Do you want sharper pictures? It’s the holy grail of many a photographer who cannot work out how to do it. You see pin sharp pictures everywhere, yet have no idea how to achieve that level of quality. You might end up spending a fortune on new cameras and lenses, but still fail even by following all the rules. Well, I am here to help.
I created a Youtube video entitled ‘How to get tack sharp images for less than $5’ and it’s been viewed over 600,000 times. So you are not alone in trying to get sharper pictures. And I am talking about pictures which you know should be sharp, but aren’t.
I am going to assume you have no camera shake and your lens is clean even through these are the commonest reasons for blurry pictures. After you’ve discounted those, there are two areas to focus on (Sorry about the pun).
1. Sweet spot: This is a term used to denote the aperture (or aperture range) where your lens is sharpest. It is a misnomer to believe lenses are equally sharp at all apertures, so when you are told to stop down for landscape photography and go wide open for portraits, what people are actually saying is use your lenses at its least optimum.
When light rays pass through glass (i.e a camera lens) they get bent and because not all light rays have the same wavelength they are bent in slightly different ways. Then some bright spark added another obstacle – an aperture – in the way. The overall result was the photographer can regulate the amount of the picture that is in focus. What you cannot do is turn focus into sharpness. The quality of the lens helps as do the special coatings on the front and back, but you cannot fix all the issues. Light hitting glass when the aperture is wide open refracts and you get chromatic aberrations which appear as soft focus. In bad instances you can actually see the different wavelengths of light separated in the fringes of objects. When the aperture is closed down you get diffraction. There are some maths and physics behind it all, but the important thing to know is these make your pictures look softer. In focus, but soft.
The best way to beat it is to stick to a medium aperture. The rule of thumb is two stops down and two stops above f/22. If you want to be more precise then you can run a simple sweet spot test. The way I do it is to get my camera level and facing down. Then on another level surface lay out some coins or something else flat yet patterned.
Then, using a remote release (to avoid camera shake), I take shots at my lowest native ISO, and shoot from the widest aperture to the smallest. I then look at the results at 100% on a computer screen and compare. You will see quite a difference. You then select the best aperture range where you get the sharpest results.
This may mean you cannot shoot lush Bokeh portraits or back to front sharp landscape because the full range of depth of field is curtailed by the quality output of your lens, but what would you rather have? Pin sharp results or passable results?
2. AF fine tune: If you find your camera is not quite nailing the perfect focus position, it may not be your fault, but that will impact the overall look of your pictures.
Not all cameras have AF fine tune, but then not all need it. Mirrorless cameras, for example, don’t need it, but DSLR cameras shooting with a shutter and mirror do. This is because focus isn’t derived from the lens to the main sensor. It is worked out via a small focus sensor. Any slight error in calibration will cause the focus to be out. It may only be slight but when you need an eye to be in focus, but the end of the nose is or the ear, then you could have an issue with your sensor. That’s where AF fine tune comes in. It allows you to manually adjust the focus sensor so it produces the correct focus onto the main sensor.
As far as my experience goes all cameras with this facility store the calibration for each lens so when you change lenses the fine tune changes with it. I have yet to come across a camera that you have to keep doing it each time.
There are special fine tune grids you can buy, but I prefer the run and gun approach which uses a ruler. You set your camera onto a tripod angled down slightly (about 45 degrees). Put the ruler so a discernible spot is in the centre of the frame. Defocus your lens and use the AF system to focus on the ruler. You can view this on liveview, although prefer to take a shot and see it at 100% on a computer screen. You can see if the camera is properly focused or if it is out. If the focus falls in front or behind the ruler point, you can adjust it in AF fine tune. Either + or – (depending on which side of the focus line you are) until you see the focus come right. You will need to manually defocus every time and refocus with the autofocus system. Once the focus is spot on press enter and that figure will be stored by the camera and you can move on to your next lens.
For zoom lenses I test at the wide angle end, the tele end and in the middle and take an average if it is out further at one end or the other. However, I have not found a zoom lens that is different at either end yet.
I do both of these techniques whenever I buy a new piece of glass so I know its limitations and strong points. I urge you to do that same so you can really nail that focus.