a21 January 2015

HDR photography tip: how many photos do I need for great HDR photo?

HDR photography tip: How many photos do I need for great HDR photo?

Today I have a short tip for you, fellow HDR photographers. Have you ever wondered, while taking HDR photo, how many bracketed photos you should take for a given scene? 3, 5, 7 or even more? Or maybe just 1? Most photographers make wild guesses here, often taking way too many photos (I often do the same so don't feel guilty!) what can result in ghosting artifacts. Or even worse - too few what results in blown out highlights and/or noisy shadows.

Guess no more - here are the steps to take correct number of bracketed photos:
  1. Set your camera to Spot Metering mode. 
  2. Set ISO to the one you will use for your HDR photo (I recommend using lowest value possible). And definitely don't use Auto-ISO.
  3. Switch to Aperture Priority mode (denoted as Av or A). Set Aperture to the value you will use for your HDR photo.
  4. Point your camera at the brightest spot you want to include in your frame (eg. source light, sky) and note down exposure time displayed by the camera, eg. 1/400.
  5. Now point your camera at the darkest spot you want to include in your frame (eg. shadow, dark rocks) and note down exposure time displayed by the camera, eg. 1/40.
  6. Switch to Manual mode. Don't change neither ISO nor Aperture!
  7. Now let's assume that you want to take your photos spacing them by 1 EV. In such case, start with exposure for brightest spot (in our case 1/400), take a photo, multiply exposure by 2 (it then becomes 1/200), take another photo, multiply exposure by 2 and so on until you take a photo with exposure which is greater or equal than exposure for darkest point (in our case 1/40).
    So in our case we would need to take photos at following exposures:
    1. 1/400
    2. 1/200
    3. 1/100
    4. 1/50 (this exposure is still shorter than longest exposure we need)
    5. 1/25
  8. As you can seen we would need 5 photos.
    There is one problem though - this approach requires using fully Manual mode. What if you would like to take photos using Aperture Priority mode and use auto-bracketing? Then instead of taking photos in Step 6, let's calculate number of exposures (you can then set it for auto-bracketing feature of your camera):

    number_of_photos = log2(slowest_exposure / fastest_esposure) + 1
    In our case it becomes:

    number_of_photos = log2((1/25) / (1/400)) + 1 = log2(16) + 1 = 4 + 1 = 5

Also note that if you would like to use 2 EV spacing you would need to multiply exposures by 4.

You can find more tips and useful HDR photography information in my free HDR tutorial.

Daily photo - In the Park

In the Park
Today I decided to share this HDR photo taken in one of the London's parks.

Camera Info

Finally some EXIF info:
Technical details:
Camera: Canon 5D MK III (read my review here)
Lens: Canon 24-105 f/4 L IS USM
Focal length: 32 mm
Aperture: f/7.1
Exposure time: 1/250 s ("middle" exposure)
ISO: 100
Number of exposures: 5
E.V. Step: 1 EV
Flash used: no
Tripod: no
Filters: circular polarizing filter
Technique: HDR, tone-mapping, luminosity masking
Software: Magic Lantern, Photomatix Pro 5 (Contrast Optimizer), Lightroom 5.4, Photoshop CC, Topaz Clarity, Topaz Detail

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