RAW File exposure latitude

The following image was taken using a Nikon D300 and the modest little Nikon 35mm F1.8 prime, that I reckon is a seriously good bargain in today's world of hugely expensive new and exotic optics.

When visiting Kingston Lacy today I wanted to get a few snaps of my wife and baby with the sunlit house and other nice features in the background, to give the images some context.  It was such a lovely sunny day that I was faced with the usual dilemmas in deciding how to deal with the huge dynamic range presented by most techniques.

Choices (or at least the ones I thought of!):

1) Place the subject in the sun and take the shot so the exposure was largely even on the subject and background...I hate this as people squint painfully or wear sunglasses.

2) Place the subject in the shade and expose for the subject, while accepting that the background will blow out totally....far from ideal if we want to retain some background detail and context.

3) Place the subject in the shade and expose for the background, then pop in some flash to throw fill light on the subject and balance the exposure....I love this option, only I didn't have a powerful speedlight on me.  My built-in flash was not capable of putting enough light in at the max sync speed of 1/250th sec and the necessary aperture to hold the background exposure to near normal.  An SB800/900 speedlight could overcome this by entering high speed FP sync mode, which enables shots to be taken at any shutter speed by emitting a continuous burst of flash for the duration of the exposure, rather than a single pop for a short period during the exposure (more on this another time).

4) Take at least two exposures optimized for both the background and subject and merge them using layers and erasing in Photoshop....I didn't have a tripod to keep the camera aligned between images and I don't like spending hours on software post-processing, especially for family snaps.  In any case I'm simply not clever when it comes to PP!

5) Compromise on the exposure and adjust it once downloaded....This is the option I chose through knowing my camera and how far its RAW files are capable of being pushed.  At a 0EV exposure the background was mostly ok with a few blown highlights but the subject was vastly underexposed.  I chose to overexpose the image by 1 stop so I blew out more highlights in the background and lifted more detail from the subject.  In Lightroom 3, I simply dragged back the highlights into the range of the histogram and introduced fill light into the subject.  I then increased contrast and added a modest curve.  Hardly any time at all.  I therefore placed the exposure between the extreme values in the image at time of capture, knowing that neither would be exposed correctly at capture, but I could work from that point later to bring the detail out.

Obviously its no masterpiece but I quite like the effect of the bright background and much more detailed subject as it enhances the separation already in place from the choice of aperture.  It illustrates what can be done with a fairly ordinary image when taken in RAW and when some thought is given to exposure at the time of capture.   The headroom available in the highlights and the detail recoverable from the shadows does vary between cameras (the D700 is stunning, D300 is good) but its surprising what can be achieved and pseudo HDR images are often composed by pushing a single RAW file above and below 0EV by a stop or two.

Golden-ringed dragonfly...more about the Carl Zeiss 85mm F1.4 Planar

I packed just the D300 and the Carl Zeiss 85mm F1.4 today for a nice walk in the end of summer sun at Moors Valley. I packed the Zeiss as I fully intended to take some portraits of my wife, Gabriela, just before she has our baby, which is due tomorrow! Yay!!

I love this lens, but its certainly a bit quirky and I have found it perhaps the most challenging lens to use of all those that I own. When it comes together its awesome, but at other times I miss focus or get less than ideal bokeh at wide apertures.

Its well known that it doesn't perform well at minimum focus distance, but to be honest many lenses don't. This is 1 metre however, which is quite a long minimum focus distance these days and probably partly due to its rather historic Planar design.

Its other main issue is focus shift which explains the main reason why its a challenge to use...I'm sure many users feel they have a bad copy, when its actually that they are failing to focus accurately on the subject. Of course with wide apertures focus accuracy is critical anyway and focus shift only serves to complicate things.

Lloyd Chambers makes very sound observations on focus shift in his comprehensive guide to Zeiss ZF lenses and I did my own casual tests to satisfy myself after thinking I was hopeless or the lens was somehow defective! Basically the lens focuses normally at F1.4 (hard enough anyway!) but when you stop down to F2.8 and beyond the focal plane shifts rearward quite dramatically. So you focus on an eye and end up with actual focus being beyond that eye, on perhaps a temple or ear.

Why!? This is the result of residual spherical abberations (RSA, non-coinciding planes of focus) where light from the outer part of the lens element focuses on a slightly different plane to that from closer toward the centre of the element.  The large size of the elements in a fast prime makes this much more likely than with slow lenses.   These RSAs also often cause the slight halation and contrast reduction visible in fast lenses shot wide open.  When you focus the lens the aperture opens to F1.4, whatever aperture you have set it to, to enable lots of light in and coverage by all the focus points.  However, the actual shot is taken at the aperture you have set, say F4, when the aperture briefly stops down for the exposure period. So the focal plane is accurate for F1.4, where focus takes place, but becomes inaccurate for F4 where the lens is stopped down to take the photo, because the focal plane of the light from the more central part of the lens element has shifted rearward. Put simply....you have focused at F1.4 but shot at F4. The increasing effect of depth of field only alleviates the issue at F8 on this lens and then only just! There are a few ways to get around it but basically it remains a pain. I have learned to focus just in front of my intended point, (e.g. on a nose to get the eye sharp) and by experience manage to get a passable hit rate. You can also use the DOF preview or live view as work-arounds, but these are not practicable in most hand-held photography.

Previous use of the ZF 85 has taught me not to bother with taking close up images as the traditional Planar design won't go closer than a metre and images are a bit soft, or suffer contrast loss and halation. Today , when this lovely golden-ringed dragonfly landed near us, I initially cursed my luck at having the 85 of all my lenses! I still decided to have a go and took a few frames at F4 and F8, using only the natural light. I was never going to get close, but I was seriously impressed by the image quality I got...detail, sharpness and contrast were top notch for any normal lens. A combination of accurate focus, suitable shutter speed and stopping down appropriately rendered quality I did not remotely expect. Its another example of using the tool correctly, whether by accident or design and learning from it, as well as a realisation that the lens I considered one of my most role-specific, (i.e. portrait) could actually surprise me with its versatility.

The lens went on to take some nice portraits within its usual comfort zone and rendered its usual natural colours with nice contrast on sharp details. I have loved learning about flash and now tend to carefully balance a manual exposure at 0 or -1EV with some very gentle direct TTL BL fill flash using a speed light dialled down a bit. The Nikon system is fabulous for this and today I just used the built-in, pop-up speed light. I hate direct flash with the exception of fill, for which it can work brilliantly. I like the way a pop of light brings more life to the face, puts a catchlight in the eyes and reduces the contrast from shadow areas under the chin, hair and eyes, or balances a bright background. I try to get my subject in diffused light, to reduce harshness and contrast. Here some diffusion was provided by a tree but relatively bright light was still falling on the subject from the left and slightly behind the subject. The flash tamed this contrast quite effectively. I'm sure I still have a way to go before fully mastering creative lighting, but I'm getting good results much of the time.