Subject dist=66 ???

[cumi]

Hi!

I have a Canon Powershot A520. When I browsing my photos on PC I see quite often that the Subject distance is 66m, althought I made the photo in a room and the photos are IN FOCUS (sharp). I can upload some examples, when needed.

Is this because the camera couldn't set the focus or didn't find any subject to focus on?

Or can it be that this heappens, when I press the shutter halfways (to set the focus and light) and then recompose and press it all the way. Actually I am sure, that this can not be the only reason, because I can remember what did I do exaclty on some photos.

Thanks for help,
cumi

 

[Rob]

Hi cumi,

I would suspect that 66m or 100ft ish is your camera's lens infinity distance. If you are shooting at a high f-number then the camera can focus for a considerable range of distances. It is likely that a subject more than 10ft (3m ish) away from you could be within sharp focus even though the camera is focussed on "infinity".

If the pictures are coming out fine, then there isn't much to worry about. Why not post some for us to have a look?

Rob

 

[cumi]

These are with 66m subj. dist.(infinite):

 

[cumi]

The first photo:

File: IMG_0668.JPG
File size: 747KB
Image Serial Number: 106-0668
Camera Model: Canon PowerShot A520
Firmware: Firmware Version 1.00
Date/Time: 2005:10:01 16:40:21
Shutter speed: 1/60 sec
Aperture: 3,2
Exposure mode: Program
Flash: Built-in + Red eye reduction
Flash EF guide number: 9,00
Metering mode: Spot
Drive mode: Single frame shooting
ISO: Auto
Lens: 5,8 to 23,2mm
Focal length: 9,8mm
Subject distance: 66 m
AF mode: Single AF
Image size: 2272 x 1704
Rotation: none
Image quality: Fine
White balance: Auto
Picture Effect: Normal

The second:

File: IMG_0673.JPG
File size: 802KB
Image Serial Number: 106-0673
Camera Model: Canon PowerShot A520
Firmware: Firmware Version 1.00
Date/Time: 2005:10:01 18:11:48
Shutter speed: 1/60 sec
Aperture: 2,6
Exposure mode: Program
Flash: Built-in + Red eye reduction
Flash EF guide number: 7,06
Metering mode: Spot
Drive mode: Single frame shooting
ISO: Auto
Lens: 5,8 to 23,2mm
Focal length: 5,8mm
Subject distance: 66 m
AF mode: Single AF
Image size: 2272 x 1704
Rotation: none
Image quality: Fine
White balance: Auto
Picture Effect: Normal


I had to compress the photos before uploading...

 

[Rob]

Well from how it looks here, the focus is fairly soft on the top one and possibly a little soft on the bottom one.

The bottom one is more revealing as it looks like your focus and metering point is that wall visible outside the window. Personally I'd say that that outside bit was what the camera latched on to and metered and focussed to.

Your lens is pretty short, so it's going to give you quite a good DOF even at infinity. Can you try doing an AF lock on a centred object say five feet away during daylight and see if it still says 66m?

I've just realised that 66m is over 200ft, not 100 as I said earlier! Not enough coffee ingested me thinks.

Rob

 

[cumi]

Can you try doing an AF lock on a centred object say five feet away during daylight and see if it still says 66m?

I allready tried this. Interresting thing is, that the manual says, that if the camera can not find a focus (a subject) the AF bracket will be yellow (signaling the problem and the possible consequences). Having a subject, that can not be focused, I have to use AF-lock. But this "infinite" subject distance appears even then sometimes. Can it be a Canon Firmware bug?

BTW, on the second photo, I was metering the light (and probably used AF-lock) on my wife. I have another photo, where I did so with the wall behind, but then my wife and son are terribly overexponated, because of the flash... Here the wall behind is underexponated, but I had no other joice...

 

[Rob]

Well I think you've probably answered your own question! It could be a firmware focussing bug, or equally it's possible that the bit which reports the focal distance just doesn't work properly (and the camera is fine otherwise).

Unless anyone else has any bright ideas?

Rob