead, I suggest staying in the tape mode all the time. To ensure that the trick of pressing photo button halfway works in tape mode, you need to buy and install a memory card. These cards are cheap, you can buy a 1GB card for $20 or even less. You do not need large capacity, any card will do. Ask your friends with digital cameras, manufacturers usually throw in a small memory card, like 8MB or 16MB. This small a card is of no practical use, so your friends will happily get rid of it.
Ok, you got a memory card. Insert the card into the camcorder. Switch to tape mode. Switch your Elura 100 to generic "Program AE" mode. Select and lock desired shutter speed from the extended menu.
Select "Simultaneous recording on the tape and memory card" feature. Without selecting this option the camcorder will not display current aperture/shutter speed settings. See page 78 of User's Manual for details.
Elura 100 users need to jump another hoop: if you normally shoot widescreen videos, then temporarily switch to standard 4:3 aspect ratio using "widescreen" button, because the photo button trick does not work in widescreen mode. Seems logical, because Elura 100 cannot take widescreen still photos. Luckily, the camcorder does not reset exposure/focus settings when you switch between 16:9 and 4:3 modes.
Whew, this is it. Frame the shot, press photo button halfway and read aperture that is suggested by the light meter. With this information and with knowledge that every EV step is 1/4 of an f-stop as long as shutter speed locked, you can fully control your camera's aperture and gain. I suggest printing out the aperture table for future use. Enjoy! Oh, don't forget to switch back to widescreen mode if needed.
Aperture Control on the DC50 camcorder
Canon DC50 has proper Shutter Priority and Aperture Priority modes. To select and lock shutter speed you have to shoot in the Shutter Priority mode.
The largest aperture at full zoom for DC50 is is f/3.0, therefore the table looks a little different.
The DC50 has several EV steps that correspond to the same f/4.0 aperture, so the EXP/aperture relationship is not as straightforward as with the Elura 100. If you happen to shoot with f/4.0 aperture you need use the same slider position within f/4.0 range. The f/4.0 anomaly is marked in the table below with letter "M", meaning that multiple EV steps correspond to this aperture.
You do not need to switch to 4:3 mode to check current aperture and shutter speed.
Aperture Control on HV10/HV20 camcorders
Like the DC50, the HV10/HV20 models have proper Shutter Priority and Aperture Priority modes. Use Shutter Priority mode to select and lock shutter speed, then use EXP slider to adjust aperture.
The largest aperture at full zoom for HV20 is is f/3.0. The HV20 has several EV steps that correspond to the same f/5.6 aperture, so the EXP/aperture relationship is not straightforward. The f/5.6 anomaly is marked in the table below with letter "M", meaning that multiple EV steps correspond to this aperture.
Another fluke of HV10/HV20 camcorders is that they have two EV steps for each of the following apertures: f/2.8, f/3.4, f/4.0, f/4.8. On the other hand, these camcorders do not report f/3.2, f/3.7 and f/4.4 apertures. Therefore, it seems that the same 1/4 f-stop scale is used, vut values f/3.2, f/3.7 and f/4.4 are not indicated. This looks like a bug in the camcorder firmware, because the cheaper and older Elura 100 reports all one-quarter steps properly.