Aperture

Hi all,

Aperture... the smallest (big number, isn't it?) will give bigger DOF right?
is there any side effect by using small number to have wide DOF, besides slowing shutter speed? (since i use tripod so it won't be a serious problem)

So, if i want to make all of subject in the photo look sharp, F22 is the best right?

thank you

Actually, f/22 will severely decrease your sharpness.

You see, after a certain point, you begin to have what is called diffraction impact your images. This results in softening of the details. The reason behind it is too complicated to really concern yourself with, though both viewing distance and viewing size can help or hurt it.

Most recent digital SLRs begin to feel the effects of diffraction anywhere between f/11 and f/16, depending on sensor size and resolution. If you're shooting a 10 megapixel APS-C format digital SLR (a Nikon D-series DSLR other than the D3, a Canon Rebel or xxD series, or any Sony, Pentax, or Samsung DSLR) you'll usually see diffraction right around f/13.

If you print smaller, or have a longer viewing distance than is standard, you can get away with a somewhat smaller aperture without getting diffraction effects that will adversely affect your output print/display.

I would say that for the optimum output sharpness, shooting at f/11 tops should be your ideal. You might want to do some tests to figure out where the 'sweet spot' of your particular lens is as far as sharpness. Also, if you're shooting reasonably wide angle, you might wish to read up on hyperfocal distance, which can help you gain more control over increasing your depth of field.

ooo ic ic.

thank you for your explanation.

For better DOF try this.
http://www.vividlight.com/articles/2314.htm

In addition to aperture, DOF is a function of the angle of the view (wide angle=inherently high DOF) and distance to the subject where the focus point is. If the subject is far away and the angle is wide, the picture is going to be pretty sharp regardless of the aperture. f/5.6 can be sharp with a 16mm lens.

I only really stop down if I am shooting landscapes, and even then only to maybe f/11 or so. Use a tripod too, to eliminate shake, and mirror lockup if you're really picky.

Diffraction isn't necessarily something you'll notice or that will bother you. It is a real thing, though. I noticed it most back when I worked at a lab making prints in the darkroom. When I would stop down the enlarger all the way, prints were noticeably softer. However, photography is always an exercise in compromises. We can talk about the sweet spot in lenses all day long. But that's purely technical and has nothing to do with creativity. If you want maximum depth-of-field, you need to stop down all the way. So go ahead and do it. And then maybe shoot another photo and back it off a stop or two. Compare them later to see if you can tell the difference. The bottom line is, there are no hard rules. Understand how all the different aspects of exposure work and make educated decisions based on that knowledge.

is it still ok if i shot a photo of bunch of people with f/5.6 at 17mm (my camera has 1.6x crop factor)? if i used f/5.6 i mean i can get faster shutter speed, so i can freeze their movement.

Thanks a lot for explaining.. :D

Actually, if freezing movement is your biggest concern, you should be shooting in shutter priority. Unless it's a fast action sport, you could set your camera at 1/250 sec. or slower, if the subject isn't moving all that fast, and let the camera choose the aperture. In other words, if dof is what's important in the shot, shoot in aperture priority, and if freezing action is important, shoot in shutter priority.

17mm at f5.6 - it's hard to say if this is enough DOF or not. This will also depend on the focus distance (if the lens is focused at 10' away, etc) and how the people are arranged. If they're shoulder to shoulder at 8-10', you'll have plenty of DOF. If they're four rows deep with the closest row 2' away and the farthest 8' away, then f5.6 won't do it. One nice thing about shooting with a DSLR is that you can change the ISO speed from shot to shot.

Most cameras still look great at ISO400 or 800 (or even higher, especially newer ones). If you needed the shutter speed you had but wanted to use f8 which is one stop slower than f5.6, you could bump up the ISO by one stop. In other words, if you were at (for example) 1/125, f5.6 and ISO100 you'd have the same exposure at 1/125, f8 and ISO200. You shouldn't see a noticable difference between ISO100 and 200 with almost any digital SLR, would be able to keep the 1/125 shutter speed but also gain the one stop of aperture to get more depth of field.

As far as diffraction goes, in my experience some lenses are better than others at this. I had a 300mm f4.5 that was amazingly sharp wide open or at f8, and then got progressively softer until f32 where it looked pretty bad (with a lens like this I would rarely even want something smaller than f11 so it wasn't a big deal). Most lenses are not like this, but usually I don't stop down past f11 - however as John says it's really all about the shot. If the shot needs f22 then I wouldn't hesitate to use it.

Well.. thanks for the help guys. it help me to understand more about F :)
thanks a lot