Welcome to what will hopefully be the first of many "Weekly Educational Topics".

    Much the same as the Weekly Theme Gallery, this weekly topic will be a chance for us all to discuss and learn about the basic elements of bird photography, bird behaviour and everything else in between. I'll start the topic off each week with a little about what I know of the subject and I hope others will follow with how they approach the topic and what they know in terms of tricks, tips and other information that is related.
    Anyone who wants to ask a question about the topic is also urged to do so. We have a great deal of collective knowledge when all our members combine so I think this will be a great resource for learning.
    It would be great if we could try and stay on topic and not go off into different tangents so if you have a query that relates to a slightly different topic, let me know and we can try and get to it in the next weeks theme or one shortly after. If there is a term or process that you don't understand in the following posts then feel free to ask. Thats how we learn.

    This weeks topic is ISO. ISO relates to the rating to light sensitivity of film and has also followed on into digital photography. On most digital cameras the lowest ISO rating is ISO 100 with the highest normally being ISO 1600 or 3200.
    As in film, the higher the ISO, the more sensitive to light and also the higher the amount of visible grain in the image. This grain is also referred to as noise and in some cases can ruin an image.
    Most photographers on this forum will have a preference for using ISO's under 800 as these ratings will show less visible noise than their higher counterparts and will in most cases be light sensitive enough to yield fast enough exposures (shutter speeds) for bird photography.
    Having said that, there will often be big differences in noise levels between camera models. Often, the larger the camera sensor, the better the amount of noise in the resulting image.
    There are many ways to reduce noise in your images after they are taken (noise reduction programs and filters for post production) but the best way to deal with noise is to expose the image properly. Under exposure (and its subsequent correction) is the main cause of most noisy images and can be remedied by exposing the image as bright as possible without "blowing" the highlights in the image.
    Also, darker colours tend to exhibit more noise than lighter ones (in my experience) so try to avoid darker coloured backgrounds when shooting at higher ISOs.

    My baseline setting is normally ISO 200 if the sun is out and conditions are good but I will often change between a few settings depending on the light and what situation I'm shooting (action/flight shots will sometimes require a faster shutter speed than the light allows and this will mean an increase in the ISO I use).
    While my camera is a full frame camera and deals with noise quite well, these settings should be applicable to those with smaller sensors like those found in the prosumer DSLRs and most point and shoot cameras. They are as follows:-

    ISO 100- I will sometimes use this when shooting silhouette shots with the sun in the frame or very bright sunlit water.

    ISO 200- As I said, this is my baseline setting and if the sun is out and I'm somewhere nice and bright then I would prefer to shoot at this rating if I can.

    ISO 400- I use this setting when the sun has disappeared for a bit but is still showing through the clouds.

    ISO 800- This setting comes in handy on days that are totally overcast. Also handy when working in the shade like in forest or some other darkish place.

    ISO 1600- This is the last resort setting, I use it when the sun has almost disappeared from the sky but there is still a bird doing something interesting that I really want to photograph (does'nt happen that often )

    There are, of course, ISO options in between these settings (320, 640, etc) which I will often use but in the smaller sensored prosumer cameras (40D, 7D, 1000D etc) it has been shown that these ratings are actually a bit misleading and can result in noisier images so I will not recommend them here. In any case, the settings above serve me pretty well.

    I mentioned briefly about noise reduction filters and programs. They are probably something that would make a good topic by itself (and one that I'm not entirely up to date on) so it would be good if we can try and keep the discussion about "in camera" noise and your thoughts and tips on it.
    I hope this brief article and its following discussion will be of use to some of you. Like I said before, ask any questions you want, we have a wealth of knowledge on here (and on the wider web) and hopefully your question will be answered.
    Also, if you have an idea for an upcoming theme (whether it be photography related or even something like stalking birds etc) then PM me and we'll try and include it in weeks to come.

    Paul 8-)