Exposure 101!

[mw_aurora]

This follows on from Salty's excellent camera dilema (http://www.birdforum.net/showthread.php?p=443199#post443199) thread, specifically for some of the recent questions. It aims at those not familiar or 100% comfortable with ‘camera technology’.


A photograph (assume digital for now) requires reflected light from the subject to hit the recording surface (e.g. the CCD sensor in a DSLR body) through the lens of your camera. This light will therefore produce the image that is eventually displayed on your computer screen. The amount of light that hits the recording surface will determine the amount of contrast, colour depth and detail of the recorded image.

The amount of light that can potentially travel to the camera is controlled by the aperture of the lens (i.e. the f number). The smaller the number, the larger the hole and therefore more light that can get to the camera. So ‘wide open’ means the smallest f number a lens can give, ‘one stop down’ is the next largest number (e.g. on a 400mm f5.6, wide open is f5.6. 1 stop down is f8). Note that a larger aperture (i.e. a smaller f number) will decrease the depth of field (DOF). So f4 will have less of the image in focus compared to f5.6 or f8.

Next in line is the camera shutter that opens, when you press the button, to expose the recording surface to light. So this also controls the amount of light that hits the recording surface to create the final image. The faster the shutter (bigger number displayed on the camera), the less light, but the more chance of ‘freezing’ motion (e.g. a flying bird) because the shutter is only open long enough to ‘see’, for example, a wing in a single position.

ISO – this was normally referred to as ASA with film and indicates the speed a film could capture the light presented to it. In the terms of digital, it is the speed that the recording surface (i.e. sensor) will capture the light. This is normally set by one stop increments, i.e. 200 ISO will capture light twice as fast as 100 ISO. However, faster (i.e. bigger numbers) will increase the amount of ‘noise’ in the photograph.

So, what does this mean to you as a DSLR user?

To correctly expose a photograph (i.e. get a bright image, without losing detail in the paler or darker areas and keep good colour rendition and contrast) you need to set the correct aperture, shutter speed and ISO.

How do you do this? First thing is to remember is that aperture, shutter and ISO are normally referred to in ‘one stop increments’ (aperture - f5.6, f8, f11 etc, shutter - 1/120, 1/250, 1/500 etc and ISO - 100, 200, 400 etc) so adjusting one of these should mean a one stop adjustment to another. For example, say the correct exposure should be f16, 1/120, ISO 100. You could adjust the ISO to 200 (so increase ‘1 stop’ faster light capture on the sensor) and the shutter to 1/250 (less light by ‘1 stop’) and still expose the image correctly, but reduce potential of blur from movement.

How do you know the correct exposure? All recent DSLRs have built in light meters that can automatically decide the correct exposure for your picture. The way the camera does this is based upon which setting you use.
In total Automatic, the camera will try to get the AVERAGE settings for depth of field and freezing motion based on the ISO setting. This will normally give pictures with more depth in focus, but loose ‘sharpness’ due to motion blur in moving subjects (such as birds).
To maximise the shutter speed, and therefore the ability to ‘freeze’ the frame, many nature photographers will normally use aperture priority. This usually means that the wheel close to the shutter button controls the aperture set on the lens (assuming the lens is automatic). The camera will then calculate the correct shutter speed based on reflected light, the set aperture and the ISO setting. By opening the aperture (setting a smaller f number) more light can reach the recording surface, so the shutter does not need to be open for as long. Therefore, the smaller the aperture, the faster the shutter speed required to get the same amount of light. This is similar to increasing the ISO, as described above.

The camera will also have other settings that controls the way that it ‘guesses’ exposure for the current view in a viewfinder (e.g. centre weighted, spot, etc), but I guess that is for the next instalment!

Finally, to answer another question, the camera's viewfinder will generally see the 'wide open' setting on the lens. Therefore an f2.8 lens will appear brighter than an f5.6 even though both may be set to f8...unless you press the DOF preview button on your camera!

Please feel free to correct my mistakes or assumptions. There is plenty more to say on automatic metering modes, use of aperture vs shutter priority, TCs, post-production etc.

[RAH]

To maximise the shutter speed, and therefore the ability to ‘freeze’ the frame, many nature photographers will use aperture priority.
Don't you mean shutter priority? If you want to freeze the action, isn't it better to use shutter priority, where you pick the shutter speed - you'd pick a fast one - and let the camera adjust the aperture automatically. If you use aperture priority, the camera might be using a slow shutter speed, which is what you are trying to avoid.

