HDR

Mach Loop Terrain, Bwlch

Scoping the Mach Loop

The Mach Loop in Wales

The Mach Loop is a set of valleys between Dolgellau in the north and Machynlleth in the south of Wales. The Mach coming from Machynlleth of course. The loop is used for low level flight training (as low as 76 metres from the nearest terrain) by the RAF. Geoff and I had heard that it was a simple matter to climb up a bit of bank and take some (nice) pictures of the Jets. Given that there had been heavy snowfalls, we wanted to scope out the terrain to see what might be involved in getting to a reasonable spot above the planes. So off we went to Bwlch to have a look.

The Weather was Against us!!

We checked out a few possible vantage points to visit from information on the internet, and off we went. We arrived at Bwlch at around 10:00am on the first of April 2013 (and it was no joke, even if we felt a little foolish). The temperature was just above zero, but felt about minus 30, due to the sharp wind. It was so cold that within no more than 3 minutes I couldn’t feel the ends of my fingertips. I scampered back to the car to re-group with a cup of coffee, before giving it another try.

After the second chilling, and a closer look at the steepness of the mountainside, I realized that I would need a helicopter winch to get me anywhere near the summit even if I was travelling without heavy camera gear. So we left to look down the road, but quickly gave up as the snow seemed deeper there. No stamina I suppose, perhaps after a year or two working out?

Decamp to Bala Lake

So a wholesale change of plan was required, and onward we forged to Bala Lake for a few photos. Hopefully it would be warmer lower down? Sadly, in the end, it was still pretty cold so I went with an HDR approach rather than breaking out my Lee Filter Holder and Neutral Density Grads. I did use my tripod though, for a change, rather than hand-holding a high speed burst.

I did think, afterwards, that I missed out an opportunity to try out my new Big Stopper. But hey-ho it was very cold, and I wanted to keep warm. I can hardly believe that a month has gone by since Bala and I’ve still to tell you about Ludlow and Martin Mere Wetland Centre!

Snowy Weather Nonsense…

I Just Cannot Believe It..

I must be getting old and Meldrew-like! I love the cold weather, and especially the snow, as an unparalleled opportunity to get outside with the camera. What I don’t like is the way that our weather forecasters seem incapable of even remotely predicting the time, place or extent of weather with any accuracy. Worse still, the very mention of the possibility (never mind the actuality) of snow throws the media into a frenzy with dire predictions of death and mayhem. These days my wife and I often have to travel, usually a long way and in different directions but that’s incidental, and an accurate weather forecast is pretty essential if snow is forecast. Can we get decent information? Certainly not.

And what about consistency of approach to travel information in the media and on the roads themselves. Forget it, no-one cares. On the M5/6 yesterday I saw plenty of signs for ‘Salt Spreading’, but never saw a grit spreader once. Neither, more worryingly, did I see any obvious grit on the road. Nor any warnings of snow on the road, or an advisory speed limit, despite several inches of snowy slush, harsh wind and appalling driving conditions!! I saw plenty of signs asking ‘is your vehicle prepared for winter?’ but for what purpose? So there we all were, driving in columns, much too fast, terrified to attempt to slow down or change lane in case a truck rear-ended you or the manoeuvre started a skid and a major pile-up. Astonishing. So I ask again was there an advisory speed limit? Were there warnings of snow? Of course not, no-one cares it seems. On the news this morning I hear that people were stuck in their cars overnight. I felt lucky to get home alive last night, this country beggars belief sometimes.

Less Moaning and More Photography

_DSC4523-EditI did manage a couple of pictures however. I was quite attracted to the image of the Collegiate Church of St Bartholemew Tong pictured here. As you can see from the link it is a listed building with a very attractive facade. So who built Tong Church and when? It seems from their website that in 1409 Lady Isabel de Pembrugge obtained a Royal license from Henry IV to found Tong Church and build the present church so that masses could be said for Sir Fulke and her two other husbands, Thomas Peyteveyne and John Ludlow. Tong church is probably the third building on the site, and is a fine example of Perpendicular Gothic Architecture, with the exception of the Golden Chapel. It’s a real pity that it was so dull on the day I went past, this would look so much cleaner with a blue sky background. On well, you have to take what you can. If you would like to see it yourself it is off the Newport Road (A41) just off J3 of the M54.

 Nighttime Snow HDR Stuff

_DSC2242-Edit-EditMany snow scenes are low contrast, and as such it is important to remember your positive exposure compensation to get clean bright whites, and to shoot to the right as far as possible. At night though, all that changes, particularly if you have things like streetlights in the scene. Here you may need HDR. One of the nice touches on the Nikon D4 is that you can select your bracket interval between 0.3 and 3.0 stops. Previously, on the D3 for example, you could only select 0.3-1.0 stops, so you would end up taking many more exposures just to get a good range. Now, many scenes can be captured automatically with a 3-image bracket of -2, 0, +2 stops. For this image, I pushed the boat out with a 5 image 2 stop bracket because of the deep blacks and the bright street lighting.

The shot was taken in full darkness using a 50mm f1.4 Nikor, hand-held at ISO bonkers (25,600), between 1/25 and 1/6400 of a second for the 5-image series. The shot was put together using lightroom 4 and CS6 Extended using the preset Scott 5 as a starting point in Merge to HDR Pro. It was then taken back to lightroom for further processing and then back to CS6 for extra tonal contrast thanks to Color Efex Pro 4. If you have never used Color Efex Pro 4 I can really recommend it to you, it is worth the asking price just for the tonal contrast feature, I use this on most of my images, even the wildlife pictures sometimes.

 

Another Ordeal, and not Just the Walk!

