Three bracketed  exposures of low, average and high contrast scenes are needed for this  exercise. I do routinely check the histogram on my camera LCD screen and when reviewing the images in LR. Additionally the highlight and shadow clipping warnings are always left on. However a histogram is just a guide , low or high key scenes will have very different histograms but this does not make them bad images. I am not a very technical person so describing how I see and interpret  histograms is actually rather difficult for me to write about  so please excuse any rather un-technical terminology I may use in my efforts!

A histogram grap below showing tonal range from very dark on the left to very light on the right.

Low  contrast.
I shall call  these my boring collection- a brick wall taken early morning !!!  My camera indicated that all three images had little tonal contrast with the values close to each other spread over only a small proportion of the histogram graph.They each have a pyramid shape.  None showed clipping but the values move towards the right hand side as the exposure is increased.  All images  F4.5 @ 14mm ISO 200. 

Darker exposure.
The tonal range is restricted to dark and medium tones. here to edit.

@ 40 secs

Average exposure.
The values have shifted slightly right towards the mid range tones.

@ 30 secs

Brighter exposure.
The values have once again moved right towards the lighter mid range tones.

@ 25 secs

High contrast.
All images taken  @ 50mm ISO 200 1/500.
The camera and on screen histogram indicated that all 3 images were clipped in the highlight and shadow areas. 
Unlike the low contrast graphs these are spread all across the tonal range with high and low peaks indicating a wide range of very dark to very light tones that will create a high contrast image
The graph indicates a darker  toned image than the other 2 exposures.

 It shows much lower peaks in the mid and light toned areas but a very high peak in the darkest area of the graph.


The graph has shifted towards the right with very high peaks in both the dark and light areas 


The graph's peaks are less prounounced moving towards the right. I actually expected this histogram to move further towards the right than it did using the larger aperture. However it does indicate there are now less dark and medium tones than before.


Medium contrast.
Looking at the medium contrast graphs I can see that although the tonal range is quite broad it creates a smoother gradual curved graph than that of the dramatic high and low peaks created by the high contrast images.
All images taken  @ 50mm ISO 200 F 5

The tonal values are spread across the graph but indicating a greater amount of dark tones due to the shorter exposure.


This graph indicate less dark and more mid tones with some highlight clipping. here to edit.


The slower exposure time has increased the overall brightness and amount of clipped highlights.



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