Otherwise, very nice summary! :-)

[Leo S]

Good post mw_aurora,

I like to keep things simple. I don't even bother metering. Instead, I tend to use manual mode, and make a best guess exposure(usually of a tree or some other inanimate object that is in the same kind of lighting that I expect to find my target) as soon as the camera is setup. Then I just review the histogram, which shows me the distribution of properly exposed pixels in the image, adjust my shutter speed as necessary, and repeat If the histogram does not look right. In practice, this only takes a few seconds, and I'm ready to shoot.

Now here comes the crucial bit, if you want to get the best out of your DSLR and utilize it's entire(hidden)dynamic range...

Firstly - Shoot in RAW mode (jpeg records less dynamic range, and is more lightly to blow out highlights and loose detail in the shadows!).

Secondly - "EXPOSE RIGHT" (which means, look at your HISTOGRAM and make sure the largest proportion possible of pixels is skewed over to the right side of the histogram, but not too far right or your highlights will start to clip/get blown out!).

Here's an article which explains the "expose right" technique:
http://www.luminous-landscape.com/tutorials/expose-right.shtml

Here's another, which goes into much greater depth about RAW converters and post-processing to maximize dynamic range:
http://www.normankoren.com/digital_tonality.html

And, last but not least, this article which has the best technique I have yet come across using Photoshop layer masking to bring out all that hidden dynamic range:
http://www.phong.com/tutorials/mask.tree/

I have yet to try the above layer masking technique, but it seems much better than most of the other ways which I have tried and seen recommended!

Leo

[SeanKP]

Don't you mean shutter priority? If you want to freeze the action, isn't it better to use shutter priority, where you pick the shutter speed - you'd pick a fast one - and let the camera adjust the aperture automatically. If you use aperture priority, the camera might be using a slow shutter speed, which is what you are trying to avoid.

Otherwise, very nice summary! :-)
Actually, I'm with Mark on this. I tend to use aperture priority and set the aperture as wide as I'm prepared to go with that particular lens (usually half a stop down but occasionally wide open) knowing that I've then got the fastest shutter speed possible. If that still isn't fast enough I'll adjust the ISO upwards. The reason I do this is that I'm almost always trying to isolate the subject from the background and if you go to shutter priority you're giving away control over the DOF. I guess that, as this thread is intended as a primer, I should explain that the wider open the aperture (the lower the f number) the narrower the depth of field so focus is more critical with a wider aperture but it helps when trying to achieve that smooth out of focus background.

This thread is a great idea Mark. I'm wondering if it might not be useful to have it 'stickied' at the top of the camera forum?

Sean

[Adey Baker]

Yes, Aperture-priority is best - if you choose shutter-priority and the light changes you could easily run out of apertures and under-expose.

It's worth stating that with long telephotos changing the aperture by a stop either way isn't going to make much difference to 'depth-of-field' (the amount of the image that is acceptably sharp either side of the point of focus).

[greypoint]

Aperture priority - which can be easily flicked either way to retain enough shutter speed. I try to always flick back to P mode between taking pictures as a safety option - I've been caught out trying to capture a sudden opportunity to photograph a flying bird with no time to change the settings. That way i can usually rely on getting something. High ISO may mean more noise but noise is easier to treat afterwards than camera shake.

[rayl]

Aperture priority(again) - its worth searching out the DoF tables for your lens, tables which will show the maximum and minimum distance a subject will remain sharp for a given focal length and aperture.

Ray

[mw_aurora]

Thanks everyone for the positive comments. Rather than loads of individual replies...

RAH, I did mean Aperture priority, although having read the paragraph again, I will update it to be more explicit! Personal preference is important here though. Now updated the original post.

Leo, good links and agree with the principles. I think some explination of other methods of judging correct exposure (e.g. in-camera metering) would help with the understanding.

Sean, agree with your technique 100%. I'm happy for this to be a sticky and to update my post(s) where/when required.

Adey, agreed, although doesn't this depend on the distance from the camera to the subject (i.e. larger difference to a close subject)?

greypoint, good point about trying to ALWAYS return the camera settings to something you know after a series of shots. This means that you know exactly what the camera settings are and can change them without thinking.

Ray, good point. Fancy explaining how to read them in laymans terms?

One thing I didn't mention - I am not an expert and do not intend to prescribe a best way of doing things. My intentions are purely to explain some basics and let people decide their own favoured methods.
Following on, I have some thoughts on in-camera metering, which I will try to add to the thread soon (unless someone else beats me to it!).

