Archive for the ‘sharpness’ Tag

Friday Foto Talk: Sharpness vs. Depth of Field, Part II   3 comments

A train runs up the Columbia River Gorge in Oregon.  This is not an image with many tradeoffs.

A train runs up the Columbia River Gorge in Oregon. This is not an image with many tradeoffs.

This is the second of two parts.  Last time we discussed lens sharpness in general, & learned how to find a lens’s sweet spot.  Check out Part I.  Did you do your homework?  Hint: it was finding the sweet spot for your lenses!  Remember all these images are copyrighted and not available for free download without my permission.  Just click on them to check out purchase options on the main part of my webpage.  If you can’t find something or have any other questions just contact me.  Thanks for your interest.

Now we come to the meat of the matter.  How much does all this matter?  For one thing, you should realize that photography has changed with the advent of digital cameras, specifically the emergence of high-quality digital cameras.  Sharpness and clarity are now expected by people.  This is not generally a bad thing.  But it is narrowing the range of images that people will look at for longer than a nanosecond.  And that is a bad thing.

Dawn on the upper Columbia in Washington.  Shot at f/22 to maximize depth of field.  Sharpness is not at maximum for this lens though.

Dawn on the upper Columbia in Washington. Shot at f/22 to maximize depth of field. Sharpness is not at maximum for this lens though.

Notice I said sharpness and clarity, not focus.  As an example take my post for Single-image Sunday, the Fog Returns.  It’s an image that, while perfectly focused, is not particularly sharp.  I’m using the word sharp in its broader sense here.  It is encouraging that I a little push-back against this quest for sharpness in all images.  But there are currents that are taking us in the other direction as well.  For example focus stacking (where several images are captured and combined in Photoshop to have several focus points in the same image) is subtly changing the expectations of image viewers.  To think I’m essentially being forced to do composites in Photoshop: ugh!

I posted this in a previous post, but here it is again because it's one of just three images I have photo-stacked thus far.

This image from Olympic N.P. appears in a previous post, but here it is again because it’s one of just three images I have thus far captured & processed by photo stacking.

But let’s leave that aside and focus on sharpness vs. depth of field.  You might be aware of all the tradeoffs in photography, and this is certainly one of them.  But before we discuss that, here are a few givens:

      • Some lenses are sharper than others, but that’s not your concern.  Your concern is to get the best pictures possible with the equipment you have.
      • Most images that are not as sharp as they could be are down to user error.  If you don’t stabilize your camera on a tripod (or shoot at a fast-enough shutter speed if hand-holding), do not expect a sharp image.  Use a cable release or timer delay as well.  Mirror lockup, if your camera has it, has a lesser effect but is still worth doing.
      • Atmospheric conditions, particularly at longer focal lengths, will also affect apparent sharpness.
      • Some lenses are capable of being sharper stopped all the way down than other lenses, and can thus give you a greater apparent depth of field.
      • The wider your focal length, the greater your depth of field will be.  Though it’s a continuous change, think about 21 mm. as the cutoff between very short/wide focal lengths and just wide/longer focal lengths.  Telephoto lengths (greater than 70 mm.) will yield much shallower depths of field.
      • Despite the above factor, aperture is still the biggest influence on depth of field.
Sandstone formations in Utah.  I was very close to the foreground and my focal length was not super wide.  While managing to get good sharpness in the foreground, I sacrificed some sharpness in the background.

Sandstone formations in Utah. I was very close to the foreground and my focal length was not super wide. While managing to get good sharpness in the foreground, I sacrificed some sharpness in the background.  Since I did not want this to be too noticeable, I used a small aperture – f/22.

Shooting “Deep” Scenes: The Trade-off

Now let’s get to that tradeoff between sharpness and depth of field.  If you want to maximize depth of field in your image (that is, sharpness from very close to very far away), you will be shooting at small apertures.  So unless you are going the focus stacking route as mentioned above, you will be shooting a good ways past your sweet spot.  Once you are two stops above the sweet spot (f/16 if your sweet spot is f/8, for example) you’ll notice a small drop in sharpness.

