Figuring out 24-70mm lens

[kitkatdubs]

I recently bought a 24-70mm and am slowly learning how to use it. I am wondering about the zoom aspect with a low f/stop. For example, can I shoot a family of 6 at a f/2.8, zoom in to 60 or 70mm and still get everyone in focus? Or do I need to stop up to f/5 or f/6 to get everyone in focus? I love the creamy bokeh look but am wondering if I can still achieve that with a f/5 or f/6? Can a zoom lens get everyone in focus at a wide aperture of 2.8?

 

[goodguy]

My rule of thumb when I shoot group shots I go to f4-f5.6, but thats my style

 

[480sparky41 41]

DOF will depend on the lens' focal length, focus distance and aperture selected. There's a billion websites and smartphone apps that can do the math.

 

[kitkatdubs]

I still don't understand why I can't get that really nice bokeh effect with my 24-70 2.8? Do I need a 70-200 or something in order to really capture that nice blur? I always thought that if I shot at 5.6 f that I wouldn't be able to capture the bokeh. This is one area that has me struggling so much and I'm trying my best to understand

 

[480sparky41 41]

DOF and bokeh are two different things. DOF is the apparent sharpness due to the aperture setting. Bokeh is the artistic quality of the out-of-focus parts of the image.

 

[spiralout462]

I still don't understand why I can't get that really nice bokeh effect with my 24-70 2.8? Do I need a 70-200 or something in order to really capture that nice blur? I always thought that if I shot at 5.6 f that I wouldn't be able to capture the bokeh. This is one area that has me struggling so much and I'm trying my best to understand

A longer focal length will also help to blur and compress the background. Also the distance between your subject and the background influences how the background is rendered. Study depth of field.

 

[Derrel]

"Group of six" and "f/2.8" go together like bathtubs and electric radios, like Jack Daniels and speedboating, like loaded guns and moonshine whiskey.

I'm not trying to be flippant...f/2.8 and group photos with anything with a sensor bigger than a smartphone sensor is just asking for issues. It really,really is.

But yeah...you have the right idea with the 24-70mm zoom, to stop down to f/5 or f/5.6, and make the shots at that much safer aperture.

The thing is that with six people, there's a good chance that one,two, or even three of the people will have their faces at significantly different distances from the central face in the middle of the image area. If you actually take a steel tape, and measure straight ahead, from 12 feet, and then at the edges of the group, framed from 24mm to 40mm, the diagonal distance to the people at the edges of the picture area will be longer than it is to the central people; longer to a degree that will put those outside faces behind the plane of sharpest focus. An this is considering that everybody's toes are on a straight line! If one or two or three of the people are separated by eight to 10, or 12 inches, or as much as 18 inches, you will have a definite focusing problem, easily visible.

If you moved the camera back a good number of feet, yes, you'd get deeper DOF, and you could probably shoot at f/2.8 and pull adequate focus. But still...f/2.8 is very critical...it offers very little margin for error, and does not allow a lot of flexibility for loosely posing groups where people are at slightly different distances.

 

[beagle100]

I recently bought a 24-70mm and am slowly learning how to use it. I am wondering about the zoom aspect with a low f/stop. For example, can I shoot a family of 6 at a f/2.8, zoom in to 60 or 70mm and still get everyone in focus? Or do I need to stop up to f/5 or f/6 to get everyone in focus? I love the creamy bokeh look but am wondering if I can still achieve that with a f/5 or f/6? Can a zoom lens get everyone in focus at a wide aperture of 2.8?

yes, shoot at f6.3 for groups

 

[Ysarex87 81]

I still don't understand why I can't get that really nice bokeh effect with my 24-70 2.8? Do I need a 70-200 or something in order to really capture that nice blur? I always thought that if I shot at 5.6 f that I wouldn't be able to capture the bokeh. This is one area that has me struggling so much and I'm trying my best to understand

First off you've got a mix up of terms going on. Bokeh isn't the degree of blur that you see it's the character of the blur. How blurry the background appears is a function of DOF and relative distances. The same amount of blur will have different bokeh from two different lenses. Bokeh is a function of the lens design and shape of the aperture blades.

