Camera Not Focussing In Certain Conditions?

[Kirislin]

I dont know if there is something wrong with my camera or is it just the way I am using it. Yesterday afternoon I was playing/experimenting with my Canon taking pics inside in fairly dim conditions (cloudy outside and about 5.50pm) I increased the ISO to 1600 and took some pics of Feather. Although there appears to be enough light to me the camera couldn't focus, it kept searching for the focus, it would go back and forth, I'd see Feather in focus for a moment but the camera went past it several times and eventually fired off completely out of focus. this happened a few times, the only way I got the pic here was by flicking the lens onto manual and focussing it myself, the camera just couldn't do it. so is it me expecting too much or is the camera dodgy and do I need to get it seen to?

[Gayle.]

The camera needs something to lock focus onto and if it can't find what it needs it "hunts" for something, hence the whirring back and forth motion of the lens. In dim light, manual focus is sometimes the best thing to do. It doesn't sound like there's anything wrong with your camera or lens.....it just couldn't find something to lock onto. Better quality lenses have the problem less than cheaper lenses. The Canon 50mm f1.8 lens is a bit of a shocker for focus lock.

The camera will almost always choose an area of strong patterning or contrast, if it's left to it's own devices. And in the pic you've got there, the area of dead sharp focus is in the lower left corner where the white line contrasts with the background.

[Kirislin]

The camera needs something to lock focus onto and if it can't find what it needs it "hunts" for something, hence the whirring back and forth motion of the lens. In dim light, manual focus is sometimes the best thing to do. It doesn't sound like there's anything wrong with your camera or lens.....it just couldn't find something to lock onto. Better quality lenses have the problem less than cheaper lenses. The Canon 50mm f1.8 lens is a bit of a shocker for focus lock.

The camera will almost always choose an area of strong patterning or contrast, if it's left to it's own devices. And in the pic you've got there, the area of dead sharp focus is in the lower left corner where the white line contrasts with the background.

actually this pic was manually focussed by me so it looks like even I couldn't get it exactly right.

[Ashanali]

Manual focus - it will focus wherever you leave it, so if you are slightly out, then obviously this is the result you get.

Auto focus - the lens likes to focus on horizontal lines. I can't remember the reason why (I used to know ) but if your camera is struggling in low light you need to either, add light from another source (torch, lamp, video light etc) or find a contrasting horizontal line to focus on.

[chezzyr]

Darned 'hunting' lenses. It happens with me occasionally, usually when I have a great

flying bird shot in sight

I am not thinking your camera or lenses are dodgy as youve posted some

nice images. You do need to make allowances for less than ideal conditions etc.

You will learn to work around certain things.

edited for spelling!

Edited November 27, 2008 by chezzyr

[Kirislin]

Darned 'hunting' lenses. It happens with me occasionally, usually when I have a great

flying bird shot in sight

I am not thinking your camera or lenses are dodgy as youve posted some

nice images. You do need to make allowances for less than idea conditions etc.

You will learn to work around certain things.

thanks for your advice and explanations everyone.

Yep Chezzyr, I suppose I sort of did work around it by flicking manual focus, even though my eyes aren't the best and I didn't get it exactly right. It's all a learning experience.

[BlenheimBoy]

The camera needs something to lock focus onto and if it can't find what it needs it "hunts" for something, hence the whirring back and forth motion of the lens. In dim light, manual focus is sometimes the best thing to do. It doesn't sound like there's anything wrong with your camera or lens.....it just couldn't find something to lock onto. Better quality lenses have the problem less than cheaper lenses. The Canon 50mm f1.8 lens is a bit of a shocker for focus lock.

The camera will almost always choose an area of strong patterning or contrast, if it's left to it's own devices. And in the pic you've got there, the area of dead sharp focus is in the lower left corner where the white line contrasts with the background.

actually this pic was manually focussed by me so it looks like even I couldn't get it exactly right.

The exif for that shot says 1/6 sec exposure - so my guess is that the 'unsharpness' is camera shake.

ETA:

Exif Sub IFD

* Exposure Time (1 / Shutter Speed) = 1/6 second = 0.16667 second

* Lens F-Number/F-Stop = 56/10 = F5.6

* ISO Speed Ratings = 1600

* Exif Version = 0221

* Original Date/Time = 2008:11:27 17:52:40

* Digitization Date/Time = 2008:11:27 17:52:40

* Components Configuration = 0x01,0x02,0x03,0x00 / YCbCr

* Shutter Speed Value (APEX) = 169408/65536

Shutter Speed (Exposure Time) = 1/6 second

* Aperture Value (APEX) = 325770/65536

Aperture = F5.6

* Exposure Bias (EV) = 0/3 = 0

* Flash = Flash did not fire, compulsory flash mode

* Focal Length = 55/1 mm = 55 mm

Edited November 28, 2008 by BlenheimBoy

[Kirislin]

Possibly, but that wasn't my concern here as much as the fact the camera couldn't find the focus, it kept searching back and forth and then fired off a shot when it was completely out of focus. I dont mean this particular photo, this one I manually focussed. I deleted all the other ones.

