When and why to use middle apertures?

[SteveKelly]

I read all about using large apertures for shallow depth of field, to single out a subject, bokeh, etc. And I read all about using small apertures for the opposite effect, sharp pictures from front to back, great landscapes, etc. But no one talks about middle apertures and their purpose. So when ARE they appropriate? Why and what are they used for?

 

[tirediron]

When you need to to acheive a particular exposure, when you want the sharpest focus (no lens is ever at its best wide open or stopped down fully).

 

[KmH]

+1 that the middle range of apertures usually gives the sharpest focus.
The middle range of apertures is sometimes also known as 'don't care' apertures in that the DoF that range of apertures deliver is often a minor image element concern.

Point of focus distance has as big an effect on DoF as lens aperture does. Many shooting landscapes run unto focus sharpness issues because small lens apertures cause diffraction and they focus way to far into a scene.
In other words, most landscape shots should be made with a middle range aperture and an appropriate hyperfocus distance.
Understanding Depth of Field in Photography
Diffraction Limited Photography: Pixel Size, Aperture and Airy Disks
Understanding Your Camera?s Hyperfocal Distance

 

[Derrel]

The middle apertures are often the very-sharpest, best-performing apertures on many lenses, and on many cameras. These days, as we get into higher and higher megapixel count sensors, the smaller f/stops, like f/5.6 and f/8 are already showing diffraction, which is an optical phenomenon that causes a loss of sharpness. So...with today's 24-MP sensors, many good lenses produce their sharpest images at surprisingly wide apertures, like say, f/4 to f/5.6 or thereabouts.

Another issue is sensor dust spots: at the moderate apertures, sensor dust spots appear on-screen as about 3mm, round, soft, gentle-edged, faint blobs--which are VERY easy to clone out using the clone stamp tool, and on areas with a lot of detail, these sensor dust blobs can often just be left in the shot, since they are very hard to spot unless they appear on broad, smooth areas, like the sky for example. At f/11, the same sensor dust blob will generate a DARK, dense, "speck", which is very noticeable, no matter where in the frame it happens to fall.

Another benefit of the middle apertures, like f/4 to f/6.3, is that they tend to keep the shutter speeds HIGHER than if a smaller aperture were used. Again, this is an issue the more that we move into the high-resolution era of 16 and 20 to 24, to even 36 MP captures. With a 24MP camera and a 70-300mm lens at 300mm length, at 1/320 second and f/5.6, if you look CLOSELY, you will see that people who are just moving normally are, fairly often, actually NOT 100% sharp on moving extremities.

It's subtle, but the difference between say 1/125 second and 1/500 second can make a big difference in perceived sharpness on many scenes, now that wee have moved away from the 6 to 8 megapixel era...

 

[WayneF]

Go to a good lens test site ( like Nikon / Nikkor (APS-C) Lens Tests ) and look at any lens there. (OK, regular lenses, lets exclude one or two of the most extreme lenses, like fisheyes)

Go to the Analysis page of that any lens, where lens resolution is shown. Typically sharpness peaks around f/5.6 (very roughly).

This is because as lenses are stopped down, they suffer from greater diffraction. But as they are stopped down, they only use a smaller center spot (ruling out the larger diameter glass areas which is much harder to correct). So this is a minus and a plus, a trade off which peaks (very roughly) about f/5.6.

(It is only my own approximation saying "f/5.6". The technology does not specify it... it just seems to work out about that way).


In the early days (let's say until the early 1960s), Kodachrome slide film was speed ASA 10 (same as ISO 10 later). It had a great reputation, color and range, etc, and it was considered extremely sharp. And it was, but the slow speed was also some of the reason. Sunny 16 was f/16 at 1/10 second, which is f/5.6 at 1/80 second equivalent. So common shutter speeds of 1/60 or 1/100 second put it that f/5.6 area, which was the sharpest for the lens too.

 

[lennon33x]

Another reason to stop down to decrease flash exposure if you're using OCF/flash

 

[flyin-lowe]

Like those said above, this can be the sharpest aperature. The "who cares" nick name was mentioned above. In terms for a beginner (like myself) you can use this range when the DOF is not vital. Lets say you are taking a picture of your child standing against a brick wall. A high or low f/ stop won't gain you much so go to the middle and get the sharpest image you can get out of your lens.

 

[Big Mike]

Welcome to the forum.

And I read all about using small apertures for the opposite effect, sharp pictures from front to back, great landscapes,

I used to think that, but we need to realize that when you use smaller apertures, your image quality will suffer due to diffraction. It usually starts when you get smaller than F11 and it gets worse at F16, F22 etc.

So rather than just using a very small aperture to maximize DOF, I've learned to use a DOF calculator (smart phone app) and hyperfocal focusing. This often shows me that I can get the DOF that I need, with something like F8 or F11, rather than just going to F16 or F22.