Cheers Mark.

[christineredgate]

Mark,many thanks,I am going to print this page,and keep it for referral.I always thought that if pics come out somewhat overexposed,one just slides the exp bar down a little,so that one is on the minus side ,and not the plus side.

[mw_aurora]

Mark,many thanks,I am going to print this page,and keep it for referral.I always thought that if pics come out somewhat overexposed,one just slides the exp bar down a little,so that one is on the minus side ,and not the plus side.

Thanks Christine (and for the kind words on Salty's thread). I am afraid I updated the original post, probably just after you printed it...sorry!

Generally you are spot on for the exposure bar.
However, I think you have seen and as said by SeanKP, usage really depends on:
the lighting on the primary subject (for me, normally the blurred bird whizzing past) compared to that on the background (normally the blurred mess as I try to keep the blurred bird in frame) and, if it wasn't hard enough already, the metering mode on the camera...
Why do we do this? |:d|

Cheers Mark.

[Adey Baker]

Adey, agreed, although doesn't this depend on the distance from the camera to the subject (i.e. larger difference to a close subject)?


Yes, but we're all going to use fieldcraft to get as close to the subject as we can to avoid all those problems of haze, trying to enlarge a tiny section, etc., etc., aren't we... ;) :eek!:

[Adey Baker]

Some (interesting?) facts on apertures! :h?:

F stops obviously worry a lot of people :stuck: so what are they?

Well, from a bird-photographers' point of view high shutter speeds are probably the most important consideration so they're usually left with whatever aperture suits the particular shutter speed chosen. From a practical point of view, then, you don't need to worry too much about them!

Shutter speeds are easy to understand as you're only dealing with one dimension - time - and doubling or halving the shutter speed makes one 'stop' difference up or down, whereas with apertures there are two dimensions as it's all about area - and a (roughly) circular area at that.

This is why a one stop 'slower' aperture is only (approx.) 1.4 times the previous number rather than 2 times (F1 - F1.4 - F2 - F2.8 - F4 - F5.6, etc.) and that F number is actually a ratio.

The ratio is focal length : aperture and a lens with a maximum of, say, F4 is described as F1:4. Divide the second number into the first and you have the actual aperture size which is what determines the depth-of-field. The smaller the size of the aperture, the greater the depth-of-field.

This is, fundamentally, why a telephoto has less depth-of-field than a shorter focal-length lens: Divide a 400mm lens by 4 and you see that you need an aperture of 100mm whereas a 40mm lens would have a 10mm aperture for its F4 setting. To get that 10mm opening on your 400mm would require an aperture of F40 and a very slow shutter speed to cope with the vastly reduced amount of light.

Depth-of-field, the amount of the image that is recorded as acceptably sharp on the film/sensor, is all to do with the angle that the light rays from the rear of the lens strike the film/sensor - please tell me you don't want a diagram to explain! - oh, and the distance you are from the subject alters the depth-of-field as well. The closer you are, the less you get - if you look at the depth-of-field table that you get with your lens you'll see how dramatically different it can be from a distant setting with the lens stopped-down several stops to a close-up at full aperture. Some macro lenses, apparently, have no d-o-f at all at the closest distance at full aperture!

[RAH]

Well, from a bird-photographers' point of view high shutter speeds are probably the most important consideration so they're usually left with whatever aperture suits the particular shutter speed chosen. From a practical point of view, then, you don't need to worry too much about them!


Don't mean to be argumentative, but you just described shutter priority mode. And this way of thinking is exactly why I said earlier that shutter priority is the way to go for beginners. Yes, of course one can use aperture priority and watch the shutter speeds that are obtained, and do it this round-about way. But the easiest way to think about it, especially for beginners (whom this posting is supposed to help) is shutter priority.

I agree completely that using aperture priority and setting the aperture at full is a great way to get the fastest shutter speed possible for your camera while still getting a proper exposure. However, for beginners, I think that shutter priority is much more straight-forward and easier to understand, as your above post illustrates.

[Adey Baker]

Don't mean to be argumentative, but you just described shutter priority mode. And this way of thinking is exactly why I said earlier that shutter priority is the way to go for beginners. Yes, of course one can use aperture priority and watch the shutter speeds that are obtained, and do it this round-about way. But the easiest way to think about it, especially for beginners (whom this posting is supposed to help) is shutter priority.