[BlenheimBoy]

Possibly, but that wasn't my concern here as much as the fact the camera couldn't find the focus, it kept searching back and forth and then fired off a shot when it was completely out of focus. I dont mean this particular photo, this one I manually focussed. I deleted all the other ones.

Krislin, I understood that perfectly.

As has been suggested, lenses will hunt for focus in low light. Maybe my point wasn't clear.

You stated:

...

actually this pic was manually focussed by me so it looks like even I couldn't get it exactly right.

The inference (I get) from your reply is that you feel you messed up the shot due to your (manual) focusing.

The 'unsharpness' in your shot is not due to focus error, in fact I'd suggest that you've nailed the focus perfectly. Your shot is the way it is due to camera shake from a slow shutter speed.

Michael

[chezzyr]

.

Edited November 28, 2008 by chezzyr

[Gayle.]

The shots actually pretty good for manual focus in low light AND a slow shutter speed. I'd be proud of a photo like that. You ought to see MY manual focus......by the time I'm done, you can barely make out the shapes! LOL!

I noticed the difference in auto focus once I switched from the cheap kit lenses to better ultrasonic and L lenses.

[Kirislin]

thanks BlenheimBoy, yep I might have missed your point initially. I understand I would do better if I had a tripod or at least a stable surface, my tripod was me sitting on the floor resting my arms on my knees .

and thankyou GayleK, Ashanali and Chezzyr for explaining about the focus probs in low light, I am relieved my camera isn't faulty.

[Tokkie]

I bit OT, Kirislin thanks for asking all the questions, I am following every one of your topics and I'm learning a lot.

[Kirislin]

I bit OT, Kirislin thanks for asking all the questions, I am following every one of your topics and I'm learning a lot.

come on now, surely you've got some questions to ask yourself, I might learn something from yours, and then you can look like the dummy!

Edited November 28, 2008 by Kirislin

[Vickie]

I agree, given the shutter speed, I think you did a great shot of holding it so still... my hand is nowhere near that steady.

Your manual focus looks good to me as well.

I spent all day yesterday taking product shots. I had a few shots where the camera struggled for focus with some of the darker products and ended up either finding some lines or switching to manual. Another thing I do quite a lot is to lock the focus the camera on the point you want & then frame your shot.

Sometimes your lense will also zoom in & out when you are too close to the subject for that lense.

[Luke W]

Manual focus - it will focus wherever you leave it, so if you are slightly out, then obviously this is the result you get.

Auto focus - the lens likes to focus on horizontal lines. I can't remember the reason why (I used to know ) but if your camera is struggling in low light you need to either, add light from another source (torch, lamp, video light etc) or find a contrasting horizontal line to focus on.

There's some very interesting information about the Canon autofocus system here:

http://night-ray.blogspot.com/2006/09/cano...nformation.html

As for the comment about horizontal lines, it depends on which focus point you are using... Some focus points recognise horizontal lines, others vertical. The center focus point recognizes both.

Here's an image of the 40D viewfinder:

The center focus point recognizes both vertical and horizontal lines for focusing.

The top and bottom focus points: vertical lines only.

The others: horizontal lines only.

[Ashanali]

Manual focus - it will focus wherever you leave it, so if you are slightly out, then obviously this is the result you get.

Auto focus - the lens likes to focus on horizontal lines. I can't remember the reason why (I used to know ) but if your camera is struggling in low light you need to either, add light from another source (torch, lamp, video light etc) or find a contrasting horizontal line to focus on.

There's some very interesting information about the Canon autofocus system here:

http://night-ray.blogspot.com/2006/09/cano...nformation.html

As for the comment about horizontal lines, it depends on which focus point you are using... Some focus points recognise horizontal lines, others vertical. The center focus point recognizes both.

Here's an image of the 40D viewfinder:

The center focus point recognizes both vertical and horizontal lines for focusing.

The top and bottom focus points: vertical lines only.

The others: horizontal lines only.

Thanks for that Luke. It was ages ago when I was given the info so I couldn't remember it clearly.

[Ripley]

I missed a shot of a squirrel in London because even my L lens couldn't focus in the low early evening light as it's only an f/4. So I had to switch to manual and increase the ISO which is always a bit dodge for me due to my eyesight!