Jump to content

How to correctly Focus a lens


glenn_carroll

Recommended Posts

<p>Hi everyone<br>

i have a rebel xsi, the 24-105mm f/4L lens as well as my recent purchase, the 50mm f/1.4 lens. With the 24-105 lens, i would usually simply look through the viewfinder, and move the focusing dial until whatever i want in focus is in focus, and then snap the picture. However, I bought the 50mm to take good wedding pics and pics in lower light in general. therefore, sometimes i dont have the luxury of being able to see the subject that well through the viewfinder.<br>

My question is essentially whether there is some way of telling if the subject (ex: a couple on the alter getting married) truely is in focus or if they are slightly out of focus. If i am shooting at f/2, then sometimes the margin for error here is pretty slim. My eyes are simply not very good when looking through the viewfinder for telling if the subject is in focus sometimes. Anyone know of a way to ensure something is in razor sharpe focus or not?</p>

<p>Any help would be awesome! thanks</p>

Link to comment
Share on other sites

<p>I had the same issue. My eyes arn't that great and autofocus is not all that reliable with a very narrow depth of field. On my 5D i purchase a split prism view finder, removed the original view finder, and installed the new one. If you position a line across the view finder the line will split into two lines if it is out of focus. The line will not be split if it is in focus. I find it very useful.</p>

<p><a href="http://www.katzeyeoptics.com/cat--Canon-DSLRs--cat_canon.html">Katzeye</a> appears to sell one for the Xsi.</p>

Link to comment
Share on other sites

<p>You could get a split image screen and focus manually. However, as a wedding photographer facing much the same situation, I can tell you that I take several images, auto focusing each time. I use the center focus point only (at the subject distances you are talking about--back of the church-- parallax should not be that great a problem), and give the point something contrasty to work with. For those times where you can only get off one shot, you pray that your auto focus technique is working for you. :^) I've found that autofocus gets me more in focus shots than manual focus, even. For those times where you have the time, and you are closer to your subject (where parallax makes a difference), use the appropriate focus point and take the time.</p>

<p>Realize that you must already have tamed the tendency for cropped sensor cameras such as yours to backfocus because the focus points are actually bigger than what is marked. You should not be putting the focus point on edges of a subject, to avoid it bouncing off the subject onto the background, particularly if the background is contrastier than the subject. On my 20D, I have also found the actual focus points are not centered under their marks--the center point is slightly lower than it's mark.</p>

Link to comment
Share on other sites

<p>I 2nd Nadine's suggestion of using AF with the center point. </p>

<p>I would also ADD that you would be better off placing the AF activation button separate from the shutter button. I have assigned the * button to activate AF. That way, I can focus and meter indipendently. Once you try that combination you'll probably never go back to the traditional controls where the shutter button activates both metering and AF.</p>

Link to comment
Share on other sites

<p>That's the nature of the beast, trusting AF. Which is why it's nice to have lens with full time manual. You can hit with auto, and then tweak manual if needed. Unfortunately, if the light is dim enough, the sensor will also have a hard time locking in and wind up hunting. F2 on the 50mm 1.4 is getting borderline sharp, with 1.4 being too soft even if in focus. That lens has a limit of F2.2/2.4 for the razor sharp. Why most folks use that lens is because having a useable image outweights something that is razor sharp.<br>

If using AF in dim lit rooms. I set for center point, depress the button half way to focus on something that's in the same plane and my subject, which is bright enough for the sensor to get a lock (i.e. shirt colar, light reflecting on glasses, etc.), recompose and fire. The other trick is a quick burst of shots while manually focusing your best guess and hopefully one will hit.</p>

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...