Getting it right with Canon Flash

[yeocsa]

yeocsa wrote:
I am using my company's 20d. Having used SB800, Canon 550EX is not as straight forward. Can you enlighten me on how to use the Canon flash correctly?

Well, it's a big subject. I'll start by giving you a few pointers:

The flash metering is independent of the ambient metering. Choosing metering mode, etc only affects the ambient.

The flash exposure is basically done using Evaluative metering (although with E-TTL II on the 20D you can select Average instead via a custom function). This means that the scene is split into 35 metered areas which are then compared to the camera's database of known scenes and exposures. For example a dark background with a light subject in the centre of the frame will probably be metered differently to the same scene with the light subject towards the edge of the frame. If you shoot in an AE mode you'll probably have become used to this, applying different amounts of exposure compensation for different scenes. Art Morris has even published a field guide specifically on this subject! Flash metering works the same way, although it's often harder to notice what's going on.

The flash metering is further modified by concentrating on the meter segments corresponding to the active focus point. Thus a white area under the active point will produce less flash than a black area under that point. Some people have had trouble shooting weddings where a slight change in composition can cause a black jacket or white shirt to be under the focus point...
On the 20D it relates to the _active_ point (on the D30/D60 it related to the _selected_ point). If you switch to MF then no point is selected or active and the flash exposure becomes more predictable. If you have AF tied to the * button then if AF is not active when the shutter is triggered then the same thing happens.

Vast differences in the flash metering are most visible when flash is your main light, but the differences are still there if you're just using it as fill. The main difference there is just that you've selected a negative flash exposure compensation, but all the same calculations are done.

That'll do to get you started (it's time I got some sleep!). I suppose we should move further discussion of this to the Canon Corral...

Hi Dave,

I have move the discussion here.

I have had problems with white balance when using 550EX with 20d. The 20d white balance is spot on when used without 550EX. Builtin Flash is okay.

Recently, I covered a wedding and found the colour temperature to be too warm.

What shoud I do?

regards,

Arthur

[DaveB]

I have had problems with white balance when using 550EX with 20d. The 20d white balance is spot on when used without 550EX. Builtin Flash is okay.

Recently, I covered a wedding and found the colour temperature to be too warm.

Do what I do: shoot in RAW. Adjusting the colour temperature for a range of images then just takes a touch of a slider (I use ACR as a raw converter, but that's up to you).

The colour temperature of the flash should be a constant value (close to daylight) and if you're using it as your main light you should probably select Flash WB. But if it's not your main light then the colour of the ambient lighting is going to have a big effect. In this scenario I find Auto WB the best bet (but I still shoot in RAW so I can tweak it later if necessary, as it's not a guarantee). None of that is particularly Canon-specific.

It's interesting to note the new WB compensation feature built in to the new 580EX flash. If you take a sequence of flash shots the voltage at the flash bulb for each shot can differ (as the capacitors aren't able to fully charge between shots). It's usually subtle, but this can change the colour temperature of the flash slightly. The 580EX will feed data on this to the 20D which (if you're in AutoWB) will use it to vary the WB slightly.
But that doesn't help you with the 550EX, and may not be relevant at all!

[yeocsa]

Hi Dave,

I had set the WB to Auto. I will set to WB to Flash and test it. This where Nikon Flash has an edge over Canon. Took me 3 days to process some 500 shots (in raw format) - too much time taken up. I tried Canon, Rawshooter, Photoshop, Helicon Filter, Capture One. Finally, settled on Capture One as the best and efficent way to batch process all the files.

What would be your recommended setting for wedding in terms of the parameters, colours space and AF? Would you use a colour chart?

regards,

Arthur

[DaveB]

I had set the WB to Auto. I will set to WB to Flash and test it. This where Nikon Flash has an edge over Canon. Took me 3 days to process some 500 shots (in raw format) - too much time taken up. I tried Canon, Rawshooter, Photoshop, Helicon Filter, Capture One. Finally, settled on Capture One as the best and efficent way to batch process all the files.

Back when I was using CS and a slow G4/350 yes it could take me days to process that many images if I had to do lots of tweaking. It's all about getting a workflow together that's efficient.

These days I use iView MediaPro as my management system, and PS CS2 as my image processor. I may come back from a shoot with several thousand images from multiple cameras (mostly RAW). One job I did recently I ended up with images from EOS 10D, 20D, PowerShot G3, and Minolta 7D cameras. The only way that mixing cameras complicates my processing workflow is when selecting optimum capture sharpening for each image along with needing noise reduction on some images (and I'm working on some scripts to automate these choices).
I process all the RAW images into DNG files, then work on those. From within iView I can call up Photoshop to tweak the conversion settings (including rotation and cropping) of one/some/many/all images, and iView will update its previews to match. Within iView I organise the images into appropriate groups, annotate them with keywords/etc. I could do most of the processing for a couple of hundred images within an evening. Of course some images will need conversion to PSDs then spotting, adjustment layers, etc which will add time. Then when it's time to produce PSDs/TIFFs/JPEGs (including building web galleries, CD/DVD directories for customer delivery, etc) it's all just a matter of using the library of iView scripts and Photoshop actions I've built up.

I guess the bottom line is there are solutions out there for reasonable workflows: you just need to find one you're comfortable with.

What would be your recommended setting for wedding in terms of the parameters, colours space and AF? Would you use a colour chart?

• Colour space in the camera? Don't care: I have ACR set to spit out everything in AdobeRGB. If I was shooting JPEG I'd probably have the camera do AdobeRGB also.
• Parameters (sharpening/contrast/etc)? Don't care: these only affect the in-camera preview, not the output from ACR. Back when I was shooting JPEG I had contrast at default, sharpening at minimum, etc.
• AF? That depends on your shooting style.
  I primarily use AI Servo, but then I have AF control on the * button and use a mixture of MF and AF (switching between AF points as required) so I don't have any issues with AI Servo tweaking back/forth on static subjects.
• I have a Gretag Mini ColorChecker chart which I occasionally shoot in in order to calculate WB/etc for different lighting conditions. I'm considering getting a pocket WhiBal as it's a bit more robust and easier to use.
• Exposure-wise I usually shoot in Manual, but again that's a shooting-style thing. Occasionally I use Av-priority if the lighting conditions are changing rapidly.

All of that applies to my normal shooting, and yes I've used the same settings when I've shot weddings.

[yeocsa]

Hi Dave,

Thanks mate. I am taking notes and start working on them tonight. Are you running any class or course soon?

regards,

Arthur

[DaveB]

Are you running any class or course soon?

Nothing scheduled yet, and probably no time to organise anything this month. I'm busy on a few other projects at the moment, so I guess it depends on how many people are interested in what.
Meanwhile I'll let you know if I'm setting anything up. Thanks for asking!

[mR_CaESaR]

http://photonotes.org/articles/eos-flash/

Great article for Canon flash systems. A bit of a read, but there's a lot of great information there.