I agree completely that using aperture priority and setting the aperture at full is a great way to get the fastest shutter speed possible for your camera while still getting a proper exposure. However, for beginners, I think that shutter priority is much more straight-forward and easier to understand, as your above post illustrates.

We could debate this for ever - I think a beginner would perhaps not keep a check on everything going on in the viewfinder so could easily miss the fact that their chosen shutter speed may not provide enough light for full aperture whenever light levels drop thus causing under-exposure.

[rayl]

[QUOTE=mw_aurora]To maximise the shutter speed, and therefore the ability to ‘freeze’ the frame, many nature photographers will normally use aperture priority. QUOTE]
Going back to the original post, the point about using aperture priority, is that setting the camera to aperture priority and then selecting the maximum aperture for the lens in use (smallest f number) you are assured of the fastest shutter speed available for the correct exposure of your subject. This is particularly relevant for birds in flight, the higher the shutter speed with a long focal length lens ie.400mm or 500mm. the more likely you are to obtain sharp images.
You can monitor your shutter speed, and if the light is not so good and the shutter speed is falling to a level where you will be unable to obtain sharp images, you can then increase your camera’s ISO setting which will give you a corresponding increase in shutter speed but in most cases a higher ISO setting means a more grainy image quality.
If the lighting conditions are such that the shutter speeds you are obtaining are very high ie. 1/4000 second, (extremely unlikely where I live) you may wish then to reduce your aperture settings (higher f number) to allow a longer exposure time, possibly 1/1000 second, and this in most cases will give you a better quality image as the lens is not operating at the extreme of its aperture range.



Ray

[christineredgate]

So,is the max aperture for a 300f4 lens,f4,or can it be altered /moved down /up/to F2.If I am using the 100-400 lens at its max setting,that would be 400,would I be able to alter the F no.Also whilst here,may I ask,if using the 100-400 with the 2x it has been mentioned that due to the loss of light stops,one should alter the F nos.So which setting should be used on the cam20d/350d,and which f,stop should be used,also the same with the 300F4 using the 1x4 .I ask this,as I find the larger lenses too heavy/too expensive.But using the extenders on the said lenses does increase the magnification.Fortunately the 300 uses auto focus instantly with the 1x4 but I find I have to use manual focus with the 2x.But I did manage a half decent shot with the 100-400 plus 2x,it was dark,but once highlighted was acceptable,but I could have perhaps improved the shot,if I had used some different setting.Just used P mode.

[mw_aurora]

Depth-of-field, the amount of the image that is recorded as acceptably sharp on the film/sensor, is all to do with the angle that the light rays from the rear of the lens strike the film/sensor - please tell me you don't want a diagram to explain! - oh, and the distance you are from the subject alters the depth-of-field as well. The closer you are, the less you get - if you look at the depth-of-field table that you get with your lens you'll see how dramatically different it can be from a distant setting with the lens stopped-down several stops to a close-up at full aperture. Some macro lenses, apparently, have no d-o-f at all at the closest distance at full aperture!

Can we have diagrams please :) Nice explination, and you knew what I meant with my original reply - thats what extension tubes are for isn't it? :stuck:

[Adey Baker]

Christine, your 300mm's maximum aperture is F4 - you can't improve on it in any way.

Divide the 4 into the 300 and you get 75mm which is the maximum opening you can get on that lens (that's why your filter thread is 77mm).

If you put, say, a 2x converter on then you've made it a 600mm lens but by doing the above sum the other way round you can see why it's now F8: i.e. divide the 75 into the 600 and you get 8.

You shouldn't have to alter any settings as (I think) the camera will automatically 'see' the lens as having a maximum aperture of F8 and will give you the correct shutter speed to match - assuming you're using one of the auto-exposure modes.

[Adey Baker]

Can we have diagrams please :)

I'm not sure what my skills are like in Photoshop, whether I can concoct an easy to understand diagram - don't hold your breath!

[christineredgate]

Thanks,Adey,I feel much happier now knowing that the cam will do everything for me.I take it that the P setting is one of the auto exposure modes.

[Adey Baker]

Yes P is full program mode where the camera chooses both the aperture and shutter speed combination

[mw_aurora]

Lets see if I can get quotes working...


So,is the max aperture for a 300f4 lens,f4,or can it be altered /moved down /up/to F2..

