Go Back   Steve's Digicams Forums > Digital SLR and Interchangeable Lens Cameras > Canon EOS dSLR

Reply
 
Thread Tools Search this Thread
Old Oct 21, 2005, 6:28 AM   #21
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,547
Default

Why don't you guys open the picture with the Canon software and post a screenshot of where the camera thinks where the AF point is. :idea:

Together with the Exif a lot of issues can be explained
NHL is offline   Reply With Quote
Old Oct 21, 2005, 7:02 AM   #22
Member
 
Join Date: Jan 2005
Posts: 95
Default

NHL wrote:
Quote:
Why don't you guys open the picture with the Canon software and post a screenshot of where the camera thinks where the AF point is. :idea:

Together with the Exif a lot of issues can be explained
Hi NHL!

THis is one of my shots (that is back focussed somehow).
350D
RAW
F4.0
1/2000
ISO 200
AWB
Focal Length: 300mm
Attached Images
 
Timberland is offline   Reply With Quote
Old Oct 21, 2005, 7:11 AM   #23
Member
 
Join Date: Jan 2005
Posts: 95
Default

Another one:

350D
RAW
F4.0
1/2000
ISO 200
AWB
Focal Length: 300mm
Attached Images
 
Timberland is offline   Reply With Quote
Old Oct 21, 2005, 8:59 AM   #24
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,547
Default

Are they all in AI mode? :idea:

This will explain a lot... Also are theses the 1st shot in the sequence (or one of the subsequent ones)?
NHL is offline   Reply With Quote
Old Oct 21, 2005, 1:13 PM   #25
Senior Member
 
bobbyz's Avatar
 
Join Date: Feb 2004
Posts: 1,423
Default

In the 2nd shot, it seems the focus is on the person behind the player. Atleast his face and kid's face looka lot more in focus than the palyer. I would suggest shooting some player where the bg is clear.

And remember using AI servo mode, you have to aqquire, track and shoot.
bobbyz is offline   Reply With Quote
Old Oct 22, 2005, 8:29 AM   #26
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,547
Default

The 2nd shot is hard to tell since the AF point straddled two areas - IMO the * button does not change the AF mode in anyway, but involves more dexterity from the photographer part... Personally I prefer to use one finger instead of finger + thumb (I use this feature sometime to alter the exposure away from the subject)

As to the AF modes this is an area where opinions diverge and it's more a matter of shooting style: Some folks prefers to time their shots and get it right on the 1st try. Others 'machine-gun' the whole thing and pick out the best - There's no right and wrong, whichever work best! :-)


There are some differences (you do the work vs the camera do the work for you):

o The single shot AF is deterministic: i.e. the camera won't release the shutter unless 'something' (it may not be your subject, but something always) is in focus which is confirmed by the red AF indicator and the green dot on the bottom of the viewfinder this is sometime referred as focus priority because the shutter won't release otherwise.

o The AI Servo mode on the other hand is based on estimate: the camera analyzes the speed and direction and then will focus the lens to a predicted position instead - Another factor according to Canon is that the very 1st shot is based on shutter priority instead which means the shutter can release even before focus is achieved: "Specifically, in a continuous AI Servo AF sequence, the first exposure is always handled as ‘release priority,' while subsequent exposures in that sequence are handled with ‘focus priority' according to Canon's definition of that term" FYI - http://photonotes.org/other/ai-servo.html

You can read the rest of the article, and see how the Canon's algorithm work to get you highest probability of a good shot, but there's some limit to the system - I found this one to be rather interesting regarding speed as well: "For USM lenses, the time limit has been set at 200 milliseconds (1/5 second). For non-USM lenses, the time limit is 250 milliseconds (1/4 second). If the subject requires more focusing time than the preset limit, the exposure is taken anyway at a focusing position that is as accurate as possible. However, this type of exposure will be out of focus towards the infinity direction."
Does this means subject speed only? Or subject speed + camera shake on a long tele which could mean a lot of displacement? :shock:

NHL is offline   Reply With Quote
Old Oct 25, 2005, 2:35 AM   #27
Member
 
Join Date: Jan 2005
Posts: 95
Default

NHL wrote:
Quote:
Are they all in AI mode? :idea:

This will explain a lot... Also are theses the 1st shot in the sequence (or one of the subsequent ones)?
Sorry, for the late reply.They were all shot in AI-Servo mode.

