The following article is about a function that applies only to the A100/A700/A900.
If you're new to the DSLR world, you may be having a hard time learning how to predict the behavior of the camera when you use a scene mode or one of the P(rogram) A(perture) S(hutter) M(anual) modes, especially when changing the aperture, your pictures may be coming out well illuminated but not eveything is in focus or maybe you wanted to isolate the subject from the background but actually the whole picture turned out in focus.
Its true that you can actually achieve pictures with focus or defocused backgrounds by learning the changes that will occur when you change the aperture, but the A100/A700/A900 have a button that makes this task easier and gives you more control on the outcome of your picture before you take your shot.
Thats the D(epth) O(f) F(ield) button.
But lets take a look about why this button exists in the first place.
The Why for the DOF Button.
If youre familiar with the concept of Depth Of Field, you will know that the amount of focused subjects or how much of a subject is properly focused in your picture depends on the aperture you use.
Using a big aperture (ie 1.4, 2.0, 2.8) will give you a shallow depth of field, where a minium portion of the picture or subject will be properly focused, and the rest will have a smooth focus or completely out of focus.
Using a small aperture (ie 8, 11, 16) will have a lot more things in focus and the background may be a bit or a lot more focused than using big apertures. This depends on the aperture selected of course.
If you are shooting macros or portraits and you want a small portion of your subject focused and the rest not, you use a big aperture. And if youre shooting a scene, landscape, etc. that you want all in focus, you use a small aperture.
You should know and remember that increasing or decreasing aperture has an effect on the overall exposition of the photo. A big aperture will allow more light in and a small light will allow less. If you over do it, you may end up with a blown out picture (horribly overexposed) or a nearly impossible to see shot (horribly underexposed).
Think of the aperture as the light intensity control. The more you allow in, the brighter the picture, the less you allow in, the darker. Along with shutter speed, you need to combine both to get a properly shot picture.
Now, back to the DOF button.
If you're taking shots and you need or want them to have different grades of focus, you need to change the aperture to have this changes take place.
The thing with DSLRs is that usually you can't see the effects take place until you take the shot, why? it's simple. In order to provide the photographer with the maximum light possible to compose a shot, even in low light, all the lenses are opened to their maximum aperture. If this wasnt done, you wouldnt be able to see through the viewfinder if youre using an aperture of F20 in low light.
The lens closes down to the aperture you selected when you press the shutter to take your shot, but it wont before that. After you take the picture, the lens opens again all the way. So if youre using a 50mm 1.4 lens, it will be always open at 1.4 until you take a picture.
The problem people may have is that they see the focus and defocused parts of the frame on that aperture, but cant see what will REALLY happen once they press the shutter with the aperture set to F 16 (or any aperture that's not the maximum for the lens you use)... unless you're using an Alpha 700 or Alpha 900.
(If you have one of these cameras, now it would a good time to get it with you if you havent already).
What does the DOF Button do and why you should use it.
If you look at the camera from the front side, you will notice a small black button on the lower left side of the mount. On the right side is the focusing mode lever so you cant mistake it.
That little black button is the DOF Button.
The purpose of the DOF Button is to close down the lens to the aperture youve selected BEFORE you take the shot. By pressing this button, you will see the focused and defocused parts of your shot and decide if thats what you want, if you want less parts in focus or more and adjust accordingly before you press the shutter.
There is one thing that will also happen that shouldnt disconcert you or confuse you. When you press this button, a screen will appear in the viewfinder, making what you see through it dark, how dark will depend on the aperture selected, the smaller the aperture is, the darker it will be. This function simulates how much light enters through the lens at the selected aperture, bear in mind though that it will not represent the final outcome of the picture, since shutter speed or ISO arent taken in account here. This is just the lens closing the aperture blades.
The good thing of the viewfinder going dark is that you can actually see the things that the aperture you select will have in focus. If you look at edges in your frame, you will see how they become sharper when you press the DOF button.
Since this button works on your command, there is one neat trick to it. If you want to see how the focus changes when going through aperture numbers, keep the button pressed and at the same time move the dial youve assigned to aperture, you will see and hear how the blades open or close as you move the dial. This will help you decide which aperture you want to use before taking a shot.
There is one thing you have to keep in mind about this button, it will only work when you use small apertures, if you use for example, F2.8, the lens wont close down, you will hear the mechanism trying to close it but it wont.
Since lenses are not the same and all of them vary in aperture, the range at which you can start using the DOF button varies from lens to lens.
If you use a 18-200mm 3.5.-5.6 lens, at 18 mm the max aperture will be 3.5, if you press the DOF button, nothing will happen. If you close it down to, F7 or higher, the button will work. If you extend the lens to 200 mm, the max aperture will be 5.6, pressing the button wont work either until you move the aperture to around F8 or smaller.
Like I said, the range at which the lens will close upon pressing the DOF button varies on the aperture range your lens has.
The use of this button will guarantee you get the shot the way you want it everytime regarding how much of the shot is in focus.
If you're shooting pictures of a leaf and you want its edges to be sharply in focus, you select a small aperture and check using the DOF button and adjust accordingly. The button will help you in any kind of shooting.
Finally, there are two tips you can use with this button.
1.- To overcome the darkness that occurs in the viewfinder when pressing this button, you can use a flashlight or any light source you can control. This will lit the scene and give you more light to check the focus of your shot without letting go of the button.
2.- You can achieve focus lock while pressing the DOF button, either half press the shutter or press the Multi selector (the joystick) to get focus lock and keep the DOF button pressed to check the shot before taking it, if its what you want, press all the way the shutter.
Now that you know whats that little black button on your A100/A700/A900, go out, use it and improve your photography!
Until next time.