DRebel Focus Points

[ejwebb]

I have been wondering about the autofocus "dots" in the viewfinder of my DRebel. Each one looks like it has a shadow slightly to the left of the actual dot. It is as if there are two screens in the camera with the dots and they are not perfectly lined up. Kind of reminds me of a rangefinder not quite in focus.

I have been having difficulty getting sharp focus at low aperture numbers and, while I know there are many other reasons for this (lens quality, camera shake, etc.), waws wondering if this might be indicative of a focus calibration/adjustment issue.

Any thoughts?

[DC]

Not sure how a "shadow" on a focus screen can affect actual focusing. The screen is not in the light path to the sensor, so anything you see on it will not affect the image recorded. Also, the lens will use the actual scene it is looking at, not the viewfinder screen, to focus.

A calibration issue would be something like the problem with 10D's people have experienced where the point of focus in the recorded image is not at the same point as was selected in the viewfinder.

As a rough test, shoot a ruler at 45 degrees to the camera. Place one of the focus points on say the 8" mark and shoot using as wide an aperture as you can to shorten the depth of field. This will give you at least an indication of any focussing problems.

[Jesper]

As a rough test, shoot a ruler at 45 degrees to the camera. Place one of the focus points on say the 8" mark and shoot using as wide an aperture as you can to shorten the depth of field. This will give you at least an indication of any focussing problems.

Shooting a ruler at 45 degrees is not the best way to test the focus, as I discovered myself... look at the following thread: http://photography-on-the.net/forum/showthread.php?t=32810

[ejwebb]

I used the term "shadow" loosely as I don' t think that is what it actually is. My concern is that if I aim the dot at an object to focus and the actual focus point is based on where the shadow is pointing - the focus could be slightly off in instances where there is a shallow depth of field (wanting to focus on the eye and actually hitting the bridge of the nose, for example). Also, this may be a non-issue but it kind of bugs me - just wondered if other DRebel users have noticed?

I intend to try the test, should the distance between in focus and out of focus on either side of the target be the same? If so, how much variation is normal/acceptable? Let's assume that the ruler is angled up wih the 1 on the lower end and the 12 on the higher end - if I focus on the 6 and it is in focus to the 5 on the bottom and to the 61/2 on top - does that indicate a back focus issue?

Thanks for your help.

[DC]

As a rough test, shoot a ruler at 45 degrees to the camera. Place one of the focus points on say the 8" mark and shoot using as wide an aperture as you can to shorten the depth of field. This will give you at least an indication of any focussing problems.

Shooting a ruler at 45 degrees is not the best way to test the focus, as I discovered myself... look at the following thread: http://photography-on-the.net/forum/showthread.php?t=32810

Fair enufski,

but without actually knowing what the issue is regarding focussing, whether it's front-, back- or just all over out of focus, this seemed the quickest way to check.
Obviously if a problem is apparent, then a more "scientific" test would be needed. I suspect however that there isn't a problem and it's down to other factors.

[ejwebb]

Jesper - thanks for the link! I searched and expected a thread like this one but did not hit it. I'll try it this way.

Still curious about the dot "shadow" in my viewfinder, though.