No news is good news
Its been ages since Nikon last sat there quietly and didn't bring out a new product so we have accumulated a few Features since our last 'No news is good news feature'. So here you are, all the featured photographs since our last feature journal
Tricks to get better focus
Fo - cus
. pl. fo·cus·es or fo·ci (-s, -k)
A point at which rays of light or other radiation converge or from which they appear to diverge, as after refraction or reflection in an optical system: the focus of a lens. Also called focal point.
As stated above (from the free dictionary .com
) focus is the point or area of an image that is at its optimum clarity.
It is important that we do not confuse good focus with sharpness as these are two different things. Some aspects of sharpness will be achieved with good focus but there is allot more to that subject that we have touched on before in our June 2011 journal
99% of you will have an auto focusing camera and for most of us it is the most commonly used auto feature on the camera as it is generally pretty fast and accurate. Auto focus is great but it has its limitations that we will explore shortly so it is important to use it correctly.
Your camera focuses by looking at an image through a focus sensor trying to find the sharpest line between two areas of contrast. However this area of contrast has to pass across the sensor for it to work.
There are two types of AF sensor, cross and dash. A dash may be vertical or horizontal and as such each sensor can only have areas of contrast running one direction requiring you to select a different sensor or move the camera otherwise the camera will just hunt. A cross sensor (as seen on higher end and newer cameras) can work both directions so are more likely to successfully focus on your subject.
Nikon's DSLR's have 3 modes of autofocus (2 if you are being picky) C,S & M, these being Continuous servo, Single servo and Manual focus that may be selected on the focus mode selector pictured above.
Single servo will focus on the subject when the shutter is half depressed. When focus is achieved you should see a circle in the viewfinder (camera may double beep if this option is turned on) then the shutter relies can be fully depressed. If the subject is not in focus the shutter will not relies (focus priority). Best used generally for all static subjects.
Continuous servo will focus on and track the subject for as long as the shutter relies is half depressed. The camera will take a photograph regardless of focus when the shutter relies is fully depressed (shutter priority). Best used for dynamic subjects or those that may move suddenly eg. Children or animals.
Manual focus is as it says achieved manually by rotating the focus ring on your lens. Shutter will relies regardless of focus. Manual focus is best used for extra precision where AF systems may struggle eg. Low contrast subjects, micro photography low light situations. Techniques for this will be discussed separately later.
Most cameras now have a number of these sensors. They can be used on their own or in groups by selecting single point, dynamic AF area or Auto area AF on the AF area mode selector as seen above.
Single point uses just one sensor for extremely accurate focusing. Either use the centre point and recompose or select a sensor close to your subject using the multi selector at the top of the image.
This is best used for a static subject where accuracy is key.
Dynamic AF area is a useful fudge for when you want to pick out your subject but gives a little lee way for when you are shooting quickly or if the subject is moving. A 51 point AF on the D3x will give you 9 points or through custom settings you can increase this to 9,21,51 and 51 3D-tracking. If you are shooting in single servo this will still act like single point using the selected AF sensor. In Continuous servo the camera will focus on the centre point but if the subject moves, the surrounding AF points will continue to track the subject.
AF area mode uses all 51 AF points and will chose the closest subject. This does not discriminate well so say your subject is stood behind a fence, the camera will focus on the fence leaving your subject left in the blur of bokeh. Ideal for when you really don't have the time to mess with AF point in fast action events where the subject is clear from obstruction.
Do note that the locking ring on the multi selector needs to be off to change selections nut is useful when you don't want your settings changing from a knock.
help your AF out
There are a number of ways to help your camera get better focus in AF that we will now explore.
Chosing a focus area over your subject will require you to move your camera less often but be aware that towards the edge of the frame your camera may struggle more to get a good focus. Also on some cameras you may have higher quality cross type sensors only in the centre area so a focus and recompose may be a better option. Also with an f2.8 or faster lens you the sensors in the centre get even more light making it even easier for them.
If you do chose to focus and recompose then be careful that you don't move the camera to much. On the side of the prism housing you will see a circle with a strike through, this line is where your sensor is. If you move your camera is such a way that your sensor moves forward or aft since focusing, you will move the focus point up away from where you originally wanted it.
Remember that DOF effects focus. Your camera will focus out till the point under the sensor is in focus. This may result in you having an in focus area of the tip of your subjects nose and the 10 cm of air in front of them in focus, not ideal. Newer systems will cope with this better but you may be able to help by moving the focus area to an eye (better contrast and more middle depth of the face) and if you are still getting problems you can fine tune focus manually (with AF-S lenses only) or by setting an offset in Menu - Setup Menu - AF fine tune. This will make the camera slightly over shoot the focus giving the desired result. Finally simply increase the DOF by changing the aperture to a larger number. Quicker and easier but you may just end up with 15cm of in focus air instead.
To focus manually you simply need to rotate the focus ring on your lens till the image in the viewfinder becomes clear. Older SLR's may have specially ground glass and split image viewfinders to help you with this as for them this is the only way to focus. Because the manual focus on modern SLR's is used far less you won't get this so it will be more difficult to fully manual focus however your cameras range finder is here to help you.
All Nikon DSLR's have manual focus assistance from the AF range finder. This will either be a dot or on higher end cameras you will get two arrows and a dot in the viewfinder. The images below show this in action on our test subject.
The arrow pointing right is telling us to focus out, left is in and a dot indicates you have achieved correct focus for the distance. Both arrows flashing means the camera cannot decide how far the subject is away so try moving to a higher area of contrast or illuminating the subject better.
On cameras that only have the dot, you will have to figure out the focus for yourself and will get a conformation dot when the focus is correct.
Alternatively you can measure the distance between the sensor and subject then set your focus to the same distance as marked on the focus ring. This will get you in the ballpark and either the ground glass or range finder will help you figure the wrest out. As you can see this is a bit of a cluncky way of doing things but it is useful if you are framing an image that you intend your subject to walk into or if it is to dark to use the viewfinder and you cannot use light.
If your camera has live view and you have the time, using live view can get you extremely precise focus on your subject.
Using out test subject, a tripod and a D3x set to live view we can set up framing quickly. Then by zooming in on the live view we can check our point of focus as you can see above. To do this varies between cameras but on the D3x you hold the thumbnail/playback zoom whilst spinning the thumb wheel others will have a dedicated zoom in/out button.
This is the most accurate way to visually focus a camera on a static subject and some cameras will even stop down the live view as you change the aperture helping you use your depth of field more effectively.
We hope you enjoy this little tutorial. There are other focusing techniques like how to use split image viewfinders that we haven't covered as if you have one of these then we would hope you already know how to use it. If there is any ideas that you would like to share, please comment below. Don't forget to vote on the Poll
whilst you are at it!