Various Beginner Questions

[Andy H]

Ok gents I'm currently attending a basic course on photography and it's raised a few random questions in my mind.

I would be interested in your thoughts on:

1) I have historically always used the automatic modes on my SLR. Sometimes the camera does a pretty good job of giving me a correctly exposed print but on occasions it looks nastily under or over exposed.

Can you explain why the camera sometimes gets it wrong? and give me some examples of the typical situations where this may happen (just general not motorsport specific)

2) A tripod - I understand the reason for using them is if you find yourself in a situation where you would have a slow shutter speed (1/30 or slower?). Is this the sole benefit of using a tripod or are there other creative situations where they may be useful? if so any examples.

3) The bloke instructing the course provided us with a table of suggested exposures for existing light - that gives shutter/aperture for a whole range of existing light scenarios (also dependent on the film type).

He suggested that you would always do better using this and setting shutter/aperture manually rather than trusting the camera. Is this true? and is this how the pro's do it?

Hope all the questions are clear if you need any more info or clarification just tell me what i missed out!

Andy

[G_Ilott]

1.

Overexposure = the subject was darker than a mid-tone
Underexposure = the subject was lighter than a mid-tone

This really depends on the metering mode you're using as some cameras will take an overall look at the image you hope to capture and apply clever algorithms to work out how best to expose the film / CCD. Cameras have three or four metering modes to compensate for the fact that the world is rarely one tone. We have variable lighting, shadows and differently coloured objects to confuse the little electronic gizmos. The modes (centre, matrix, spot and evaluative) allow us to take overall readings from the scene or pick the exact spot we wish to be perfectly exposed, for example the face of someone wearing a dark T-shirt, or a ray of sunshine illuminating an otherwise dark wooded glade.

Cameras take 18% grey as a mid-tone, meaning if a subject or scene is either lighter or darker, we need to compensate the exposure to achieve the correct exposure. That is why your camera set on auto sometimes get it wrong, though modern SLRs are surprisingly accurate for most subjects.

2. There are several benefits to tripods :

(a) they dampen camera vibration and movement when releasing the shutter, resulting in sharper pictures
(b) they allow you to take your time over a shot, fine-tuning it to perfection
(c) they allow to shoot from difficult angles (e.g. in a stream, over a cliff, across a fence at a firework display to avoid people's bloody red-jacketed elbows and kids trying to look into the lens when you're doing a 20-second compound shot!)
(d) they enable timelapse or long exposure photography
(e) demanding high magnification macro photography can be achieved
(f) they free your hands so you can shoot for longer with heavy equipment, and in cooler conditions

3. Depends on the time you have. If you're trying to capture a deer running along the edge of a wood, in and out of sunlight, at 400mm I'd rather trust the metering system on my EOS. Each technique has its right and wrong time and the table method can be much more precise in the right conditions, but I'm not sure how he's saying you work out exactly how intense the existing light is. I assume you really mean metering ambient light, that is, the light falling on the subject, rather than reflected from its surface. This is indeed a more precise method but it really does depend on what you're shooting. Ambient light is very useful for architecture and landscape photography for instance, as long as you can get near enough to the elements you wish to represent. There's no point standing on a hill with your handheld meter when the valley below is shrouded in mist or shadow.

I know the more technically capable motorsport photographers take along a handheld meter to perfect exposures, but they need to constantly take readings for the changing light conditions, especially here in the UK.


Hope that all makes sense.

[KC]

For most makes of cameras, the autofocus systems start to get dodgy past f6.0 . I know Canon recommends you switch to manual focus beyond f8.0 in their manuals. My Rebel will hunt about and sometimes find the mark, but sometimes it just gives up. If the camera is struggling with autofocus then it will surely struggle with auto-exposure when the focussing is done.

With a little practice you can get as quick and accurate with manual zoom as the camera does and if your camera does not have focus lock (ie: Nikon) you can do it yourself.

One of the things I noticed at Silverstone in 2000 was the way the shooters where setup in the bunker at Copse. They had their cameras sandbagged in to prevent vibration. No tripods and a lot cheaper too.

