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

Reply
 
Thread Tools Search this Thread
Old Jan 7, 2005, 3:34 PM   #21
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,547
Default

geoffs

This is very strange...
Is the above picture a crop or full size?

What I've determined earlier on (at least on the 10D) is that the AF sensor is actually larger than the area etched on the viewfinder screen :O

-> What this means is area of high contrast (not the squirrel) that is outside of the etched area in the viewfinder can be picked up by the edge AF sensor (bark chip) and be in focus instead!
http://www.stevesforums.com/forums/v...m_id=37&page=2
NHL is offline   Reply With Quote
Old Jan 7, 2005, 5:51 PM   #22
Senior Member
 
geoffs's Avatar
 
Join Date: Jun 2004
Posts: 2,025
Default

NHL, thanks for looking in. The lens is going back regardless as I am not comfortable with it's performance. I was suspicious of it from the start when I first unpacked it because it appeared to me like it had been previously opened - not in a factory fresh condition. I had feared that I'd gotten someone else's returned item.

In any case, what you saw in my previous post was a 100% crop. Here's a few more showing the AF point in Canon's EVU utility. Could the focusing sensor really be so big as to cause it to misfocus in these instances given how much space there is around the AF sensor in the same plane in each image?

Pic #1 (the squirrel)...


Attached Images
 
geoffs is offline   Reply With Quote
Old Jan 7, 2005, 5:52 PM   #23
Senior Member
 
geoffs's Avatar
 
Join Date: Jun 2004
Posts: 2,025
Default

continuation of message above...

Pic #2 (stationary golfer - to me it looks like the cart behind him is more in focus than he is):


Attached Images
 
geoffs is offline   Reply With Quote
Old Jan 7, 2005, 6:10 PM   #24
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,547
Default

... Out of this two pictures, it seems like there's not enough contrast (in the AF area) for the CPU in the camera to work with -> IMO I would give it some help like on the stiching on the jeans for example (the 1st one may be due to low-light)

The camera might just give up on the focusing... was the green AF confirmation LED lit in the viewfinder?
NHL is offline   Reply With Quote
Old Jan 7, 2005, 6:16 PM   #25
Senior Member
 
geoffs's Avatar
 
Join Date: Jun 2004
Posts: 2,025
Default

Yeah, I agree that in the 2nd picture it would be easy to give the camera's af logic an assist by first focusing on the the jean stitching and then moving the camera to frame the shot.

But, although the contrast may be too low at the target in the first shot, I don't know how you'd get decent shots of such a subject unless you go to manual assisted AF - 1. you don't have much time to take the shot before the animal moves, 2. the animal is quite uniform in texture with no area presenting any more contrast than another.

The green led did light up in both case along with the accompanying "beep".

geoffs is offline   Reply With Quote
Old Jan 7, 2005, 6:24 PM   #26
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,547
Default

Yeap - that's the dilemma we all live in :?

In lens tests, the camera is mounted on a tripod with the subject fixed (with clear high contrast B/W test charts), but in real life it's not that simple hey?
... plus the lighting is real lousy and not helping at all
NHL is offline   Reply With Quote
Old Jan 7, 2005, 8:09 PM   #27
Senior Member
 
Join Date: Nov 2004
Posts: 276
Default

Geoffs - we have had and ice storm in Kansas and our power has been off all week. Just read your post and your right, I need a caddy for my lenses. I really overlooked that. LOL

I looked at you golfer pic and really does look soft and out of focus. The golf club heads [since I'm a golfer, I know these things] appear to be more in focus than the back of the golfer.

Hope you can get it worked out. Best wishes.:-)
Golfer is offline   Reply With Quote
Old Jan 7, 2005, 8:16 PM   #28
Senior Member
 
geoffs's Avatar
 
Join Date: Jun 2004
Posts: 2,025
Default

Golfer - it was actually peripatetic that mentioned you need a caddy, not me. It was a cute statement, though (and somewhat true).

I thought the golf clubs were sharper too, and the towel hanging down from them...
geoffs is offline   Reply With Quote
Old Jan 8, 2005, 12:27 AM   #29
Super Moderator
 
peripatetic's Avatar
 
Join Date: Nov 2004
Posts: 3,599
Default

Geoff - nice shots with the 300mm, I'm sure you're right about your copy of the 70-200; but as a general principle, on the squirrel shot, might it have helped to focus on the squirrel's edge? Focussing on the back of a fuzzy, dark, moving animal must be a nightmare for the focussing algorithm. Same with the golfer - would it have made it easier to focus on the point where his arm/torso "intersected" with the trolley or grass?

Not trying to teach granny to "oops" eggs here, just interested in the general principles of trying to get the best out of the autofocus.

Amusing aside: it seems the forum software doesn't like the normal expression and replaces the four letter common verb for "to create partial vacuum against an object using the mouth" with "oops". Actually I think the expression "Teach granny to oops eggs" is quite rude! :-)
peripatetic is offline   Reply With Quote
Old Jan 8, 2005, 1:13 AM   #30
Senior Member
 
geoffs's Avatar
 
Join Date: Jun 2004
Posts: 2,025
Default

Funny about the forum software filtering bad words. So it doesn't like suck eggs, hmm. Interesting because in the People gallery people are allowed to post nude photographs but the words themselves aren't acceptable...

In any case, you are probably correct about trying to help the AF mechanism along by trying to focus on an edge. My only concern about that is that, if as NHL says is true that the AF sensors are larger than the squares in the viewfinder indicate, wouldn't trying to get an edge of a subject increase the chances of the AF logic to "lock on" to an extraneous bg or fg object?

Also, if my technique were no different using the 300/4 with or without the 1.4x, and I can get nice in focus shots from that combination, why would I not be able to do the same using the 70-200? Something doesn't add up. I can get sharp shots using my 17-85, the 300/4, and the 300/4 with the 1.4x. I can't get even a small percentage of sharp shots using the 70-200 with or without the 1.4x. I just don't believe that it is me (although I did in the beginning).

The subjects in the pictures I posted are not easy AF targets, though, I'll grant you that.

geoffs 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 9:37 PM.