Nikon Strobe Info

I extracted the following from a Nikon support document

The following strobes support these modes on the D200, D80, D70s, D70, D50, D40

SB800
i-TTL, Auto Aperture (AA), GN, Auto, Manual, Rear Curtain, Repeating Flash, Red-Eye Reduction, AF, Zoom

SB600
i-TTL, Manual, Red-Eye Reduction, AF, Zoom, Rear Curtain

SB400
i-TTL, Manual

i-TTL
The camera controls flash output. This is a TTL auto flash mode in the Creative Lighting System. Monitor Preflashes are fired at all times. The subject is correctly exposed by the light from the flash and the exposure is less affected by the ambient light than in the conventional TTL mode.
Supported cameras: D2X, D2Xs, D2H, D2Hs, D200, D70, D70s, D50, D80

i_TTL as described in Nikons CLS document
Monitor pre-flashes are emitted from a Speedlight before the main flash and reflected off every object in the frame. Monitor pre-flashes are picked up by either the five-segment TTL flash sensor or an RGB sensor. This information, along with data from the Matrix Metering System is analyzed to adjust flash output for the most balanced background/foreground exposure possible.

Exposure - The Confusion Factor

I hope we are not moving to fast here but we should all have a pretty good grasp on how exposure is controlled. Another quick overview, we have 3 things on the camera to adjust to effect exposure aperture (f-stop), shutter speed and ISO (light sensitivity). When taking a photo we can let the camera's auto modes choose all of these settings, we can set all or some and the camera will set the others. The camera uses the built in light meter to determine the settings it will use.

I just realized I'm wrong when saying that there are 3 things on the camera used to effect the exposure. Indirectly there a more ways to alter the exposure but on camera a fourth way to effect exposure would be the camera's metering mode. The various metering mode's interpret the light in the scene differently. The use and effects of the different modes will be covered in a future article. The default matrix metering mode attempts to be intelligent and compares current readings with what Nikon has programmed into the camera and the camera will set the aperature and shutter based on this. Most of the time this 'intelligence' works pretty good but the problem I have is that I really never know just how that intelligence is going to set the camera for my next picture. While on this topic I might also add that we can also indirectly effect exposure outside the camera by adding filters or controlling light that is in the scene.

Confusion Factor
In the last article I introduced the standard set of f-stops 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32. The f-stop is our aperture measurement and remember a bigger aperture, opening in the lens, lets in more light. Now for the confusion factor, the actual size of the opening in the lens (aperture) is inversely proportional to f-stop numbers. So, f/1.4 is a bigger aperture opening than f/2. There is 'scientific' reasons that they are backwards but we won't go into that. You just gotta remember if you want more light to get in the camera, you need a bigger aperture opening which means a smaller f-stop number. It takes time but will sink in. Also remember that opening the aperture, smaller f-number, will decrease the depth of field.

Stop Down
If you read much about photography you will frequently come across the term stop down. When you stop down a lens, you are going to a larger number/smaller aperture and therefore less light. Changing an f-stop from f/1.4 to f/2 is referred to as 'stopping down'. The opposite is opening up, going from f/2 to f/1.4 is moving towards the smaller number/larger aperture and therefore more light.

So now hopefully we all know, or are at least getting a grasp on, the basic mechanics that cameras use to control exposure. In order to take your photography to the next level you must understand these basics. If you just leave the camera in auto mode all of the time you will get good pictures a lot but not all of the time. As you get more experience you will start to see some particular lighting scenarios where the camera goofed up, this is where your knowledge of exposure will start to come into play.

While writing this article I came across a dated but very easy to read site that goes into slightly more detail than I have here. If you want to dig a little deeper or read from a different view point here is the site.

Whats Next
Now that we know what all goes into exposure the next step is to learn when we need to step in and change the exposure for our current scene. In low light we need to make sure the shutter speed is fast enough to not blur movement, in an action shot we must make sure the shutter speed is fast enough to stop the action, if so desired. In a landscape scene we would probably want a large depth of field which means a smaller aperture, bigger f-stop number. While photographing a single person in a crowd we will probably want a shallow depth of field so we will 'open up' by larger aperture, smaller f-stop number.