[G_Ilott]

Good point about beanbags, although they are really only suitable for a limited range of subjects when you have an object on which to place the bag. Bags can be more adept at dampening vibration, however, than tripods.

Sometimes use a beanbag for ground-level wildflowers if I can't quite get the shot I want using my four-legged Uni-Loc tripod (although laying down with a beanbag distastefully flattens a load of flora).

KC, I can't quite see what autofocussing and autoexposure have in common, as autofocus is determined by the overall light levels and contrast of a subject (and the electronic processor) whereas exposure is determined by the tonality of the subject and its surroundings. For example, if it's getting late in the afternoon and the light level drops to a point where the widest aperture to give a useful shutter speed is F8, then there will not be sufficient contrast for the processor to home in on sharp lines. But when you click the shutter, the exposure itself is governed by the light entering the camera through the aperture.

So I don't understand...

[Aysedasi]

Originally posted by KC
For most makes of cameras, the autofocus systems start to get dodgy past f6.0 . I know Canon recommends you switch to manual focus beyond f8.0 in their manuals. My Rebel will hunt about and sometimes find the mark, but sometimes it just gives up. If the camera is struggling with autofocus then it will surely struggle with auto-exposure when the focussing is done.

I must admit I didn't know that.

My "old" EOS 100 and lenses never seemed to hunt at all.

[KC]

I have had trouble with my Canon's autoexposure meter not correctly identifying the exposure level and I think this could be tied in to the fact that the autofocus is struggling as well. It only occurs if the exposure is above f8.0 or so. I won't bother to take my Rebel to the Chili Bowl Midget Nationals in January because of exposure levels. Its kind of dark in there. I don't have a flash of sufficient power to illuminate the cars from long range and the pics will turn out dark and of poor quality. The strange thing is that the exposure won't stay the same. One image will be lighter and one will be darker and its far too frustrating to mess with.

I don't knwo if the autofocus and autoexposure systems are tied together, but I do knwo that the more probelsm I have with autofocus, the more probelsm I have with exposure as well.

[G_Ilott]

KC,

You've just answered the question yourself about why you seem to have problems with exposure if you have problems with autofocussing. Autofocus will struggle in dark, low-contrast conditions and this is exactly the conditions when your camera will overexpose your film. I guess if it also underexposes there must be variations of tone in the image area that you're not aware of when shooting. E.g. white hoardings against a predominantly dark indoor arena. What you'd need to do is take a meter reading from an evenly-lit mid-tone (such as a light grey T-shirt or, better, a grey card you can buy from photo shops) then switch your camera to manual and set the appropriate aperture and shutter speed. You'd need to be aware of light level changes, taking a reading every say 10 minutes and adjusting the exposure accordingly.

Your autofocus problems are probably mainly due to the maximum aperture of your lens not being 'fast' enough at the focal length you are using for the conditions you are shooting in. What lens are you using? The indicated exposure of f/8 you mention has nothing to do with autofocussing as this is only the aperture diameter when you press the shutter, not when you're just looking through the viewfinder.

As I've said elsewhere, all my lenses are f/2.8 which allows me to autofocus in pretty low light.

[Andy H]

Thanks for the comments gents that's helped me out a lot.

To give some background on the course instructor he appears to have been a professional in most fields (portaits/fashion, products, medical, travel etc) but alas has never done much with sport or wildlife my two areas of prime interest!

G_Ilott - my question about the exposure tables was kinda prompted by me wondering for example how do I tell if the conditions downtown in Toronto on a saturday night are nearer to:

1) "neon signs and other lighted signs"
or
2) "brlightly lighted theater districts"

both the above being scenarios from the tables we were given. I guess they give you a head start on having no information whatsoever but I presume you are right to really do things well you would need to meter the ambient light as you suggest (if that's practical)

[Andy H]

PS - I also note the mention of grey cards. Would you recommend using them for potential tricky situations such as the one KC described?