{"id":1228,"date":"2010-05-09T11:41:54","date_gmt":"2010-05-09T19:41:54","guid":{"rendered":"http:\/\/ralphnordstromphotography.com\/wordpress\/2010\/05\/09\/photography-tutorial-light-meter\/"},"modified":"2018-09-09T19:46:13","modified_gmt":"2018-09-10T03:46:13","slug":"photography-tutorial-light-meter","status":"publish","type":"post","link":"https:\/\/ralphnordstromphotography.com\/wordpress\/2010\/05\/09\/photography-tutorial-light-meter\/","title":{"rendered":"Photography Tutorial – Light Meter"},"content":{"rendered":"

There\u2019s something I\u2019ve been puzzling about for a long time.\u00a0 So I finally decided to check it out and share the results with you.\u00a0 I wanted to know the relationship between the camera\u2019s built-in light meter and the histogram.\u00a0 OK, sounds geeky so what exactly am I talking about and why do I care?<\/p>\n

If you read up on light meters you know that they measure the brightness of the scene and set the exposure so the average is neutral gray.\u00a0 OK fine, but what is that?\u00a0 Neutral gray is a pure gray that doesn\u2019t appear light or dark but is right in between.\u00a0 That\u2019s been determined to be a gray that reflects 18% of the light that falls on it,.\u00a0 Or put another way, it absorbs 82% of the light that falls on it.\u00a0 By comparison, a white surface reflects nearly 100% while a black surface reflects nearly 0%.\u00a0 So 18% is right between light gray and dark gray.<\/p>\n

And that\u2019s what your camera\u2019s light meter tries to do with the scene your shooting \u2013 make the average brightness neutral gray.\u00a0 Those areas that are brighter than the average will appear brighter and those that are darker will appear, well, darker.<\/p>\n

So, I understand that.\u00a0 But the burning question is, \u201cWhat does the camera\u2019s histogram show?\u201d\u00a0 Remember, a histogram shows the amount of each shade of gray in your image from maximum black to maximum white.\u00a0 Maximum black is on the left end of the scale and maximum white is all the way to the right.\u00a0 All possible shades of gray from black to white are distributed along the histogram from left to right.<\/p>\n

So another way to put the burning question is, \u201cWhere does neutral gray show up on the histogram?\u201d\u00a0 Since it\u2019s \u2018neutral\u2019 gray, that is, neither light or dark, does it show up in the middle?\u00a0 Or, because it\u2019s 18% reflectance, does it show up to the left of center, toward the dark end?<\/p>\n

To determine this I needed to take a photograph that was uniform color and uniform luminosity.\u00a0 Well, a wall works pretty well.\u00a0 So I found a wall in our house that was uniformly illuminated and photographed it.\u00a0 Pretty exciting.\u00a0 It recalls memories of watching grass grow and paint dry.\u00a0 But for the purpose at hand it is perfect.\u00a0 It produces a very narrow histogram, pretty much a spike, which is exactly what we need.<\/p>\n\n\n\n
\"_A1P5315\"\u00a0<\/a><\/p>\n

 <\/td>\n

\"IMG_2030\"\u00a0<\/a><\/p>\n

 <\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Here\u2019s the picture and next to it is the histogram as displayed on my Canon 1Ds Mark III.\u00a0 If you look at the histogram you see that it\u2019s pretty narrow, just like we want it, and slightly to the left of center.\u00a0 The histogram scale is divided into five zones and this histogram falls near the middle of the third zone.\u00a0 That\u2019s good to know.\u00a0 Also, the three colors of the RGB histogram done quite line up, indicating the paint has a slight warm hue.<\/p>\n

But as is so often the case in life, the answer to one burning question raises another.\u00a0 This one has to do with exposure compensation.\u00a0 If I overexpose one stop, how far to the right will the histogram move?\u00a0 Let\u2019s check it out.<\/p>\n\n\n\n
\"_A1P5316\"<\/a><\/td>\n\"IMG_2031\"<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

This image was exposed at +1 EV, or, overexposed by one stop.\u00a0 And, as expected, this histogram moved to the right.\u00a0 Now it\u2019s in the fourth zone.\u00a0 It moved about one zone to the right.<\/p>\n

What about a two stop overexposure?\u00a0 How will that affect the histogram?<\/p>\n\n\n\n
\"_A1P5317\"<\/a><\/td>\n\"IMG_2032\"<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

At +2 EV the histogram moved further to the right but not a whole zone.\u00a0 Now it\u2019s straddling the fourth and fifth zones.<\/p>\n

Let\u2019s go for three stops of overexposure.<\/p>\n\n\n\n
\"_A1P5318\"<\/a><\/td>\n\"IMG_2033\"<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

This histogram made it all the way to the right wall and the highlight clipping warning was triggered (that\u2019s the black part of the image where the clipped area is flashing).<\/p>\n

Let\u2019s go the other way. Let\u2019s see what happens when we underexpose by one stop.<\/p>\n\n\n\n
\"_A1P5319\"<\/a><\/td>\n\"IMG_2034\"<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

