Need a really good explanation of reciprocity, etc.

[TheFlyingScotsman]

Hey all,

I'm new to the forums, but I've been a long time fan of the DPS website. About three years ago, I bought my first digital camera (a small Nikon Coolpix). This I managed to break, so I replaced with a Cannon Powershot, on the advice of a photographer who showed me that it took great pictures and it fit right in my pocket.

For the last couple of years, I've taken thousands of pictures, focusing on composition and using that little camera. I've read a number of books, browsed this website and others, made notes. I took a lot of really, really bad pictures, but slowly they've have gotten better - or at least good enough, that my wife surprised me this year with a Nikon D5100 with the AF-S VR DX 18-55 mm lens for Christmas. It was the best gift ever (even though I still love my little PowerShot). I also got an excellent book, Complete Digital Photography (Sixth Edition) by Ben Long.

I decided the time had come learn how shutter speed, f-stops, and ISO settings all work together. I asked my photographer friend and he just said, "Don't worry about it. Most people never use those." I can't believe that, because I read that people use them all the time.

Well, I did my research, read up and I have basic understanding of how they work in theory. What I'm struggling with is making them work on my camera. The camera takes wonderful pictures in auto (with the flash off), and in Program mode I can survive. But manual is killing me.

As I said, I understand the basic principles (I think). What specifically happens is I'll set my stops and shutter speed by some numbers in the book - based upon, say, a couple of test shots where I'm studying the auto meters, but my pictures still turn out with camera shake.

(And, yes, I've read the "water in the bucket" analogy a half-dozen times. ). So I'm confused. Do the "numbers" work differently for different cameras (or lenses)? When changing the stops and shutter speeds (increasing one and decreasing the other), do you get the "same" picture or does the same amount of light hit the sensor in a "different" way, producing a different picture?

Sorry if this is in the wrong place on the forum or if my question is too basic. Thanks for any help.

TFS

[inkista]

minor note 1: don't use "reciprocity" when asking about this subject. Use "exposure triangle". "Reciprocity" tends to make us think of "reciprocity failure" which is this film thing that doesn't apply to digital.

I would highly recommend that if you can learn from books, that you go find Bryan Peterson's Understanding Exposure. Probably the best explanation of the exposure triangle thingie I've ever seen. I won't go into all that here, you've already read it a gazillion times and repetitions aren't going to help much.

But first thing you need to understand is the meter in your camera works a little differently in M mode than it does in A/S/P. In the automatic modes, the camera's auto-exposure system is looking at the meter readings, and then adjusting settings until your needle sits on 0. This is what the AE system always assumes is a good exposure (and it usually is). So you probably never pay much attention to that needle, unless you're dialing in some compensation one way or the other.

But in M mode, that needle is now your light meter, rather than your compensation meter. The needle shows you how much light is coming in, and you have to adjust the settings to get it bop around. You can add more light by increasing the iso, opening up the aperture (smaller f-numbers), or slowing the shutter speed, and decrease light by moving the numbers the other way. It's up to you which settings you want to use and how. But paying attention to that needle is key, so start looking for that.

Then watch how the "needle" moves around as you change the settings. Putting the needle on "0" is doing what your AE system would do.

Simple as that.

After you take the picture, the histogram can be used to tell you if you're overexposed or underexposed.

With motion blur, if it was from camera shake, the basic rule is that your shutter speed has to be 1/focal_length or faster (i.e., if you're shooting with a 50mm lens, 1/50s or faster, if you're shooting with a 200mm lens, 1/200s or faster). This is only a rule of thumb, of course, and depends on your personal handholding ability as well as whether you've got VR turned on. If it's subject motion blur, the you have to get a faster shutter speed.

[Biomech]

You'll probably find that manual is a bit much at the moment, contrary to popular belief not everyone shoots manual all the time! Most of us shoot in A or S (sometimes Av and Tv) - that is, in A mode you set the Aperture and the camera works out the shutter, in S/Tv you set the Shutter Speed and the camera does the aperture for you. So it might be worth playing with this a bit more.

I always liken aperture to a tube - like a toilet roll tube. If you look down the end of a short tube, you see a big hole of light. If you look down the end of a long tube, you see a little circle of light. So;

Short or "small" tube - small F number - lots of light
Long or "big" tube - large F number - not as much light.

If that makes sense.

When you take a photograph, you need the Aperture set to allow X amount of light in, for the length of time the Shutter is open and with the appropriate "sensitivity" or ISO. All 3 need to work together to make the picture look correct. As you change one, the others need to change too.

So if you open you shutter twice as long (say 2 seconds instead of 1), then it's going to be twice as bright as before. So you need to do something to cut that down. You can do this by decreasing your Aperture (or hole) size.

