Focus in this pic

[ksasidhar]

I have taken some b'day snaps last week. While mist of them turned out fine, there were some pictures (like one posted) in which it seems that not all the important persons are in focus. In the picture, it feels to me that the girl eating the cake is on focus but the one giving the cake is slightly of the focus. I shot this with 50mm f1.4 in shutter priority to avoid any blur images. I try to focus between both children but it is impossible to do that with everolyone moving quickly. What can I do to get both children in focus in such snaps?

 

[Designer]

The depth of field (or depth of focus if you prefer) is very thin. The range of acceptable sharpness is usually expressed in inches, (which of course can be converted to metric). If you would like to know the DOF at the time of shooting, use a DOF calculator (free online). Enter your focal length, aperture, and distance to your subject, and you will find the DOF.

Starting with what you know to be the desired range of acceptable sharpness, you can also work backward starting with the depth of your subject(s), and focal length to find your aperture.

You can either download the website to a smart phone, or do this calculation enough times to become familiar with the normal range of values so you will know beforehand what values to give your camera.

 

[ksasidhar]

Thanks for your reply. But considering that the movements of children are very fast, should I be using a zoom lens with larger focal length? I had the 18-105mm kit lens with me, but I was afraid that the lighting would not be sufficient.

 

[PJM]

First let me say you caught a nice moment there. You even got a bit of falling frosting.

The other thing that will affect your DOF is aperture. You had it at f/1.4 which is pretty wide open. You could close it down a bit to get more DOF. To do that you would have to up your ISO to compensate or lower your shutter speed which you said you were concerned about. You didn't say what your shutter speed was.

Telephotos tend to compress distance and I liked what you got with the 50mm so I probably would not go in that direction in this instance.

All of this is easier to contemplate in hindsight. My solution is to take test shots to try and get things where I like them and then hope the real shots work out as well.

 

[Braineack]

Thanks for your reply. But considering that the movements of children are very fast, should I be using a zoom lens with larger focal length? I had the 18-105mm kit lens with me, but I was afraid that the lighting would not be sufficient.

What does focal length have to do with the amount of light? Everything about your post here suggests an significant lack of understand of the basic principles of photography.

You need to learn the basics. Your struggle here is like lesson number one in the intro to photography...

I shot this with 50mm f1.4 in shutter priority to avoid any blur images.

This quote for example. You say you shot in shutter priority to prevent blur -- that's good and typically correct -- however, you also used a flash on your shot. This means you now have two different exposures in your single shot. Shutter speed is only going to affect the ambient exposure, where the flash itself is your shutter speed for the second flash exposure.

You could put your camera at 1/20 sec and shoot this same picture with flash and end up with a completely blurred background, with perfectly sharp kids. This is a technique called dragging the shutter.

Ultimately your issue is not a shutter speed issue, or a focal length issue, or even an insufficient light issue; it is a Depth of Field issue stemming from the combination of the focal length / aperture / focusing distance this was shot at. Understanding the basic physics of a lens and how all these factors affect each other and how to overcome them going to improve your photography in spades. A camera is a fairly simple tool, learn to master it from a technical standpoint and watch your photography improve in spades...

 

[Peeb]

Yep- google the term "depth of field" and you will learn a lot. It's fixable. I'd suggest stopping down to f/8 and using a flash to compensate for lack of light.

 

[ksasidhar]

What does focal length have to do with the amount of light? Everything about your post here suggests an significant lack of understand of the basic principles of photography.

You need to learn the basics. Your struggle here is like lesson number one in the intro to photography...




This quote for example. You say you shot in shutter priority to prevent blur -- that's good and typically correct -- however, you also used a flash on your shot. This means you now have two different exposures in your single shot. Shutter speed is only going to affect the ambient exposure, where the flash itself is your shutter speed for the second flash exposure.

You could put your camera at 1/20 sec and shoot this same picture with flash and end up with a completely blurred background, with perfectly sharp kids. This is a technique called dragging the shutter.

