Why use lower F stop?

[JoeW28]

Okay so say you're using a 35mm, and you're shooting something 100 feet away. There are no water, no clouds, no moving starts, nothing between you and the scene 100 feet away, and no people walking about, why use f1.4 and a quick shutter speed versus say f8 and a slower shutter speed? Bokeh and focus distance is no issue since the focus point is so far away.

You are looking at aperture solely in terms of DoF.

1. Yes it's true that if you're focusing in the distance, there is little practice difference between f1.4 and f2.8 and f11 (assuming no foreground exists). But if your focus is off just a little bit than the difference between setting at f1.4 and f8 is going to be extreme and noticeable.

2. If you open that aperture up to the max you're going to change skin tones vs. shooting the exact same model or person at a narrower aperture.

3. Depending upon the lens, setting the aperture at the extremes may produce a drop-off in sharpness or create some chromatic aberration. For instance, the Nikon DX35mm f1.8 is a nifty little lens but is well known to produce chromatic aberration when you're shooting at f1.8 (as opposed to f2.8).

The point from all this is that aperture is more than just about DoF. That's our primary (no pun intended) focus with aperture. But it also shapes the quality/nature of the light entering the camera, it interacts with the lens and may produce effects.

 

[Derrel]

Okay so say you're using a 35mm, and you're shooting something 100 feet away. There are no water, no clouds, no moving starts, nothing between you and the scene 100 feet away, and no people walking about, why use f1.4 and a quick shutter speed versus say f8 and a slower shutter speed? Bokeh and focus distance is no issue since the focus point is so far away.

Using most lenses at their widest f/stop setting (like the 35mm f/1.4 lens in your example AT f/1.4) usually compromises the technical image quality a bit, compared to what the lens yields with the diaphragm stopped down a bit to say one stop smaller, or f/2. At f/2.8, most f/1.4 lenses are approaching their best performance zone, which generally is around f/4 to f/5.6, as a general sort of rule. So, at what is called , "Three stops down", meaning f/2.8 on a lens that opens to f/1.4, you'll be approaching the zone where the LENS performance is usually quite good.

At wide-open, many standard and wide-angle and normal telephoto lenses are a little bit imperfect, let's say. Maybe some chromatic aberration, perhaps a very slight bit of veiling flare (looks like a very,very,very fine 'mist' or 'ever-so-slight-fogginess') over the whole image, and quite often, some light fall-off at the corners, and a sharp central region that has much softer, less-sharp outer and corner areas. Typically, on "most" lenses, the wide-open image performance is a bit less than optimal, and at one stop down, there is often a disappearing of the veiling, and a minor,yet noticeable, improvement in overall image quality, yet there is usually STILL SOME room for improvement. At three stops down, the lens will be better yet again, and at four f/stops down, the lens will usually be about as good as it can get. We are speaking here of "fast" prime lenses, like 35/1.4, 50mm f/1.4, and 85mm f/1.4 lenses, and a sort of general rule.

On expensive, f/2.8 pro-type zooms, f/4 is usually quite good, and f/5.6 is usually excellent. On many slow-speed (like f/3.5~5.6) consumer zooms, f/8 is usually quite good. On some, and I stress, some, exotic lenses,like the 200 f/2 lenses, optics wide-open are excellent, and improve to truly sublime by f/2.5, or only 2/3 of a stop down from wide-open.

You have a range of f/stop + shutter speed equivalent exposure settings. Sometimes a specific speed is best, like when panning, or when trying to freeze fast motion. 1/250 or faster (1/320, 1/400) usually helps ensure fairly sharp images in normal, everyday shooting hand-held. FOr many sports, 1/500 is the bare minimum, and 1/750 to 1/800 is better, and 1/1000 to 1/1250 is really where you "wanna be at". So....it all depends, ya' know?

 

[glun]

For lower f stop, I assume you mean from f4 to f16. Doing this will increase the depth of field of your picture which is ideal for landscape photography. Your pictures will have more focus overall in the picture but you need more lights.

For higher f stop, say from f8 to f2.8, less light is needed and your picture will have a better blur in parts of your image.

Hope this helps!

 

[vintagesnaps]

If you're photographing a scene and there are no clouds or people etc. then no, you wouldn't need to use a larger aperture. If I want to shoot across say, a lake and I want the far shore and sailboats etc. all in focus then I'm going to use a smaller aperture. If I want to take a close up of a flower then I would probably use a larger aperture because I want mostly that one object in focus.

I use the meter to tell me with a given aperture what shutter speed will I need. I usually don't go slower than 1/125 or maybe 1/60 unless it's getting dark and I'm losing light (and then I'll have to brace myself to support the camera). My starting point and where I reset the camera when I'm done is usually f8 and 1/125 and then I meter and adjust from there.

