Photoforum Photography Challenge 2011-14 - Narrow Depth of Field & Bokeh

[TCampbell]

I've been saving this particular challenge for the holidays because nothing really shows off bokeh quite like holiday lighting in the background.

From Wikipedia.org:

In photography, bokeh (Originally /ˈboʊkɛ/,^[1] /ˈboʊkeɪ/ boh-kay, and also sometimes heard as /ˈboʊkə/ boh-kə,^[2] Japanese: [boke]) is the blur,^[3][4] or the aesthetic quality of the blur,^[5][6][7] in out-of-focus areas of an image, or "the way the lens renders out-of-focus points of light."

Recall that just a few challenges ago, we covered "long depth of field and hyper focal distance" -- well, this is the opposite effect.

When you're trying to get a foreground and background object to both be nicely focused, you want a long depth-of-field and that means you set the camera to shoot at a fairly high focal ratio. When you want to call attention to your subject and deliberately blur the background, use a narrow depth-of-field and that means you set the camera to shoot at a very low focal ratio.

You might notice that sports photographers often show crisply focused athletes, yet the spectators on the far side of the field or are softly focused and unrecognizable. This helps the subject (in their case the athletes) "pop" by providing much stronger subject isolation. Other times, however, it isn't so much that you want to keep the viewer's attention on the foreground subject, but rather that a deliciously blurred background as a very beautiful aesthetic quality... and that's we're going for here.

To create the effect, you'll want a lens capable of a low focal ratio. This means if you own a "nifty fifty" (that 50mm prime lens with the f/1.8 focal ratio that you can usually buy for about $100), now would be a good time to reach for it (or any other lens that offers a low focal ratio). If you've only got the "kit" lens (e.g. an 18-55mm f/3.5-5.6) it'll be more difficult to achieve, but you can still do it. You'll want to put more distance between your foreground subject and the background and force the camera to use the lowest focal ratio you can manage. You don't need to go lower than f/2.0 -- you certainly can and you'll get even more intense bokeh... just recognize that the depth of field will get so thin below f/2.0 that it'll be more difficult to get the subject's entire face in focus (assuming your subject is a person.) You may notice, for example, that their eyes are focused, but their ears are not.

Here's our example:


Holiday Bokeh by Tim Campbell1, on Flickr

This particular shot was taken at f/2.8 (it's the Canon EF 24-70mm f/2.8L USM lens). Remember... you want a low focal ratio lens and you want to manually set the lens to a low focal ratio.

My friend Cory "volunteered" (meaning: I harassed him until he caved) to model for the shot. Cory is sitting fairly close to the camera -- probably about 6' away. The tree in the background is probably about 12' away. If Cory had been standing just in front of the tree, the effect would not be very strong.

If you have a point & shoot, it's more difficult to create the effect, but not impossible. If you cannot manually control the camera to force a low focal ratio, try setting the scene dial to either the "portrait" mode (which usually tells the camera to go for a low focal ratio) ... or optionally try the "sports" mode, which forces the camera to use the fastest shutter speed possible, but in doing so has the side-effect of forcing the aperture to the widest possible setting (in other words the lowest focal ratio it can manage.)

Longer focal lengths also tend to enhance the effect... put the subject fairly close to the camera and the background far away (lots of distance separating them).

And now for the rules:

1. Only photos taken during the challenge period should be posted.
2. Limit of 2 pictures per post for this topic.
3. Discussion of technique and/or inspiration is encouraged!
4. Remember - this is NOT a contest - no voting, no prizes - other than better photos!

And the most important rule: Have fun!

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[Preeb]

Canon T1i, EF-S 17-55 f2.8 taken at 31mm focal length; f2.8 and 1/13 sec at ISO 3200. My niece and her 2 boys under natural light in a bar where her dad (my brother-in-law) plays in a band. Very little pp, just some noise reduction and a tiny bit of adjustment for WB and exposure. It may not be allowed though because it was taken on Dec 16, apparently one day before you started this thread? If so I'll try again.

[paddlehiker]

Hi,
Brand new at this, just joined 5 min. ago. Been trying to increase my photographic skills this fall. I like the idea of doing challenges as a learning tool, so thanks to you (and others on this board) for providing stimulating tasks. I actually did the previous challenge involving large DOF, which was faily easy for me. This particular one requiring a narrow DOF is a different story. I'm submitting two attempts which I'm not really fond of, but would like some input on. The first, a toy soldier decoration, was taken at a nearby steam train yard. BTW, I'm using a Canon SX-30 superzoom with manual controls. I was standing about 5 feet from the soldier; settings were f/2.7, 1/1000, 25.6mm. According to what I've always heard, and what the DOF calculator you referenced told me, everything behind the soldier should be a lot more out of focus than it appears, so why isn't it?
Not being satisfied with my outdoor attempts at creating bokeh, I headed indoors and the second photo is the result. I stood about 4 feet from Santa and the tree was about 12 feet away. I had to zoom in a bit for a decent composition, and settings were f/4, 2 seconds, 415mm. So, I guess I got a little bokeh here, but not as much as expected. Any constructive criticism is welcome!

