Aperture and shutter - Sweet Spot

There are tons of usefull information about those basic camera parameters. I will not explain them any better that any other webpage on the web did already. As I'm mainly concerned about quality of images (maybe you too?) then I would like to share some less known aspect of those. Probably you already know that shutter speed affects how blury will be your image during movement (you, or your subject) - so to keep it sharp usually you want to make it as small as possible (usually 1/125 is enough to freeze normal body movement). Lowering this parameter however reduces amout of light that is comming to a camera, so to increase that light you have few options: raise aperture, raise ISO or add additional light source. Raising ISO will usually degrade image quality (especially in shadow areas), so natural option would be to raise aperture (by lowering aperture number), usually to maximum of lens capability (thats what I was usually doing). Important part here is something called "sweet spot" - you might not notice this at first shoots, but lenses on their highest aperture do not perform very well - they can work OK, but by the cost of a defocus (more at Optimal Aperture at wiki).

What if you want to shoot in sweet spot, and have not blurry image because of small movements? Here comes why most photographers shoots with strobes (even outdoor). You can minimize this effect using tripod, however best results you will get using additional moving light source. Usually Sweet Spot is around f4-f8, for example:

 - Canon 17-85mm f4-f5.6 typical Kit Lens - Sweet spot around f8,
 - Canon 50mm f1.8 - good quality starts from f2.8, sweet spot from f4,


(Click on a photo above to check author of photo and its description)

Conclusion of this post would be - take a look at lens tests to know at what aperture you might get best results. But dont stick to it always - sometimes you need to open shutter to max. However when you have good light condition - it's worth to give it a try.

Zoom lenses also adds some quality variation (they are not same in whole range of zoom) - so again, a good advice is to check image quality for given lens across different focal length set. Example for a Canon 17-85 you can read here: http://www.lenstip.com/12.4-Lens_review-Canon_EF-S_17-85_mm_f_4-5.6_IS_USM_Image_resolution.html