When I've done sports I usually use a midrange to smaller aperture most of the time because I want a number of players across the field of play/arena all in focus. If I want a more close up portrait style shot of one player then I'll open up the lens more.

Think about how much of the area in front of you and your camera you want in focus, everything between you and something off in the distance? or just a relatively small field of view in front of you?

Have you been looking at something online that makes you think you should be using larger apertures? Try taking some test shots of the same subject/scene at different apertures and look at the differences so you can learn how the field of view changes when you change aperture.

 

[Scatterbrained]

Okay so say you're using a 35mm, and you're shooting something 100 feet away. There are no water, no clouds, no moving starts, nothing between you and the scene 100 feet away, and no people walking about, why use f1.4 and a quick shutter speed versus say f8 and a slower shutter speed? Bokeh and focus distance is no issue since the focus point is so far away.

Because at f/1.4 iso 100 you may not be able to get a propper exposure with the max shutter speed of you camera. The difference between f/16, iso 100, 1/100th (Sunny16 rule) and f/1.4 iso 100 is 2/3 of a stop, putting you at almost 1/16000th for shutter speed. Since most pro bodies stop at 1/8000th and consumer bodies tend to stop at 1/4000, I can see a good reason to stop down a bit.

Beyond that, as has been pointed out, the lens is likely to sharpen up when stopped down, as well as helping to eliminate chromatic aberrations. This doesn't mean you need to stop down to f/16, for example, my Sigma 35mm f/1.4Art is sharpest at f/4. My 85mm f/1.2 is also sharpest at f/4, but my 24-70mm f/2.8 is sharpest at f/5.6. When you want absolutely as much clarity and detail as possible it's best to find the lenses "sweet spot" and shoot it there.

Another thing to bear in mind when discussing DOF and wide angle/ultra wide angle lenses is that focus falloff is very gradual compared to a telephoto lens. For example, this first shot was taken at 17mmf/4 (on FF) from just over arms length away (very close) yet you can still clearly tell what everything behind her is:



This shot was taken at 85mmf/4 from about 13ft away and by the time you get 2ft behind the point of focus everything is already becoming a blurry amalgam of colors:



This was taken at 600mm and f/8 and the area of sharp focus is less than a foot, the area of discernible detail isn't much larger than that:




So as you get wider the shallow DOF matters less because the falloff is so gradual. Shooting wide open or stopping down becomes more a matter of preference as the focal lengths get shorter. When you get really wide you can get just about everything in the frame sharp with the lens wide open. This can be especially advantageous in low light.

 

[shaylou]

Okay so say you're using a 35mm, and you're shooting something 100 feet away. There are no water, no clouds, no moving starts, nothing between you and the scene 100 feet away, and no people walking about, why use f1.4 and a quick shutter speed versus say f8 and a slower shutter speed? Bokeh and focus distance is no issue since the focus point is so far away.

Most lenses are sharper stopped down a bit.

 

[KmH]

Okay so say you're using a 35mm, and you're shooting something 100 feet away. There are no water, no clouds, no moving starts, nothing between you and the scene 100 feet away, and no people walking about, why use f1.4 and a quick shutter speed versus say f8 and a slower shutter speed? Bokeh and focus distance is no issue since the focus point is so far away.

Most lenses are sharper stopped down a bit.

Actually, stopping down to improve sharpness applies to 'fast' lenses a lot more than to consumer grade lenses that have a max aperture of f/3.5 to f/6.3 or slower (let in less light).

Most of the lenses out there have the slower f/3.5 and slower max apertures.

agp doesn't yet know that bokeh is not adjustable and in the context used is really referring to depth-of-field, that is adjustable.

It is true that DoF gets much deeper as the focus point gets further from the camera and at some 10's to hundreds of feet the far limit of DoF effectively become infinite regardless the lens aperture used.

 

[minicoop1985]

Okay so say you're using a 35mm, and you're shooting something 100 feet away. There are no water, no clouds, no moving starts, nothing between you and the scene 100 feet away, and no people walking about, why use f1.4 and a quick shutter speed versus say f8 and a slower shutter speed? Bokeh and focus distance is no issue since the focus point is so far away.

Actually, I wouldn't use f/1.4. I's use f/8 or f/11, whatever is the sweet spot for the lens I'm using.

I've got a 58mm f1.4 Rokkor for my old Minolta MD mount stuff. First thing I did was fire it off at f1.4. That did not end well.

There's a few lens review sites out there that provide rather clear data (if I can figure it out... you know) to point to where the sweet spot is on a specific lens. I like Photozone personally-here's an example using my main lens:

Tamron AF 17-50mm f/2.8 SP XR Di II LD Aspherical [IF] (Canon) - Review / Test Report - Analysis

I'm sure there's plenty others that do this too, but this one's been the most straightforward to me.