IMG_2809 (Large).jpg IMG_2885 (Large).JPG

[TCampbell]

Welcome to Photo Forum!

One of the tricky bits with a point & shoot camera is that the focal lengths are usually stated in terms of "35mm equivalent" but not true.

For example, your SX30 lens, according to Canon, is a 4.3-150.5mm lens (that's what it really is). But they state that in terms of "35mm equivalent" lenses, it's a 24-840mm. It's not _really_ 24-840mm... but to get the same angle of view on a 35mm (or full-frame DSLR camera) you'd need a 24-840mm lens.

You said that you shot the toy soldier at 25.6mm. On a 35mm camera, that would be a fairly wide angle of view and, I'd estimate that the photo looks to be just about what I'd expect. But to get that on your camera, your lens is REALLY a 4.3-150mm and your 4.3mm wide angle works out to be equivalent of 24mm in the "35mm equivalent" category.

If you go to DOFmaster and punch in the 5 ft distance at f/2.8 and a 24mm lens, you get the following (I told DOFmaster it was a 35mm camera)

Subject distance 5 ft Depth of field Near limit 4.1 ft Far limit 6.42 ft Total 2.32 ft

When you go back and convert it back to what you really have... same 5 ft focus distance and f/2.8 (can't enter f/2.7 on DOFmaster but this is close enough) and using the SX30, you get the following:

Subject distance 5 ft Depth of field Near limit 2.31 ft Far limit Infinity Total Infinite

That's QUITE a difference. The other thing going against you is that the wider the angle of view, the more it shrinks the size of the "circles of confusion" (the diffuse circular pattern that causes blur).

One more example. If I leave everything alone except for the focal length... and instead of using 4.3 (which your camera may read as 24mm) we switch to about 10mm (which your camera probably reads at about 55mm) then this is what you get:

Subject distance 5 ft Depth of field Near limit 4.12 ft Far limit 6.36 ft Total 2.24 ft

Notice that this is pretty close to what you'd expect to get from the 35mm camera. The point here is that you'll get a narrower depth of field when you use a longer focal length, and this should help soften the background blur to something you can notice. I don't own an SX30 so I can't test this myself, but you should give it a try. Just note that as you increase the focal length, the variable focal ratio on your lens won't let you use f/2.7 anymore. It'll drop to f/4, then f/5.6, etc. As the focal ratio increases, the background blur decreases.

[TCampbell]

I grabbed one of my old point & shoot cameras (a Powershot S80) just to do a quick test:



The card you see in the foreground is my Spyder LensCal (it's a lens calibration target used to detect front & back-focus ... my 5D mark II allows me to calibrate the focus on each lens). You can see that I've focused the target in the foreground sharply. The lights on the tree in the background have a small amount of blur -- not a lot of bokeh, but still it is definitely there.

The target is about 3' away. The tree is about 12-15' away (I didn't specifically measure it.) The camera has a 5.8-20.7mm lens (true focal length) which is the equivalent of a 28-100mm lens on a 35mm camera. This photo was taken at 20.7mm (a 100mm equivalent on a 35mm camera) and f/5.3 (the best I can do at this focal length... it won't let me set it lower.)

So you can see the effect. It's much easier to create great bokeh with a DSLR -- especially given the large selection of lenses with low focal ratios and the fact that the "nifty fifty" is a very inexpensive lens. You can do it with a point & shoot -- but it's harder and, of course, you can't switch lenses to something that makes it easier.

[Fred Berg]

[BRAINY]

First of all, I'm new to the forum, so I hope I respect the criteria!

I did some bokeh with my christmas tree and a nutcracker :

DSC00749_modifié.jpg

DSC00756_modifié.jpg

DSC00771_modifié.jpg

Voilà! Hope you like it

[paddlehiker]

Tim,
Thanks so much for your prompt and very helpful reply. We had overnight guests during the holiday so wasn't able to reply as soon as I'd wished. Plus, took me awhile to wrap my head around what you said. Now I have a better understanding of the true focal lengths of my Canon SX30. I played around with the DOF calculator to get a feeling of how each parameter affects depth of field. Also learned something new about my SX30...I'd noticed in the past that, when zooming from full wide angle, 4.3mm (24mm), the lens actually moves in a little before extending out as you go through the zoom range. I took some test shots and looked at the EXIF data. At the point where the lens retracts a little before extending out, the focal length is ~ 8.8 (51.6), then goes to 12.9 (75.6) and so on. I'm thinking this was done intentionally to provide a quick way to get close to a "nifty fifty" equivalent lens. My minimum aperture at that focal range would be f/3.5, and with a subject distance of 5 feet, should give me pretty good bokeh. I will give it another "shot" and post something.

[SONYNUT]

round and round we go........

[arian29]

nice shots.. @BRAINY