back button focus

[jann1033]

this video is on flash and he says use manual mode & back button focus this is on a canon 5d....is he meaning the auto exposure lock button or some other button the rebel xt doesn't have? http://www.shootsmarter.com/infocenter/pg000.html


yikes i'm getting nervous about flash...does the ettl not work right or why is it so tricky?

 

[Groucho]

The link is for members only so we can't see it.

I would guess that it's a button to do a one-time focus when in manual focus mode?

 

[gruZ]

There is a custom function on the 20D (and I'm assuming the 30D and 5D - not sure about the Rebel series) that allows you to focus using the button on the back of the camera - the one that is marked with an *. This allows you to meter using the shutter button, and focus independently, using the * button.

You might ask, why would you want something like this? I wondered as well, but after using it for about a year, it's second nature and I wouldn't want to focus any other way. A couple examples of why I use this:

1. Imagine taking a picture of a family in front of the castle at WDW. I will point the camera at the castle, and push the shutter half way to meter for the sky and castle, then holding the shutter at half way recompose the picture so the family is where I want them in the frame, and use the * button to focus on the family. I now have metered for one part of the picture and focused on another, and combined with some fill flash provides for a picture that has proper exposure throughout.

2. Taking pictures of kids playing softball. I will use the * button to focus on the batter, then use the shutter button all the way down to take the picture and meter immediately regardless of the current sky (cloudy or sunny) at the moment I need to take the picture. Focusing in this situation also prevents the lens from hunting at inopportune times - right when the batter is swinging, for example, because I have already set the focus.

Hopefully this gives you some insight as to why you would want to do this. It takes a bit of getting used to, but once you are in the habit, you'll wonder how you took pictures beforehand!

Hope this helps,

Scott

 

[Groucho]

A handy feature. I have to do it the "cheap" way and do a half-press to get my focus, then flip the switch to manual focus to keep it there, and flip it back when I'm done.

Of course, years of shooting with a manual focus camera (and still using it occasionally) mean that I'm just as likely to leave it in manual focus.

 

[handicap18]

It sounds like its not to much different than using one of the different auto focus areas with AE lock. On my D50 I can set the AE/AF lock to do both or one or the other. So I could have it set to AE lock only, then meter, press the AE lock button then focus seperately. Or like in the old days, meter where you want, set the readings in manual, then focus where you want.

But I guess having a short cut for a short cut can be handy.

 

[jann1033]

i couldn't figure out if he meant ae lock or something else but now i see in my manual if it's in 1 shot af and evaluation metering pressing the shutter 1/2 way locks the ae...which i thought pressing the shutter 1/2 did anyway...i must be missing something i mean other than brains

 

[DueyDooDah]

i couldn't figure out if he meant ae lock or something else but now i see in my manual if it's in 1 shot af and evaluation metering pressing the shutter 1/2 way locks the ae...which i thought pressing the shutter 1/2 did anyway...i must be missing something i mean other than brains

Yes, pressing the shutter halfway down locks both. But, if you need to refocus, such as during recomposition, then pressing the * button allows you to refocus without changing the metering. Although this is a great feature, it is one that takes practice. I am still coping with it. I am too foul-fingered, I guess.

 

[0bli0]

A handy feature. I have to do it the "cheap" way and do a half-press to get my focus, then flip the switch to manual focus to keep it there, and flip it back when I'm done.

do any of the Pentax AF lenses have full-time manual focus? it's nice not to have to worry about flicking the af/mf switch.

i occasionally use the * button for focus. i used to do it all of the time, but I seldom do any more - i prefer to use it for AE lock

 

[jann1033]

Yes, pressing the shutter halfway down locks both. But, if you need to refocus, such as during recomposition, then pressing the * button allows you to refocus without changing the metering. Although this is a great feature, it is one that takes practice. I am still coping with it. I am too foul-fingered, I guess.

ok now i get it

 

[Groucho]

do any of the Pentax AF lenses have full-time manual focus? it's nice not to have to worry about flicking the af/mf switch.

Most (all?) of their current digital lenses have what they call "quick-shift" focusing, which means that it'll focus when you do a half-press, then you can continue to focus manually before taking the shot. The kit 18-55mm and the 50-200mm are this way, which are the only digital lenses I have. The 50mm 1.4 locks the focus when in autofocus mode, and my other lenses are all manual-focus only... they can be used in autofocus mode but the camera won't fire the shutter unless it thinks that you're focused. It's easiest just to stay in manual focus mode, it'll still give a focus confirmation beep and visual conf. in the status bar in the viewfinder but you can fire the shutter whether it thinks you're focused or not.

The MF/AF switch is right on the side of the lens mount of the body so it's pretty easy, but I do find myself looking at it to remember which is which - which is pretty dumb on my part, as I'm pretty sure that it lights an "MF" in the viewfinder status bar, so I can just look for that... and you'd think that I could remember which one's "up" and which one's "down"! Alas, senility sometimes rears its ugly head even though I'm "only" in my mid-30s!

I'm going to be a real mess if/when I upgrade to a K10D - not only is there the rear focus button (which can also be switched to "disable AF" via custom menu), the MF/AF switch has settings for MF, AFS, and AFC... it'll definitely take me a while to get to where I can use all the buttons and such without trying to remember what they all do. I'm almost picturing the scene from 2001, with the apes before the monolith...