At -1 EV the histogram moves from the middle zone down to zone two.<\/p>\n\n\n\n
\"_A1P5320\"<\/a><\/td>\n\"IMG_2035\"<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

At \u20132 EV the histogram now is on the line that divides zone one and two.<\/p>\n\n\n\n
\"_A1P5321\"<\/a><\/td>\n\"IMG_2036\"<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Finally, at \u20133 EV the histogram is close to the left wall but not quite there.<\/p>\n

So we can see that adjusting the exposure up or down by one stop moves the histogram about 2\/3 of a zone.\u00a0 (Now, I\u2019m talking Canon speak here when I say 2\/3 of a zone because the Canon histogram is divided into five zones; other camera manufacturers divide their histograms differently .)\u00a0 Another way to think if this is that each of the five zones represents 20% of the total histogram range.\u00a0 So adjusting up or down one stop will move the histogram about 2\/3 of that distance or 14%.<\/p>\n

What\u2019s the value of knowing all of this?\u00a0 In landscape photography we frequently find ourselves in positions where the light meter is fooled and we need to overexpose or underexpose the image to get the \u2018correct\u2019 exposure; i.e., exposure compensation.\u00a0 That\u2019s such an important function that most prosumer digital SLRs make this really easy to do.\u00a0 But often you end up guessing, taking the shot, checking the histogram and deciding you didn\u2019t compensate enough or you compensated too much.\u00a0 With this knowledge it is possible to make more informed guesses as to how much compensation you need to dial in.\u00a0 For example, if I needed to move the histogram to the left one zone (about 20%) I\u2019d dial in -1 1\/3 stops of exposure compensation.<\/p>\n

Another useful piece of information is that highlight clipping kicks in when an area is three stops overexposed.\u00a0 This is useful if you\u2019re spot metering a scene and want to know how much to overexpose the clouds or the snow to get it to turn out white.\u00a0 You don\u2019t want to go over 3 stops so you may choose 2 1\/3 just to be safe.\u00a0 (Hey, maybe I should do a post on spot metering.)<\/p>\n

Another useful piece of information related to this is that there is a practical dynamic range of about 6 stops.\u00a0 At +3 stops you get highlight clipping and at \u20133 stops you\u2019re in such a dark area of the of the sensor\u2019s dynamic range that you could be getting into trouble as far as noise goes.\u00a0 I should mention that in Lightroom you can often eek out another stop on either end with the Recovery and Fill Light adjustments.<\/p>\n

I must hasten to add that these results are for a Canon 1Ds Mark III.\u00a0 The results on your camera may be different.\u00a0 When it takes 1 1\/3 EV adjustment to move the histogram 20% one way or the other, on other cameras it may be just 1 EV.\u00a0 So I encourage you to find a blank wall and check this for yourself.<\/p>\n

Hopefully this little journey into the geeky side of exposure sheds some light on a couple of things; namely, how the camera\u2019s light meter works and how that gets represented on the histogram.\u00a0 Exposure is one of the most critical components in creating great photographs and hopefully this will help you nail those exposures.<\/p>\n

To see more of my photographs click here.<\/a><\/p>\n

Join me on an upcoming workshop.<\/a><\/p>\n

(1484)<\/p>\n","protected":false},"excerpt":{"rendered":"

There\u2019s something I\u2019ve been puzzling about for a long time.\u00a0 So I finally decided to check it out and share the results with you.\u00a0 I wanted to know the relationship between the camera\u2019s built-in light meter and the histogram.\u00a0 OK, sounds geeky so what exactly am I talking about and why do I care? (1484)<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[4],"tags":[266,279,280,12,10],"class_list":["post-1228","post","type-post","status-publish","format-standard","hentry","category-how-to-articles","tag-exposure","tag-histogram","tag-light-meter","tag-phtographer","tag-ralph-nordstrom"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p9Nl7-jO","jetpack_likes_enabled":true,"_links":{"self":[{"href":"https:\/\/ralphnordstromphotography.com\/wordpress\/wp-json\/wp\/v2\/posts\/1228","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ralphnordstromphotography.com\/wordpress\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ralphnordstromphotography.com\/wordpress\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ralphnordstromphotography.com\/wordpress\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/ralphnordstromphotography.com\/wordpress\/wp-json\/wp\/v2\/comments?post=1228"}],"version-history":[{"count":4,"href":"https:\/\/ralphnordstromphotography.com\/wordpress\/wp-json\/wp\/v2\/posts\/1228\/revisions"}],"predecessor-version":[{"id":3981,"href":"https:\/\/ralphnordstromphotography.com\/wordpress\/wp-json\/wp\/v2\/posts\/1228\/revisions\/3981"}],"wp:attachment":[{"href":"https:\/\/ralphnordstromphotography.com\/wordpress\/wp-json\/wp\/v2\/media?parent=1228"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ralphnordstromphotography.com\/wordpress\/wp-json\/wp\/v2\/categories?post=1228"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ralphnordstromphotography.com\/wordpress\/wp-json\/wp\/v2\/tags?post=1228"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}