Photo Answers
Crazed by CMOS? Mixed up over memory cards? Send your technique and camera questions to digitalcamera@futurenet.com
Sensor dirt and macro advice
Long-exposure dirt
QWhy does sensor dirt show up on my long-exposure landscapes, but not so much on other images? Charlie Posner
AThe length the shutter is open doesn’t affect whether any dirt on your camera’s sensor is visible in the image, but there is another factor that’s often connected to long-exposure photography, which can make it seem as if this is the case. In fact, it’s the aperture you use that will make the most amount of difference. A smaller aperture that gives greater depth of field, such as f/11 or f/16, will increase the chances of sensor dirt being seen.
With a long-exposure landscape image, the photographer is often using these kinds of apertures to help extend the exposure time, since a small aperture lets in less light. The very nature of a long exposure means that areas such as cloudy sky or water will smooth out and often be relatively light in tone, meaning that darker marks are very likely to stand out.
Sensor dirt is a quite normal, if rather annoying, part of digital photography. While many cameras have built-in sensor ‘cleaning’ that attempts to vibrate dirt off, it’s highly likely that you will need to get the sensor cleaned properly at some point in your camera’s life. There are various products on the market that help you do this, or you can send your camera to a professional lab for cleaning. Digital Camera World has a guide to DIY sensor cleaning at www.bit.ly/dc221sensor
I’ve used both options over the years.
If I only have one or two marks, I’m never too worried, as it only takes a few seconds with the Healing Brush in Photoshop to remove them; but when the sensor dirt really builds up (which it will, no matter how hard you try), it needs to be removed.
Losing colour
QI want to turn an image to black and white but keep one colour – but I don’t use Photoshop, only Lightroom. Can I still do it? Lucy Heaps
AYes you can, Lucy, simply by desaturating each of the colour channels except the one that relates to the colour you want to keep. Obviously this way, anything else within the frame that is the same colour will be retained too, so it’s not absolutely selective. But if you were to photograph red, yellow and green peppers against a blue background then go to the HSL Panel in Lightroom, select Saturation, and take all the colour sliders except the red channel to -100, you would get the result you want.
It’s worth noting that some colours can naturally overlap. For example, your red tomato might contain some orange, so when the orange Saturation slider is set to -100 the red hue can change. However, you can turn the red channel saturation up to give it a colour boost. I’ve done exactly this process for the image above, with only the bright red car and the pair of red pants in the top left-hand corner retaining colour.
The commonly used term for this technique is ‘colour popping’. You will find it used occasionally in advertising to make something stand out, and at one time it was a favourite post-production technique among wedding photographers. I don’t think it’s used as often these days, but if you are able to find the right image where you can isolate the colour as you wish, then it can be something fun to have a play with.
Lighting macro
QI love macro photography, but often find the lack of light an issue. What’s the best way to solve this issue: using flash or reflecting natural light? Connie Smith
ABoth options will be useful on their day, Connie, so I wouldn’t rule either out. When possible, I prefer to use natural light, so a small reflector is definitely something I would recommend you have with you so that you can diffuse or redirect the natural light that’s available. I like to use a white reflector to bounce light back onto subjects like fungi, but that’s very much a matter of choice. At times a silver reflector can give the extra bit of edge required to get the shot how you want it.
Of course, trying to use a reflector with an active and probably an easily spooked subject, like a butterfly or damselfly, is an entirely different thing. Apart from scaring them away, it’s not always possible to find a position amongst the undergrowth to actually place a reflector anyway. In these circumstances, using flash can make a big difference.
The key is to try and make the flash look as natural as possible, so you want to light your subject without overpowering the scene. You can get a dedicated ring flash for close-up work, but you can use a normal flashgun and get excellent results. I work manually with the flash off the camera so I can position it an angle to the subject, and I make sure the flash is diffused to soften it.
The shot above was taken with my 100mm macro lens and an exposure of 1/160 sec at f/5.6. The damsel was in foliage, so wasn’t receiving much light: I lit it with a flashgun slightly above and to the right. The flash was manually set to an eighth power, just to trickle enough onto the subject to make it pop out.
Going full-frame
QI am considering upgrading to a full‑frame camera. Can you explain the benefits of full-frame to me? Toby Weir
AThe most obvious, and possibly the most important, factor is that full-frame sensors – so called because they are based on a 35mm film frame – allow you to shoot at higher ISOs without running into issues with noise. That’s not to say that full-frame sensors don’t suffer from noise issues – they do – but they will allow you to shoot at higher sensitivities without fear of noise ruining your shot. This means you can work more confidently and effectively in low-light conditions. With a full-frame sensor, you also get a greater dynamic range, so in theory you can capture more of a scene with a wide range of tones, including strong highlights, midtones and deep shadows.
The other thing to consider is that a full-frame sensor can give you a shallower depth of field, which can be very important for certain types of photography – portraiture in particular.
Other than my first-ever DSLR, pre-full frame cameras being available, I have always used a full-frame camera. This way I don’t need to consider the crop factor inherent in smaller sensors that means focal lengths are magnified. If I put on a 50mm lens, I get 50mm! Maybe this doesn’t really matter, but I think it can be confusing to photography newcomers to learn the focal length on their lens is different for their non-full-frame camera.
The size of the camera sensor won’t dictate whether you take a good image or not, but full-frame sensors give you an advantage at higher sensitivity and capture greater detail. Full-frame cameras are inevitably more expensive, so you have to weigh benefit against cost.
In the catalogue
QWhat is a Catalog in Lightroom Classic, and should I be using one? Ruby French
AIf you are using Lightroom, you already have your images within a Catalog. Most people only need to use one Catalog: it’s the easiest way to organise your pictures, because you can only view one Catalog at a time.
Think of a Catalog as an inventory that holds all the information about your images. It doesn’t hold the images themselves – just a record of the keywords, ratings or edits you have assigned to each image.
Some people do use more than one Catalog – for example, one for each year. However, if you do this then want to search for older images, you will have to switch between different Catalogs, which can become confusing.
Portraits not sharp
QI’ve just splashed out on a Nikkor f/1.4 85mm lens, but I find that my shots often aren’t quite sharp when I shoot at its widest setting. Is this normal, or is the lens at fault? Roger Corden
AThe lens could be faulty, but I think you first need to consider your technique to make sure that it’s not you! If you aren’t used to shooting with such a shallow depth of field, it will take getting used to. At f/1.4 the area of sharpness is tiny, so the first thing that’s important is that you accurately pinpoint the place you want sharp – the lead eye. That means a single active AF point positioned right on it!
On top of that, make sure there is no movement from you or the subject. Even slight movement can mean the plane of focus is shifted. I actually prefer to use continuous focus for wide-aperture shots, even with a static portrait, so try it.
Water blur
QI’ve been shooting slow shutter speeds for water movement, but nothing seems very consistent. Is there a simple way to remember which shutter speed works best? Kevin Foley
AThere is a rule of thumb that says the longer your exposure and the faster the water is moving, the more it will blur, but that’s about as precise as it gets. It’s impossible to find a shutter speed that works for every shot, because water flows at different speeds. If you are shooting on a little stream with water tumbling over rocks, anything from 1/15 sec to over a second will give you some blur.
Of course, how much blur you want is a matter of taste. I like to give a sense of blur without everything going to an indistinct ‘mistiness’, so I will often shoot at 1/8 sec, 1/15 sec or 1/30 sec on fastmoving streams.