Is there such a thing as DOF bracketing?

October 4, 2008 7:55 AM

Another photography question regarding bracketing aperture and locking exposure. Is this possible on either a Canon or Nikon dSLR?

Say I like the metering/exposure as is on my camera just fine especially shooting in RAW, but I want to be able to shoot in bursts with "bracketed aperture..." For example let's say I have a shot at f/4 with a shutter speed of 1/100s based on whatever metering in either a basic time or aperture priority mode which I'm familiar with. Can I make my camera do a bracketed burst of shots at f/2.8 & 1/200s, f/4 & 1/100s, and f/5.6 & 1/50s? In other words I want to vary the depth of field in a burst but maintain the exposure. Is there a named function for such a thing? This may be obvious but I can't seem to figure out how to pull it off on my basic Canon XT and I'm also curious if the newer Canons or Nikons can do this.

I ask this because as a camera noob, despite practicing a ton I still have lots of trouble guestimating my DOF per aperture/focal length/distance on the fly. It wouldn't be such a big deal if I shot everything at f/16 but I'm trying to work in varying amounts of bokeh to my backgrounds and it ain't easy to predetermine how things will turn out. Any additional tips are much appreciated on this front.

posted by drpynchon to sports, hobbies, & recreation (15 comments total)

As a corollary, does anyone actually find the DOF preview on Canons useful? To my eye it doesn't really predict how shots actually turn out very well at all.
posted by drpynchon at 7:59 AM on October 4, 2008

i found the dof preview on my elan IIe to be effective. oftentimes, the camera will select a focal point that causes the entire scene in the viewfinder to be out of focus, but you just have to take it on faith. it the scene could be shot in acceptable focus, in my experience it was. frequently, it can't be and then the camera just does the best it can under the circumstances. what it will not do, if the fore- and backgrounds are too far apart, for example, is choose one or the other to focus on. they'll both be out.

i don't know exactly how the camera calculates "acceptable focus" but if it's not working for you, you may be a) using too large an aperture, b) too long a lens, or; c) your subjects may be too far apart.

did i find it useful? not really, but mostly because it was a pain. a little bit of practice and the dof preview are really all you need.
posted by klanawa at 8:22 AM on October 4, 2008

This doesn't necessarily answer your question, but I can do this on my Canon S3 IS with the CHDK firmware.
posted by Mach5 at 8:34 AM on October 4, 2008

I know this doesn't answer your question, but:

Set everything to manual and don't be afraid to do lots of chimping. Try lots of combinations on your shots, after a short while you will have much more idea of what your camera and individual lenses produce.
posted by mandal at 9:22 AM on October 4, 2008

Believe me I try, mandel, but the problem is that sort of chimping and manual adjustment is really hard when you're taking candids or street shots.. But the point is taken.. I'm continuing to futz around with different settings on the lenses all the time.
posted by drpynchon at 9:25 AM on October 4, 2008

I'm not sure about burst mode, but if you use aperture priority, you can quickly take several shots and change the aperture between them. The camera will choose the corresponding shutter speed to keep the exposure consistent.

Many cameras auto-bracket, but I understand you dilemma, because you are not truly bracketing. Bracketing generally means a change in actual exposure, but it sounds like you want consistent exposure with varying combinations of aperture/shutter speed.

If you are having trouble getting proper focus on the subject, while getting enough bokeh in the background, keep in mind that the longer the lens, the less DOF field you will have for a given aperture setting. f 8 with a wide angle lens might focus on everything from 4 feet to infinity, but f 8 on a 300mm lens might only give you a foot or so. Experience and practice, practice, practice, will eventually allow you to see in your mind's eye what the result of any given focal length/aperture setting will likely be. As you view your photos, make it a habit to look at the exif info and take note of the aperture. It won't take too long until it becomes second nature.

