ive noticed that a picture taken with an slr having an aperture of 2.8 has a bigger depth of field than on a digital camera. the only way to achieve one is to use a macro setting, why is this? It's going to be darn hard to "de-focus" too much using a digital camera while keeping the main subject in sharp focus. The smaller the sensor, the greater depth of field you will have. Generally speaking, the smaller the camera, the smaller the sensor. Most of the pictures you take with a digital camera are quite sharp from near to far distances and there is a reason for that which I will explain.
While we speak in terms of the 35 mm equivalency of digital lenses, don't forget that the digital sensors are usually smaller than a full-format 35 mm frame. Most of the more popular point and shoot cameras have the smaller sensors. It's only about 5 mm wide and 4 mm high. The lens on required to cover that angle of view is an ACTUAL 6-17 mm zoom lens. At these true focal lengths, the background is going to almost always be in pretty sharp focus. In other words, if you WANT to defocus the background, you are going to have to work pretty hard at it. You would have to zoom to the longer end of the lens and set the aperture open as wide as it will go, if your camera even allows you to control the aperture, and get pretty close to your main subject while having the background a fair distance away.
The bigger the sensor, the easier it will be to achieve pleasing bokeh. This means moving to a dSLR, which all have sensors about 20 times bigger than the typical P&S digicam. If you want to really go for brokeh (very bad pun intended), you can get a Canon 5D and you will get exactly the same effect you are accustomed to in a 35 mm camera, since the sensor is the same size as 35 mm film. That's me. A smarty pants. All my life. 垄-{-= See? Report It
Because on the SLR it's a physical aperture, while on the digital camera it's virtual, meaning made by the software. maybe howstuffworks.com
can answer your question Because the sensor sizes are different.
Point & shoot cameras have an "effective" lens size, when compared to a 35mm lens. Since no P&S actually has a 35mm sensor size, manufacturers give what the lens focal length would be when compared to a 35mm camera. After all, who is going to buy a camera with a lens that goes from 6 - 60mm? But that's what you're getting when you buy a 10x zoom point & shoot camera.
Depth of field is controlled by more than just the aperture size, it's the aperture size as a ration when compared to 35mm, if you want to compare DOF between point & shoot and DSLR digital cameras.
Because the DSLR has a much bigger sensor, the depth of field will be different than the same picture taken with a point & shoot.
The greater DOF with the smaller format can be either an advantage or a disadvantage, depending on the desired effect. For the same amount of foreground and background blur, a small-format camera requires a smaller f-number and allows a shorter exposure time than a large-format camera; however, many point-and-shoot digital cameras cannot provide a very shallow DOF. For example, a point-and-shoot digital camera with a 1/1.8鈥?sensor (7.18 mm 脳 5.32 mm) at a normal focal length and f/2.8 has the same DOF as a 35 mm camera with a normal lens at f/13. Halthron has it right but I'll try to break it down a little further.
With a digital SLR or DSLR the sensor (digital version of film) is smaller than a patch of 35mm film. If you are comparing SLRs to DSLRs using the same exact lens you are essentially cropping your picture on the DSLR since the sensor is smaller. The lens displays the same size image onto a smaller patch of something to capture it, if the sensor was the same size as a patch of 35mm film it would be the same. There are DSLRs with a "full frame sensors" but they get pretty spendy.
Now if you are reffering to the edges blurring at f/2.8 on film more than on digital thats because digital is missing that outer edge due to a smaller sensor.
Now with those tiny point and shoot cameras the sensor is so close to the lens that your image doesn't get a chance to blur. In fact my Kodak point and shoot allways shoots a f/2.8 because anything higher wouldn't allow in enough light. The lens and sensor are both way too small.
As for the common mis-conception that DSLRs are like having a zoom its a misconception. Since when printing out they usually print the same size prints and compare them it appears to be a zoom effect. But since the DSLRs sensor is smaller to begin with its more like a crop and enlarge process. The image wont be any more clearer. DOF is determined by:
1. Lens aperture (larger is shallower)
2. Lens focal length (longer is shallower)
3. Camera to subject distance (closer is shallower)
The shallow DOF of f2.8 aperture is counteracted by the short focal length, which makes it deeper.
You get shallow DOF in macro mode because the very small camera to subject distance overrides everything else. I agree with Dr. Sam, 100 percent! and then sum!!!! Dr. Sam you hit the nail right on the head!!! Great answer!
Thank You,
Bob | 