One thing that keeps recurring in many Constructive Critique threads is 'this image could be sharper' or
'this image needs to be sharper on the <insert critical part of subject, e.g. eyes>'.
I've taken information from several discussion threads (a few started by Kiwi) here on AP and consolidated the key elements into one thread.
So what are the main things to consider in obtaining a tack sharp image?
The answer is in several parts that all need to work together.
('tack sharp' from the phrase 'sharp as a tack')
Stating the obvious - If your image is not in focus then it won't be sharp.
Make sure you focus carefully on the key part of your subject which for people and animals is the eyes (not the nose).
Remember: You can manually set the focus point as needed.
Some cameras allow micro adjustment for compensating for front/back focusing of the auto focus system.
Do some research on this subject as it can make a big difference to AF performance.
Also consider using continuous focus mode (AI servo) when shooting action, sport and wildlife.
All lenses have a sweet spot where they are their sharpest. It is usually a few stops closed down from fully open.
Eg. for a fast prime (f/1.7) it may be around f/4; and for many zooms is often around f/8.
Zooms also have an optimal zoom where they are sharpest.
You can google your exact lens model and the phrase 'sweet spot' to find out your lens characteristics or experiment!
For tack sharp images work with your lens sweet spot.
Another factor is the image quality (IQ) of your glass. Very simply, cheaper kit lenses don't
always have the same IQ as more expensive glass. You do, to a large extent, get what you pay for.
Some lenses have inbuilt optical stabilisation (OS) / vibration reduction (VR) / image stabilisation (IS)
(called different things by different manufacturers).
These lenses usually cost more than the un-stabilised versions.
Some cameras have shake reduction (SR) built into the camera body (Pentax and Sony).
You can expect stabilisation to give 2.5 to 4 stops performance.
We know that as you close a lens down the depth of field (DoF) increases so you might think
that closing the lens right down to f/22 or more would mean sharper images. But, another
effect comes into play called the limit of diffraction.
This physical limit is the reason that lens sweet spots are closer to f/8 than f/22.
- Shutter Speed / Support
Shutter speed has a direct effect on two main sharpness issues; first, camera vibration; secondly, subject movement.
- Camera Vibration
Camera vibration can be tamed by the use of several techniques, shutter speed, support and/or special features.
Camera vibration when hand held requires a shutter speed of at least the reciprocal of the focal length x the crop factor.
Eg. a 100mm lens (non VR) on a Nikon D90 (1.5 crop) needs a minimum of 1/150 shutter speed.
But many have found adding another 1/100 to the formula makes for much sharper images.
So in the example above 1/250 is going to give your best results.
Again, some cameras and/or lenses have stabilisation which gives 2.5 to 4 stops performance.
The other way to stabilise your camera is to use some form of support. You have several options.
The main method of support is to use a tripod. You may also elect to use a monopod or bean bag
or simply brace yourself against a solid object.
Please review Stability - Why use a Tripod (or monopod) and
How to hold your camera.
When using a tripod for long exposures camera vibration can be significantly reduced by using
special features such us mirror up delay. You need to read your camera manual to find out
how to do this.
You can also use remotes (either IR, wireless, or cables) to activate the shutter reducing vibration.
When using your finger to activate the shutter you should squeeze not jab at the shutter.
A more advanced technique is to roll your finger onto the shutter, and once mastered, will give
you the smoothest action. You make use of knurled bit of the shutter release so you can roll
your finger off that onto the shutter release gently without shaking.
Demonstrated here about 3 minutes into the video.
- Subject Movement
If you are shooting sports or wildlife then shutter speeds of 1/500 or faster are typically needed to
freeze subject movement.
If a person is running perpendicular to your lens axis (across in front of you) you will need
a shutter speed about 1/1000 (or more) to freeze the action.
You will need to experiment as the crop factor and focal length affect the speed you need.
Of course if you are panning to get a blurred background you may elect to use slower shutter speeds
compensated by your panning action. Typical speeds range from 1/30 to 1/100 when panning.
Remember: If you need to get your shutter speed up, open up the aperture and/or raise your ISO speed.
A noisy sharp image is always better then a less noisy blurred image.
Noise can be handled in post processing.
- Post Processing
This tutorial Why all Digital images need SHARPENING gives a very good explanation of why you need to sharpen your images in PP.
PP can help, but try to capture the image as sharply as possible in the camera for best results.
As you can see getting tack sharp images is a balancing act and there are trade offs needed.
You now have the information needed to understand the main issues in getting those sharp images.
We look forward to seeing your tack sharp sharp images posted on AP
An example (hand held), PP in Lightroom was: crop and sharpen.
Note: The eye and feather details, the non standard bird pose meant keeping focus on the eye.
Camera Model: PENTAX K-7
Lens: Sigma Lens
Focal Length: 500.0mm (35mm equivalent: 750mm)
Exposure Time: 0.0013 s (1/800)
ISO equiv: 400
Metering Mode: Matrix
Exposure: aperture priority (semi-auto)
White Balance: Manual (Cloudy)