Work’s Been Hectic…

So not so much time for the photography this month. Nevertheless a fresh ordeal had been planned (more walking around the Sandstone Trail) and executed with somewhat less pain than previously. Small 20 minute walks several times a week seem to have helped my general levels of fitness, so there was definitely more energy to think about the pictures. Sadly, on Sunday 26th February 2012 the weather was not brilliant with featureless grey skies to accompany dull scenery. The sun did peak out once or twice, but this was not a tripod-wielding foray, and I had left out my gradient neutral density filters to save weight, so hand-held HDR seemed the order of the day.

Walk of the Week

A Sign of things to come…

The walk this week was a circular trek around Beeston Castle which began in the car park opposite the castle entrance which walkers also use. You can find out more about the castle on the English Heritage site. You may remember the previous walk along the Sandstone Trail after Christmas.So off we set, Helen, Rebekah, Cyril, Suzie (complete with new hat) and myself.

The snowdrops looked lovely as they graciously carpeted several areas of the route, and contrary to initial expectations, the sun graced us with its presence on several occasions. This did not resolve the issue of high-contrast shooting conditions however, and the need for HDR (3-5 stop range) persisted through most of the day. Particularly for those shots of the castle where the foreground was in sunshine but the castle in shadow.

HDR shooting has become part of my routine these days, although I usually try to retain some subtlety in the final shots, but as with everything else this brings choices… There is necessarily a trade-off between speed and precision when it comes to HDR, attempted during a brisk walk with friends. Being generally slower than my fitter peers it would be bad-form to dally too long over multiple shots. Often in overcast situations with deep shadow areas it would be tricky to determine the exact range of exposure to capture everything anyway, so for these reasons quick and dirty frequently rules the day.

Dial in a 3-5 stop auto-bracket and then shoot and check the histograms to see whether that number caught the range or not. If not dial in another couple of shots and go again. Otherwise, if you are shooting in more relaxed company, use spot metering to check the difference in range between the highlights and shadows. It helps when auto-bracketing to use continuous high-speed shooting as this helps you to keep the camera still between shots and lets you know clearly when the bracketing sequence has finished – if you use single shots and lose track of your count, you’re sunk with your next photograph.

Dynamic Range Issues

High Contrast Scene…

My D3 has a dynamic range of 8.6 EV at ISO 200, though if I shoot at 14-bit in RAW (my default) then with ACR I have nearer 12 EV to work with. You need to shoot a range of exposures, in aperture priority, that will ensure that there is no clipping of the shadows in the longest exposure, or of the highlights in the shortest one.

Because of the way that the digital sensor works it is necessary to make sure there is a good margin between the end of the shadow peaks and the left-hand wall of the histogram to avoid posterization and excessive noise in the shadows in the final result. This is because digital sensors have a linear ratio of exposure to “negative” density. Clearly digital cameras don’t produce film negatives, but you know what I mean.

For the sake of example, let’s imagine that a photo sensor has a dynamic range of 6 stops. If you imagine these 6 stops as test tubes arranged in a row, then a 12-bit RAW image file contains 4,096 tonal levels. The first test tube is equivalent to the brightest stop of exposure. When it is filled to the top it will contain half of all the available levels i.e. 2,048. The next test tube along will represent the next stop of exposure which is half as bright and will therefore contain 1,024 levels, thus being only half full. Likewise the third stop will be half as bright again – 512 levels (a quarter full), the fourth 256, the fifth 128 and the darkest stop only 64 levels (just 1/32 of its capacity). The signal to noise ratio increases massively at these low light levels, making sure that the shadow detail is not only poorly represented by brightness levels but also very noisy. This theory has been incorporated into the notion of “shooting to the right”. This means adjusting the exposure value to keep the brightest values as close to the right-hand edge of the histogram as possible in order to maximize the number of levels in the shadow areas.

If you are interested in learning more about practical HDR, digital exposure issues and extreme lighting take a look at the references cited below.

White Balance

These days, when shooting my wildlife photographs outside, I generally use a White Balance preset of 5880K. This works well with landscape shots too, and keeps the white balance constant when shooting panoramas or HDR sequences. If you like technical accuracy there is no substitute for an ExpoDisc white balance filter.

HDR Software Choices

I use Photomatix Pro 4.1.4. Photoshop CS5 HDR Pro can also be useful, but seems to take more fiddling with to get a pleasing result. I generally aim for a very flat result, with well preserved highlights, as this gives more scope for the second and third pass processing in ACR and Photoshop. Everyone seems to prefer a different spin on HDR, from photo-realistic through to incredibly surreal. I’m not a fan of strong haloing, but other than that I don’t mind a strong visible HDR effect. I really like that hyper-saturated postcard look. See references below for more information on resources.

So What was the Ordeal?

Nikon announced the D4 and then, shortly afterwards, the D800. I want both, they are very different animals and each is clearly useful for different purposes. Of course I can’t have both, so where should I spend my money? More on the issues, the dilemmas and the solution next time.

References

  • Mastering Digital Exposure and HDR Imaging. Understanding the Next Generation of Digital Cameras. Chris Weston. RotoVision SA 2008.
  • Practical HDR. A Complete Guide to Creating High Dynamic Range Images with your Digital SLR. David Nightingale. ILEX 2009.
  • A Guide to Extreme Lighting Conditions in Digital Photography. Duncan Evans. AVA Publishing SA 2006.
  • Extreme Exposure. Pushing the Limits of Aperture and Shutter Speed for High-Impact Photography. David Nightingale. ILEX Press Ltd 2010.
  • The HDR Book. Rafael Concepcion. Peachpit Press 2011.