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Nono pointed out that the 20D too, supports rear-button focusing (RBF)! This means that you can use the AE Lock (Exposure Lock) button [at the back of the cam] for focusing, and not be forced to half press the shutter button.
I’ve then since added some information about the function to my previous post.
This has a number of obvious benefits – mostly during sports/events photography where people prefer tracking using AISERVO. But in a practical sense, RBF is great as you can take your shot regardless if you’re focused or not. Normally, if you’re on AF (auto focus mode), you’d have to focus by half pressing – and as long as it’s not yet focused, you can’t trip the shutter.
This is a sensible approach, but can be frustrating at times: If you focus on a subject, and know that you’ll be taking another shot of them (assuming you’re not on continuous drive), you’d still have
to half-press and waste time as the camera re-focuses on [probably] the same point (which is ridiculous if you think about it)
RBF allows you to trip your shutter regardless, so it’s a kind of pseudo AF/MF focusing mode, which I think is pretty cool and useful.
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However, there’s a supposed drawback. Rob Galbraith’s 20D review points out a caveat when assigning the AE Lock button for RBF:
Flash Exposure Lock (FEL) junkies (which includes us with Canon models prior to the EOS-1D Mark II) should note that the 20D doesn’t have a dedicated FEL button, like 1-series digital SLR’s do. While FEL can be set using the AE Lock (*) button, this is only possible when the camera is not configured for rear-button focusing. This is the same as the 10D. With that camera, however, C. Fn 13 can be set to 13-4, thereby turning the Assist button into the FEL set button. When the Assist button disappeared from the 20D, so too did this functionality. While the new multi-controller’s function can be changed through a Custom Function, FEL is not one of the available options.
While we haven’t used FEL nearly as much since the EOS-1D Mark II’s inception, it still seems short-sighted to not provide a way for the rear-button focus crowd to set an FEL from time to time, without having to resort to front-button focusing temporarily.
As far as FEL is connected with AE lock (and it’s button), the manual does state this [about RBF and AE Lock]:
Convenient when you want to focus and meter seperately. Press the <*> button to autofocus and press the shutter button halfway to attain AE Lock.
So normally one would think that the function of the AE lock button, which governs FEL on most shooting modes, is still available via RBF (and likewise FEL should be too). As of the moment, I’m getting pretty confused about this whole FEL business. I seem to be misunderstanding (or missing entirely) the concept of FEL. It is said that FEL is achieved through the AE Lock button (this will display a * icon in the viewfinder). I noticed however, that if you half-press the shutter on RBF, it does lock the exposure (and shows that * icon, ergo it seems to still have EL/FEL functionality on RBF). Or so I would like to think so.
The caveat mentioned pretty much is confusing me right now as I now am forced to research on the definition and concept of FEL (which I though I already knew). Galbraith is probably read as much as DPReview, and for the site to claim FEL is “crippled” in such a way, it really makes me wonder if I got the concept of FEL right to begin with.
Of course there’s also that one in a million chance that it was a simple oversight on their part. I mean no one’s perfect right? So it is possible that they simply assumed that AE Lock / FEL was disabled – since you’ve already assigned the AE Lock button for focusing, which is perfectly understandable.
Anyways, as of now, I still dunno what to believe, maybe I ought to join the forums and ask a question about FEL in general (something like what is FEL exactly?) – then address my concern about the review (if applicable).
I gathered some noise “swatches” from DPReview. This should help people who want to compare general noise levels of the corresponding DSLR cameras.
Also found some NeatImage noise profiles for the different ISO and quality setting.
Download NeatImage noise profiles (1.9MB)
While I’m at it (uploading useful stuff), here’s a little app that can test your camera’s sensor for dead pixels
Download DeadPixelTest (190KB)
And here’s the PDF version of the 20D manual. Funny thing is, Canon USA’s website doesn’t have the manual available for download until now. But you can get it on the other Canon sites. You could also get it here if you want to save some effort looking for it.
Download EOS 20D user manual (4.5MB)
If you haven’t already figured it out, here’s the resolution to the confusion you’ve been having about what happens to FEL when you switch to RBF. A half-shutter press does indeed lock exposure, but only ambient light exposure. When using flash, there are two different meterings – ambient, which controls aperture, shutter or both, and flash, which controls flash pulse duration. What you lose when switching to RBF is the ability to trigger a preflash that assesses and locks the flash strength. You merely lock the ambient exposure.
David
Hey David, thanks for the detailed explanation. I did indeed figure out eventually that the preflash was missing, but this post of yours clarifies it further so thanks for the info!
Cheers