December 15, 2017, 09:05:22 PM

Author Topic: DOF: When is shallow too shallow?  (Read 4726 times)

Pippan

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Re: DOF: When is shallow too shallow?
« Reply #15 on: November 10, 2017, 07:28:44 PM »
Depth of field is too shallow when you loose resolution and details on your subject. Since digital/internet, very shallow DOF looks somewhat ok because of the low resolution of photos displayed on today's low resolution screens. Blurry parts become sharper when resized. But when printed big, you start to think that it looks wrong when most of the subject seem to swim in a pool of their own blur. Basically when there's more blur than actual sharp subject, it's a waste of ink.

Traditionnally in portraiture, you want the visible part of your subject sharp, especially the contour/silouhette/edge against a blurred/non-distracting background. That creates the separation and make your subject pop-out 3D like. With a too shallow DOF, the background is indeed smoother, but so is the subject: separation is not increased (in fact, it is visually decreased because, as you said, the subject start to melt in the background).
A human head depth is around 20 cm, so your DOF needs to be at least ~15cm (5 in front, 10 back) so you get all front parts of the face + half of the head to get the edges in sharp focus. Including the body, you may want a DOF of 20~60cm depending of the size and position of the subject.
Now, just like macro photography, the closer you get, the narrower the aperture needs to be for a decent DOF, but here is a thing: the tighter the framing, the less background you get, therefore the less important the background/subject separation needs to be. So a shallower than the theorical 15cm DOF for a headshot is still acceptable, as long as the entire face remains sharp and not just the eyes with some bits here and there.

Personnally, I usually shoot at the following apertures that I set as standard for myself:
Headshot: f/8 (7cm DOF)
Head and shoulders: f/5.6 (10cm)
Medium (at the waist): f/4 (14 cm)
American (above knees): f/2.8 (20cm)
Italian (under knees): f/2 (28cm)
Full body: f/1.4 (40cm)
(Coincidentally, shooting distances are increased/decreased by 1.41 - square root of 2 - for every other of those standard framings in portraiture, just like standard lens focal length and extenders, and so are my chosen f/numbers and therefore resulting depth of field).

Now that it's understood that apertures for controlling DOF are more or less set in stone depending on the size and distance (given for a focal lenght) to your subject, how do you get a even smoother and more blurry background? That is done with distances.
First, the more you physically separate your subject from the background, the more... separated your subject will be from the background (duh!). With greater distance between subject and background, there will be more of the former, but it will be much more blurred.
Second, working with long focal lengths to force yourself further from your subject. Backgrounds are magnified = less of it in the frame and magnified blur. This works only in conjunction with the first condition: if there's no distance between subject and background, then there's no perspective to compress.
Of course, every of those things is not always possible in all situations. Having to back up constantly gets really annoying very quickly, very compressed/flattened portraits you get with long lenses are impressive at first, but they feel unnatural and cold and you'll eventually get bored by the same look. Photography is always compromise and there are much more important things than blur in portraiture, so don't get too obsess with the bokeh thing.

About fast lens and portraiture, they are great for:
- full body shots: at longer framing distances, DOF gets much deeper that a standing human body, so no problem with very large apertures. Just don't be afraid to stop the aperture down if you want a decent DOF as you get closer, it is not forbidden.
- available light portraiture: you are willing to trade subject sharpness/separation for a cleaner image. In return you also get impressive bokeh.
- stopping motion for candid/unposed portraits: they are usually done with some distance, so depth of field don't get too shallow and you are allowed fast shutter speed with low ISO settings.
Thank you so much for this explanation of DOF in portraiture, it is by far the clearest and most helpful I've ever read. I'm going off now to practice on my children ...

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Re: DOF: When is shallow too shallow?
« Reply #15 on: November 10, 2017, 07:28:44 PM »

abcd1234

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Re: DOF: When is shallow too shallow?
« Reply #16 on: November 10, 2017, 09:33:33 PM »
Thank you so much for this explanation of DOF in portraiture, it is by far the clearest and most helpful I've ever read. I'm going off now to practice on my children ...

You're welcome, hope that helps!

A little bit of explanation about the apertures I use for each framing:
- For full body, you get f/1.4 which is about the widest you can get with DSLR lenses (with few exeptions).
- Making your way closer to american framing, this is the tightest framing where most of the body is in the frame while still having an at least equal amount of background. So this the tightest framing where I still want the edges of the subject nicely sharp. F/2.8 gives you just that with a DOF of ~20cm.
- F/5.6 for head & shoulders shots again works well, most of the subject is in sharp focus, especially women with their big feminine parts.
- And finally headshots: distance between human eyes is around 6cm. If the face is turn at a 45 angle left or right, the depth between the two eyes therefore is around 4.3cm (like FF diagonal!). And guess what? F/8 allows just enough DOF to get both eyes in focus (considering perfect focus is achieved): about 2.4cm of sharpness in front of the point of focus, and 4.6cm behind, reaching the furthest eye. Not to mention that f/8 is about the sharpest and narrowest aperture you want to use before diffraction kicks-in in our today's 30-ish MP cameras.

See how everything seems to fall magically into place? Plus, those 1-stop increments make it easy and fast to remember during actual shootings. Of course, those numbers aren't strict rules, there's nothing wrong if you want to achieve something else playing with more or less depth of field, and f/5.6 or f/8 are not ideal apertures to work with in available/low light for exemple. But I believe those are very good numbers.

