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Archive 2012Fine tune needed when using outer focus points: field curvature?
p.1 #1Fine tune needed when using outer focus points: field curvature?
I've had the sigma 85mm a while and shooting portraits (using outer af points) with shallow dof recently I've been convinced it has been back focusing but I tested the af again and again and found every time that no fine tune was needed. Today I decided to test the outer af points rather than the centre one and I have found I need -17 fine tune to get the focus dead on and this is exactly the same on both sides.
I don't know much about the workings of phase detect autofocus but is field curvature the issue? Ie. the af is fine but the actual focal plane of the lens is curved? Maybe even a small amount may be enough to send the af 17 points out. Rather ironically this may mean centre point and focus/recompose might be more accurate than moving the af point in this case.
I don't know much about the workings of phase detect autofocus but is field curvature the issue? Ie. the af is fine but the actual focal plane of the lens is curved? Maybe even a small amount may be enough to send the af 17 points out. Rather ironically this may mean centre point and focus/recompose might be more accurate than moving the af point in this case.
Jan 09, 2012 at 03:03 PM
p.1 #2Fine tune needed when using outer focus points: field curvature?
I have a problem with my sigma 24-70 as well. Always misses focus. Would sending it to sigma fix it?
Jan 09, 2012 at 05:47 PM
p.1 #3Fine tune needed when using outer focus points: field curvature?
I had this issue with my d700, posted about it, nobody believed me 
for me, every lens has 5-10 ma steps difference between the center and outer points.
The issue with the sigma 85mm, more than any field curvature, is how big each step is.
Atleast that is my current theory.
for me, every lens has 5-10 ma steps difference between the center and outer points.
The issue with the sigma 85mm, more than any field curvature, is how big each step is.
Atleast that is my current theory.
Jan 09, 2012 at 08:08 PM
p.1 #4Fine tune needed when using outer focus points: field curvature?
I have a very similar issue but with my Nikon lenses using the outer focus points on the D700. The farther out I go, the more back focused the shot.
Jan 09, 2012 at 08:44 PM
p.1 #5Fine tune needed when using outer focus points: field curvature?
I believe everyone is dealing with multiple issues.
3. Non cross type senors on the edge combined with field curvature, softness on the outer part of the lens, and aspherical aberitions. I have also noticed that shooting indoors under fluorescent bulbs can cause focus issues.
3. Non cross type senors on the edge combined with field curvature, softness on the outer part of the lens, and aspherical aberitions. I have also noticed that shooting indoors under fluorescent bulbs can cause focus issues.
Jan 09, 2012 at 10:32 PM
p.1 #6Fine tune needed when using outer focus points: field curvature?
rbromfield wrote:
I have a very similar issue but with my Nikon lenses using the outer focus points on the D700. The farther out I go, the more back focused the shot.
have you seen this with any other nikons? I am new to the nikon camp, but have only seen this with one copy of a d700. The d7000 checks out just fine.
Bruce Sawle wrote:
I believe everyone is dealing with multiple issues.
3. Non cross type senors on the edge combined with field curvature, softness on the outer part of the lens, and aspherical aberitions. I have also noticed that shooting indoors under fluorescent bulbs can cause focus issues.
Non issue with the same lenses on canon, non issue with a d7000 (sensor size makes this comparison difficult, I know)
I have a very similar issue but with my Nikon lenses using the outer focus points on the D700. The farther out I go, the more back focused the shot.
have you seen this with any other nikons? I am new to the nikon camp, but have only seen this with one copy of a d700. The d7000 checks out just fine.
Bruce Sawle wrote:
I believe everyone is dealing with multiple issues.
3. Non cross type senors on the edge combined with field curvature, softness on the outer part of the lens, and aspherical aberitions. I have also noticed that shooting indoors under fluorescent bulbs can cause focus issues.
Non issue with the same lenses on canon, non issue with a d7000 (sensor size makes this comparison difficult, I know)
Jan 10, 2012 at 12:21 AM
p.1 #7Fine tune needed when using outer focus points: field curvature?
Bruce Sawle wrote:
I believe everyone is dealing with multiple issues.
3. Non cross type senors on the edge combined with field curvature, softness on the outer part of the lens, and aspherical aberitions. I have also noticed that shooting indoors under fluorescent bulbs can cause focus issues.
This is quite possible, there are a lot of variables. In my case I am very confident in the finding: the outer focus points are only about half the way out from the centre point and lens performance even wide open is still very good here, every time -17 brings it in, it's perfectly repeatable on both sides.
I'm going to try my 50mm and 70-200 and see what the results are. It could be the camera for all I know.
I believe everyone is dealing with multiple issues.
3. Non cross type senors on the edge combined with field curvature, softness on the outer part of the lens, and aspherical aberitions. I have also noticed that shooting indoors under fluorescent bulbs can cause focus issues.
This is quite possible, there are a lot of variables. In my case I am very confident in the finding: the outer focus points are only about half the way out from the centre point and lens performance even wide open is still very good here, every time -17 brings it in, it's perfectly repeatable on both sides.
I'm going to try my 50mm and 70-200 and see what the results are. It could be the camera for all I know.
Jan 10, 2012 at 06:46 AM
p.1 #8Fine tune needed when using outer focus points: field curvature?
Update, cannot see this on my 50 or 70-200. Here are some pics (target is a magazine page) each shot was done 10 times ensuring focus variation was not playing a part:
Outer 0
Outer -17
Centre 0
Centre -17
Outer 0
Outer -17
Centre 0
Centre -17
Jan 12, 2012 at 10:02 AM