HDR, or High Dynamic Range, is a method of keeping detail in the brightest highlights of your picture whilst also allowing the shadow detail to be seen.
In a very contrasty scene our eyes are constantly adjusting to give us the best vision possible whether we are looking across a bright sunlit farmyard or peering into the deep shadows of a barn. It is generally assumed that our eyes have a bigger dynamic range than a camera sensor but actually it is this constant adjustment that gives our eyes the edge. The camera sensor can only have one setting when it records a scene and cannot make any allowances for very dark or very bright areas in that scene. Which is where HDR comes in.
Inside Peterborough Cathedral this is what a photograph showing the lovely detail in the beautiful stained glass windows looks like.
Nice windows…shame about the rest of the picture.
So to get a more pleasing photograph of the intricate roof carvings we need to increase our exposure considerably, which means losing all the window detail.
It really is a fantastic roof, I must have stood underneath that for at least 30 minutes gazing up in awe, It seemed strange to think that 800 years ago some of the best carpenters to be found in England were making these wonderful carvings.
So, it’s a nice roof, in fact it’s much more than nice, It’s the only surviving wooden roof from this period in England, and one of only four that survive in Europe. It took 20 years to build so it deserves to be seen clearly, but almost everything else in the picture is badly over exposed, which is a shame as the Cathedral itself took over 100 years to finish.
What I’ve shown you above is the first and last picture in a series of seven that I took from that position. I decided on my viewpoint, set up my tripod (£2 for a tripod permit in the Cathedral) and took my seven pictures. It is important to set all the camera controls manually so you have total control over what the camera does. I shot (as I always do) in Camera RAW and chose an ISO of 400 at f8 on an 18mm lens. Once you’ve decided on your composition and exposure, using either a remote shutter release or the camera timer to minimise camera shake, take your first picture. The next six pictures, without moving the camera or altering the focus, should be taken 1, 2 and then 3 stops underexposed and 1, 2 and then 3 stops overexposed. In total my exposures ranged from 1/20th sec to 0.8 sec.
when all seven photos are carefully merged in an HDR program such as Photomatix the end result (hopefully) is a photograph which looks completely natural.
This is much more like the way we remember it looking when we were there. Actually, we never did see the Cathedral as it appears in that photo but our eyes and brain are excellent at combining the various bits of something we see and presenting it to us as a nice tidy memory.
Those of you with an eye for detail may also be wondering why the best stonemasons of the Middle Ages decided to build a crooked Cathedral. Actually it just appears that the walls are sloping outwards because of the way I took the photo. If the camera is not completely level when taking the picture any vertical lines appear to diverge. This effect can often be used to enhance an image, but in this case it looks wrong so we have a last editing job to do to finish this picture,
So, there we have a very acceptable photograph as a reminder of a visit to a stunning Cathedral. I hope you enjoyed reading this blog post.