Weird focus issue, or me?

In yesterday's shooting I have what seems like a weird situation. For example... two virtually identical shots. One horizontal, one vertical. Both used the same spot in the foreground as the chosen AF point, though different AF points within the camera considering the rotation.

Both shots look fine in the foreground. The horizontal shot looks fine in the background (a house & barn off in the distance), but the vertical shots is horrible fuzzy. I notice a similar pattern from the whole day... the horizontal shots look better than the vertical shots.

Camera was a 40D, 24-105L lens, Kirk Arca-type system w/L-bracket, IS turned off.

Could it be the lens or the camera? Could it be something I did? This does not make sense to me.

It's the autofocus. It uses different sensors in the vertical and horizontal shots, and something in the vertical shots is throwing it off. Perhaps the mode it is in. Or the framing.

Mode was Manual, for whatever that's worth.

Can you show us a sample?

20droger wrote in post #10188375
It's the autofocus. It uses different sensors in the vertical and horizontal shots, and something in the vertical shots is throwing it off. Perhaps the mode it is in. Or the framing.

If it's the sensors, what would I do about it? Is there some trick or piece of knowledge that I need to know when framing vertically? Do I do manual focus instead?

I'm not doubting this may be it, but it still seems weird. If the focus point is virtually the same, and the aperture is the same, should the DOF be virtually the same regardless?

Shoot in Av mode or manual, and the DoF should remain the same.

You might also use partial or spot metering. The layout of the sensors presumes horizontal shooting. In evaluative or center-weighted average metering modes, especially evaluative, rotating vertically places a lot of sky over sensors that would normally not see sky. This can change the aperture if not in Av mode or manual.

If you're indoors, substitute "ceiling" for "sky." The effect is the same.

20droger wrote in post #10191174
Shoot in Av mode or manual, and the DoF should remain the same.

You might also use partial or spot metering. The layout of the sensors presumes horizontal shooting. In evaluative or center-weighted average metering modes, especially evaluative, rotating vertically places a lot of sky over sensors that would normally not see sky. This can change the aperture if not in Av mode or manual.

If you're indoors, substitute "ceiling" for "sky." The effect is the same.

I normally shoot spot metering, but have been trying evaluative lately. But... I was shooting Manual, so if I understand you correctly that should be moot.

photoguy6405 wrote in post #10191613
I normally shoot spot metering, but have been trying evaluative lately. But... I was shooting Manual, so if I understand you correctly that should be moot.

Depends. Were you using matchneedle exposure? If you were, then you were only partially manual and subject to the aforementioned exposure variations.

20droger wrote in post #10192353
Depends. Were you using matchneedle exposure? If you were, then you were only partially manual and subject to the aforementioned exposure variations.

What is "matchneedle exposure"?

Where you simply follow the exposure needle around to make sure it is centred.

That is simply Auto but with manual controls (the camera is deciding on "correct exposure").

If you used the exact same aperture in both shots, I can't see why there would be a difference in DOF - but when you rotate the camera and are using Evaluative metering, you're changing what the camera sees and it may meter differently. If you changed the aperture in the second shot to compensate for that (to re-center the needle, as 20droger and neilwood32 are talking about), I could see where the DOF would change.

ISO was 400 and the aperture was f8 in both orientations. I was trying to get a shutter speed fast enough to freeze the grass from swaying in the breeze, otherwise I would have used f11 or f16. I used the camera's meter as a guide, but did not depend on it blindly. I compensated a tad based on the scene, and even then I chimped and took two shots in each orientation, both horizontal shots are fine, both vertical shots are questionable.

Can you post one of each with the exif? And, if there is a part of a shot that you have a question/complaint about could you post a close crop of it? It's hard to guess at what problem may exist without seeing an example!