Meanwhile, (and I'm not sure if this is part of the issue) make sure you are accurately focusing on the part of the scene you want to be sharp. This sounds obvious, but sometimes cameras "help" too much in this regard. My Nikon D40 has 3 focus sensors, (left, right, and middle) and by default it tries to figure out what part of the frame to focus on. this might be good for snapshots, but it's extremely inaccurate for the type of shooting I do. A friend had the same issue: she couldn't figure out why so many of her photos were improperly focused. I changed my setting to force it to use only the center area for focusing. I use that sensor to focus by holding the shutter release halfway down and locking focus, then reframe before shooting. I had my friend do the same, and it's much better.
posted by Fuzzy Skinner at 9:33 AM on October 4, 2008

My own inclination would be to lock the shutter speed, let the exposure autobracket adjust the aperture up and down, and photoshop in another stop of exposure either way after the fact. It's not perfect, but especially for learning purposes it should be fine. By prioritizing the shutter speed, you'll end up with the same image in terms of motion freeze, and the bracketing will adjust aperture (eg, DOF), and for one stop, the digital fakery should look fine and give you three nearly-identical images with effectively the same exposure and different DOFs.
posted by Tomorrowful at 9:33 AM on October 4, 2008

Also, I really miss the depth-of-field guides that used to be engraved on all lenses, and now seem to be vanishing. I guess the manufacturers think that auto-focus has negated their usefulness, but I disagree.

It used to be easy to glance at the lens and see what would be in focus for a given aperture. In the linked example, the lens is focused at 10 feet. You can see that at f8, the depth of field would be about 7 feet to 15 feet. The lens is set to f16, so DOF is about 6 feet to 25 feet.

Just a side-note, but it might help your thinking process.
posted by Fuzzy Skinner at 9:42 AM on October 4, 2008

My own inclination would be to lock the shutter speed, let the exposure autobracket adjust the aperture up and down, and photoshop in another stop of exposure either way after the fact. It's not perfect, but especially for learning purposes it should be fine.

Good idea. Especially when shooting in RAW, the exposure will have tons of leeway.
posted by Fuzzy Skinner at 9:44 AM on October 4, 2008

I don't know of any cameras that will automatically bracket like that, but if you hold the auto exposure lock button in and then turn the dial you can accomplish this in camera. The only problem is, at least with my Nikon D50, you either need three hands or a tripod. It would probably be easier with a Canon since the main dial is on top near the shutter button.

I also had no problems with depth of field preview on my Canon 7Ne. I think the biggest problem is not having a viewfinder that is bright enough.
posted by robtf3 at 9:46 AM on October 4, 2008

Going along with Fuzzy Skinner, I've had good success with a narrow DOF by using an almost inappropriately long lens -- if you use a 200mm to shoot stuff that's on the close end of your range, you'll get a great narrow DOF.
posted by lockestockbarrel at 10:00 AM on October 4, 2008

but the problem is that sort of chimping and manual adjustment is really hard when you're taking candids or street shots.

Agreed on the chimping, but for candids and street shots manual really can be your best friend if you know how your equipment is going to react, which is why it can be better better to write off a few weeks getting to know the equipment in manual mode before you start going for keepers. YMMV.
posted by mandal at 10:00 AM on October 4, 2008

PhotoCalc might be of use to you if you have an iPod Touch/iPhone; it does DoF and hyperfocal distance calculations along with flash exposure and other useful things.
posted by heeeraldo at 11:07 AM on October 4, 2008

This is a reason why a lot of street photographers use prime (fixed focal length) lenses. With a constant focal length, you can memorize a rough table of DOF at every f stop.

Pick up a 28mm or 35mm prime lens (or tape your zoom lens at a fixed focal length) and then check out this DOF table. Set the units to "Feet". Assume a working distance of 10 ft to the subject and then subtract "Far" from "Near" to get the DOF at each f stop. Print it out on a sheet of paper if you want. Go out and shoot, keeping in mind the DOF from the tables and that DOF distance extends halfway from the focal point towards your camera and halfway away from your camera. So if the DOF is 4 ft and the subject is 10 ft away, then everything 2 ft in front and behind the focal point will be in focus. With time and practice, you'll be able to look at a subject and be able to determine the necessary aperture without thinking.
posted by junesix at 2:33 PM on October 6, 2008

Can't you just put in in aperture priority and then turn on auto-bracketing? Wouldn't the camera just hold it at, say, f/8, and bracket with shutter speed?
posted by Lukenlogs at 12:01 AM on November 10, 2008