Ultimately your issue is not a shutter speed issue, or a focal length issue, or even an insufficient light issue; it is a Depth of Field issue stemming from the combination of the focal length / aperture / focusing distance this was shot at. Understanding the basic physics of a lens and how all these factors affect each other and how to overcome them going to improve your photography in spades. A camera is a fairly simple tool, learn to master it from a technical standpoint and watch your photography improve in spades...

Thanks for your reply. Focal length was mis-typed word here. I actually meant to ask if it is better to shoot these kind of pictures with lens like 18-105mm f4.5-5.8 nikon which has smaller aperture openings leading to better depth of field. However I was worried that the lighting will not be sufficient with that lens.

Didn't know about the flash dragging the shutter speed concept. I have to read more about it. But I was under the impression that when flash is in TTL mode, the flash operation is governed by the camera settings.

 

[ksasidhar]

Yep- google the term "depth of field" and you will learn a lot. It's fixable. I'd suggest stopping down to f/8 and using a flash to compensate for lack of light.

Thanks Peeb. Does it mean that I can use 50mm f1.8 lens (sorry, it is f1.8 and not f1.4) in manual mode while setting aperture to f8 with a fast shutter speed and use the external flash for better light.

 

[Peeb]

Thanks Peeb. Does it mean that I can use 50mm f1.8 lens (sorry, it is f1.8 and not f1.4) in manual mode while setting aperture to f8 with a fast shutter speed and use the external flash for better light.

Yes- the 1.8 means maximum light-gathering (wide open). You can stop-down the aperture by either shooting in manual, or in aperture priority setting (you tell the camera you want f/8 and the camera will figure out how to adjust the other parameters to get proper exposure). If your flash is smart, it can do that too. BTW, as @Braineack noted, there are just 3 components to proper exposure: 1. shutter speed, 2. aperture and 3. ISO.

Oh, one more thing, even if the shutter is set slower (which can introduce motion blur), the flash has the effect of freezing motion too. Experiment. Have fun!

 

[wfooshee]

Why make two threads about this? You have an identical post in the beginner's forum. Multiple posts doesn't give you wider exposure, it just makes multiple conversations on the same subject, and confuses everyone responding.

 

[Braineack]

Thanks for your reply. Focal length was mis-typed word here. I actually meant to ask if it is better to shoot these kind of pictures with lens like 18-105mm f4.5-5.8 nikon which has smaller aperture openings leading to better depth of field. However I was worried that the lighting will not be sufficient with that lens.

That number is simply the widest the aperture that lens can achieve at a given focal length.

Didn't know about the flash dragging the shutter speed concept. I have to read more about it. But I was under the impression that when flash is in TTL mode, the flash operation is governed by the camera settings.

TTL is automatically determined flash power based on your camera settings. You can still use TTL and manual shutter and aperture settings.

When using TTL your camera will send a quick small blast of flash, then based on what it saw, change the flash power accordingly to achieve a good exposure. Then it will fire again at the power it determined and capture the image.

 

[ksasidhar]

Why make two threads about this? You have an identical post in the beginner's forum. Multiple posts doesn't give you wider exposure, it just makes multiple conversations on the same subject, and confuses everyone responding.

I first posted it here but felt that the post is more suited to beginners forum and posted it there. Only later I found that I cannot remove this thread.

 

[RAZKY]

The depth of field (or depth of focus if you prefer) is very thin.

You were right the first time - depth of field and depth of focus are two entirely different subjects.

 

[Lez325]

I first posted it here but felt that the post is more suited to beginners forum and posted it there. Only later I found that I cannot remove this thread.

I answered it here fella

Getting focus correct

I have taken some b'day snaps last week. While mist of them turned out fine, there were some pictures (like one posted) in which it seems that not all the important persons are in focus. In the picture, it feels to me that the girl eating the cake is on focus but the one giving the cake is...

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