digital cameras have some tools to help you check the accuracy of your exposure. And the main tool is a hist aground on to help explain what the hissed a gram is actually telling you. I've enlisted the help of Thomas the Tank engine. So what is the history Graham actually telling us? Well, the HIST Graham is just a bar chart. Along the horizontal axis, you have shades of gray from black on the left to pure white. On the right, on the vertical axis is a number of pixels that have that particular shade of gray. Now they'll tell you that the perfect hissed a gram should be in the shape of a bell in that it has a range of tones from black to white. The thing is that there is no such thing as a perfect hissed a gram, because history am cannot be read in isolation. It has to be read in conjunction with what you're photographing now, in this particular scene, as we can see that we actually do have a range of tones. We have quite a lot of mid tones in the blues and the reds. We have some white...
s in the very front. We have some blacks in the front of the tender. We also have a nice like graze in the clouds and then along the connecting rods and the coupling rods. I have some dark rates. So in this particular scene, I would expect to see a history Graham that was very much representative of that bell shape that we often talk about. But what happens if you were photographing, for example, a pile of coal in a big pile of coal? There are no light tones. There are no whites. There are no light grays or no medium graves, so you wouldn't expect to see that classic bell shaped hissed a gram in a big pile of coal. There are just dark grays and blacks, so in this sense you'd expect to see the hissed, a gram completely skewed over to the left hand side. So the hissed a gram has to be read in conjunction with the scene that you're photographing. What you have to do is a photographer is try and match the tones in the scene with the tones in your hissed a gram. Whether it is a match, then that is an indication of a faithful exposure where there isn't a match. If the hissed a gram is skewed either to the right or to the left compared to the scene, then that is an indication of either overexposure or under exposure. And that's when you have to make a change, I don't know.