TAv mode — do you use it?

Started Nov 19, 2012 | Discussions thread
miles green
miles green Veteran Member • Posts: 7,797
Scenarios with TAv, Av, Tv and Manual mode in changing light

TAv mode is designed precisely for those action moments with dim but changing light when you would rather concentrate on AF and composition rather than exposure control.

Lets analyze the following scenario:

Lets assume you're photographing a dance performance. You know you need 1/320th of a second exposure to really freeze the dancers movement. Stage lights will give you on average ISO of 2000, with the aperture wide open at f/2.8. You also know that at iso 2000, you won't get any more detail out of your lens by stopping down a stop, especially if that means raising ISO a stop too. The stage lights change all the time.... What to do? (other than fix white balance and/or shoot raw, and maybe dial in some negative exposure compensation (-0.7) to protect the highlights a bit)?

At the end of the performance, all the bright white lights are turned on and the artists come back out on stage for the ovation...

1. TAv Mode

Dial in a shutter speed of 1/320th and f/2.8, and some negative exposure compensation (-0.3) for the highlights. The camera adjusts ISO to the rapidly changing lights, so you're always shooting with slowest speed widest aperture and smallest ISO possible. You can concentrate on composition and focusing alone and forget about the lighting. Iso is continuously changing from 1000 to 3200, about 4 stops away from overexposure danger.

At the end of the show, as you see the iso come down, you must change your aperture to 5.6 (a flip of the thumb) to avoid overexposure and get better lens performance now that you're in the ISO 200 range. The thing is you must remember to do it, because during the show the camera took care of lighting and optimal settings and you've forgotten you have to control exposure too!

2. Av Mode

Dial in f/2.8 and iso 3200. Any lower iso and low shutter speed will cause motion blur when the continually changing light get dimmer. Your average shot is at 1/640th of a second and many of your pictures will be shot at 1/1000th of a second, a bit of an overkill...

At the end of the show, you're still shooting at f/2.8, ISO 3200, 1/2000th of a second! Flipping you thumb to shoot at an optimal f/8 won't do much as you won't see much difference at ISO 3200: you've gotta change the ISO setting. So indeed if you forget to adjust exposure, you won't burn any shots, but you'll be quite far away from optimal settings!

3. Tv mode

Dial in 1/320th and iso 3200. You're shooting at f/4. One stop of light less, and you'll be undexposing your pictures as you lens can't do faster than 2.8. When the lights get brighter, the lens stops down, but you're still shooting at a high ISO.

Again at the end of the show, you're better off changing the ISO manually.

4. Manual mode

No secrets here. You're constantly adjusting exposure, composition and trying to ficus at the same time. You will not forget to adjust exposure at the end as you've been doing it all along.

So what's the outcome of this scenario?

TAv is indeed by far the best at keeping optimal low light action settings, and you can almost take your mind off exposure:

But there is a risk: say you completely forgot about exposure and did not see the camera warnings. In our scenario, with...

TAv: 4-5 stops of light more will overexpose your pictures no doubt. Of all the shooting modes, TAv has the most "expensive" mistake, as the ruined shots should have had the best IQ.

Av: Low risk of losing a shot completely, but most of your shots are a little too grainy

Tv: 2 Stops of light less and you'll be pushing exposures in post. shot at ISO 3200... Not the best recipe for keepers, despite the K5's DR!

M: you're quite the photographer, but you're exhausted and didn't enjoy the show!

My conclusion?

If on average I'm shooting 4-digit ISOs i prefer TAv, as it takes a lot more light to ruin my shots, and the cost of using the wrong ISO becomes greater. If much stronger lights are turned on, all I need to do is change the aperture with my thumb... but I must remember to do so!

If on the other hand the average ISO is 400, you're probably better off shooting in Av or Tv mode. There is little cost in shooting iso 400 rather than 200, and you avoid the danger of completely ruining your shots due to overexposure.

Thanks for reading all this, i hope it was worthwhile! 

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Miles Green
Pentaxian with chronic LBA
Corfu, Greece

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