D700 continued

<p>Thanks everyone on your comments about my question about FOCUS using an 85mm 1.8 with a D700. I now understand that if my subject is slightly out of focus... i.e. one half of the face, or the shirt, etc... then I should increase the F stop. What I don't understand is that if I go to an F stop of lets say 5.6 or more, aren't I defeating the purpose of the 1.8 lens... i.e. won't the background come into focus the higher my F stop?</p>

<p>"if I go to an F stop of lets say 5.6 or more, aren't I defeating the purpose of the 1.8 lens... i.e. won't the background come into focus the higher my F stop?"</p>

<p>jonas, there are a lot of f-stops between 1.8 and 5.6. it's up to you to select the correct aperture for the desired effect. if you want OOF elements but a wider DoF, stop down to 2.8 and stand back a bit. there's no law saying you can only shoot wide open at 1.8 or stopped down all the way to 5.6.</p>

<p>the purpose of a 1.8 lens is to allow you to shoot at extremely narrow apertures if need be, not to defy the laws of physics.</p>

<p>the awful truth is few lenses are designed to perform that well at 1.4 or 1.8...it's there because it's there, just in case you need it (i.e. low light or to isolate your main subject). if you want sharper results than you're getting from the 85@1.8, you'll need a manual focus 1.4 lens like a Zeiss or Voigtlander. but even then, you'll still have to stop down if you want the entire face in focus.</p>

 

<p>The background blur will be there if you are 2.5 feet from a person and the lens is set to f5.6, but if your are 70 feet away (for example,) the person and the background will be pretty much 'all in focus.' If you are looking for really disturbed background, you may try to rent a AF 85mm f1.4D Nikkor lens that will do better in the out-of-focus area behind your portrait subject.</p>

<p> </p>

<p>You have to compromise. Any lens the more you stop it down the sharper it gets. <br>

also the purpose of a f/1.8 lens is not only to blur the BG but to be able to use your camera in darker places and also they are easy to focus since there is more light getting into your viewfinder.</p>

<p>Take a quick visit to <strong><a href="http://dofmaster.com/dofjs.html">this DoF calculator</a></strong>, choose your camera body and the 85/1.8, and then start adjusting the paramters for aperture, and distance to subject. The calculator will show you how many inches (or feet - depending on the recipe) of reasonable focus you can expect. After you play with it, you'll start to get a sense of the workable portrait distances, and what you can expect varying apertures to do to the background.</p>

<p>I use the DOF claculator that Matt recommended all the time. Excellent tool.</p>

<p>If I recall correctly, you can still push the background out of focus, if you just get the object or person to be further from the back ground. As long as the object is the only thing in the range of focus you'll get nice isolation and blurry backgrounds.</p>

<p>Now, as to your defeating the purpose of the fast lens... it some regard, yes. But at f1.8 the depth of the zone of "in focus" stuff is also based on how close you are to stuff. As some one else said, this low f stop also allows you to SEE better and the camera to focus better, even if the aperture doesn't stay thet size when you shoot.</p>

<p> </p>

<p>The f/1.8 lens will be able to autofocus in lower light. It will also be easier to manually focus.</p>

 

<p>To get a better idea of how you can best use this lens, I suggestion you conduct a simple test shoot - set up a subject close to you and choose a specific area to focus on. Shoot in a sequence of shots in A mode, take one shot at each aperture from f1.8 to F10. Examining the in-focus areas of each shot may give you a better understanding of what this lens can do for you. </p>

<p>It is not only important to know the distance between you and the subject. The distance between the subject and background can affect your DOF choice, too.</p>