You have control over iso, yes, but only in a 'secondary' capacity, (ie its not the primary input, only the result of the primary inputs) - its not really the mode for setting ISO at all - that would be Sensitivity Priority (is that Sv on the dial??)

We are diverging now! Stepping up from ISO 100 to 200 is doubling the sensitivity / gain, and I think that is a lot. Yes, the effects will mostly be visable in lower light scenes and at bigger enlargments, but for me it would be a concern.

Well yes, but surely Smeggy down on that platform you're near your limits in this respect already (ie at or near wide open, and at a speed just fast enough to prevent the woman blurring - unless you were using flash, not allowed either )

I think that yellow colour noise (and other noises) is something to think
about for all serious digital photographers, not something that is just 'each to their own'. It imposes very real technical limitations on us and can obviously affect the choice of modes and camera settings we must consider.

What is a cool or not cool picture is clearly down to personal taste - I can't see the relevance of such an observation to a thread about optimum f stops and shooting modes and how they influence technical quality. My posted shot is nothing more than a tree and some houses (but I love it!), so I wouldn't be interested in others artistic judgements. But as far as its technical attributes or lack of, hey, I positively welcome a right free-for-all.

I believe for my output purpose it is important to maintain full control over ISO. Certainly on the K7 the jump from 100 - 200 - 400 would be significant. So Tav wouldn't give that full control. Just like a film photographer wouldn't bung in any old 100 or 200 film when taking a considered shot for very large printed output.

I'm not actually trying to say that Tav is inflexible for Smeggy's shot - if the main factors to be controlled are limited to shutter speed and aperture only, then fine - take what the camera gives you. But you have to take any compromises that come with that (such as the colour noise I pointed out). This may be OK for the web or at small sizes.

I think I'd be well into tripod terrain for that Alan. But if Smeggy tried that he'd have to be even quicker than usual before being told to 'put it away' over the PA!

Just as an example of the sort of shot I am saying would require a fair stopping down as well as low ISO - here the subject has equal importance at its edges as in the centre, so I have needed to control noise, vignetting and detail equally right to the edges.

I still remain unconvinced that Tav mode really is such a 'flexible friend'. It still comes down to our output intentions.

I mean, Smeggy, yes the young woman on the underground platform is certainly a subject pleasing to the eye, but I couldn't use this photo for wall display as I do for many of my shots due to the great whopping amounts of yellow colour noise in the blacks!

Attempts to reduce this and print out at any decent size would just reveal smudgyness that would be a distraction. I would suggest that the settings here have resulted in an ISO far too high for such a purpose (I know it wasn't your purpose, but just the make the point that we should choose our modes and shooting settings depending on our individual requirements.)

Regarding the auto mode - I think a good point was made earlier about the great flexibility provided on Pentax DSLRs with the 'Program Line' options - you have Speed (High / Low), DOF, or MTF. This provides some degree of customisation within the P mode, taking us worlds away from just 'point & shot'.

But I fear that the effects of these program line settings will be minimal on all but the more expensive wider glass - as Gartmore staid earlier, often the MTF aperture setting is only 1 - 2 stops down from wide open. So on a standard 18-55 zoom, thats the difference between f3.5 and f5.6 or so. At much of the zoom range you won't see a lot of difference I fear.

Mattie, not sure if you saw my post just above, but in relation to the power output, I think from looking at your last question we are actually saying the same thing.

Quoted from above ... 'The 'units' (if you like) for flash power and flash exposure compensation are different - power is rated in fractions of full output, so 1/2, 1/4, 1/8, 1/16 etc.

Compensation is rated in 'stops', as in aperture values, so -0.5 (half a stop), -1.0 (1 stop) etc. I use minus because for fill this is the more common direction to head in, as we are not trying to completely illuminate the subject (which will have ambiant light on it), but rather to 'fill in' darker areas like shadows on faces or under the brim of a hat.

Of course, despite the different units of control input, we are effectively doing the same thing. 1 stop less of flash would be the equivalent of 1/2 power I believe'

Um... well I hope others more experienced than me will comment too - but 'half flash power' I believe relates to the power output (strength of light) that the unit puts out. How it technically achieves this I believe is to do with the 'Thrystor' circuits that use coils to store charged energy and the amount from each recharge that is released.

Flash duration would have an effect only at longer shutter speeds, ie beyond the 'Flash Sync' speed (180th sec on my K7) - generally the flash duration is significantly less (faster) than the shutter is actually open, so in these conditions just reducing the flash duration would have no effect.

Just as an extra thought here, it's perhaps worth mentioning that even though we think of Flash Exposure Compensation in terms of 'Aperture Stops', it is not of course actually affecting that actual aperture setting of the lens (only the lens aperture ring or camera control wheel will do that).

Flash exposure Compensation is actually controlling flash power output - so -1.0 stop caused the flash to fire at 1/2 power, just the same as if you dialed in 1/2 power on a flashgun.

The 'units' (if you like) for flash power and flash exposure compensation are different - power is rated in fractions of full output, so 1/2, 1/4, 1/8, 1/16 etc.

Compensation is rated in 'stops', as in aperture values, so -0.5 (half a stop), -1.0 (1 stop) etc. I use minus because for fill this is the more common direction to head in, as we are not trying to completely illuminate the subject (which will have ambiant light on it), but rather to 'fill in' darker areas like shadows on faces or under the brim of a hat.

Of course, despite the different units of control input, we are effectively doing the same thing. 1 stop less of flash would be the equivalent of 1/2 power I believe.

As far as 'computing' this value, well I'm not sure if there is a formula or not! But, its something that comes with experience both with the subject type and the particular camera also - flash exposure metering is affected in the same way by a subjects 'reflectivity' just as ambiant light metering is. So, for example, a light toned face would require a bit more fill flash than a dark toned one. I've always understood that a good starting point for most fill situations is -1.5 stops. I'm sure others will have other experiences to relate as well.