So for example, these 2 settings will give the same exposure:

1/125th of a second at F/8 and
1/250th of a second at F/5.6

This works because, despite the numbers, F/5.6 is half the size of F/8.0. What comes next is when to use long or short shutter speeds and the effects of different apertures on the look of the picture!

For now, I'd say leave your ISO on 100

HTH

[Jonbar18]

Originally Posted by TheFlyingScotsman

(And, yes, I've read the "water in the bucket" analogy a half-dozen times. ). So I'm confused. Do the "numbers" work differently for different cameras (or lenses)? When changing the stops and shutter speeds (increasing one and decreasing the other), do you get the "same" picture or does the same amount of light hit the sensor in a "different" way, producing a different picture?

ISO, aperture, and SS have effects aside from the amount of light, so yes, you will get slightly different pictures.
Lets start with the easiest one: ISO. Higher ISO means you get more noise (those annoying dots everywhere), so best to keep it as low as possible
SS: A slow shutter speed means the shutter is open longer, so camera shake is more apparent. however, (USE A TRIPOD), it also means you can capture motion, or those pretty silky waterfalls, while with a faster shutter speed, it will be sharp and detailed. (on my phone, so I can`t show an example. Anyone have one they are willing to share?)
Aperture: Affects the depth of field (there other factors involved, such as subject&background distances, and focal length). Simplified, a larger aperture (smaller F/stop (i.e. 2.8 is bigger than 5.6. I like to explain it like steering a paddle boat. Just do the opposite of what seems logical)), will give you a smaller depth of field, meaning a smaller area in focus, so you can have a sharp subject, and an out-of-focus background. A smaller aperture (big fstop), will keep everything in focus.

[Biomech]

[RichardTaylor]

You may find this exposure tutorial, on this site, helpful.

Exposure (1) A balancing act

[BryanC]

Originally Posted by Biomech

A good example of reciprocity at work. First, it has to be the same scene, amount of light and exposure value for the concept to work.

Photo 1 is exposed for a certain amount of light, but the shutter speed is slow enough to blur the water.

In order to freeze the water as shown in Photo 3, a faster shutter speed was needed. For example purposes, let's say it was a 3 'stops' faster shutter speed than Photo 1. Just changing the shutter speed would freeze the water, but will underexpose the image by 3 stops in comparison with Photo 1. To get the same exposure as in Photo 1, you have to regain 3 stops of light to make up for this loss. Opening your aperture 3 stops, or bumping up your ISO 3 stops, or a combination of the 2 that equals 3 stops more light will give you that same exposure value as in Photo 1.

.

[NathanFranke]

As I said, I understand the basic principles (I think). What specifically happens is I'll set my stops and shutter speed by some numbers in the book - based upon, say, a couple of test shots where I'm studying the auto meters, but my pictures still turn out with camera shake.

So the shake is the problem? The images are exposed correctly? It could be a couple of things--how you're holding the camera to how you're pressing the button. If you can post some example images, it might help.

[TheFlyingScotsman]

Thanks for the very helpful replies.

@ inkista: Thanks for the recommendation. I was lucky enough to find the 2004 version of Peterson's book at my undergrad library and checked it out. I'll read it over the weekend.

Your explanation of the needle was helpful. I've been ignoring it because, well, I wasn't sure what it did. I suppose I thought that simply changing the shutter speed (SS) and reciprocally adjusting the f stops would produce the image I wanted. It's probably a mental holdover from using Program mode for so long: I have some flexibility to adjust white balance and even make other adjustments, but the camera takes over where I leave off.

@ Biomech, Jonbar18 and BryanC:

The pictures are great way to explain the principal! Let me see if I understand correctly: all three pictures are taken from the position and the only "difference" is the f-stop/SS settings. So despite letting the same amount of light in, you do get three very different pictures with the same "exposure." (Did I say that right?)

Maybe I should try an experiment with traffic or something? Just set up my tripod in from of my house, take one picture on the "auto" settings, then switch to manual and adjust? I should get the same (basic) effect, right?

@ RicharTaylor: Thanks for the link, I'll check it out.

@ NathanFranke: There may be a couple of causes actually.

First, I'm not using a tripod and maybe I need to do that (because I'm pretty certain I'm holding the camera right and not getting "shake" in every picture).

Second, I know I'm shooting in low light (yeah, I have to work during the good daylight hours) so my auto readings are coming in at like 30 SS or sometimes lower. I tried to adjust the SS to get rid of low light artifacts (e.g. noise). Instead, I got either dark pictures or blur.

Thanks to everyone for their help. I appreciate it.

TFS

[inkista]

Visual aid on how to hold your camera: