How do you know which f-stop to use?

[Neeper]

I don't know if this is a beginner's question or not. But say shutter speed didn't matter, and DOF (or bokeh?) didn't matter. How do you decide which F-stop to use? I guess what I am asking is, how do you know which F-stop will give you the sharpest picture?

[xerubus]

if shutter speed and dof etc didn't matter, i guess the answer to your question would depend on the lens being used. each lens has it's own 'sweet' spot.

cheers

[Neeper]

Would there be a list somewhere of different lenses and their sweet spots?

[gstark]

Unfortunately, no, but it really wouldn't be of too much use. Each lens has its own characteristics, and what I'm seeing as a sweet spot in my lens might not be the case in your example of the same lens.

Getting back to your question, it becomes a rather arbitrary decision, kicked along more than a little bit based upon your gut feeling of how you want the image to look.

Do you want a lot of DoF? If so, you'll cose the lens down. Conversely, if you're wanting shallow DoF you'll open it up. Once your aperture is chosen, the measured available light will give you an EV, and your shutter speed will follow just like the tail on your dog.

But if your subject is fast moving, you might decide to freeze that motion, or you might want to shoot it to get a blurred motion effect. Either way, yu've just changed the way you're thinking of shooting the photo, and your primary consideration has just become the shutter speed.

Select the shutter speed, and your aperture choice (just as it was before) is simply a matter of metering.

HTH.

[Onyx]

JT, there's s saying: "f/8 and be there".

[Neeper]

Thanks for the reply guys.