I was wondering if anyone can give me an insight into how Auto-Focus works.
My camera seems to have trouble focussing on bright objects especially if they are reflective. Is this a camera fault of something that happens?
An example is the image I posted to my gallery today. I wanted to focus on the large flower top right yet the camera seemed to have problems. I changed the focussing box/area so that it covered the flower in the frame yet results were dissappointing. In the end I hung a darker leaf over the flower the camera focussed, I locked that, removed leaf and took shot. With this image I am pleased with the focus I didn't want pin sharp because it was to represent a soft flower and spring. The problem has occured before with light reflective objects, I have had to resort to manual or focussing on something about same distance etc.
Your thoughts or ideas would be appreciated :)

Richard.

Message edited on: 01/22/2005 16:15 he he got the spelling right now I think

Message edited on: 01/22/2005 16:19

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html

Richard - AF works a number of different ways depending on the camera. They usually fall into one of two types ... active and passive.

Active is used by most point and shoots. What this means is the camera emits some kind signal that it then uses to figure out how far away the subject is. I think most of the active AF systems today use a pulsed IR beam. Sort of like radar. Send a pulse, recieve it back off the subject, figure out how long it took for the beam to return and you know how far the subject is from the camera. While that has its problems, the upside is they can focus in total darkness if need be.

Passive is what most DSLRs use. These systems read the image at the focus points and use edge contrast (difference between small light and dark areas)to figure out when the lens has focused correctly. That's why you can't get a DSLR to autofocus on something like an evenly colored wall. Its also why they stink at low light focusing and require AF assist lights.

-=>Donald

Message edited on: 01/22/2005 17:11

Thx Donald Just looked in spec. sheet for mine and it says - "TTL Auto focus ..........9 point (AiAf)/1 point (AF) (any position available)." It seems to emit some sort of beam of light I notice when the light is poor eg I went to zoo to try it out and I noticed a beam of light would come on (reflected in glass). Sounds to me like it maybe the second type even though it is a compact digi. This would explain why it has trouble focussing because what I am asking it to focus on is all the same colour within focus box. It works fine at other times just in macro where focus area is on something that is all same colour and lightness.

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html

I hate the way it ruins "candid" shots. A few times there has been "the perfect picture", but with low light, the flash goes off 5 or 6 times to give the lens enough light to focus, then finally it takes the picture. :) Rich

what kind of cam do you have, richard??? my first sony...(717)... they had a recall on it...some kind of problem with focusing. you don't happen to have this cam do you???

It is a Canon G6. Beginning to wish I had stuck with my old camera. This one has more than 3 times as many pixels and on paper should do everything better, but I am not up to the same level as the camera. With my old camera I never had a shot out of focus etc. was literaly point and shoot, whereas this one I thought I would be able to handle, but even in full auto I can't manage images anywhere near as good. Think I will take the old camera out for the day and have some fun.

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html

A friend has this camera. The G6 is a great point and shoot. But like many people who go from lower-end/older cameras (that includes P&S as well as DSLRs), you need to understand how to utilize the more advanced cameras.

Are you shooting macro or normal? If macro, are you switching into macro mode? When you are focusing, what does your camera indicate? If I remember correctly, the G6 gives you a steady green light next to the viewfinder on the back of the camera when focus locks. Also, the AF frame should turn green. If you are getting a locked indication before taking the photo and it's still coming up out of focus, then you have 1 of 3 problems I can think of:

1. You do not have the subject in the focus point. If the focus point locks on to something in front of or behind your subject, that's where the camera will focus.

2. You are changing focal length after you lock the focus or moving. That one would be obvious, some I'm doubting that you're doing that.

3. There is something wrong with your camera. You should contact Canon.

The G6 has one of the coolest AF focus points I've seen. You can move the AF box around the middle 2/3's or 3/4's of the screen to focus on what you want. Also, have you tried switching the camera into Manual Focus mode to see if you still have the same problem?

Thx Donald I think it is probably my fault. I did move the focus box to the point where I wanted the shot to be in focus. It does turn green if it manages to get a focus, or amber if it is having difficulties. I will have to set up a test for it to determine if there is a fault with the camera. But for now I am off out for the day, I will take it with me, probably not shooting any macros and hopefully get some straight forward shots out of it. Richard.

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html

A more successful day :) - of course I couldn't resisit shooting some macros, they came out and in focus so the camera is forgiven :)) Result is in my gallery no postwork only resized and bordered. Thx for the info Donald I do like to know how things work. I should read up more on it but there is always such a long list of things I want to read up on. I am convinced yesterdays problems (which had occured before) were due in part to the subject being difficult for the camera to focus on, and in part due to my ineptitude. Lifes a journey they say, we learn along the way. Richard.

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html

just commented...that was fantastic, Richard!!!!! sometimes we just have hard day, or like you said, some subjects are just a bit harder. You did grrrrreat!!!! oh...you were talking about spring in your gallery. It was 19 degrees when i went outside a couple of hours ago. it's supposed to be 50 degrees by Wed!!!! too bad i'll be inside all day... :(