Do EV adjustments change F-Stop or Shutter Speed or...?
Can someone help me understand the a little better, please?
I know I can make an EV adjustment on my digitial cameras of up to 2EV in 1/3 EV increments. I know that going the plus direction (+2 EV) increases the "exposure", etc.
What I'm less sure about is how this is accomplished. Does the camera secretly increase/decrease the shutter speed when an EV setting is changed? Or does the camera secretly adjust the F-Stop setting up or down? Or does the camera secretly adjust BOTH shutter speed and F-stop to accomplish the change?
Or am I completely off-base, and therefore completely misunderstand what EV adjustments are all about? Does it perhaps make an "adjustment" to the sensor itself without touching the shutter speed or F-stop. Does it adjust the ISO-setting perhaps? :dunno
Related question: I can also make similar adjustments to the Flash setting when the on-camera flash is turned on. I'm assuming that "plus" adjustment on the flash just boosts the output intensity of the flash, and a "negative" adjustment does the opposite.
What I'm really trying to get straight in my head is the relative significance of these adjustments, especially when made simultaneusly :scratch
What does a +1/3 or a +2/3 EV adjustment correlate to in terms of either an F-Stop tweak, a Shutter Speed tweak, or an ISO tweak....AND, how much of an adjustment to the FLASH output at the same time an adjustment to the EV setting is made factors into the equation.
Is there an online reference that discusses this in not-too-overly-technical terminology?
I know I can make an EV adjustment on my digitial cameras of up to 2EV in 1/3 EV increments. I know that going the plus direction (+2 EV) increases the "exposure", etc.
What I'm less sure about is how this is accomplished. Does the camera secretly increase/decrease the shutter speed when an EV setting is changed? Or does the camera secretly adjust the F-Stop setting up or down? Or does the camera secretly adjust BOTH shutter speed and F-stop to accomplish the change?
Or am I completely off-base, and therefore completely misunderstand what EV adjustments are all about? Does it perhaps make an "adjustment" to the sensor itself without touching the shutter speed or F-stop. Does it adjust the ISO-setting perhaps? :dunno
Related question: I can also make similar adjustments to the Flash setting when the on-camera flash is turned on. I'm assuming that "plus" adjustment on the flash just boosts the output intensity of the flash, and a "negative" adjustment does the opposite.
What I'm really trying to get straight in my head is the relative significance of these adjustments, especially when made simultaneusly :scratch
What does a +1/3 or a +2/3 EV adjustment correlate to in terms of either an F-Stop tweak, a Shutter Speed tweak, or an ISO tweak....AND, how much of an adjustment to the FLASH output at the same time an adjustment to the EV setting is made factors into the equation.
Is there an online reference that discusses this in not-too-overly-technical terminology?
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On my D50, if I'm in AV mode, it adjusts the shutter speed. If I'm in TV mode, it adjusts the aperature. If I'm in program, it adjusts shutter speed. You should be able to see those values change as you make the EV adjustments.
Not sure about the flash.
I believe that doubling the shutter speed and doubling the ISO will both give you the same resulting exposure. Same with going up 1 stop or aperature (or is it 1/3 stop? 3.5 to 4, 5 to 5.6, etc).
Does that help at all?
here is what i think happens, and if im wrong im sure somebody will be around quick enough to point it out........
if you're in Av mode ( aperture priority ) the camera automatically selects a shutter speed based on the f-stop that was operator selected. For example lets say I chose in Av mode f/8 and the camera then selects 1/200 for a standard exposure. Well if you dial in +1 EC the aperture stays the same but the shutter speed is affected. So in our example there is a one stop addition ( more exposure ) so the shutter speed goes to 1/100.
If you're in Tv mode ( shutter priority ) the camera automatically selects the aperture based on shutter speed selected by the operator. So if you selected a shutter speed of 1/100 and the camera in Tv mode selects an aperture of f/5.6. If you dial in -1EC, shutter speed stays the same but the aperture changes (less exposure) the aperture gets smaller so it changes to f/8. I hope what i said is right....
Regarding flash, Hmmmm something i know very little about! I'll pass on that one
Canon cameras behave like...
The flash EV is similar to what happens above, but its a way of controlling how ETTL works. So with Canon, there is a preflash of a known intensity thats sent out. The camera calculates how much light is needed to expose the shot then shoots off the main flash. If you preview the shot and notice ETTL's calculation was off, you can jack up the flash up to -/+ 3EV. So lets say someone is wearing a big white wedding dress. There's a good chance the flash will underexpose the shot. Now on the other side of things, if you pump up EV to get the people exposed, you may blow out the highlights of the dress. ... the life of a wedding photographer! HA!
Sirsloop, Windoze, Rustic:
Thank you...it all helps. I had not even thought about how the different modes (AV, M, AP, SP) would impact this...but it's clear they MUST!.
I certainly have a better understanding of it now. Knowing how to apply the knowledge is a bit trickier!