RTFM - Read The Freakin Manual
So for now pull out the manual, look at how to change the ISO, set the shutter speed and aperture. Get familiar with how to get to the various settings I have talked about so far. Check out the different metering modes by taking some photos of the same thing in various modes, a back lit or scene with a lot of contrast will be particularly reveling in comparing metering modes. Take the camera out near dusk and change the ISO settings note how this effects the shutter and aperture speeds chosen by the camera. Take a picture looking down a fence row or for city dwellers a line of parked cars, change the aperture and note the effect.

I think the next article will be on white balance, check that out while you have the manual out. Luckily, the D40 does a pretty darn good job at white balance in auto mode but there are times when you will want to change it. Til next time get the camera out and play with it, all it costs is time.

Exposure - Getting Technical Now

Ok, so now hopefully after the first article on Exposure you have the concept of how the camera controls the amount of light exposed to the sensor. A quick refresher, a bigger hole in the aperture means more light and less shutter open time for same exposure as a smaller aperture opening and longer shutter open time.

Camera Meter
The cameras metering system is responsible for figuring out how much light it thinks is needed to properly expose a photo. In all modes but manual (M) the camera will always set at least one of the 3 things it can set to make what it thinks is the proper exposure for the current scene. There are various metering modes and they all effect how the camera actually figures what it thinks is a correct exposure for the current circumstances. I have a future article in mind for this topic alone but for now we will just stay in the default matrix metering mode.

Astute readers may be wondering what the 3rd thing is that the camera can change, that would be ISO and it is basically a light sensitivity setting. The higher the ISO setting the less light it takes to make a proper exposure. It doesn't come for free however, more sensitivity brings more noise into the photo. So we now have another choice when it comes to getting a proper exposure. This choice is typically along the lines of, I don't have enough light under the current circumstances to make the photo so I must up the ISO. Sometimes there will be enough light for a properly exposed photo but we need a faster shutter speed because we have things moving in the picture and we don't want them to be blurred. In this case again we can up the ISO, this will allow us to use a faster shutter speed because we now don't need as much light for a proper exposure.


Camera Modes
The camera's various full auto modes will set both aperture, fstop and sometimes ISO as it desires. In P, S and A modes you can effect either the aperture or fstop used and the camera will automatically select the other setting to make the exposure as the camera thinks it should for the current ISO setting. Actually, P mode you effect both shutter and f-stop, more on that later. In full manual mode, M, you set both shutter and aperture as desired, in this mode you can, and should in most cases, use the exposure meter for reference. The camera's exposure meter is still measuring the scenes light and the metering bar tells you if it thinks you will over or underexpose the photo and by how much for the current fstop, aperture and ISO settings you have chosen.


F-stop's and Shutter Speeds
Finally I we must introduce the actual f-stop numbers and shutter speeds. I'm not going to get anymore technical than need be here, you can find much more detail if needed via Google. The camera industry long ago derived a standard set of f-stops as follows 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32 that go along with a standard set of shutter speeds 1, 1/2, 1/4, 1/15, 1/30, 1/60, 1/125, 1/500, 1/1000, 1/2000, 1/4000, 1/8000, 1/4000. These f-stops and shutter speeds are in what the industry calls 'one stop' increments. Most all cameras now days have these number in 1/3 stop increments so there is probably 2 numbers between each of these standard stops on your camera. i.e. going from f-stop 2.8 to 4 is one stop but in 1/3 increments we have 2.8, 3.3 and 3.5 before we get to 4.

The beautiful thing about these 'standard' f-stop and shutter speeds are their relationship. You can derive the same exposure by changing either the aperture or f-stop by 1 (or more) stop(s) each. Lets say for a photo we want to take, the camera metering system tells us or auto mode has chosen, f/8 @ 1/250 as the exposure for the current scene. We can alter the look of the photo by choosing a new f-stop and aperture, all we have to do is change each by the same 'stop' amount. An exposure of f/4 @ 1/1000 will provide the same exposure as f/8 @ 1/250, the f-stop went down 2 stops and the shutter speed went up 2 stops.


