A Question

[Trillium233]

I've been playing about with a Rebel EOS XTI for a long time now, and while the pictures I'm getting are decent, I've noticed that the focus is milky/soft when the pics are viewed at 100%.

I'm shooting at ISO 100 to minimize noise. I'm using a tripod and am using miror lockup to minimize camera shake. (I don't have a remote shutter release yet.) Here's a photo to show you what I mean:

I used an EF100mm macro Lens, a f16 aperture, and a shutter speed of 1/40 sec. I had the focus set on the third pencil from the left, and even -it- isn't sharply focused. It looked fine through the viewfinder (The AF lights blinked to confirm it was in focus.). I'm not sure what else to do to sharpen my pictures up. I'm going through the links listed under the tutorials thread, but thought I would ask about it here. -I hope that's ok.

Thoughts?

 

[Josh66]

As you stop down, diffraction starts to affect sharpness - and f/16 is getting into that territory...

I could be wrong here, but I'm pretty sure sensor size is a factor too when it comes to diffraction. You'll start to see it sooner on smaller formats.


Try some around f/8 or f/5.6 and see if you notice any improvement in sharpness.

 

[Trillium233]

Here's f8:

f 5.6

f2.8

Focus is on the far right pencil this time. The smaller apertures are better, but still...

 

[pgriz]

Josh is right. Above f/11 the diffraction effects start to become more and more pronounced. There are times when you're willing to give up a little detail sharpness to get the greater depth-of-field, but that is a trade-off you, as the photographer, should decide on. As for the AF, don't rely on it too much. Depending on the camera's calibration, it may signal "in-focus" when in fact the focus is actually a little in front or behind your intended focus point. So if you use live-view and the 10x magnify option, you have a much better chance of nailing the focus at the right place.

 

[djacobox372]

DOF is very narrow when shooting macro. Your 5.6 shot looks a bit sharper then the f8 shot, which is undoubtedly due to focusing difference.

The kind of tack-sharpness you're looking for probably only lies in 1mm of your DOF, so focus is critical.

I typically use manual focus and bracket my focus by moving the camera slightly in and out when shooting macro.