Tnx again. Papajay
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Thanks Andy:
That makes sense...I'll pay more attention to the histogram...I usually have it turned off and defer to the little slider display that only gives one indication of light availablity....guess I need to get a bit more sophisticated.
I'd be dead without it. :hide
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When using the LCD to review the photo for exposure, use the histogram. The image portion of the LCD can be used to check for "blinkies" (what the camera thinks is/are over-exposed pixels) but don't use that image to judge the over-all exposure. Depending on how you have the brightness of the LCD set, that LCD image can/will lie to you!
The histogram will never lie to you, especially if you have a camera that will display a separate histogram of each of the red, green, and blue channels.
As a final hint, referring back to this:
If you have a white dress (or any other large white/bright subject) in the image, you should have a spike very near the right side of the histogram. If it's right up to, but not on, the right edge, you probably have a well exposed image. Left to it's own devices, the camera will attempt to turn the white dress to 18% gray, which is why the camera will have a tendency to under-expose the image.
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Scott and Wxwax:
Thank you both for additionally weighing in on this thread. I think I got some "bum" advice way back when..."turn off your histogram...it will just confuse things" (WRITTEN in a book I read about how to take good digital photos).
I'm going to do as you have all suggested now, and actually use the histogram to help me with my exposure control.
Papajay
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At the risk of making an ememy out of someone who I'm sure knows a ton more about digitial photography than I'll ever know....
Understnding Digital Photography by Bryan Peterson...AMPHOTO Books 2005
Pg. 74, Quote:
"TIP...FORGET THE HISTOGRAM. If you haven't discovered the histogram on your camera, consider yourself lucky. For those who have discovered it, forget you ever did---if you can."
In fairness, he goes on to say, "Currently [2005, I guess], most DSLR cameras can only record a 6-7 stop range. Until there's a camera that records the full 16-stop range of light seen by the human eye, blown out highlights and blocked shadows are here to stay."
Until just this minute (before finding, reading and posting this paragraph for this reply) the ONLY part I remembered ever reading was the part about "Forget the histogram"! So until now, that's what I've done.
It was in his chapter on backlighting, so "blown-out highlights" and "Blocked Shadows" more or less go with the territory, implying the histogram would only confuse matters in these conditions.
Perhaps Bryan would assess the situation differently with DSLR's of the 2007 vintage, and much broader F-Stop coverage and higher ISO capability.
I'd get the book for a chuckle but I'd rather buy a box of rusty nails than spend one dollar on that rubbish!
@wxwax: I never realized how the histogram made me lazy till you stated it like that. I get it pretty close then just adjust to histo taste. Yawn, I'm gonna go take a nap now.
You do understand that the dynamic range of digital is still something less than 7 stops, right?
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Since Mr. Bryan Peterson disagrees with every other known authority on the topic of using a camera's histogram to meter the image just taken, I'm sure he feels he is in a class of his own. I assure you that he is not in the accelerated class.
Safely ignore anything he has to say about exposure because he has abundantly demonstrated his lack of knowledge.
A camera's histogram is a very reliable and accurate method of gauging the values of light that the camera just recorded. Learn how to read the histogram and you will be a better photographer.
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Actually, I think the answer to your question would be..."No, I guess I was blissfully unaware of that!"....even the term "dynamic range" of a camera is a bit over my pay grade, I think...but I'm learning a bit more every day.
My current digital camera (the nearly 4-year-old Panasonic DMC-FZ10 I want to replace) has a 10-step F-stop range from 2.8 to 8 (yes, 8 min!!!), and an ISO max of 400 (which is virtually unusable due to excessive digital noise).
Nearly every DSLR I look at today has F-stops down to 22, and ISO max of at least 1600...so yeah, I guess I figured that meant the range of the number of stops had broken the 6-7 stop barrier mentioned earlier.
Thanks Scott for asking the question...it just proves I still have a lot to learn.
Papajay
I know all you guys that sleep, eat, and breathe this stuff are way over my head in photographic capability, experience, and knowledge...and as I've seen in this and other Dgrin forums, you are all very helpful to each other and to relative n00b's like me.
[and not so-uncharacteristically hard on a fellow professional, like Bryan Peterson]...
I can tell you, as a beginner in the digital photography world, I got a lot out of his book that was very useful, and it helped improve my picture-taking ability many-fold (IMHO). I still marvel at some of the photos in the book, and just say "Wow" to myself..."I wish my pictures looked like that!"
So while the pro's in this forum obviously take issue with his 3 year-old opinion of the value of the histogram, my guess is you and he are really kindred spirits when it comes to your attempts to capture, record, and share the best images possible.
The moral is, not everyone is perfect & don't take everything from any one book as the only correct way. I agree with all the others in that Bryan is completely wrong in his "ignore the histogram" advice. It's more like "learn to understand what the histogram is telling you." It's useful, but can also be misleading at times, so understanding what it's telling you is important.