Let’s take an example.  Say you are shooting a sunrise over a lake, with interesting rocks close by and beautiful forested mountains in the background.  If you get low and close to those rocks, you might choose a very wide angle in order to get everything in.  This will also help to maximize depth of field, but to really get there you will also use a small aperture like f/22.  In order to show the fascinating detail in those foreground rocks, you will be  focusing fairly close, perhaps only a foot or two past the closest rock.

Sunrise at Lost Lake with Mount Hood emerging from the fog.  This is the same scene as last Wednesday's post, the Fog Returns.

Sunrise at Lost Lake with Mount Hood emerging from the fog. This is the same scene as last Wednesday’s post, the Fog Returns.

This all sounds wonderful doesn’t it?  But as with many things in life, there’s a hitch.  One of photography’s tradeoffs has raised its ugly head!  Depending on your lens the overall sharpness of your image will be just a bit less than what it is at the sweet spot (say that is f/8).  This is because of diffraction, as mentioned in Part I.

But that’s not all.  With most lenses, that image will also have its background slightly out of focus.  If you’re lucky (rich?) enough to have a Nikon 14-24 mm. or other similar lens with a big curved front element, this effect is certainly minimized.  But it is still there.  You can focus deeper into the image, but then your foreground will be slightly out of focus.  Shooting at a very wide angle and with a high-quality lens helps out with this tradeoff, but it will always be a balancing act.

This is hot off the presses, from last night.  If you are interested in the high-resolution version, just click on it.

This is hot off the presses, from last night. If you are interested in the high-resolution version, just click on it.

I normally just accept some diffraction-related softness and go with f/22.  But this is when I’m using my Tokina 16-28 mm. lens.  With my Canon 24-105 f/4, I know it’s softer at f/22 than the Tokina and does not attain quite as large a depth of field.  This is only partly because of the longer focal lengths; some has to do with the lens optics. The Canon does more things than the Tokina, so it can’t do the one thing as well.  More tradeoffs.

Focal Point & Depth of Field

Let’s dive a bit deeper into the focal point: where to focus?  It’s a question many photographers struggle with.  For me, it not only depends on my desired focal length, but on the balance between background and foreground in the image.  You should ask yourself, which is the dominant feature in my image: is it in the foreground or background?  That main subject is what you should try to keep as sharp as possible.

Sometimes I will sacrifice and move back from my foreground, especially if my background subject is a strong one.  This will increase apparent depth of field, but it might also force a longer focal length, which in turn decreases depth of field.  Again, a balancing act.

Death Valley, California.  Good detail in the foreground sand was most important here, and the background dunes were not as big a part of the image.  So I shot at f/16 and focused on the sand in front of me.

Death Valley, California. Good detail in the foreground sand was most important here, and the background dunes were not as big a part of the image. So I shot at f/16 and focused on the sand in front of me.

Blooming beargrass on Silver Star Mountain in Washington, with Mt Adams in the background.  At this focal length (165 mm.), no chance for sharpness in both fore- and back-ground.    But I still shot at f/22 so the mountain wasn't too out of focus.

Blooming beargrass on Silver Star Mountain, WA. At this focal length (165 mm.), no chance for sharpness in both the flowers & Mt. Adams. But I still shot at f/22 so the mountain wasn’t too out of focus.

Focal Point & Subject

Say you have a strong foreground and a less important background.  It’s a seascape with a fascinating foreground and no interesting boat or other element in the background.  You may just focus on the foreground and not care much about the background, even shooting at f/11 in some cases.  This is how I handle those scenes.  But I will often bracket my apertures, shooting at f/11 to f/22 (or whatever the minimum aperture is).

Now say you’re shooting a scene where your background subject is most important, yet you still want maximum depth of field.  First off, definitely consider putting your foreground a bit further away as mentioned above.  But this time, since the background is dominant, focus closer to it; about one third into the scene is the rule of thumb.  Since your background is most important, you might increase focal length to make it bigger (longer focal lengths increase magnification).  But careful!  You could lose too much depth of field, putting your foreground out of focus.  This is more likely if you’re tempted to shoot at wider apertures (smaller f/number) to get closer to that sweet spot.

Mount Rainier in the morning.  This is a shot where sharpness on the background is important but so is good depth of field.