 

[alexharris52]

That's true, what 480sparky said... The lense has a sweet spot and it's typically not at the extremes. I shoot video as well and none of my stuff is ever super shallow just because the lens isn't normally working at it's prime in that area (people also walk back and forth) I have a sigma 24-70mm and even though it can stretch to 2.8, I kind of usually just keep it at f/5.6 whenever I can (assuming there is enough light)
My site is Noble Studios if anybody cares to see how a sigma 24-70 looks for video, 90% of my stuff is filmed at high f stops.

And for agp: It's usually easier to be wrong about the focus with a small f stop, you have to really dial it in. f/11 means you have much more room to be "in focus" as far as the focus ring is involved.

 

[hamlet]

I just shot something at f/11 with a f/2.8 lens. Blasphemy.

If you want to really get peoples knickers in a bunch, buy an f/1.2 lens and shoot it primarily at f/8-f/16.

Pfff... 1.2? You might as well shoot at 8 or 16 with an aperture that small.

 

[hamlet]

Okay so say you're using a 35mm, and you're shooting something 100 feet away. There are no water, no clouds, no moving starts, nothing between you and the scene 100 feet away, and no people walking about, why use f1.4 and a quick shutter speed versus say f8 and a slower shutter speed? Bokeh and focus distance is no issue since the focus point is so far away.

Actually, I wouldn't use f/1.4. I's use f/8 or f/11, whatever is the sweet spot for the lens I'm using.

This is usually true, but it also really depends on what lens you've got this advice is not always 100% applicable to every lens. Here is a website where they have done the tests for you: link. But be aware that even lenses that are of the same model aren't completely identical, because no two lenses will ever be completely the same.

 

[480sparky41 40]

.........But be aware that even lenses that are of the same model aren't completely identical, because no two lenses will ever be completely the same.

That's why I do my own testing on every lens I own. I never go by what some website says is the sweet spot.

 

[timor]

But don't stop down too much. Going with too small aperture, depending of the size of your sensor, you will run in another problem called diffraction. Smaller sensor, quicker diffraction will ruin sharpness of your DoF. Ever noticed that small compacts are going only to f8 ?

 

[hamlet]

But don't stop down too much. Going with too small aperture, depending of the size of your sensor, you will run in another problem called diffraction. Smaller sensor, quicker diffraction will ruin sharpness of your DoF. Ever noticed that small compacts are going only to f8 ?

Here is what btobey says about my crop sensor for instance:

DIFFRACTION LIMITATIONS


The D3200 pixel pitch (pixel size) is only 3.85 µm (microns). What does this mean? Well in order to capture full detailed images at 24 MP many factors come into play, primarily diffraction limitations. Diffraction is an aspect of the lens and a limitation of physics. The ability to observe the effects of diffraction are determined by the area of the sensor and the density or pixel spacing. The D3200 packs a lot of pixel in a small area and is more sensitive to diffraction than previous less dense sensors (D3100, D5100, D7000, etc).

Based on the Rayleigh diffraction limit ~1600 / f-number. The D3200 is diffraction limited around f/5.6 when viewed at 100%. Now most of us do not view pictures at 100%, therefore when viewed at normal screen sizes, or on standard print sizes (11 x 14) it is hardly diffraction limited. But in order to attain the most detail, you should shoot at f/5.6 and below. The 18-55mm VR kit lens is superb, but it is not sharp until about f/8. So in order fully take advantage of the full resolution of the sensor, I would recommend a prime lens such as the 35mm f/1.8G ($199) or the 50mm f/1.8G ($219), as these lenses are phenomenally sharp at f/5.6. However, this is only a suggestion for those looking for ultimate detail, as this is not the case for most photography application. Remember that sharpness is generally over emphasized, and nobody cares about a super sharp image that looks like crap!

But just because you are shooting with a full frame doesn't mean that diffraction stops being a problem, here is what they had to say about the d800:

According to these theoretical approximations, we conclude that ideally we would want to shoot the D800 at f/8 or below in order to prevent diffraction from softening pictures. However, the calculation is flawed in that in accounts for only a single frequency. In our case, we selected 500nm wavelength, which is the color green, the most sensitive to our eyes, to replicate daylight. However, daylight has many colors or frequencies and therefore we must consider the entire bandwidth. This calculation becomes more complicated, but when analyzed across a bandwidth, diffraction becomes more forgiving, which means we can shoot the D800 up to f/11 and be perfectly satisfied with the results!

 

[naturallymaternal]

To achieve a nice blurred background