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DPChallenge Forums >> Tips, Tricks, and Q&A >> Aperture in Infinity and Landscapes
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10/27/2006 12:08:34 AM · #1
Hi,
Does f-stop matter when shooting subjects at a distance of infinity when there is a lot of light? What aperature should someone have when they are taking a picture of, say, a mountain in the distance and the foreground is already at the furthest focus distance? I tend to have a habit of opening my aperature as far as it will go so that I have more light and I can therefore use the fastest shutter and avoid camera shake. I've read that shooting with low f-stops gives poorer quality and that f8 is around ideal. Should I always instead be shooting at the highest f-stop allowable under my particular light conditions to get the highest quality shot? This is also considering that everything is at infinity and I'm not looking for a blurred depth of field effect.

I understand aperature in situations of low light or portraits when i want some of the photo blurred. I just dont know how to use it when everything is at infinity and there is enough light to shoot at most levels of aperature.

Thanks, any help would be totally awesome!

Martin

Message edited by author 2006-10-27 00:09:44.
10/27/2006 12:13:23 AM · #2
Shooting at the highest (smallest) aperture is rarely recommended. The best sharpness is usually 3-4 stops down from the widest aperture. The exception is specialty macro lenses. Those are generally sharp at all apertures.

Use the smaller aperture when you have a foreground subject that you want in focus along with the background.

With your kit lens, use 5.6-11 for the sweet spot of that particular lens.


10/27/2006 12:32:57 AM · #3
How does one determine the "sweet spot" of a particular lens?
10/27/2006 12:53:46 AM · #4
In general, 2-4 stops down from widest aperture will be the sweet spot for a lens. F/5.6 - 11.0 for an f/2.8 lens, f/8.0 to f/16 for an f/4.0, and so on. In general, the longer the lens the more you can stop it down and still be in the sweet spot, since f/stop is focal length divided by physical size of the aperture, and one of the limitations on sharpness comes from the "circle of confusion", which becomes a problem at physically smaller apertures regardless of the f/stop they represent.

In plain English, f/22 on a 10mm lens is less than half a millimeter, and that's a WAY tiny aperture, way too tiny to get maximum sharpness. So on the extreme WA lenses, which are typically f/4 lenses, f/8 is about as much as you want to stop down to balance DOF with sharpness issues. On the other hand, a 200mm lens is likely to be close to optimum all the way up to f/16, even if the maximum aperture is f/2.8.

There are other considerations, of course, with lens being designed to generate maximum optical performance at a given f/stop (they can't be perfect all the way through, it's impossible pretty much especially with zooms) but good modern lenses have very nice optical performance pretty much throughout their range, with CoC becoming a real limiting factor especially on WA lenses.

It took me a while to learn this about my 10-22mm, shamefully. I used to use it at f/22 all the time, for maximum DOF, but the DOF is outstanding even wide open, and the CoC really comes into play at the smaller apertures.

R.
10/27/2006 12:59:26 AM · #5
Thanks for the explanation, Bear!
10/27/2006 08:27:44 AM · #6
Wow - that was an excellent response by Robert. I am really paying a nominal fee for this education.

Message edited by author 2006-10-27 08:34:15.
10/30/2006 03:15:50 AM · #7
I was going to add a small note that if you have a look around at some of the more accomplished landscape shooters around here, you will find a lot of photos in the f/11-13 range. I was thinking of a few of Bear's recent shots in particular...
10/30/2006 03:26:18 AM · #8
bear, you have learn't me once again.

I ALWAYS shoot f/22... get out that tripod, I want everything in focus. I didn't know I was making a mistake. The one complaint I have about my 10-22 is that it is often soft around the edges. Is this the result of not using that "sweet spot" right? If so, that would be great if I solve that by using a smaller number.

drake
10/30/2006 03:28:38 AM · #9
Not only that, but diffraction is a bit of an issue at f/22 for most current digi's. read up... Cambridge in Color has a great bit of info on it. Google is your friend!
10/30/2006 12:17:07 PM · #10
Originally posted by fstopopen:

bear, you have learn't me once again.

I ALWAYS shoot f/22... get out that tripod, I want everything in focus. I didn't know I was making a mistake. The one complaint I have about my 10-22 is that it is often soft around the edges. Is this the result of not using that "sweet spot" right? If so, that would be great if I solve that by using a smaller number.

drake


I'm not sure, but my gut tells me "yes".

The main reason a WA lens will appear soft around the edges is that different colors of light have different wavelengths, so they can't all be in precise focus at exactly the same plane even when they are perpendicular to that plane (i.e. the center of the lens/sensor). Modern lenses attempt to compensate for this with various forms of optical wizardry, but this has to be tuned to specific apertures (layman's explanation) and hence the sweet spot. With extreme WA lenses, the image at the edges of the frame is being constructed from light rays that hit the sensor at a VERY oblique angle, and so the different focal planes of the different wavelengths (colors) of light effectively have their deviations magnified, and thus the softer edges.

