Tuesday, February 24, 2009

Shooting in TAv Mode

In the previous post I mentioned that I was shooting TAv mode. I needed the higher shutter speed as I was hand holding a 300mm tele and needed a bit of depth of field so that most of the squirrel was in focus and the lighting was mixed sun to varying depths of shade as I was chasing the squirrels around the yard. In this article I will talk a bit about the humble TAv mode.

Now I could have shot those squirrels in Tv mode to help keep the hand steady and let the aperture follow, but in the shade the aperture would be wide open and the DoF a bit too shallow making focusing critical. I could have set the camera to Av and let the shutter follow but again in the shade the shutter speed might have dipped to low and caused some camera motion blur. And I know some of you are saying “I could have set the ISO higher so the shadow areas were properly exposed, and shot in Tv mode for the tele lens”. While this is true, what happens to my tight DoF when I hit a patch of sunlight? It increases maybe a couple of stops and I lose the DoF separation effect I was trying to achieve. I will admit in this case the difference between sunlit and shade probably wasn't that drastic and I could have gotten away with a higher ISO and called it good. But why do that when TAv mode is available and works quite well?

TAv is a manual mode in that you set your desired shutter speed and lens aperture diameter for the effect you are going for yet allows the ISO to range automatically to adjust for different light levels. Wouldn't it be nice if you could turn the sun up (or down) sometimes just so you can get the perfect shutter/aperture combo say when shooting a waterfall or stream in dense covered forest? Shooting action sports with a mix of sun shade, concerts with their ever changing light, low light/night street photography, and intermittent cloudy sunny days are other conditions suited for TAv also. And all you old-timer (me included) film users, how many times have you done a mid-roll film change just so you could get a different ISO? With digital, a manual ISO adjustment is easy; With TAv, it's automatic.

To use TAv mode, turn the mode dial to TAv. Use the front and rear wheels to set the desired shutter and aperture values based on your desired results. Then set the Auto ISO range by pressing the Fn button and pressing the 4-way controller button to the right. In TAv mode the ISO will be locked in Auto and you set the lower and upper ISO limits with the front and rear wheels. I keep mine at 100-800 and only use 1600 in extreme cases like theater lighting or when I don't mind a little noise.

Now as with any mode there are some limits and in the case of the K10D and the TAv mode there is even a bug. The ISO range is limited at the low end at 100, so make sure you aren't over exposed at ISO 100 in sunlight. Also the ISO tops out at 800 (1600 if you're careful or don't mind a little digital noise) so you will only be able to shoot 4 stops worth of shade.

The bug is, if you have upgraded your K10D firmware to V1.3, the exposure does not lock while half-pressing the shutter release like it does in Tv or Av modes. I kind of like the idea that the exposure is not locked in this mode, I mean I am chasing my subject around in varying light conditions. What if conditions changed after I pressed the shutter halfway and was about to take the picture? While this is not a big deal and Pentax may have done this on purpose, if you want to really lock the exposure, you have to use the exposure lock button (AE-L) to hold the current ISO value.

Armed with this information, go shoot some subjects in TAv mode in varying light and see the results. You'll find TAv a very useful mode and I hope you remember to use it when the conditions are right.

Till next time when we talk about flash and exposure modes, here's wishing for Spring!


ccxx said...

I've never (?) used the TAV mode but, are you sure about "the bug" ?
There is a line in the menu to lock the focus with the exposure when half-press.
I don't use this feature because i love to get the light on a position and get the focus from other. I use the AE-L key for this reason.

Photography Rulez said...

Yes, there is a setting to link AF and EL and supposedly it works with V1.1 firmware, but I know for sure the exposure does not lock with shutter half press in Version 1.3 firmware.

Here are some sample photos