My Shooting Guide

My family always grumble at how long it takes me to take a picture. Is it any wonder when there is so much to take into consideration. This guide is a work in progress designed to reinforce in my mind, all of the steps I need to consider when setting up - the alternative would be to just point and click with fully automatic settings. Not altogether unthinkable - automatic settings just keep getting better and better and it would make my family happier.

Shooting Guide:

  • Adjust Depth of Field (DoF): use aperture between f8 & f16. Maximum image quality is achieved between f8 - f16. Image sharpness suffers at very small apertures due to diffraction. Use the DoF Preview button to manually focus at apertures between F8 - F16

    Increasing DoF- If the light is such that good exposure speed is not possible at F16 then, subject to noise issues, increase ISO, (use Auto ISO if noise is unlikely to be a problem).

    Reducing DoF- If DoF is too wide, increase aperture (i.e. from F8 to F5.6). Then if still too wide at the maximum aperture stand further back from the object and increase focal length or be resigned to correction in Photoshop.

    Hyperfocal distance calculators and articles are available at http://www.dofmaster.com/ , however, my advice is to understand the physics, but don't get drawn in to using overly complex procedures unless you have to - if you paid for a DoF preview button on your camera , use it.


  • Noise: Consider a radio subject to a constant level of static. The static will be bearable to the listener if the station signal strength is strong, i.e. there is a high Signal to Noise Ratio (SNR). However if the signal is poor (remember Radio Luxemburg) the static will spoil the listening experience, i.e. there is a low SNR. The same is true of a photographic image, but the signal strength is determined by the number of photons hitting a photosite on the sensor.

    It follows that Noise will be more apparent in shadow areas where the signal strength is low.

    Given that SNR improves the more light a photosite recieves (for a fixed level of 'background' noise), then by increasing ISO we require less light to form an effective exposure and we automatically reduce the SNR. (ISO noise isn't really apparent below ISO 400 on the Nikon D80).

    During exposure the sensor heats up causing electrons to escape and cause noise. This type of noise is minimal for exposures less than 8secs.

    So we can minimise noise by:
    keeping exposure speeds high (to stop the sensor heating up) and the ISO low (to reduce sensor amplification).

    Note: by exposing for highlights we reduce noise in highlights, but risk noise (reduce SNR) in the shadows. By exposing for shadows we reduce noise (increase SNR) in shadow detail but risk overloading the capacity of the photosites exposed to highlights (i.e. blown highlights).


  • Dynamic Range (DR): - the extent to which the sensor is able to record detail. The Nikon D80 has a DR of 8 stops. This compares with the human vision of 14 stops, and a typical outdoor sunlit scene of between 9 & 11 stops.

    Clearly some compromise is needed when taking a photograph - either clip highlights and retain detail in the shadows, clip shadows and retain detail in the highlights, or, clibp both highlights and shadows.

    The camera histogram and Highlight screens are both useful reference tools. However I find the Highlight screen slightly more useful by enabling you to 'expose for highlights' and provided you dont go too far still be able to 'post process' for shadows.


  • Exposure: Personally I find blown highlights are more unsightly than blown shadows, and because the D80 matrix metering algorithm tends to overexpose in high contrast scenes (consistently clipping highlights)I've taken to compensating my exposures by -1ev in order to retain those highlights.

    I use the Aperture Priority exposure mode (with aperture set to achieve the required DoF). ISO is set to 100 (to minimise noise) with Auto ISO enabled to increase ISO up to a maximum of 400 whenever exposure requires a speed of less than 1/30 sec.



No comments:

Post a Comment

Copyright

© All rights reserved

Search This Blog