I usually shot about 3 photos of an action. But all 3 were out of focus.
Timberland is offline   Reply With Quote
Old Oct 25, 2005, 7:28 AM   #28
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,547
Default

Timberland wrote:
Quote:
Sorry, for the late reply.They were all shot in AI-Servo mode.

I usually shot about 3 photos of an action. But all 3 were out of focus.
Exactly my point!

Print out this ISO-12333 chart - Don't even use AI, but use the single shot AF only and see if the AF can lock on @ various zoom setting and distances in the static position - I've been testing my EF 100-400 L f/4-5.6 IS USM against my Sigma 120-300 f/2.8 EX and was shocked by how effective the high-precision AF sensor of the camera work @ f/2.8...

If your test is positive it'll confirm mine as well that the AF will not lock at F/4 (at least with this chart) in the single AF mode at various distances and zoom settings - Guess what if the camera do not lock AF in the single-shot mode:
1 - In AI mode the camera will fire anyway because the 1st shot is in shutter priority regardless of the focus
2 - Subsequent shots are limited by the AF time (200/250ms) and not by the subject movement which you can alter by panning (and hence reduce their relative speed) - This is where it get tricky because the AF time also depends on the lighting (see the link previous):"If the subject requires more focusing time than the preset limit, the exposure is taken anyway at a focusing position that is as accurate as possible. However, this type of exposure will be out of focus towards the infinity direction."

The best way to verify this is to lock yourself in a dark closet with the camera in AI-servo mode and fire away - Is there any picture in focus?
In single-shot AF the camera just won't fire... unless the AF has locked :idea:


-> BTW folks with the 70-200 f/2.8 (or f/4) can also verify my findings with the above ISO-12233 chart
NHL is offline   Reply With Quote
Old Nov 1, 2005, 8:32 AM   #29
Member
 
Join Date: Jan 2005
Posts: 95
Default

NHL wrote:
Quote:
Timberland wrote:
Quote:
Sorry, for the late reply.They were all shot in AI-Servo mode.

I usually shot about 3 photos of an action. But all 3 were out of focus.
Exactly my point!

Print out this ISO-12333 chart - Don't even use AI, but use the single shot AF only and see if the AF can lock on @ various zoom setting and distances in the static position - I've been testing my EF 100-400 L f/4-5.6 IS USM against my Sigma 120-300 f/2.8 EX and was shocked by how effective the high-precision AF sensor of the camera work @ f/2.8...

If your test is positive it'll confirm mine as well that the AF will not lock at F/4 (at least with this chart) in the single AF mode at various distances and zoom settings - Guess what if the camera do not lock AF in the single-shot mode:
1 - In AI mode the camera will fire anyway because the 1st shot is in shutter priority regardless of the focus
2 - Subsequent shots are limited by the AF time (200/250ms) and not by the subject movement which you can alter by panning (and hence reduce their relative speed) - This is where it get tricky because the AF time also depends on the lighting (see the link previous):"If the subject requires more focusing time than the preset limit, the exposure is taken anyway at a focusing position that is as accurate as possible. However, this type of exposure will be out of focus towards the infinity direction."

The best way to verify this is to lock yourself in a dark closet with the camera in AI-servo mode and fire away - Is there any picture in focus?
In single-shot AF the camera just won't fire... unless the AF has locked :idea:


-> BTW folks with the 70-200 f/2.8 (or f/4) can also verify my findings with the above ISO-12233 chart
Once again, sorry for the late reply NHL!

I've (finally) printed the chart and did the test.

There is absolutely no problem at all focussing at F4 (used the singleshot mode), the focus lock is always (at all focal lenghts) spot on. The HSM AF of the Sigma is seriously fast (and accurate)!

In fact I tried to shoot soccer again (using AI servo and single shot mode) last week and got lots of sharp photos (75-80%). So I just have to practice a lot more :lol:.
Timberland is offline   Reply With Quote
Old Nov 1, 2005, 8:38 AM   #30
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,547
Default

Excellent!
NHL is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 7:11 PM.