Sunday, February 22, 2009

Using MTF Priority

Found this quick tip from topgun2007 on the Pentax SLR Forums on DPReview. He writes that using the MTF program line will let the camera (K10D and K20D) select the best aperture/shutter speed combination based on the camera's knowledge of the lens attached. Basically every lens has it's "sweet spot" programmed into the circuitry, and MTF allows the camera to prioratize for that sweet spot on lenses it knows (ie: DA, D FA, FA, or FA J).

To set this up on a K20D (or K10D or *ist-D) you need to do two things. First, go into your menu, select the custom functions tab, and it's the first option there: #1 - Program Line. In there are four settings:

  • Normal
  • High Speed
  • Depth
  • MTF
Normal is the default, high speed will try it's best to prioritize for faster shutter speed, depth will try for largest depth of field, and MTF will, as described before, select the sweet spot based on the lens.

Second, you need to be shooting in "P" mode, or this won't come into effect. "P" mode is the Program mode from Pentax (and I can't believe that Canon or Nikon don't do this, at least on the cameras I have played around with) that allows you to set either the aperture or shutter speed, and the camera will adjust the other to match. Hitting the green button will reset to the default.

So for example if the default for a scene is 1/20th @ f/4.0, if you adjust the shutter speed two stops down, to 1/10th, the camera adjusts to f/5.6. If you go the other way and go 5 stops slower aperture, to f/9.5, the camera sets 1/4 second as the shutter speed. Nifty huh? Makes very fast and easy changes in the field, and is my default mode.

The big question is, where does the "default" come from? That is as you probably have already guessed, from the program line setting in the custom menu. It'll be a faster shutter speed, or a higher f-stop, based on what you have your custom setting set to.

Also in the same thread there's also a good post from GaryDen about blown highlights, and why Pentaxians complain sometimes about how their shots are underexposed.

More information about MTF can be found here, and here.

Up until now I honestly didn't know what MTF was, and I'm thankfor for topgun2007 for pointing it out! My question now is how does this affect exposure when you use a lens that isn't recognized, like an old M lens? I have set my camera to use the MTF program line and am looking forward to seeing what happens the next time I'm out.


Jeff said...

Nice write-up. Must be old Canon habits of mine, but I usually shoot in Av-priority because I simply forget that there is the Hyper P mode on the Pentaxes!