I learnt something new this week, proving that everyday really does provide you with opportunities to improve yourself. What did I learn you might ask?
Well it all started with my attempts at a sunset and a long exposure of a seascape to try and get a misty water effect. I did end up with a couple of photographs I am relatively happy with, but certainly not what I was looking for.
The sunset just wasn't working. Because I was shooting directly as the sun, I couldn't help but overexpose or under expose certain areas of the image. The best effort is shown here and the final image was processed using HDR in Photoshop CS6. I've never really understood or mastered HDR but I certainly think it works here.
I had started the shoot of the seascape using my B&W 10 stop screw on filter I tried numerous times at varying exposure times (from 3 minutes to 6) to capture a peaceful seascape. For my second time of using this particular filter I did end up with one or two images that were ok, but both were really noisy. The last one didn't come out at all. So I took a quick 10 second exposure - no filters this time and was left with this and plenty head scratching... What was I doing wrong with this long exposure lark.
I started with the basics of learning a bit more about exposure techniques. The main one being reciprocity.
According to the dictionary, the word "reciprocal" means "any equivalent value, or a ratio that is the same." In photography a reciprocal value is used to determine the f/stop to shutter speed relationship. For example, if you choose to shoot at f16 at 1/125sec, this lets the same amount of light in as shooting at f11 at 1/250sec, and the same as f8 at 1/500sec and so on. The only determinable difference between these with be depth of field the aperture gives you.
Most people know that the camera's aperture and the shutter speed settings determines the volume of light hitting the sensor of your camera. So If you have an f-stop opening such as f22 (the preferred stop for landscapes on a full frame camera or f16 on a APS-C camera) , you need to have the shutter open longer to allow enough light in to properly expose the shot. The smaller the f-stop number, (a larger aperture), the shutter needs to be open for a shorter amount of time to let in the right amount of light in.
So far so good... but imagine your ready go shoot your masterpiece. Your camera shows that the setting you need to get the photograph is f22 at 1/60sec. But you want to use an aperture of f8 to blur out the background? Well you have to adjust the shutter speed accordingly. In this example f8 is 3 stops more open than f22. So the shutter speed needs adjusting by the same amount of steps. This would mean a shutter speed of 1/500sec.
The same equation can be used if you're working from shutter speeds to apertures.
So this is great for learning about correct apertures/shutter speeds, but relies on you using the camera manually and understanding all the terminology that goes with it.
I would say this doesn't really help with long exposures as any shutter speeds longer than 1-2 seconds result in reciprocity failure - this equation basically doesn't work properly after this length of exposure. But, I think, as with all information, this is very useful to know. Particularly if you're on a cropped sensor camera or full frame, or you know that your lens is sharpest at a certain aperture you can work out the correct shutter speed for that aperture.
Ultimately though, it can be quite a complicated technique, and will always depend on your subject matter or technique you are trying to use.
The main lesson for me was I need to use my light meter more and be less reliant on the camera getting it right. So don't panic. I'm not suggesting you go out and purchase one for several hundred quid. There is a fantastic one available from the App Store for iPhones and it's free. It's also really good, and you can use this to work out long exposure times when using a big stopper filter.
How you might ask? Ok, so I want to shoot at f22, but get a misty water effect? The only way I can expose long enough is to add a big stopper filter to the lens. This has the effect of 'adding' 10 stops onto you aperture. Using this app, I can adjust the aperture to f128, and then sample the light on the app - giving you your shutter speed.
It's worth a look anyway.