Fotoartist Loc: Detroit, Michigan

Interested in the opinions of UHHers who bracket the ISO when shooting HDR.

imagemeister Loc: mid east Florida

I use the Sony in camera JPEG 3 exposure HDR function - and it brackets either by SS or ISO - but I have always thought it was by SS - OR - could be a combo of the two - I really do not know .......but however they do it , it works pretty darn good IMO.

Wanda Krack Loc: Tennessee, USA

I have taken shots both ways, but I prefer speed as the variant. What has been your experience?

Billyspad Loc: The Philippines

Surely if you bracket by anything other than with a constant Aperture you will end up with shots with different depth of field and will get problems with the sharpness of the combined image?

selmslie Loc: Fernandina Beach, FL, USA

As Billyspad said, you can't really bracket by changing aperture.

The fundamental problem with changing only the ISO is that the sensor actually has only one physical sensitivity. Changing the ISO alters the gain. You get the same effect by moving the Exposure slider during raw conversion.

That pretty much leaves you with one choice, keeping the aperture and ISO constant while varying the exposure time.

kymarto Loc: Portland OR and Milan Italy

NOT a good idea, as the varying noise characteristics will not blend well, just as varying aperture is not a good idea. You can try, but the recommendation is only to vary shutter speed.

speters Loc: Grangeville/Idaho

The only question I can see about this is, how many brackets one wants to do in a certain situation, stick to 3, do 20? But all that is a choice of personal preference (and should only be influenced by that)! I guess, a little depends on too, how wuch time you're willing to spend doing pp work/fun!

selmslie Loc: Fernandina Beach, FL, USA

A more important question is, "Why bracket?" I can think of only two reasons to bracket for exposure:

1. You are uncertain about the correct exposure (more common than we would like to admit) and want at least one to be optimal. When in doubt, use the lowest practical ISO to get the most out of your camera's DR, don't blow the highlights (for that you might need to bracket) and recover the shadows during raw conversion.

2. You recognize that the scene's DR is too great for your camera and you intend to combine multiple exposures into an HDR image. This takes more effort and skill. Most of us are not particularly good at it, especially me.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

I never bracket ISO, and I also take far fewer images than most - rarely more than three, often two. I will make each image as good as it can be, then blend. It's much easier to remove ghosting and other issues when you have fewer exposures. My first exposure will be to protect the highlights. Then I take a second to place the shadows a stop or two below middle tone. I will adjust the highlights in post to show what I want, and leave the murky shadows alone, then I will use the lighter exposure with blown highlights to make sure the shadows look good, often darkening and adding some contrast. Then I merge. Doing this in LR is great, because after you merge, you still have a raw file (dng) to make additional adjustments, which I usually do in curves.

As Scotty has observed, more gain on the ISO means more noise, and ultimately no different than moving sliders in LR or ACR. So aperture and ISO are constants, leaving only the shutter speed as an adjustable parameter.

kymarto Loc: Portland OR and Milan Italy

There is a rule of thumb, which can help determine the number of brackets necessary. For HDR, the lightest frame should have the darkest shadows present with detail, and the darkest should have NO blown highlights (apart from the sun or bright point sources of light). If the normal exposure meets those conditions there is no reason to do HDR, as normal post processing can give you any tonal spread that HDR tonemapping can.

If the dynamic range of the scene exceeds that of the camera, then you bracket. Now let's take a case where you need a frame that is 2 stops darker than the normal frame to keep the highlights from blowing out, and you need a frame 2 stops brighter than the normal one to retain detail in the deep shadows. In that case three brackets -2,0,+2 will be absolutely sufficient to do a decent HDR image. However in a more extreme case, in which you need the darkest frame at -4EV and the brightest at +4EV, then you will need five frames: -4, -2, 0, +2, +4. If you need -3EV to +3EV, I would go with -3, -1, +1, +3.

I have done experimentation to see if there is any advantage to doing brackets of less than 1EV steps, and my result has been that it is unnecessary. I have done 9EV brackets (from -4 to +4EV in 1EV steps) and done HDRs with every frame and with every other frame, and they were basically identical.

There is one potential advantage to doing 1EV or less brackets, and that is if you use Photomatix and need to do selective deghosting. In that case having more frames gives you that many more options for choosing base frames for the ghosted areas. Selective deghosting base frames have to be within 2EV of the optimal exposure for that section of the image to really succeed. If they are too dark there will be too much noise in those areas, and if too light you will have blown highlights, which look terrible. But if you do not intend to deghost, then steps of 2 EV are absolutely fine.

It's worth noting that including more bracketed images in the HDR process takes only a little more time in the initial process of making the .hdr image to process. Generally speaking, when I do an HDR image, I always shoot 9 brackets 1EV apart. I've had too many good images ruined because my darkest frame was too light and/or my lightest frame was too dark, which I discovered only in the processing. It's easy enough to delete frames you don't need, and you generally can't reshoot if you discover you don't have enough after the fact.

selmslie Loc: Fernandina Beach, FL, USA

I have done similar experiments and found the same result.

It also confirmed why, with most normal (medium to low DR) scenes, an exposure error of +/-1 EV is insignificant. With a low DR scene, +/-2 or even 3 EV is also easily compensated for during raw conversion.

It's only the wide DR scenes that are a challenge, even at base ISO. I need more practice with Photomatix Pro before I am any good at it.

photoman022 Loc: Manchester CT USA

I'm not being obnoxious, but isn't it easier to just bracket your shutter speed? (oops, I split an infinitive here, but I don't care! My college English prof is having a fit!)

selmslie Loc: Fernandina Beach, FL, USA

Yes, it's pretty simple. Just remember to think about why you are doing it.

joseph premanandan

i do not see any advantage of doing HDR with different ISOs.the very idea of doing HDR is to bring out the details in highlights and shadows.that means,obtaining an ideal image in an ideal exposure.the ISO is a component of exposure triangle.keeping the ISO the same around 100 0or 200, and changing the exposure compensations either to 3 or 5 images and merging them together should do the job,joseph

TheDman Loc: USA

I'm not a fan of the word 'bracketing' as it tends to imply a blanket approach to shooting every scene. Each scene is different, and you should shoot as many exposures as you need to capture the dynamic range, motion, etc.

Other reasons for shooting multiple exposures besides the ones selmslie mentioned include stopping motion (such as blowing foliage), giving yourself several options for subjects like moving water, removing people, focus blending, and many others. These will require you to change ISO, aperture, and shutter speed as the situation dictates.