Focus question and advice please!

Started 3 months ago | Questions thread
Rick Knepper
Rick Knepper Forum Pro • Posts: 17,126
Re: Focus question and advice please!

mtakeda wrote:

I am quite confused. Do you think, knowing my landscape shots, CoC 38 is happy compromise or do you different number for me? I do not think I can live with F5 which true DOF pro app sets as the max for wider DOF.

Actually, he cannot tell you what the optimal setting would be 1.) because that will change constantly with distance and FL and he does not know what you intend to do with the image in terms of printing or displaying 2.) because this will change with print size and your tolerance for blur. This is why testing is important.

If you are willing to compromise, use the Merklinger method I have mentioned dozens of times in this forum on scenes such as the one below.

I take every new camera and lens to this location. It's a bridge overlooking a river and has a wide range of elements conducive to evaluation. The camera is level on all axis. The center focus point lands naturally on the horizon where I typically use the Merklinger method (which is sort of a misnomer since Merklinger also taught hyperfocal).

I shoot the scene at every full aperture. I started this back in the day because Canon wide angle lenses were terrible in the corners and while I still had a chance to return the lens, I wanted to make sure I could live with it. However, I began to see that other determinations could be made by this "testing".

Doing this with a familiar location, I could detect flaws in the lens or camera such as a tilted sensor (rare but it happened to me) and decentered lenses. I could also check out distortion and false detail. I learned a lot about diffraction too and how much I could tolerate. I do this scene in the morning so that left bottom corner is in shadow and that helps me determine DR. Testing tells me a lot and if I do it quickly, I can send the camera/lens back if it does not please me.

However, if you do not want or cannot make time to test, why not shoot every scene in the field at f8, f11, f16 & f22 and make the decision later. This is digital so those extra images do not cost you anything and it takes about 10 seconds to run through the other apertures. After so long, you will begin to get a feel for the correct aperture at a given distance and FL and you can stop shooting every aperture.

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