Part 8 - Test of Faith

Just occasionally (and only occasionally, thank God!), something happens, when you're reviewing pictures, that really makes you sit up and take stock of what you've done recently and this month it happened to us! We had been looking for competition entries by trawling our tranny files and digital CD's for suitable examples, when one overwhelming fact struck us right between the eyes - the slides were just stunning quality, so bright, saturated and contrasty. We had a real moment of complete and utter self doubt and wondered, have we spent the last six months leading PP readers up the garden path with our tales of digital quality?

We have used 35mm Velvia slide film for many years and have extensive files of pictures compared to just a few months for digital but we still have plenty of material for comparison. At first glance the digital shots just didn't have quite the same kick as Velvia. It was a real shock, because our switch to digital equipment has been total and we haven't used film or a light-box for months. However, despair not, we've worked out a couple of reasons for this difference. Firstly, viewing slide film on a light-box gives the best possible view of an image - the moment it's projected, printed or viewed on a monitor, some of that punch is lost. Since we can't view our digital images on a light-box they have an immediate disadvantage. Secondly, because digital can capture a wider range of contrast than Velvia, the raw images produced from the camera actually tend to show less contrast and saturation (more like images from negative film). Now, we can easily correct this in PhotoShop, but it's often surprising just how far we have to push the contrast to match that of Velvia. Nevertheless, this usually works to our advantage, as it is always possible to increase the contrast of a "flat" digital picture but it is impossible to recover detail from those dark shadows on a tranny

Phew, we're safe! Digital is still our flavour of the month, but we're a little wiser now about the amount of 'after-shooting' effort required to produce the best results. Now we're pondering if it's worth having trannies written from our best digital files, as they will always have more impact when viewed on the light-box.

This comparison of film and digital technique has made us think about a couple of rules of thumb we've regularly used for shooting film. One is the "1/f" rule which says that the slowest shutter speed it is safe to hand hold is given by the reciprocal of the focal length of the lens. Would this still hold true for DSLR's where the"effective" focal length of the lens is multiplied by 1.5? We decided to test this rule by actually shooting a test subject at different shutter speeds. The unfortunate result, is that the rule no longer applies - with digital you have to divide the minimum shutter speed by the 1.5 factor, so when shooting with a 100mm lens for example, 1/150th is the minimum shutter speed which you should handhold. The "rule" becomes 1/effective focal length. This led us to question another major effect on image sharpness - what about depth of field? Will we get more or less using a DSLR? Now this one really had us scratching our heads and reaching for the calculator. We have worked out DOF for the same size finished print and suffice to say, that after much button pushing, we concluded that for a lens of equivalent angle of view, a DSLR will always give more depth of field than a 35mm camera. Not surprisingly - 1.5x more! This means it's great for landscapes, but can be a real drawback if you want to isolate a subject by throwing the background out of focus. Now, I bet it doesn't say that in the instruction book for your DSLR!