Yes, f4 is the maximum that the lens can open. It can only be set smaller, e.g. f5.6


If I am using the 100-400 lens at its max setting,that would be 400,would I be able to alter the F no.

Yes, but only smaller than f5.6, e.g. f8


Also whilst here,may I ask,if using the 100-400 with the 2x it has been mentioned that due to the loss of light stops,one should alter the F nos.So which setting should be used on the cam20d/350d,and which f,stop should be used,also the same with the 300F4 using the 1x4.I ask this,as I find the larger lenses too heavy/too expensive.But using the extenders on the said lenses does increase the magnification.Fortunately the 300 uses auto focus instantly with the 1x4 but I find I have to use manual focus with the 2x.


OK, the teleconvertors (TCs) will give extra magnification (often termed reach) but with the cost of light passing to the recording surface. The 1.4x TC will reduce the maximum aperture of the lens by 1 stop, so your 300 f4 will become a 420 f5.6. The 2x will reduce the aperture by 2 stops, so the 300 will become a 600 f11. You will loose Autofocus (AF) on the Canon 20D and 350D with a maximum aperture of f5.6. The Canon 1 series will AF at f8 (sorry, I am a Canon user). Remember that the AF actually works with the lens aperture fully open, not the aperture set by the exposure. AF will generally be faster and more accurate with brighter lenses, so larger maximum apertures.

As you mention, larger leses have greater reach, but are larger and heavier for larger glass to allow more light and maintain the larger apertures (as described in Adey's post above).

Cheers Mark.

[mw_aurora]

I'm not sure what my skills are like in Photoshop, whether I can concoct an easy to understand diagram - don't hold your breath!

I was joking, but if you think it will help others...

[Adey Baker]

I was joking, but if you think it will help others...

I couldn't do it in Elements - if there's any straight-line drawing tools, etc., in there, I don't know where they are!

Anyway, I've done a very crude, not to scale mock-up in 'Paint' to give an idea.

The black line is the film plane, the yellow dot is an object that is 'in focus' and the magenta dot is behind it and thus out of focus.

Light rays from each dot are gathered all over the lens surface but to simplify I've just shown the outermost ones. As you can see the yellow ones are brought to focus at the film plane and then they diverge behind it whereas the magenta ones come together behind the film plane and thus where they strike the film they are spread out.

When you stop the lens down you exclude the outermost rays and just use a smaller number from the centre of the lens. The red lines from the magenta dot through the smaller aperture have a narrower angle and thus are not spread out so much where they pass through the film so they're more in-focus compared to the full aperture ones.

It would be more confusing to put any more in but if there was a dot in front of the yellow one then that would focus in front of the film and wouldthus already be diverging when it hit the film and also look out of focus

Time I went to bed, I think, to rest my brain!

[rayl]

Sleep well Adey, don't be dreaming about circles of confusion all night :gn:


http://www.sigmaphoto.com/images/LensesDepth/APO800mmF5.6EX(J).pdf

This is a link to a depth of field table for Sigma's 800mm lens, I think it is reasonably straight forward to understand.

Ray

[rezMole]

Yes, Aperture-priority is best - if you choose shutter-priority and the light changes you could easily run out of apertures and under-expose.

It's worth stating that with long telephotos changing the aperture by a stop either way isn't going to make much difference to 'depth-of-field' (the amount of the image that is acceptably sharp either side of the point of focus).

I still prefer shutter priority. I agree, you may "run out of apertures" and end up underexposing, but in the viewfinder, there is an under/over exposure scale which would show how much you are under-exposing by (Nikon D70 - not sure what Canon do). I keep an eye on this and as long as it shows an underexposure of less than a couple of f-stops, then i am usually not that concerned. A slightly under-exposed shot can be brightened up to something usuable later. A blurred shot cannot!

The other way of working is to set the ISO to auto, then as the light fades, the ISO will increase to compensate. I have had some success with this method, but some disasters too (where the camera ends up at ISO 1600). Still - even that produces a more usable shot than a blurred one.

[Adey Baker]

Each to his own, then!

To illustrate how light levels can change (in the UK, anyway), yesterday afternoon I took two shots 24 minute apart. The first, when the sun was shining was 1/1600th, F5.6, ISO400, the second when the sun went behind a cloud was the same aperture and ISO but the shutter speed was 1/60th - nearly 5 stops slower in 24 minutes!

