Focusing on multiple subjects while using Nikon D3100 with 50mm 1.4 lens

[erin_mathias]

<p>So I bought a new lense to give me more depth of field. It is great with single subjects. However, when I use the new lens on multiple subjects it seems that usually some of the people are out of focus. Is it just as simple as adjusting the apeture, or should I be adjusing something in the focus. The way I have it set now, is on Dynamic area AF. It gives me one focus point. <br>

Thanks for your help!</p>

[AJG]

<p>If you are using this lens at its widest opening (f/1.4) then you will have very limited depth of field (only what you actually focused on and a tiny distance in front of and behind that rendered as sharp). If you have several people in the frame and they are not in the same plane and parallel to the camera, then only one of them will be sharp at large apertures like f/1.4 and f/2. This isn't an AF problem. If you want all of them to be sharp, then stop down the lens. Try different f/stops and look at the images on your monitor (not the camera screen) to see how it works. When you see the "look" you want, check the metadata for the f/stop that you used. </p>

[Matt Laur]

<p>You need to read up on depth of field. You'll get <em>more</em> of it as you stop the lens down (a higher f/stop number), and less of it as you open the lens up (a lower f/stop number).<br /><br />f/1.4 = very shallow DoF<br /><br />f/11 = quite a bit more DoF<br /><br />What you focus on is important, too. If you don't want the camera to guess, you have to tell if what you want. Put the camera is Single Server (AF-S) mode, and just use a single focus point. Press half-way down on the shutter button while putting that point on the item you want in focus, then don't let up on the button as you (if necessary) recompose your frame, and then push the rest of the way down in order to take the photo.<br /><br />But if you have multiple people, and they are at <em>different distances from you</em>, you need to stop the lens down enough to get deep enough DoF to capture them. Remember that some of the distance <em>closer to you</em> than where you focus will be suitably in focus, and some of the distance <em>past</em> where you focused will be so. The more DoF you get, from more stopping down your aperture, the greater that in-focus range of distances will be.<br /><br />You can use <strong><a href="http://www.dofmaster.com/dofjs.html">this DoF calculator</a> </strong>to plug in some example numbers, and you'll see just how far in front and in back of your chosen focus point you'll get acceptable focus for a given aperture and working distance. Play with it for a few minutes, and you'll understand how it works.<br /><br />Typically, you'd reach for a lens like your 50/1.4 so that you can have <em>less</em> depth of field, when you want your subject in focus, but want to isolate that subject by throwing the background more out of focus. Less expensive kit lenses (which can't open up to those faster apertures) won't be able to create such <em>shallow</em> depth of field.</p>

[erin_mathias]

<p>Thanks so much! I think that is exactly why! I keep mixing up less vs. more when talking about depth of field too! I will play with my f/stop and see if that helps. I like the DoF calculator! <br>

Thanks!</p>

[jcuknz]

<p>If you want greater depth of field you can use a shorter focal length lens. The 50mm is a short telephoto lens on an APC DSLR. Maybe the 18mm setting on your zoom lens that might have come with the camera. The 50mm has an attractive perspective for some uses but not how you appear to be using it. Though If you can obtain the required DoF then the 50mm will bring the people together where a shorter lens will appear to separate them. It depends on the visual effect you are seeking. Another approach is to take two shots first focusing on the near person and the second focused on the far person and combine them in editing for yet another visual effect available to you.</p>

[Spearhead]

<blockquote>

<p>The 50mm has an attractive perspective </p>

</blockquote>

<p>This is incorrect. Lenses do not impact perspective. This has been said so many times on here that it is amazing to see it repeated at this point.</p>

[bobcossar]

<p>+1 Jeff....</p>

[steve m smith]

<p>Whilst it is correct to state that the lens does not affect perspective, it would be a good idea to explain why.</p>

<p>Perspective is dependant only on position. Having a shorter lens might make you move closer to the subject. It is this change of position which changes the perspective, not the focal length of the lens.</p>

[jcuknz]

<p>The lens causes one to work at a distance which has attractive perspective therefore the lens has attractive perspective ... <br>

The above just emphasises how silly I can be at times when I indulge in these purist arguments. As the NYT wordsmith once said "Words mean what I mean them to mean"</p>

[lachaine]

<p>It's been discussed many times for sure, and every time it's brought up, it's as pedantic an exercise as it was the first time. I think we can safely assume that when somebody uses the word perspective in connection with a lens of a given focal length, it sorts of takes in the whole idea of the distance to subject having been affected by the lens being used... and I'm sure I'm not the first one to say that either.</p>

[frank_skomial]

<p>Some practical expressions of a lens behavior will trigger response from the "purists" or scientists who perhaps never shoot a picture.</p>

<p>E.g. saying that: "this long lens nicely compressed perspective", is an expression of practical use of a lens, and not of pure science.</p>

<p>Purists would go to extent and argue, that all and any perspective can be achieved with just one fixed focal length lens, and using tele-lenses is therefore not necessary. - but how is the practicallity of such a purist approach?</p>

[jcuknz]

<p>I just hope these subsequent postings do not detract from the points made about using different focal lengths to bring together or separate people at different distances from the camera for artistic point, which is how we should be using our lenses rather than to save our legs.</p>

[Karim Ghantous]

<p>Beginners come to this forum specifically to get advice from experienced and possibly mature photographers. To be vague with terminology does not help. Correct use of terms within the discipline (that we all know and love) helps better communication.</p>

<p>Changing lenses and changing perspective are by no means the same thing. It is a mere fact, there is nothing 'purist' about it. Once beginners know this, they can then understand what people mean when the term 'perspective' is used casually. I hope, Erin, that you do not think that I am hijacking your thread. :-)</p>

[diane_madura]

<p>Erin, if you have an iPhone or an iPod Touch, there are apps for depth of field. Rather than trying to guess what's in focus or trying to see it on my LCD, I refer to my depth of field app. You can plug in the necessary figures (and the type of camera you are shooting with) and it will tell you what your depth of field will be. I refer to my depth of field app a lot.</p>

[richardsperry]

By the time a beginner figures out what is being said, they would already know what was meant by the statement.

 

I suppose to a true beginner it looks more like pedantic-message-board-one-upmanship bickering.

 

Saying that the focal length of a lens has nothing to do with apparent perspective is a bit disingenuous. All one needs

to do is compare a subject shot with a 24 and a 50 to see that there really is a difference in perspective of the

subjects. You and I know that it is really the objective to subject distance. When was the last time you taped out the

distance or even cared about it? For me, let me think hard and try to remember.... Uh never.

 

Anyway, it is the focal length which allows for the subject to objective lens distance that causes apparent perspective,

in the first place.