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Thanks, Ziggy....
Yes, the linked article helped my understanding considerably (me thinks!).
I've discussed histograms with Bryan Peterson enough to speak in his defense ( not that he needs me to defend him ). Bryan Peterson does not use Histograms, as a matter of fact he told me in person that he turns it off and calls them hysteriagrams.
From Bryan:
I want to address one of the most common questions I get in my on-line course on Understanding Exposure. “Hey Bryan, why not just shoot in the fully automatic exposure mode, (better known as PROGRAM MODE)?” After doing so I can then quickly review the ‘histogram’ on the monitor at the back of the camera. If the histogram shows me that my exposure is wrong, I will make some adjustments by using the + or – controls on the camera and shoot it again. Do you see a problem with this?”
Although the question is valid, it fails to take into account so many other variables that go into the ‘art of creative exposure’. First of all, when shooting in Program Mode, there is no real control over your depth of field or your shutter speed. I am fully aware of the latest offerings being made on some cameras such as Program Landscape Mode, Program Action Mode and Program Close-up Mode. These are, for all intents and purposes, nothing more then a narrow and pre-set exposure parameter for shooting some landscapes, some action filled scenes and some close-up scenes, but the key word here is SOME, not all! Students who have fallen into the trap of shooting in these modes are quick to discover the lack of consistency in their exposures. The Histogram is nothing more then a record of the quantitative value of the exposure relative to its highlights and shadows and has nothing to do with the creative value of the exposure. Save yourself both time and trouble. Turn off the histogram and if necessary, get a pair of reading glasses so you can better see the creative exposure you are hoping for when you view the monitor.
The greatest lesson you can teach yourself in the exposure arena is how to use your camera in manual exposure mode and then calling upon manual exposure mode for those ‘difficult’ exposures. Short of that, shooting in semi-automatic mode is a good idea as it saves time, but you should resign yourself to the Aperture-Priority or Shutter-Priority modes only since either mode allows you to still retain full creativity over your exposures.
Secondly, it does not take into account another important element of image making and that is what Henri Cartier Bresson called the “decisive moment”. In the time you took to check your monitor, then review the histogram and make whatever adjustments you feel were necessary, the subject before you has either turned away from the camera, (the rutting Bull Moose in the pond is now giving you his back side) or your subject has moved on to another activity, (your one year old child has grown tired of taking his/her first steps and now wants to sit down and play with a toy) or your subject has disappeared, (the bee that was pollinating the very flower you composed has since moved on to another). All of these ‘decisive moments’ are now gone.
How is your histogram going to help you in situations of strong backlight and action? It can’t! IF you blow this difficult exposure, what are you going to do, ask the kids, whom you don’t know, to run through your foreground again in the same manner as they did when you tried to get the exposure right the first time? Learning how to ‘read’ difficult exposures is the most logical step and when metering backlight for the silhouette effect, I always take my meter reading, in manual, from the sky to the left, right or above the sun.............. "
I'm not knowledgeable enough or technically qualified to criticize (or defend) anyone about cameras or picture taking. I don't know Bryan Peterson. I bought his book (two different ones, in fact), that's all, and felt I got a lot out of it/them...and said so.
I originally asked for help understanding EV adjustments, and now I'm sorry I did. The last thing I want is to see a group of experts (from whom I can learn valuable lessons about taking better pictures) slugging it out like a bunch of prize fighters.
Tempest in a teapot. In context, Peterson's quote makes perfect sense. Because it's so provocative, it's understandable that it might be better remembered than its surrounding text.
Good discussion, lots to be learned from it (without donning flameproof suits!)
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So the "Stops" of dynamic range are different than the "Stops" of the F-variety??? Just when I think I'm beginning to understand another nuance of photgraphy, somebody throws me a curve ball I hadn't expected!
The "Understanding the Historgram" article Ziggy linked-to talked about dividing the histogram into five sections horizontally from darkest on the left to brightest on the right....and mentioned "stops" a number of times in the discussion. Soooooo, I made what may have been a logic jump, and mentally equated those "stops" to F-stops. That's how I drew the conclusion (erroneously, it would appear) that DSLRs of the 2007 vintage must have a broader dymamic range....my 2003 model only goes from F2.8 to F8...and most of the newer cameras seem to go from at least F2.8 to F22, and beyond.
I went out last night and tried to take a few "sunset" pictures. Turned my histogram "on", only to realize that it is physically so small on my display screen (not even 3/4 of an inch square) I couldn't really see enough detail at the extreme edges to know for sure if I was within or outside the dynamic range capability of the sensor. (I pretty-much figured I had to be outside the range anyway, since I was facing the sunset....cloudy and pink as it was).
Here's a perfect example of a photo that has a dynamic range past the limitations of the sensor. Obviously not a flattering shot... it was playing around checking light before a shoot at that location.
http://photos.tallmanphoto.com/photos/208357176-L-4.jpg