Confused about what aperture to use

[Iman]

I have read a number of books on photography, in an effort to accelerate my education (as well as shooting). Recently I read a number of Bryan Peterson's books where he advocates what he calls "story telling apertures" primarily for landscape shots of f18, f22, and higher. What is confusing to me is that when I look at the galleries on this site, Brian's beautiful landscapes are usually shot at between f8 and usually f11. I have also read on this site and others that shooting at apertures above f11 starts to degrade the sharpness of the image. So what's "correct" , realizing that there is no one best aperture etc. I'm just looking for some general guidance.
Thanks in advance and I apologize if this is a dumb question, to the more experienced shooters here.

[HDNitehawk]

I think you might get several diffrent answers here.

At narrower apertures F/13 or higher you might see some noticeable degradation. For instance I have found it noticeable when shooting macro with my 180mm L macro lens, where I am really looking for razor sharp images of a small creature or plant. If you are doing other types of photography you might not notice at all.

With wide lenses and landscapes you would use the narrower apeture if you were shooting with ND filters or at night, where you are purposely trying to get longer exposures. With a wide lens like a 24mm you wouldn't be using the narrower apertures for DOF, because at F/8 or F/11 your DOF is getting so deep it goes to infinity.

With Macro you might go narrower because of the razor thin DOF you get, but like I pointed out you start to loose IQ. That is why many macro shooters focus stack.

For me I usually go to the narrower if I am trying to get longer exposures. Maybe others have uses but for me that is about it.

[Richard Lane]

There are no dumb questions, only dumb answers.

There is something called Diffraction Limited Aperture or DLA:

As your aperture becomes too narrow, the incoming light gets diffracted or dispersed by the edges of the diaphragm blades, and it is this dispersion of light that can lead to a loss of resolution.

http://www.luminous-landscape.com/tu...fraction.shtml

In this example below you will see that as the aperture went from f/5.6 to f/16 there was a loss of resolution:

http://www.the-digital-picture.com/R...mp=0&APIComp=7

Usually with most higher-end cameras you should be pretty safe in avoiding diffraction if you keep your aperture between f/8 to f/11. Commonly referred to as the Diffraction Limited aperture (DLA). You shouldn't be afraid to use f/13, just be aware that the narrower you go, the greater the affect from diffraction.

Some people do feel that diffraction is a bit over-rated, namely the well respected Bryan Peterson in his book entitled "Understanding Exposure." He prefers the greater overall increase in DOF, over the pixel-peeping loss in micro-resolution. Personally, I wouldn't rule out the overall increase in DOF either, if the micro-resolution was considered less important for a particular image.

Diffraction is certainly more noticeable with pixel peeping. However, it is an accepted physical limitation.

I do think as long as you're aware of it and you don't shoot everything at the narrowest apertures then you'll be ok. It's also good to know what the DLA is for the particular camera and lens combinations that you'll be working with.

Here's another article:

http://www.cambridgeincolour.com/tut...hotography.htm

Check out the fabric example and DLA Calculator towards the bottom of the page.


Rich

[DavidEccleston]

I just checked with DOFMaster. If you were to use the kit lens, at 18mm, f/8, and focus a mere 7.1 feet away, everything from 3.54ft to infinity will be in focus. Which a fairly depth of field.

Some lenses require stopping down to get sharper images, but even fairly low grade lenses are fairly sharp by f/8, so I don't see why you'd need a narrower aperture... at 18mm. You'll want narrower apertures for macro, and for longer focal lengths.

Doing the same check on DOFMaster with the 85mm lens, at f/8, I need to focus atleast 154ft away to get infinity in focus, and as near as 77.6 feet would also be sharp. To get a more reasonable front distance to what's in focus, you'll need to stop down, well past f/8. Dropping to f/22, and focusing at 56ft, brings 27.9ft to infinity into focus. F/32 and focusing at 40ft, gets you 19.8 to infinity.

So, depending on your lens's sharpness, and it's focal length you may need large f values, but for wide angle landscape, f/8 should be plenty.

[Richard Lane]

Here's a DLA Chart and some additional info:

http://www.the-digital-picture.com/C...op-Factor.aspx

[thekingb]

Some people do feel that diffraction is a bit over-rated, namely the well respected Bryan Peterson in his book entitled "Understanding Exposure." He prefers the greater overall increase in DOF, over the pixel-peeping loss in micro-resolution.

I agree that this is an area of caution. If you get real technical and focus just on the science, you'll decide that you shouldn't shoot a 7D at narrower than f/8 due to diffraction. And generally I try to max out at f/11 on my 7D. But funny how things work. One of my favorite images, which I printed at 24x16, was taken by accident at f/13 and looks great printed at that size. I could easily print at 30x20. I suspect that f/16 would have been ok too, but probably not f/22. So the science always needs a reality check.

[Dr Croubie]

I haven't read the book in question, so my answer is going to depend on: What camera/lens/system is he using? (and what are you using?)
On a crop sensor, 7D etc, I wouldn't go much higher than f/8. For wide-angle landscapes (24mm and wider), I'd even get away with f/5.6. (I use my Sigma 8-16mm at f/5.6 ll the time, I only stop down to f/8 for worse centres but better borders)
On FF (5D/1D), take that up to f/13, wide angles around f/8. If you've got a 14mm or 16-35, you can probably shoot at f/5.6 or f/4 even and have everything sharp, if you haven't got much in the foreground.
Stopping down further can increase DOF, but not so much to be useful for anything but macro work. If you want to stop down further to get a longer speed for blurring motion, a good ND filter gives better IQ than f/45.

And if digital is all you shoot, you can stop with one of those answers.
But, the next difference, if shooting FF Film (35mm), there's not much harm in going to f/16, most film can't resolve enough to see the diffraction.
Medium Format Film, anything up to f/22 is usable before you can see diffraction (not that i've tested much, film processing is expensive when you only get 12 shots to a roll).
But when you get up to Large Format, remember that Ansel Adams was a member of a group called Group f/64, because that's not only the size of aperture you need to get everything within DOF using such huge plates, but also because when using those huge plates you don't see much diffraction anyway...

[Agilulfo]

There are no dumb questions, only dumb answers.

Here's mine: get a tripod, frame a landscape, try all of the apertures possible and examine the results. Then you can draw your own conclusions and show your work for different opinions.

[Sean Setters]

While DLA does introduce some softness to an image, don't let that stop you from shooting at narrower apertures than the specified DLA if depth of field is what you need.

An extreme example?

Canon 7D
70-200mm f/2.8 L IS
f/32, 1/250 sec, ISO 100
1.4x Kenko Extender
Extension tubes



The Chosen One by budrowilson, on Flickr

[DavidEccleston]

Didn't one of Daniel's threads say that the extra resolving power of the larger f value outweighed the loss of sharpness from diffraction, and that the point where you'll start to see no benefits is something ridiculous like f/250?

Still, that's theoretical, all math based. Agilulfo has the best suggestion.