03-16-2011, 02:45 PM
(This post was last modified: 03-16-2011, 02:47 PM by Brightcolours.)
As promised, I made a few sequences of cars moving at around 50 km/h, trying to stay as close as possible to what imaging resource in their review of the Sony A55v described they did to test AF tracking.
Their description:
Sony A55v with Sony 70-200mm f2.8 G SSM lens, one of Sony's top lenses.
Focal length used: 150mm
Shooting distance: "perhaps" 70 feet (about 21 meters) to "perhaps" 15 feet (about 5 meters).
Subject: A car traveling about 30 mp/h (about 50 km/h) towards the camera.
What I did:
Canon EOS 450D with Canon 70-200mm f4 L USM. Not the Canon 70-200mm f2.8 L IS USM II, as it is the cheap f4 lens that I own. I do realize that the f2.8 lens focusses faster AND that it offers the f2.8 advantage to the AF sensor, but it is all I have available to me <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/tongue.gif' class='bbc_emoticon' alt='
' />.
Focal length used: 145mm (lens only has 70/100/135/200mm markings, I ended up actually using 145mm.. no big deal, as the crop factor of the cameras is a bit different anyway, and 145mm is pretty close to 150mm.
Shooting distance: starting at 20 meters.
Subject: cars traveling at about 50 km/h towards the camera.
The IR crops can be found on this page:
http://www.imaging-resource.com/PRODS/AA55/AA55A.HTM
Crops specifically:
http://www.imaging-resource.com/PRODS/AA55/zA55focustrack.jpg
Here are my results (also 100% crops):
![[Image: gallery_10230_63_4253.jpg]](http://forum.photozone.de/uploads/1294181849/gallery_10230_63_4253.jpg)
What we notice right away is that my crops are bigger, and the car logo's are bigger too. The Sony has a higher resolution (14mp versus 12mp), so the only conclusion can be that they shot the car from further away than they suggest in their texts. Advantage for the Sony: car further away means less taxing job for the AF.
What we notice about the IR crops:
first 4 are "green", pointing to back focus. Last 4 are purple, pointing to front focus. 5th, middle crop appears to be best in focus.
My crops:
Lexus BMW-3 series clone.
1st back focus.
2nd in focus.
3rd in focus.
VW fox
1st: back focus.
2nd: in focus.
3rd: back focus.
Audi A4:
1st: in focus.
2nd: back focus.
3rd: in focus.
The A55v does 10fps, the 450D a bit over 3 fps. So, a series of 3 with the 450D is within the same duration of the 9 crops from the A55v.
When I compare the crops, to me it looks like the 450D does at least equally as good, even though the light conditions were a lot less bright, the lens only was an f4 lens, and the shooting distance was closer.
This all the more points to that the IR phrase "We shot side by side with the Sony A55 and a Canon 7D, and felt that the A55's AF performance here was pretty similar to that of the much more expensive Canon." should make one a bit skeptical, especially since people who have gone from a 450D or alike to a 7D to comment on the superior AF tracking abilities of the 7D.
My conclusion: The IR "claim" should not be used as evidence of the AF tracking of the A33 and A55v. The crops provided for sure are not impressive.
Their description:
Sony A55v with Sony 70-200mm f2.8 G SSM lens, one of Sony's top lenses.
Focal length used: 150mm
Shooting distance: "perhaps" 70 feet (about 21 meters) to "perhaps" 15 feet (about 5 meters).
Subject: A car traveling about 30 mp/h (about 50 km/h) towards the camera.
What I did:
Canon EOS 450D with Canon 70-200mm f4 L USM. Not the Canon 70-200mm f2.8 L IS USM II, as it is the cheap f4 lens that I own. I do realize that the f2.8 lens focusses faster AND that it offers the f2.8 advantage to the AF sensor, but it is all I have available to me <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/tongue.gif' class='bbc_emoticon' alt='
' />.Focal length used: 145mm (lens only has 70/100/135/200mm markings, I ended up actually using 145mm.. no big deal, as the crop factor of the cameras is a bit different anyway, and 145mm is pretty close to 150mm.
Shooting distance: starting at 20 meters.
Subject: cars traveling at about 50 km/h towards the camera.
The IR crops can be found on this page:
http://www.imaging-resource.com/PRODS/AA55/AA55A.HTM
Crops specifically:
http://www.imaging-resource.com/PRODS/AA55/zA55focustrack.jpg
Here are my results (also 100% crops):
What we notice right away is that my crops are bigger, and the car logo's are bigger too. The Sony has a higher resolution (14mp versus 12mp), so the only conclusion can be that they shot the car from further away than they suggest in their texts. Advantage for the Sony: car further away means less taxing job for the AF.
What we notice about the IR crops:
first 4 are "green", pointing to back focus. Last 4 are purple, pointing to front focus. 5th, middle crop appears to be best in focus.
My crops:
Lexus BMW-3 series clone.
1st back focus.
2nd in focus.
3rd in focus.
VW fox
1st: back focus.
2nd: in focus.
3rd: back focus.
Audi A4:
1st: in focus.
2nd: back focus.
3rd: in focus.
The A55v does 10fps, the 450D a bit over 3 fps. So, a series of 3 with the 450D is within the same duration of the 9 crops from the A55v.
When I compare the crops, to me it looks like the 450D does at least equally as good, even though the light conditions were a lot less bright, the lens only was an f4 lens, and the shooting distance was closer.
This all the more points to that the IR phrase "We shot side by side with the Sony A55 and a Canon 7D, and felt that the A55's AF performance here was pretty similar to that of the much more expensive Canon." should make one a bit skeptical, especially since people who have gone from a 450D or alike to a 7D to comment on the superior AF tracking abilities of the 7D.
My conclusion: The IR "claim" should not be used as evidence of the AF tracking of the A33 and A55v. The crops provided for sure are not impressive.