[christineredgate]

Having read all the info presented,I guess I should have taken up photography 30yrs ago,when brain could absorb info.You guys have really explained in excellent detail.Thankfully todays modern cams do seem to do most of the work.But I do hope this info really can be of help to newbies as you have all take a great deal of time to explain the settings and why /how they work etc.So hopefully someone will benefit from your expertise.

[bob hastie]

Keep this stuff coming folks, some of it is starting to sink into the old, and rather stodgy grey matter

[Leo S]

Leo, good links and agree with the principles. I think some explination of other methods of judging correct exposure (e.g. in-camera metering) would help with the understanding.


Mark, actually, now that I think about it, there were a couple more things which might be helpful to someone trying to get their exposure spot on... and that I think is really the crux of it; If you get your exposure spot on, that is what gives you the most flexibility when playing around with the photo in post-processing, and the power of post-processing should not be underestimated... It is, I admit a bit of a steep learning curve at first (one I am only just starting to climb myself!), but well worth it for the view from the top! :)

The real bonuses that come with mastering the techniques I mentioned are :
Rich tonal quality throughout the image, even into the deepest of shadows whilst retaining detail in the highlights in all but the most contrasty conditions. Conditions you probably would not want to soot anyway most of the time!

Knowing the limitations of your equipment as well as when to shoot and also when not to shoot is also a very important skill IMHO.

Just out of interest, how many of you here know the dynamic range of your DSLRS ? I know mine - a modest 9.81 stops on my D70. Check the table about 2/3 of the way down this page if you want to know yours:
http://www.imaging-resource.com/PRODS/EOS1DS2/1DS2IMATEST.HTM

Anyway, back to question of judging correct exposure in camera - together with checking your histogram, checking the blown-highlight warning screen can also be very helpful, in letting you know when you are achieving a good exposure or not, as long as you know your own camera and how much if any headroom it provides.

The important thing to remember is that the exposure warning for most cameras AFAIK is based on a jpg, even if shooting in raw mode, which means that when the camera is telling you you have blown out highlights, in actual fact, you can usually recover all the highlight detail in post processing in all but the most grossly overexposed cases.

One person that I know of on another forum has even gone as far as uploading a custom curve to define the exact point at which his RAWs start to blow out in his DSLR!

In practice, some might like to meter off the the brightest part of a scene (usually the sky), and then, having set the exposure compensation to 1 stop under this (to preserve all the highlights with some head room to spare), whenever you expose under those conditions, you will have a minimum of about 8-9 stops of shadow detail to play with depending on which DSLR you are using (10-12 on some of the better performing DSLRS), when shooting in RAW mode.

I hope that helps a bit! The links I pasted in do a much better job of explaining most of the above than I could ever hope to do! It's allot for a first time DSLR user to get their head around as I said earlier, but to understand exposure properly, its necessary IMO to understand how dynamic range and post-processing all tie in with it, if you want to use your DSLR to its fullest potential!

Leo

[rayl]

I can't remember where I found this table, so no link, but I think it serves as a good comparison with the human eye.
Don't forget, 1 f-stop larger means twice as much light or double the intensity range

"Typical values
The following is a comparison-guide of typical (average) values quoted in various books and articles. Some variation exists between articles, which may be due to:
- interpretation of how much of the dynamic range is actually useful in maintaining image detail at the extremes of highlight and shadow (due to the flattening-off of the characteristic curve, or the influence of noise)"

[Leo S]

Ray,

Here's where the table came from :

http://www.photoreview.com.au/Articlexasp/13f37675-e17f-4011-8d82-9943db73c239/Default.htm

Keep in mind it's 2 years old now, so Dynamic range has improved significantly in DSLRs since then... their pro-DSLR numbers are about 3 stops less than the best of todays DSLRs, which is on par with professional scanning backs from 2 years ago!

[redshift]

One more hint: in between shooting carefully exposed shots in aperture-priority RAW - which indeed is what I usually use - leave your camera in Sports Mode. Birds are sports subjects: always moving, even if it is just the wind ruffling their feathers, and it needs a fast shutter speed to freeze the action. (This is why image stabilisation "gaining 2 stops" is a myth for bird photography.)

Sports Mode will provide the fast shutter speed, adjusting the ISO / aperture as necessary, even if (on a Canon 300d) it shoots in lousy JPEG. But JPEG / Sports has the advantage that if you DO see something unexpected you can instantly go into machine-gun mode with your camera and take loads of images without being brought up short by filling the RAW buffer. Sports Mode (on the 300d) also provides continuous autofocus for moving subjects.