Mount Rainier in the morning. This is a shot where sharpness on the background is important but so is good depth of field.

Recent foggy shot at Lost Lake. While sharpness is somewhat important for the baby tree, great depth of field is not that important.

Recent foggy shot at Lost Lake. While sharpness is somewhat important for the baby tree, great depth of field is not that important.

You can always keep a very wide angle and crop later, thus helping to get better (apparent) depth of field and sharpness both.  The tradeoff in that case is a smaller digital file, which is not really good if you’re thinking of printing the image large.  If you’re using focal lengths of 50 mm. or greater, focusing one third into the scene should be your default point of focus.  Just don’t get too locked into this, and always try to check focus right after the shot by zooming in on your LCD.

Okay, that’s enough for now.  I’m willing to answer any questions on this somewhat convoluted topic, so fire away.  If you’re not getting a quick answer it means I’m probably out shooting!  Have a great weekend everyone.

It's getting dark earlier!  Although some depth of field is important here, I opened aperture up a bit (f/8) to avoid using a high ISO and keep exposure time reasonable (to avoid smearing the clouds and moon out too much).

It’s getting dark earlier! Although some depth of field is important here, I opened aperture up a bit (f/8) to avoid using a high ISO and keep exposure time reasonable (to avoid smearing the clouds and moon out too much).

Friday Foto Talk: Sharpness vs. Depth of Field, Part I   15 comments

Good morning Sunshine!  One more shot from my recent trip to Olympic National Park.  I needed maximum depth of field here and so things are not at maximum sharpness for this lens.  Is it enough?  I think so.

Good morning Sunshine! One more shot from my recent trip to Olympic National Park. I needed maximum depth of field here and so things are not at maximum sharpness for this lens.  Is the image sharp enough?

This is a bit of a sore subject with me.  One reason is that it’s one of those things in photography that is a trade-off, a limitation if you will.  When you’re going for either super-deep or super-shallow depth of field, a fall-off in image sharpness can occur.  This is a much bigger deal with the small apertures (big f/number) used to maximize depth of field than it is with large apertures (to throw background out of focus).  It’s also more noticeable with some lenses, and generally speaking the higher quality your lens the less falloff in sharpness.

But there’s another more important reason I’ve avoided this topic on Friday Foto Talk to this point: I think it’s an overdone subject, at least the way it’s discussed on so many photog. forums.  Too many folks obsess too much over the sharpness of a particular lens or lens/camera combination.  In my experience, images that are not as sharp as I would have liked are not the fault of my equipment. They’re my fault!

An example of a shot with foreground so close it is difficult to get everything sharp front to back.

An example of a shot with foreground so close it is difficult to get everything sharp front to back.

The Sweet Spot: Testing your Lenses

You might have heard of this before.  The sweet spot of a lens is that aperture where sharpness is at its peak.  It is generally about two stops above (smaller than) the lens’s maximum aperture.  So for example with a 24-70 mm. f/2.8 lens, the aperture that will yield the sharpest images is about f/5.6 give or take.  Since the sweet spot varies quite a bit by lens, you need to take each lens and experiment to find it.  Once you find it, it’s a good go-to aperture for images where depth of field is not a concern, particularly if you’re printing very large.  But don’t be like so many others and over-emphasize this.  Photography is about making pictures; it’s not a sharpness contest.

If you want to make this a real test, one where you can check your lenses’ real-world sharpness at the same time as finding their sweet spots, you’ll need to pick a day with clear air.  Dawn is usually clearest.  Go up high or out away from pollution, on a mountain or out on the prairie or desert is good.  Hey, you might as well have fun doing this!  Pick a mountain or hill at least a mile away with some good detailed features.  Trees backlighted along a ridge-line are perfect!   You want everything at infinity, and you want details at a variety of sizes.  If you’re testing a long tele lens, heat waves or dust will ruin the test, so a clear day is key.  If you’re testing a macro lens, print out a focus test chart from the internet and set it up carefully (google a tutorial).

A simple shot where it's easy to have everything in focus, thus the choice of f/8 for aperture.

A simple shot where it’s easy to have everything in focus, thus the choice of f/8 for aperture.

