innaccurate focus

[tmonatr]

I have a 30D with a Sigma 17-70 2.8-4.5 lens. I love this camera and the lens is very sharp. But, when taking extreme close-ups(manual focus) what is sharp through the viewfinder is not what is sharp in the final image. This is very noticable at large aperatures. The point of focus seems to shift back in the photo slightly. Is this a lens or camera issue?:confused:

[racketman]

I have a 30D with a Sigma 17-70 2.8-4.5 lens. I love this camera and the lens is very sharp. But, when taking extreme close-ups(manual focus) what is sharp through the viewfinder is not what is sharp in the final image. This is very noticable at large aperatures. The point of focus seems to shift back in the photo slightly. Is this a lens or camera issue?:confused:


One would normally be using smaller apertures for macro due to the narrow DOF. If the images are consisitently back focused I would try a test to see if you have a back focusing lens or camera.
Place 3 similar objects on a table in a line with the first slightly in front of the middle one and the third slightly behind the middle. Using a tripod take a few shots at wide aperture and focused on the middle object. If the third object is consistently the sharpest something is amiss (make sure centre point focus is selected if using AF). Try another lens and if the results are the same get Canon to recalibrate the body. They did mine in 4 days and a front focusing problem with a new 350D (first object was always the sharpest) was fixed foc - work sheet shows they replaced a part. Prior to that none of my photos seemed to be really sharp but you say your non macro work has no problems so that may point to someting else :confused:

[tmonatr]

Thank you. I will try that.

[Mstar]

You could try the following:

1) Get your eyes tested- you just never know. We had a member of staff and we checked his general eyesight- he was amazed to learn he needed glasses.

2) I just changed my focus screen to a split screen- Now I know what the camera is actually focusing on as opposed to what it is not focusing on.

3) Give up drinking.

The above answer to mine seems a good test. Should give it a go myself.

Mark

[ron chappel]

Be carefull using the 'three objects' test.It can be very dodgey !
This is because the actual focus sensors are far larger than the brackets in the viewfinder ....it's easy for the camera to accidentally focus on the wrong object

Use a proper test like the one linked on this page -
http://www.focustestchart.com/chart.html

[vinnie_h]

I may be out in left field, but....... something that you may not have thought of and along the lines of YOUR vision.....have you checked or adjusted the diopter in the viewfinder? That is a real issue for me because my vision isn't the best....anyways I don't do a lot of manual focus because of this, I prefer to trust the camera.......

just a thought...

[tmonatr]

Thank you. This will definitely give me my answer.

[Hellashot]

I have a 30D with a Sigma 17-70 2.8-4.5 lens. I love this camera and the lens is very sharp. But, when taking extreme close-ups(manual focus) what is sharp through the viewfinder is not what is sharp in the final image. This is very noticable at large aperatures. The point of focus seems to shift back in the photo slightly. Is this a lens or camera issue?:confused:

Are you using a tripod for macro work? If not when you are so close to an object, wide open your DOF is very shallow. If you sway even a little bit it'll through your focus point off noticeably.