Daily Archives: October 11, 2010

How many images should I shoot for my HDR?

 

One of the most confusing parts of shooting HDR images is, “How many images should I take ?” and then,” How many stops apart should they be?”

 

For most images, 3 shots, 2 stops apart is sufficient. Many people shoot too many frames and they really don’t add anything to the image, in fact they can cause problems with loss of detail and processing time because the software has to align more images and there is a better chance for error with more images. These errors smear the detail in an image.

But if the dynamic range is high enough in your scene you may need to shoot more frames just to cover that dynamic range. I will say this, If the sun itself is in the frame, you probably should shoot more frames.

Now I told you in another post how to determine if you should even use HDR photography. We can use a similar method to determine how much range is in a a scene and  what our two end points for exposure should be. Again set your camera’s meter in either spot or partial metering. Then meter the brightest part of the scene and set it as 0 meter. Now look at your settings (shutter speed only remembering that we keep out aperture and ISO constant) That will be your highlights end point setting.

Okay once again I DO NOT want anyone pointing their camera directly at the sun or looking into the sun so I am going to give you some numbers to use if the sun is in the scene. If the sun is before sunset, (assuming f/16 and ISO 100) your shutter speed should be 1/6000 or there abouts. ( EV20 or 21!!) If the sun is near sunset, your shutter speed for the sun itself  will be about 1/1500 ( EV17 -18)

So with the brightest portion of our scene metered (even if it isn’t the sun) we can now move on to the shadow or darkest area of our scene and zero meter that.

So let’s say that  our shadow meter is 1/10th  and our highlight meter is 1/6000. If we sit down and figure we can see that we have a  little more than 10 stops from brightest to darkest (remember, what we measure for our darkest area will now be our brightest exposure) So if we were to use 1 stop intervals we would take 10 shots, if we wanted 2 stop intervals we would take 5 or 6

Now here is a easy way to shoot it on your camera so you don’t even have to think about how many stops it is or even know how to figure out how many stops that is. Most Digital SLRs separate stop into three part stops, some do it in two or you can change a custom function to two part stops. You can check it by setting your shutter speed to 1/100 and then  counting how many clicks it is to get to 1/200.

So if it is three we can do our shoot like a dance, specifically, the Cha Cha. That’s right the Cha Cha. Set your camera on a tripod and set up your composition. Now set your shutter speed to the slowest number you calculated, in this case 1/10th. Take your first shot, Now adjust your shutter speed in clicks, 1,2,3 (Cha Cha cha), Fire, 1,2, 3 Fire. Repeat that dance until your shutter speed is up to the top number (1/6000) and stop after that fire. Done. No calculations needed. If you want two stop intervals between shots, you will need to do a Waltz…1,2,3  1,2,3 Fire

Now let’s take a look at three images of the same scene and shot differently to see how much of a difference it really makes.

Even I was surprised by this, But that is the cool ting about actual vs. theory. It’s not always what it should be.

The first image is a 11 shot 1 stop series, f16 ISO 100 from 1/10th to 1/8000th. The second is an Auto Bracketed  3 shot, 2 stop series from 1/20th to 1/350th. The same settings for Image combining and tone mapping were used in Photomatix

11 Shot 1 stop

3 shot 2 stop

Surprisingly, not a lot of difference, There is a little better defined sun in the 11 shot and the color seems to have more bit depth (more shades of blue as you go up the sky), There is a bit better shadow detail too.

Both images on close inspection seem to have the same detail and sharpness, but on pixel peeping at 250% the 3 shot seems to have a little  more noise in the shadow area but just barely. Again at 250%!

3 shot Crop

3 shot crop

10 shot crop

10 shot crop
Then the last ting I tried was a 6 Shot 2 Stop HDR
Again, Not much difference
6 shot
So as you can see, unless you have a really broad rage to cover, 3 shots will really do the trick. Even in this image with a really wide dynamic scene, the 3 shot fared quite well. What would I shoot here? Well actually I would do about a 7 shot, 1 stop HDR. I really don’t think the last 3 images at the fastest shutter speed that only captured the sun really added a lot to the image I think 7/1 would have been just fine
Equipment for this post
Canon DSLR
Canon 24-105L 4.0 Lens
Manfrotto Tripod
Photomatix Pro 4.0