 

[SteveKelly]

So with megapixels so high these days you can actually see diffraction at f/8? Can you get something from two feet away to infinity in razor sharp focus at f/8 or even 5.6?? If not then why buy any camera over say 16 megapixels? Also if diffraction starts so small why have a camera even equipped to go to f/11 or f/22?

 

[Derrel]

So with megapixels so high these days you can actually see diffraction at f/8? Can you get something from two feet away to infinity in razor sharp focus at f/8 or even 5.6?? If not then why buy any camera over say 16 megapixels?

YES, on high MP cameras, diffraction easily can be seen at f/8. And why buy any camera over 16 MP??? Well, good question. It seems that 16 million pixels is a sort of "sweet spot"...it's enough MP for a good, high-quality image, but not so many MP that it necessitates huge memory cards and lots of hard drive space. But the fact is, there are lenses that can deliver super image quality at wide f/stops, and on full-frame sensors, one can go above 16MP and not have a lot of issues withy diffraction at good, workable f/stops like f/2.8 and f/4 and f/5.6. Many people shoot a fair amount of wide-aperture stuff, like at f/2.8, especially with "big glass" and "high-end primes" (35/50/85/105/135/200/300/400), many of which have excellent image characteristics at wide apertures. For people who want medium-format-like image quality in a smallish, lightish, fast-focusing body with TONS of lenses available, the NIkon D800 and D800e exist. Big prints, high detail levels, and loads of "Crop-ability".

The 24-megapixel full-frame cameras from Nikon and Sony, available since 2009, make BIG files, with gorgeous images possible. It started with the D3x and the A900 back in 2009, when Sony made the first 24 MP d-slr sized sensor, and it has only continued. A number of the people who want to make BIG prints, mostly landscape shooters and fine art types, really like these high-resolution cameras' images. QUite a few of these types of people are happy to do focus-stacking at "optimum" f/stops, and they skirt around diffraction effects pretty well.

There is also that "because we can" issue too; I wonder, why do the motorcycle makers make the various superbikes, capable of 200 MPH, when the speed limit is 55 to 65 most places?

 

[pgriz]

Diffraction does reduce the fine detail. However, you'll notice that only if you have focused perfectly, there's no camera motion blur, and you aren't complicating your life with "protective" filters. And you have a sensor that is capable of revealing that fine detail. Do your own test - put the camera on a tripod, the shutter on delayed release, focus manual & with liveview if you have it, turn off your IS/VR, and shoot a series of shots from f/4 through your smallest aperture (say f/22 or f/32), using something with fine detail (a newspaper classified ad listing, or cloth with visible threads). Compare the shots on your computer after downloading and enlarge them to 100%. Now you can see for yourself how the quality of the image in the target area changes with aperture.

That's your benchmark. Now try the same thing handheld - same target, same distance, same focal length, but focusing the way you'd normally do it. Compare the hand-held vs. tripod mounted at various apertures. I think you'll find that the hand-held shots will almost always be more blurry or soft than the tripod mounted shots.

So, yes, diffraction does affect the fine detail. But for most people, under common shooting conditions, the reduction in quality is barely visible.

 

[WayneF]

Megapixels and diffraction are simply different stories, not related. Yes, lenses suffer greater diffraction as they stop down, no matter what size your frame.

Images show higher resolution as the frame size is enlarged (the past popularity of medium size film, and 4x5 and 8x10 sheet film were even better).
Even 35mm film was FX size too. Their lenses suffered diffraction too.

Enlargement degree is a factor - not same as resolution, but both allow seeing all detail better, including diffraction.

Tiny compact sensors simply don't allow stopping down much past f/4, due to diffraction (same diffraction as other f/4 lenses, but enlargement of tiny frame shows it so much). i.e, big frames are still better.

But diffraction is NOT about megapixels.

 

[Braineack]

There is also that "because we can" issue too; I wonder, why do the motorcycle makers make the various superbikes, capable of 200 MPH, when the speed limit is 55 to 65 most places?

So I should stop saying for that $40K 40MP Hasselblad?

 

[Derrel]

Yeah...stop the Hassy savings fun, and spend the money on a big long vacation with the wife! Not naming names, but last week I saw some tripod-mounted landscapes shot at f/22. Man, they looked fuzzy. Just simply NOT good. Sure, totally adequate depth of field, but very soft. The effects of diffraction were pretty evident.

 

[Braineack]

We are in the process of planning a trip to CA in May/June. Flying into LAX (will try to see a taping of Conan), a few nights in Santa Barbara, a drive up the coast, a few nights in SF, and a few nights in Napa, flying back out of SFO.

Shopping for bags for it, looking at the Lowepro 250 Urban Sling. Plan to bring the 24-70, 70-200, and a flash. Looks like that will fit it all perfectly.