CanonFanBoy

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Re: DOF: When is shallow too shallow?
« Reply #17 on: November 16, 2017, 05:39:30 AM »
CFB, this isn't really about how much/less DOF is correct. It's about what you're trying to accomplish with the image and the effect you're looking for.

1.2 @ 3 feet or 1.2@ 50 feet.  It's the distance that you need to consider and what you want in focus or not. Do you want to isolate your subject or not? Many make the mistake of just cranking wide open because they saw a great image somewhere and never consider the implication of that act. I always think about what I want first and then plan accordingly. Your best bet is to think of the final image and use the tools you have to accomplish it. Sometimes you want some butter, sometimes you want crispy. Portraiture comes in many different flavors and formulas don't work once you get past the basics. If you're using a strobe and want a thin DOF then use a ND filter... but is that what you want is the more important question.

And speaking of tools...that 70-200 will work wonderfully for portraiture. Sometime better than the 135. I have the 200 f/2 but honestly you can get a very similar look with all the lenses you mention. It's why I've said here many times, great lens but not necessary. It's heavy and a PITA to lug around everywhere... especially when you have a 135 or 70-200 or 85 or 50...etc. I know that won't stop the blood lust though ;)

Sure it's nice to have loads great lenses at your disposal but knowing how to accomplish what you want is a better use of your time and money. Many lenses can serve multiple purposes and help you narrow down the lens swaps and camera juggling (and save you 30-50lbs off your back). I guess my point here... lenses and cameras are just tools in the bag and they won't do you a bit of good if you don't know the why's and how's.

And thanks...

Sage advice as usual! Thanks Pookie.
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CanonFanBoy

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Re: DOF: When is shallow too shallow?
« Reply #18 on: November 16, 2017, 05:41:25 AM »
Thanks guys! Lots of great thinking and I appreciate all of it.
5D Mark III, Canon A-1, Voigtlander Vito, Tamron SP 15-30 f/2.8 Di VC, 24-70 F/2.8L II, 70-200 f/2.8L IS II, 35 f/1.4L II, 135 f/2L, Helios 58 f/2 (x3), Canon FD 50 f/1.8, 600EX-RT (x7), Streaklight 360ws. Jumping ship to SoNikon any day now.

Viggo

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Re: DOF: When is shallow too shallow?
« Reply #19 on: November 16, 2017, 05:56:50 AM »
I shoot most or all of my portraits with my Siros L and wide open aperture, but change distance and focal length to control DOF. Simply because I feel that wide open pop goes away even a stop down so I want to keep it. But if I want my subject sharp, I use the 35 and use little distance instead of longer FL and stop down. When I use my flash and a a “studio background” where bokeh doesn’t matter I can stop down a bit more, but often closer with longer FL.
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Ian_of_glos

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Re: DOF: When is shallow too shallow?
« Reply #20 on: November 16, 2017, 07:13:44 AM »
There is no right answer to this, because it really depends what effect you want to create. You might want the shallowest possible depth of field in order to focus attention on one particular item - a ring on the model's finger, or an award that the model is holding for example. Alternatively you might want to show the model in context - a workman in a workshop or a chef in the kitchen. For this type of picture you will want the background to be in focus, even if it is not as sharp as the actual subject.
Recently there has been a lot of discussion about bokeh and the quality of bokeh, almost as if it is a separate and competing subject in the scene. However, to me it is just a way of removing a distracting background by throwing it out of focus, or at least making it so out of focus that you cannot tell what it is. It is an alternative to over or under exposing the background, changing the shooting position so the distracting background is no longer in the frame or using an artificial background. All these techniques are valid and will come in useful from time to time.
In the studio, where I am able to control the light and the background I don't worry about depth of field and just use an aperture that is somewhere in the middle - F8 usually.
Outside, sometimes I deliberately use a narrow aperture because I want the background to be sharp, for example a farmer leaning on the farm gate with the rolling hills in the background. At other times the background might be so ugly that I want to throw it completely out of focus, and that might mean that only the model's eyes are really sharp and the ears and nose are beginning to blur.

Jack Douglas

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Re: DOF: When is shallow too shallow?
« Reply #21 on: November 16, 2017, 10:01:02 AM »
As a novice I'm appreciating all these comments!

Jack
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Re: DOF: When is shallow too shallow?
« Reply #21 on: November 16, 2017, 10:01:02 AM »

ethanz

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Re: DOF: When is shallow too shallow?
« Reply #22 on: November 16, 2017, 03:54:49 PM »
You can actually have both bokeh and full subject in focus with this:
https://petapixel.com/2014/07/28/bokeh-problem-focus-backgrounds-hold-can-get-fast-prime/

 ;D fake bokeh FTW!

That's actually a pretty cool idea.
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stevelee

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Re: DOF: When is shallow too shallow?
« Reply #23 on: November 16, 2017, 05:02:52 PM »
A distracting background can be just about as distracting when out of focus. Pick your backgrounds if you can, and don’t expect blurriness to cover your laziness.

A blurry background that calls attention to itself is calling attention to itself. No matter how poetic you wax in fractured Japanese, you are missing the point of the picture, unless the point of the picture is that my fast prime is better than yours at blurring things.

With a bad combination of focal length, subject distance, background distance, and aperture, a portrait can look more like a picture of a cardboard cutout or the Photoshop equivalent.

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Re: DOF: When is shallow too shallow?
« Reply #23 on: November 16, 2017, 05:02:52 PM »