Follow up on ” What to Focus on”

By Peter | Published
Oct
06
2011

In response to the article on “What to Focus on – Hyperfocal Distance and more“

Dunne W asked the question: “What would you recommend when you want place you focus for the Hyperfocal point in the scene, but also a Good Midtone for metering for our HDR’s. I guess what if a midtone is not in the area of the Hyperfocal area?”

Which really is a great question because depending on what Focus mode you are in, The focus point used may also be the point used for the camera’s metering.

Now if you are shooting in manual exposure mode. This really isn’t too big of a problem. Simply before you lock your camera into the tripod. get a 0 metering point from your scene ( as Duane says a midtone) remember that shutter speed and then work to each side from there. ( Quick tip if you don’t want to do the math of what the shutter speeds  you need to shoot at for your exposures, do this. Set your 0 exposure shutter speed and then for your next exposure count the clicks of the exposure wheel, 3 for each stop you want, 6 if you were doing 2 stops. No need to even look in the viewfinder)

This really is a more important question if you are doing Automatic Exposure bracketing in Aperture Priority mode. Because establishing a correct 0 exposure will ensure that those exposures that are bracketed around that o point are correct as I talked about in this post.

But the truth is these are two separate steps because when we use Hyperfocal Distance. It is best done ( as maybe I should have explained) with the Autofocus turned off . Using the Distance Scale on our lens (which hopefully your new lens still has , not all do) we set it for the hyperfocal distance and then turn off Auto-Focus. In fact turning off Auto Focus while shooting an HDR is actually really important for two reasons. One, because we want the focus point to stay constant in each exposure we shoot. And also when  we focus at a distance as opposed to close up, the zoom and  framing of the images changes ever so slightly, not a lot but it is noticeable if you take two shots on a tripod a different focal points and  switch between the two. Both things lead to loss of sharpness in our final image.
 
Anyway, getting back to Duane’s question. So now that you have locked  focus, you need to worry about locking exposure and depending on which focus mode you are in (even though the AF on your lens is turned off) But if you are in Matrix or Evaluative focus mode (Nikon/Canon) the focus point selected is where you meter is biased towards. In all other modes, Spot, Centerpoint average etc. The meter is biased towards the center of your focus screen. So wherever that is pointed is where it is going to get it’s 0 reading from regardless of where you may have focused.
 
We can correct for this by:
  • Adjusted our exposure manually as I stated earlier
  • Using the exposure lock button on our camera. Unfortunately, this only stays active for 5 seconds if you take your finger off the shutter release. So even if you lock it, if you don’t take the image within 5 seconds it will re-meter the scene
  • Use Exposure compensation along with Exposure Bracketing,  Which is something I do very often.

You can use Exposure Compensation by either just figuring it out mathematically. The sky where I am pointed at is 1/400 and my midtone is 1/100 therefore I need to set -2 stops EC. Or you can let the camera do the thinking, Point it at your midtone and get a reading and then put the camera in shooting position and adjust the compensation till you get the same reading you did when pointed at the mid-tone.

Of course EC is usually limited to 2 stop +-, so if it is really far off between the two areas. It’s always best to just resort to manual exposure

 

Hope that helps

 

PT

2 Comments

  1. Duane October 6, 2011 at 2:16 pm #

    This completed the puzzle and the lightbulb just went off!!!!! Just did a quick test and it worked perfect. Now to reproduce this in the field

    Thanks again!!! :))

  2. Peter October 6, 2011 at 2:48 pm #

    Great Duanne, can’t wait to see what you shoot. When you get home send us an image and we will feature it here on the HDR Image