A little help with exposure

[Tired but willin]

Hi there,

Gotto say this is my first post and have just been reviewing the web site and recent posts - looks really informative and definitley something i've been looking for.

So here's my problem guys - i'm fairly new to photograghy but have the bug pretty hard (much to the distress of my wife sometimes!). I've recently been exploring night photography, and as a starter have had some pretty good results! Over the weekend i took the family to Whitstable Bay (small fishing town in Kent), which was very cold but enjoyable. I took a ton of pics as it was a faily cloudy day with the sun shining through the bottom part of grey clouds, over the little fishing town, including boats and sea breakers. As soon as i load the pics onto the laptop i notice i've got a problem with exposure with the two parts of the photo. Large areas of the sky are over exposed with the sun coming through against the grey clouds, with the bottom part of the photo under exposed being too dark. I tried focusing on the darkish lower part of the pic then repostioning the camera but it didn't work - any help greatly received......

Thanks in advance

Dan.

 

[tirediron]

Welcome! Looks like you've discovered "dynamic range" which is the difference in brightness of a given between the darkest and lightest elements. Unfortunately the real-world's dynamic range often exceeds that which are camera's sensors can record leading to what is known as "blown highlights" in the case of over-exposure, or deep shadow for under exposure.

There are a couple of ways of dealing with this. One is to use a technique known as "HDR" or "High Dynamic Range" imaging. This involves taking a series of pictures at different exposures so that all of the various elements are correctly exposed, and then blending the images with software. This can lead to some really interesting images, but if it's not done carefully, tends to make the end result look rather cartoon-like.

The other option is to use filters. There are a series of filters called "Graduated Neutral Density" filters which have dark, but optically neutral (that is, they reduce the transmitted light, but don't affect the hue, colour, or saturation of the image) band at the top which gradually reduces in density toward the bottom of the filter. These allow you to effectively reduce the dynamic range between highlights and shadows by blocking some of the light from the bright part of the scene. Cokin is one popular brand.

 

[Big Mike]

Welcome to the forum Dan.

What you are seeing is the limitations of your camera...the limitations of photography in general.

Our digital camera can capture a range of about 5 stops, reasonably well (Dynamic Range).
(a 'stop' just a way of saying a doubling or halfing of the amount of light...so 5 stops is actually a range of things that are up to 32 times brighter or darker). However, the world of visible light has a greater range...and any given scene that you might look at...may have up to 10 or 10 stops difference between the darkest parts and the brightest parts.
So our job, as photographers, is to decide which 5 stops we want to capture in a single photo...and which parts we want to leave outside out camera's "Dynamic Range". If we choose to expose for the brightest areas, the darkest area will appear as black shadows with no detail. If you choose to expose for the shadow areas, then the bright areas (highlights) will be 'blown out'...white with no detail.

This has always been an issue in photography. Different film types had different ranges that they could capture. Slide film had a narrow dynamic range and black & white film often has a much wider dynamic range. Modern digital SLR cameras are somewhere in between.

There are, of course, many ways around this limitation. For example, you could just avoid it altogether. For example, if the sky is so bright that you can't capture it at the same time as the foreground...then just compose your shots so that the sky is not in the scene.
Another example it just go with it. In your case, you could expose for the sky (or even under expose it for drama) and let the boats become dark silhouettes.
Yet another trick is to use gradient or split filters. These are filters that only darken part of the image, so you could use the filter to darken just the sky, hopefully bringing it within your camera's dynamic range.

Of course, this limitation is only limited to one exposure. You can take multiple shots at different exposure values (bracketing) and then choose your favorite. Or, you can use those multiple shots and combine them (with software) to take the 'best' of each and create an image that has more dynamic range than any single photo could have. This is often called 'HDR' (high dynamic range)...and you can search that term to your hearts content.

 

[KmH]

Our eyes work in a non-linear way.

The camera sensor is strictly linear so it does record images the way we see them.

Mike and tireiron have covered things pretty good.

If you would like a resource that offers a bit more of an in-depth technical explanation Understanding Dynamic Range in Digital Photography

 

[Tired but willin]

Thanks guys you've certainly given me a few things to think about!! I did try a few bracketing shots, but on reflection didn't make the stops wide enough, so little effect change. At least next time the oppertunity arises i'll have a little more knowledge on my side - plus gonna look at getting a set of filters to play with.

Thanks again for the pointers - really appreciate the help....

Dan....