Back up on the mountain, put your camera on a tripod and use a shutter release or timer delay, plus mirror lockup if your camera has it.  Put it on aperture priority mode and focus by using Live View and zooming in.  Focus is of course critical.  After you focus, look at the focus indicator on the lens.  That is the point of focus for infinity, a good thing to know for each lens.  (I use this knowledge, for example, to focus for night shots of stars.)  It’s also good to check autofocus while you’re at it.  Just focus using AF then go to Live View and check the focus by zooming in.  If it’s off, you can adjust that on most DSLR cameras.  Check the manual or internet for directions on this.

Farmhouse in the Willamette Valley, Oregon.  Depth of field not a big concern, but shot at f/11 just to make sure.

Farmhouse in the Willamette Valley, Oregon. Depth of field not a big concern, but shot at f/11 just to make sure.

 

Now you’re finally ready to shoot.  Start with your lens wide open (max. aperture).  Keep shooting, stopping down one stop with each shot, until you come to the lens’s minimum aperture.  Then view each image on your computer monitor, zooming in to 100% to check sharpness.  Look at a variety of edges, from large shapes to small detail, and narrow it down to two or three to view in compare or survey mode in your software.  Don’t obsess, just make a call.  After you find the sweet spot take another look to see how the sharpness falls off in both directions from that aperture.  Don’t worry if you find some flaws in sharpness, especially if they’re in the corners.  It doesn’t mean your lens isn’t a good one.  This is just telling you its limitations, that’s all.  Always remember that sharpness is a relative thing and certainly not the most important thing in photography.  You’re just gaining information about your lenses, not seeing if you want to sell them!

A full-moon shot from the other night, the low light made me shoot at f/8.  I needed some depth of field here, and not everything has perfect sharpness.  But using my sharpest lens (a Zeiss) plus tripod sure helped.

A full-moon shot from the other night, the low light made me shoot at f/8. I needed some depth of field here, and not everything has perfect sharpness. But using my sharpest lens (a Zeiss) plus tripod sure helped.

You’ll see in your experiment that sharpness starts out pretty good, gets better to a certain point, then falls off (with some lenses quite dramatically) as you go to smaller and smaller apertures.  With every lens I’ve had, sharpness is much worse when the lens is stopped all the way down (minimum aperture) than when it is wide open (maximum aperture).  This is because of diffraction.  As light rays pass through a smaller and smaller opening, they are bent to a greater and greater degree.  Since your lens is the thing that’s supposed to do the bending of light rays, it’s obvious that if the rays also bend when going through the aperture opening then sharpness will be negatively affected.

Same place as previous shot but next morning.  I shot it at f/11 because the trees across the lake are much closer than the mountain.  So I needed good (not great) depth of field.

Same place as previous shot but the next morning. I shot it at f/11 because the trees across the lake were much closer than the mountain. I needed good (but not maximum) depth of field.

With large apertures you’ll probably see the softening coming in more at the edges (and especially the corners) of the image, not at the center.  Who puts their subject in the corner when shooting wide open anyway?  Still, better-quality lenses tend to minimize this.  Controlling diffraction at the small-aperture end, on the other hand, is a lot tougher. Some wide-angle lenses have large, curved front glass elements.  The Nikon 14-24 mm. f/2.8 and a few other ultra-wide-angle lenses account for diffraction at the small end, at least to some degree.  But diffraction is part of the physics of optics, so it cannot be eliminated, only controlled.

So now that we know what we’re dealing with, the question is: how does it affect our photography.  Let’s dive into that topic next Friday.  In the meantime, you have your homework.  Go out and determine where the sweet spot is for each lens in your bag.  Don’t worry if it’s hard to tell the sharpest point, say between f/5.6 and f/8.  If you shoot mainly for a lot of depth of field, write down the smaller aperture (f/8).  If you do a lot of portraits, wildlife and other shallow depth of field stuff, record f/5.6.  See you next time, and happy shooting!

The Willamette Valley.  Though I was not real close to the barn, I shot this at f/11 to keep the background trees in focus and the clouds from going too soft.

The Willamette Valley. Though I was not real close to the barn, I shot this at f/11 to keep the background trees in focus and the clouds from going too soft.

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