Does using a different lens affect the dynamic range for HDR post-processing?

Question

I am a bit new to HDR photography and lately I have been trying to carry out the post-processing with Photomatrix. After many trails and errors, I am still unable to get the effect that many other HDR pictures usually have.

Picture Setup:

Canon DSLR 550D: 18- 55 mm lens, three pictures at different exposures (-2,0,+2) - JPEG format - Evaluative mode, 2 sec continous shooting.

Post-processing software:

Photomatrix 4.1.4.

I have three parts to my question:

1) Would using a different lens (50 mm) affect the dynamic range of the photograph and help me in post-processing?

2) If the above is No, is it always related to the proper tone-mapping of the picture to produce the HDR effect?

3) I usually have a cloudy climate around the place I live, should I change any camera settings in order to take a proper picture first with the above settings to get the desired HDR effect?

Answer 1

• 1) No, the lens has very little influence on the dynamic range captured, except in exceptional circumstances, for academic interest only, see this question:

  Is it possible for a lens to produce too much contrast?

• 2) Yes, the look people attribute to HDR is the result of converting a high dynamic range image to a low dynamic range image suitable for viewing. This step is usually achieved by tonemapping. Merging images to HDR is straightforward, there is usually one possible result. Tonemappig is difficult and requires aesthetic decisions to be made. See:

  What is tone mapping? How does it relate to HDR?

• 3) It depends on what your goals are. Often in overcast situations the dynamic range of the scene is not so high that you need HDR in order to capture a detailed image, if your intention is to produce an ultra detailed high contrast unreal image then you can simply apply tonemapping to a single good exposure.

Answer 2

The dynamic range of an image depends completely on the sensor. Every sensor has limitations on how much light it can take before the place go completely white on the picture and also it is limited by a minimal amount of light that has to be present so the place is not totaly black. You can see huge differences between camera models varying in the range that there is between completely black places and completely white places.

HDR means composing an image where both the light and dark places are well-exposed. Here, it is important to understand that human eye is an incredible instrument and no camera is even near that. Your eye takes (without you realizing it) images in many different exposure settings quickly after each other and in your brain, those images are composed to one.

Using a camera, you have to do exactly the same (but you have plenty of time taking the pictures) - take at least one picture with good exposure on light places (where most probably other parts of the image are in the blacks) and one with exposure set to uncover the dark places (where the lights are already burned over and totaly white) and one in the middle. Then what HDR applications (like Photomattix) do, is taking the well exposed parts form all the pictures and putting them in one well exposed image.

So back to your question - no, lenses are not going to do it. With the camera you have, it was enough for me in some cases to take one picture that was exposed normally and I could create +2EV and -2EV images in post production. That is of course not the best way, but in most cases your camera model has enough dynamic range to be able to fake it this way (actually the chip is so good in this model that in RAW, you can easily go from -3EV to +3EV in one picture and it looks fine using a low ISO). So taking three different pictures with 2EV steps, as you say, must give briliant results.

Possible reason of not getting what you need:

• Do NEVER use JPG for HDR resources as RAW saves a lot lot more information and you need as many of it as possible. Always save pictures in RAW format for that purpose.

• Some scenes are just not fitted to become HDR. Simply because there is not enough dynamic range in the scene - and cloudy weather is typical for that. That is why cities in the night are so common HDR scenes.

• just taking three images and "shrinking" their dynamic ranges may technically produce HDR image, but what you see as wallpapers is a lot more - you need to decide which part of the range will be shrinked how to produce visually attractive output. This usually is not done by automated processors like Photomattix, but hard manual work including Photoshop, many layers and some sleepless nights.

Good luck :)

Jakub

Answer 3

1) Not really, but... Dynamic range is sometimes defined as the ratio between the largest and smallest recorded signal, which is not obscured by noise. If you use this definition with this last statement, then you could say that a sharper lens will produce more dynamic range, because some darker details won't be blurred out to the extent that they are indistinguishable from noise.

2) What people usually mean by HDR effect is the effect of tone mapping.

3) Shoot in raw format, not JPEG! It has more dynamic range. I assume you are shooting from a tripod - definitely use ISO 100 in case you aren't doing so already. With some cameras ISO 200 has more dynamic range, but I think the Canon 550D isn't one of those.

You mention "2 sec continous shooting". You should use Av mode and let the camera choose the exposure time that's right for the light conditions. Your darkest picture should have no clamped highlights - this often means a somewhat dark overall picture.

You might also want to use the camera's Auto Exposure Bracketing feature (maybe together with exposure compensation to get the darkest image correctly exposed for the highlights).

Answer 4

"JPEG format" - use full resolution RAW instead. Compression such as JPEG is discarding valuable data.

I will relate my personal experiences;

I am a NIK HDR Effex Pro user so I can't speak to the proper tone mapping in Photomatix but if photomatix gives you some basic set of presets you could use the one that is closest to what you want to achieve then adjust the tone mapping and other effects including the effect strength, saturation, structure, etc. until you like what you see. My goal is usually (but not always) realistic colours and tones and the software I use exaggerates saturation and structure so those sliders usually go down right away...

Also, not all images are suitable for HDR; I usually shoot landscape with 3 exposures by default but only some images are suitable for the "HDR treatment". Also, some HDR software automatically corrects for ghosting and alignment... Personally I have had better success with disabling these features as these automatic corrections often produce strange artifacts.

Cloudy is good for HDR but the effect does often over-exaggerate clouds which is good but it often makes the skies so dramatic that it steals the focus away from the actual subject.

Lens does not matter although better lens will yield a better image. Personally, I like to use a wide angle lens.