How do I shoot massive bonfire in order to produce an HDR image?

Question

I am looking for advice on how to shoot a massive bonfire to produce an HDR image. My school has a massive bonfire every year for homecoming — it is 30+ ft. tall. I have been shooting and HDRing my photos for a year now and have gotten decent results during daytime shooting, but I have never really taken an HDR shot at night.

I have a tripod so I am not worried about getting an image; I am more concerned with the best way to get the series of images for an HDR'd image. Should I take one RAW and manipulate it into five JPEGs during post, or shoot five shots that night? Also, I would like to get as crisp an image as possible of the flames. Are crisp flames a pipe dream?

Just in case this helps: I will be shooting with a Sony a33, which is pretty good in low light, and either a 50mm/f1.8 or a 28mm/f2.8. All mounted on a tripod.

The fire is pretty bright during the initial burn, so that should help cut down my exposure time.

What tips do you have for me?

EDIT: Thanks for all the suggestions. I thought I should share my results from the bonfire.

To give scale here is a before shot:

And during the burn:

Answer 1

Pulling out multiple JPEGs from a single RAW file always results in lower quality HDRs than the one done with bracketed RAWs. Specially the dark parts of your image will show noticeable noise. On the other hand, bracketed shots require static scene which isn't the case for you but I believe is the right thing to do. If I were you I'd shoot as much bracketed shots as possible and try playing around to get the best outcome. Flame shots at night typically ends up requiring 1/30-1/40 (considering you already have some fast enough lenses) shutters which will not stop the action to a full stop but wont be bad either.

Worst case, when merged, resulting HDR will show some crowd movements and a dreamy flame, which isn't bad either, in fact it will add some interest in the photo ;)

Answer 2

I would shoot series of identically exposed shots with tripod, underexposing them enough to not blow the highlights on the flames too much. Then you can stack the set either manually or with programs like Anti-Lamenessing Engine (ALE) to get the surroundings parts properly lit and then use layers and masks to pick flame part from some single frame.

In situation like this, where the subject changes wildly, hefty stack of exposures with identical settings also gives you lots of frames to pick flames from, so you can handpick the version of flames you like most, or even combine it with couple of frames with layers and masks.

Developing with different settings from same raw does not give you any more signal than just converting the same raw to 16-bit image, so there is no real use on doing that, unless you are using photo processing program like GIMP that lacks support for 16-bit images.

Shooting the "normal" HDR stack, ie. set of 3+ images with exposure bracketing has the problem that if subject changes between the shots, like it certainly does here, you easily end up with ghosting. With identical (underexposed) exposures you need more shots to get enough information, but the ghosting in that methods turns to just regular "motion blur", which is more pleasing to human eye.

Also, flames are bright and self-illuminating - if your plan is to capture just the flames, a single exposure might very well be enough. But because memory card space is cheap, shooting couple of series from tripod will leave you with lots of material to choose from.

Answer 3

The most common method is the multi-exposure, but you may have to experiment as the flames will obviously be changing shape and intensity across the period of time taken to take the three or more exposures.

Another method of capturing a changing scene in HDR is by using two or more cameras right next to each other with framing and focal length that minimises the parallax between them. Have each set to their respective exposures and somehow trigger them all to fire at once. This however is probably not practically for many people though.

A final method may be to expose a single raw file making sure to underexpose enough to keep the highlights from clipping. Use the lowest ISO possible then adjust aperture and shutter speed to compensate. Using a full frame camera will also yield a higher detail raw file. You can then pull the shadow detail out and see what it looks like.

Here is a photo taken by Flickr user Danny Gibson. It seems to work fairly well.

http://www.flickr.com/photos/dannygibson/3348483281/

Answer 4

I'm not sure there is a good way to get a "crisp" HDR photo of a bonfire. Using multiple bracketed exposures at different exposure values will make the flames from one exposure look brighter or dimmer than the flames from the other exposures.

To get crisp images of flames, you need a fairly fast shutter speed. The gases venting off the fuel are changing rapidly! This is a wood fire at 1/1250 esc.
_{EOS 5D Mark II, EF 24-105mm f/4L IS, ISO 1600, f/5.6, 1/1250 sec. Color Temp. 2500K, +1.33 Exposure and other minor adjustments in post.}

This is what the same fire looks like at 1/60 sec. With the exposure adjusted for the crowd.
_{EOS 5D Mark II, EF 24-105mm f/4L IS, ISO 6400, f/4, 1/60 sec. Color Temp. 2800K, -1.50 Exposure and other adjustments in post.}

I was shooting manual and may could have captured more detail of the flames if my exposure had been less, but other shots that night with less exposure but an equally slow shutter were a motion blur of flames.

I was standing in roughly the same spot for both photos. The first was at 73mm, the second at 24mm focal length. The second was also cropped a little more than the first in terms of height.

There are about 4 1/2 stops difference in these two images by the time you account for post processing. The flames on the first have a few isolated areas that were at 255,255,255 before exposure compensation was applied, but most of the bright spots are in the high 240s and low 250s. By increasing exposure 1.5 stops I blew many areas of the flames out in order to recover detail from the pallets and ground, but there is still a lot of detail left in the fire. The flames in their entirety in the second were at 254, 254, 254 when exposure was reduced -0.67 in post, so they were clipped by about 2/3 stop.

To get any detail in the flames for the tone mapping to work with, the rest of your scene is going to be very dark. Even though the fire is quite bright, the heat is so intense that the people are kept a safe distance away and the inverse square rule comes into play.

Using fairly heavy handed tone mapping on the first image does recover detail (and considerable fixed pattern noise) from the deep shadows but has very little effect on the flames!

I felt my best efforts of the night involved images that captured the reflected light of the fire.