As Sparky noted there are a number of factors that determine DOF and background blur in a photo. You're after a blurry background. To get that you need to deal with both DOF and relative distances.

DOF is a function of f/stop and magnification. Magnification is a function of lens focal length and distance to the subject. With magnification held constant changes in the f/stop of 1 full stop (eg. f/2.8 to f/4) increase or decrease the DOF by approx. 50%. With the f/stop held constant changes in magnification by a factor of 2 (double or half) change DOF by a factor of 4. In other words magnification changes have a bigger effect than f/stop changes. You get to manipulate both the f/stop and more importantly magnification over relative distance. You know already that you can use larger apertures to reduce DOF and so increase background blur. That only takes you so far.

Now let's look at magnification. To change magnification by a factor of 2 double or halve the distance to your subject or double or halve the lens focal length. These would all be the same magnification: 100mm lens at 10 feet, 200mm lens at 20 feet, 50mm lens at 5 feet. And at the same f/stop all three would give you the same DOF. This is important because if for example you're shooting a head and shoulders portrait then the size of that head and shoulders in the frame will dictate the requisite magnification. That requisite magnification could then be achieved using any of the above combinations. Although the DOF at the same f/stop will be the same, the degree of blurriness in the background remains variable relative to the significance of the subject to background distance because:

Although in the above three examples the magnification is constant at the subject distance it's changing for the background. Let's assume the background is 30 feet behind the subject. (NOTE: This is critical. This works because the background is 30 feet away. If your subject were 3 feet in front of a wall this doesn't work and you get bupkis). With a subject to background distance of 30 feet the 200mm lens distance to the background is 50 feet. For the 100mm lens the distance to the background is 40 feet and for the 50mm lens the distance to the background is 35 feet. Magnification at the subject position is the same for all three lens/subject distance combinations, but it's substantially less background magnification with the 50mm and substantially more background magnification with the 200mm. Increasing the background magnification magnifies the blur.

Joe

 

[KmH]

Understanding Depth of Field in Photography

Going from f/2.8 to f/5 is stopping down to a smaller lens opening.
f/2.8 is a bigger number, and a larger lens opening (aperture) than f/5 is.

What you want is a shallow depth of field (DoF).
How much DoF you can get depends on - the point of focus distance, the lens focal length, the image sensor size in your camera, and the lens aperture.

The bokeh any make/model of lens can produce is not adjustable.

Play with different settings in this calculator to gain a better understanding of how DoF works.
Online Depth of Field Calculator

 

[beagle100]

I still don't understand why I can't get that really nice bokeh effect with my 24-70 2.8? Do I need a 70-200 or something in order to really capture that nice blur? I always thought that if I shot at 5.6 f that I wouldn't be able to capture the bokeh. This is one area that has me struggling so much and I'm trying my best to understand

you can get "nice bokeh" on a 24-70 2.8 (Canon)
but for group people photos it's better to use longer focal lengths at smaller apertures

 

[kitkatdubs]

All very helpful info. thank you everyone. I'm just brushing the surface of photography and practicing on friends and family. So my question now is, what is the 24-70mm good for? Is it a good lens to use for portraits? Tomorrow I am practicing on two siblings aged 5 and 7. In the past, I've been using my 50mm prime lens but was feeling limited. I want to be able to take full body shots and then quickly zoom in and get a detail shot of a smile or close up face in the moment. Does that make sense? Is the 24-70 good for this?

 

[Braineack]

So my question now is, what is the 24-70mm good for?

taking pictures between 24-70mm.

I want to be able to take full body shots and then quickly zoom in and get a detail shot of a smile or close up face in the moment.

youre going to have to zoom with your feet if you wanna do this.

 

[beagle100]

All very helpful info. thank you everyone. I'm just brushing the surface of photography and practicing on friends and family. So my question now is, what is the 24-70mm good for? Is it a good lens to use for portraits? Tomorrow I am practicing on two siblings aged 5 and 7. In the past, I've been using my 50mm prime lens but was feeling limited. I want to be able to take full body shots and then quickly zoom in and get a detail shot of a smile or close up face in the moment. Does that make sense? Is the 24-70 good for this?

yes but a large aperture prime like the 85mm 1.8, 200mm f2, etc. is better for portraits (blurred background)