That's not going to change regardless of f/stop, really. But when you throw in the circle of confusion, the diffraction issue, you are adding another unsharp element on top of the focal plane issue, and this will effectively multiply the edge softness factor. That's my guess, but I haven't actually seen anything "scientific" on this.

I'd love to see Kirbic weigh in on this one; he;s much more knowledgeable about this stuff than I am. I just know I get better WA performance at f/8 or f/11 than I do at f/22 :-)

R.
10/31/2006 01:25:16 AM · #11
Gosh - wish I had seen this BEFORE this last weekend. I must have taken 300 shots at F/22 aiming for the greater DOF. This goes a long way towards explaining some of my frustrations.

Robert - how then do you deal with the DOF? Do you focus towards infinity, or on a forground object?
10/31/2006 02:17:48 AM · #12
Originally posted by PaulE:

Gosh - wish I had seen this BEFORE this last weekend. I must have taken 300 shots at F/22 aiming for the greater DOF. This goes a long way towards explaining some of my frustrations.

Robert - how then do you deal with the DOF? Do you focus towards infinity, or on a forground object?


As a rule of thumb, for any given amount of DOF, 1/3 of it is in front of the point of focus and 2/3 of it is behind that point. That is to say, if you have 12 feet of DOF at a given aperture and point of focus, 4 feet of it will be in front and 8 feet of it will be behind the point of focus. So, as a rule of thumb, for non-infinity work you focus 1/3 of the way into the area you want to be sharp. With extreme WA lenses, though, the proportions seem to go "off", with little of the DOF in front and most of it behind.

It gets more complicated when dealing with infinity + near objects in landscapes, because there comes a point in which you have reached effective infinity focus. For example, the tree is 10 feet in front of you and the horizon is 6 miles from you; that doesn't mean you need to focus at 2 miles.

It's all dependent on the focal length of the lens you are using. With the extreme WA lenses I am mostly talking about here, where you can't stop way down without losing critical sharpness to CoC, the lens itself has very extreme DOF to begin with. Back in the old days we used to have lenses that showed markings on each side of the central focus mark, on the barrel. So you had an f/8 maek to left and right of center, an f/11 mark to left and right, and so forth. You'd manually focus so infinity was over f/11 on the right, say, and then look at the number over f/11 on the left, and that would be your DOF range.

Here's an online DOF calculator: //www.dofmaster.com/dofjs.html

Here's a page you can use to download a free DOF chart generator you can use to create a DOF chart for a specific focal length and print it out: //www.dofmaster.com/charts.html

As an example, the calculator shows me that if I use my 10mm lens at f/8.0 and focus at 3 feet, everything from 1.26 feet to infinity is in focus.

Take it out to 22mm at f/8, focus at 10.5 feet, and DOF extends from 5.25 feet to one mile. Stop down to f/11 and DOF extends from 4.35 feet to infinity. In fact, at f/11 I can focus to 7.5 feet and have 3.75 feet to infinity in focus.

It's basically the kind of thing you internalize by trial-and-error. For example, acceptable DOF is print-size and viewing-distance dependent; did you know that? One manifestation of that is an experience we've all had, of lookign at what seems to be a really nice thumbnail which, upon clicking to get the 640-pixel image, we find the image is not sharp AT ALL. And it is possible to get away with focus/DOF errors at 640 pixels that would be unacceptable at 11x14 inch print size.

Robt.
10/31/2006 08:33:56 PM · #13
Thanks.

And once again I am in awe of your knowledge base.
10/31/2006 08:57:51 PM · #14
Bear makes my brain hurt. But, I love him anyway :)
10/31/2006 09:02:57 PM · #15
I was experimenting with this very question last night and the difference in quality between f22 and f8 is amazing. I would post pics but I've just entered one of them in the free challenge and it would be a bit of a give away.

On my kit lens the range of f8-14 seems to give the best results for sharpness - but I was experimenting with up to f29 to try and get some more motion blur happening. I knew that I didn't need anymore DOF than f8 but that was letting in too much light. (so today I went and got some filters to cut down light)

I cant really add much to what robert has said except this - shooting at anything higher than f16 will show up every single bit of dust on your sensor like pimples on a 16 year old.

PS has anyone else downloaded the new version of firefox? I love how it's spell checking my forum posts as I type - awesome!!!

Message edited by author 2006-10-31 21:03:36.
10/31/2006 09:12:01 PM · #16
Originally posted by dr_timbo:

PS has anyone else downloaded the new version of firefox? I love how it's spell checking my forum posts as I type - awesome!!!


Not to hijack this thread, but the FF2 spellchecker's been doing weird things for me. The weirdest by far is that, on my computer at work, no matter what word it thinks is misspelled, the first suggested correction is always "pregnant". I could misspell "toast" and it will suggest "pregnant"!
10/31/2006 09:15:19 PM · #17
bear, you have helped me become so much better as a photographer, and I'm sure this thread will just add to the way I work. Thank you. You are an asset to this community and to me personally.

drake
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