Whew....
I hope we didn't get to technical here, I will end this article before we get brain overload. In quick summary, exposure is effected by 3 things f-stop, aperture and ISO. A higher ISO means it takes less light for an exposure at the expense of more noise in the photo. F-stops and shutter speeds have a corresponding relationship, the same exposure can be had by various combinations. Knowing the effects of the various f-stop and shutter speed settings is what will let us alter the effects/looks of our photos.

Please post comments, questions or mistakes in my writings to this in the D40 Plus groups thread on this article.

RAW versus JPEG

A tickler for a future D40 Plus article.

I found that I was spending more time behind the computer than taking pictures when using camera RAW format. For the most part I have quit using RAW as I'd rather take pictures than sit behind the computer and twiddle with bits.

I discovered that once I got my camera set up properly and if I take the picture 'correctly' there is no advantage to RAW as seen in the printed pictures.

RAW will definetly allow you to easily correct pictures shot with the whitebalance not set correctly and is really nice for those mixed lighting photos as well. These are the only conditions I now use RAW for.

Here is are some direct RAW to JPEG comparisons http://www.kenrockwell.com/tech/raw.htm

Here is a good article on the technical aspect that to me provides all the proof I need to saw RAW is not everything many make it out to be
http://danheller.blogspot.com/2006/07/business-aspects-of-raw-vs-jpg-mode.html

Exposure

In order to move beyond the P mode of your camera you must understand the basics of exposure. In terms of photography exposure refers to letting light get to your cameras film or sensor, in the case of digital cameras.

A big part of making a good photograph is getting the proper or desired amount of light onto the film or sensor. When you click the shutter release on your camera the shutter opens for a small amount of time allowing the light reflected from the scene to pass thru the aperture opening in the lens and fall onto the sensor. The camera uses the f-stop and shutter speed to vary the size of the hole in the aperture and length of time the shutter is open. The camera can do this totally automatically (Auto mode) with help from you (P, A and S) and it can give you total control (M). The other special modes not mentioned leave the camera in full control.

Aperture and Shutter Speed
The size of the hole in the aperture is referred to as the f-stop and the length of time that the shutter is opened for is referred to as the shutter speed. Now think about that a little, we have 2 ways to control the total amount of light hitting the sensor. A big hole in the aperture will let a lot of light in while a small hole only lets in a little light. A longer shutter open time will also let more light in while a shorter shutter time opening will let less light in.

The proper exposure of light to the sensor can be had with various combinations of the aperture and shutter. A big hole in the aperture with a short shutter open time will allow the same amount of overall light in as a smaller aperture opening and a longer shutter speed. So now its starting to get a little confusing whats the difference between big hole (aperature) and short time (shutter speed) or little hole and a long time.

How Do You Choose?
Understanding how the various shutter speed and aperature opening sizes (f-stop) affect the looks of the photo is the key to picking a faster shutter or smaller aperature. A larger aperture while letting more light in also reduces the depth of field in the photo. The shutter speed will effect things that are in motion in the photo. If you have a longer shutter opening and a quickly moving subject, the subject may vary well be blurred in the photo.

Another motion issue to deal with in relation to shutter speed is camera shake. The longer the shutter is open the more prone you are to shake the camera while the shutter is open. The longest shutter speed that you can use without moving the camera will vary based on the zoom level of the lens and your ability to hold the camera still.

Sometimes You Can't
Now that we know how the 2 exposure control methods effect the looks of the photo we can start to decide when to use a larger versus smaller aperture or faster versus slower shutter speed. Sometime you really can't choose and are forced to go one way or the other based on the current lighting situation. For instance if in a low light situation, you don't have a tripod and your subjects are moving you know you must steer towards a larger aperature to get a faster shutter speed. i.e. a bigger hole (aperature) lets more light in so the shutter can stay open for a shorter period to reduce possible blur.

I have purposely left out any specific measurements and settings so as not to confuse you any more at this point. I have also not mentioned the effects of the ISO setting either. Right now it is just most important to remember that bigger hole (aperture) lots of light means shorter shutter open time while the same exposure can be had with a smaller hole (aperture) and longer shutter open time.

Next lesson will be on ISO, actual f-stop numbers and shutter speeds.

Please post comments, questions or mistakes in my writings to this in the D40 Plus groups thread on this article.