Question about focus confirmation while manual focusing

[fetching]

I have the 350XT and I do a lot of night photography where it's too dark to auto focus. So I manual focus and sometimes will get a beep and light showing that I have achieved focus. But alot of times I don't and I have no clue if I am focused or not. I am wondering why it seems to work sporadically or if there is some reason for it doing this. And if I can't get this feature to work regularly, how do I assure that I have focus?

[tim]

I think you have to have the shutter half pressed, and maybe it's possible it's too dark for the camera to realise things are or aren't in focus?

[fetching]

I think you have to have the shutter half pressed, and maybe it's possible it's too dark for the camera to realise things are or aren't in focus?

yes, i do press halfway on the shutter button, and as for the low light, that's the point of manually focusing. Tonight I was focusing on a building bathed in light and got nothing, but an hour early I was shooting across San Francisco Bay at the skyline and got beeps. The skyline was actually much darker than the building, and further away.

[randalcandari]

AF seems to have problems focusing on flat surfaces, even if there's enough light. try pointing you're AF point to something the camera can use to test if its in-focus, like window edges or a rough wall. I think, XT focuses by comparing light instead of measuring distances.

[GeForceFX]

I think, XT focuses by comparing light instead of measuring distances.


idd, all (d)slr's with AF do


read this: http://electronics.howstuffworks.com/autofocus3.htm

[DocFrankenstein]

I find focusing with those small screens and pentamirrors is a good way to frustrate yourself and lose your vision.

If you're in a dimly light room, you can use a laser to focus. Locks instantly...

Or you could use some EX flash with AF assist beam... that beam is invisible AFAIK

[fetching]

AF seems to have problems focusing on flat surfaces, even if there's enough light. try pointing you're AF point to something the camera can use to test if its in-focus, like window edges or a rough wall. I think, XT focuses by comparing light instead of measuring distances.


but i'm not using AF in this case.

[Jackal]

Or you could use some EX flash with AF assist beam... that beam is invisible AFAIK

If I'm doing night shots I use the 420ex for it's focus beam.

Isn't the assist beam that red pattern it shines? If so it's visible :p

[randalcandari]

but i'm not using AF in this case.

AF or MF, XT would still check if its in-focus. so if you're doing manual focus, point to something that xt can use as a reference. if XT thinks the image is in-focus, you'll see the red dot and the camera will beep (if beep is on) whether AF or MF. but if you place the AF point on a smooth (especially white) surface, you'll not see any focus confirmations even though everything on the viewfinder is perfectly in focus.:D

[chris maddock]

but i'm not using AF in this case.

But it's still the AF system that is trying to tell you if you have focus or not.
Whether or not it's moving the lens, the same system is measuring the contrast.

KRs
Chris