TAv mode — do you use it?

Started 6 months ago | Discussion thread
Gerry Winterbourne
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Re: TAv mode — do you use it?
In reply to rakore, 6 months ago

rakore wrote:

I wouldn't say that TAv is the most useful mode but it certainly does have its uses.

It's a fundamental principle of digital photography that you should always use the lowesr possible ISO to maximise DR and minimise noise.

Whenever possible, therefore, I use an exposure mode that lets me choose ISO. For example, if I want control of DOF (whether narrow or wide) I use Av and let the camera determine shutter speed.

It's when the light gets too low, or if I need to control both aperture and shutter that I go to TAv. How often this happens is obviously personal; for me it's under 5% of all the shots I take.

I agree with you that the lowest possible ISO value is almost always the most desirable. To me that's an argument for using TAv: Selection of ISO value is a no brainer, and therefore the variable best left for the camera to descide. It can safely assume that this value should be as low as possible. Not so with shutter speed and aperture.

That's not how it works. TAv doesn't choose the lowest ISO; it chooses the "right" ISO as calculated by the camera's exposure meter.  So there are three possibilities: (1) the aperure and shutter you've set happen to need exactly the lowest ISO your camera has, in which case exposure will be right and you get the lowest possible ISO; (2) the A and S you've chosen need ISO higher than the camera's lowest, in which case exposure is still OK but you aren't using the lowest possible ISO; (3) the A and S you've chosen need a lower ISO than the camera can give, in which case you get the lowest possible ISO but the shot is overexposed.

I think TAv can be useful in any light. Let's say you do street shooting on a sunny day. You want a shutter speed of 500 to freeze motion and ensure sharpness and an aperture of 11 for good DOF. TAv could then be very handy. Of course you should still watch the exposure and the ISO, but you wouldn't have to be changing the ISO manually all the time.

Yes, this is an example of what I said "if I need to control both aperture and shutter".

I'm much more comfortable with letting the camera control ISO (within user defined limits) than either shutter speed or aperture. Jay Maisel supposedly leaves his ISO at 1600 all the time for convenience since he thinks it's "good enough".

We all make our own compromises.  Wasting DR for convenience isn't one that I'll ever make.

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Gerry
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First camera 1953, first Pentax 1985, first DSLR 2006
http://www.pbase.com/gerrywinterbourne

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