R.G. Loc: Scotland

We're all familiar with the idea that with fast movement, shutter speed is a priority, if depth of field is critical, aperture is a priority, and if neither of those are critical, keeping noise low (i.e. low ISO) is a priority. When it comes to choosing camera settings in those situations, our priorities are clear.

But what about the most demanding situations where we can be pressurised from all three directions and our choice of shutter speed, aperture and ISO could all end up being less than ideal? What are our priorities then?

In that sort of situation, instead of thinking about what our priorities are we need to think about what the most compromisable variables are. To answer that question we need to ask what has the most potential to negatively impact the quality of a shot, perhaps to the point of spoiling it altogether.

Everybody will have their own take on that subject depending on what area of photography they operate in. There are various ways in which a shot can be degraded or spoiled (for example over- or under-exposure), and it will very often be caused by user error. However, degradation can also be caused by unavoidable compromise. Looking at the latter situation, and looking at it from a very general point of view, my suggestion for what the worst shot spoilers are (in order of significance) would be:-

1) Motion blur / camera shake (i.e. a shutter speed issue).

2) Excessive loss of sharpness and/or detail due to insufficient depth of field (i.e. an aperture issue).

3) Excessive noise, possibly accompanied by a loss of sharpness, contrast and colour accuracy (i.e. an ISO issue).

Still speaking in very general terms I would say the main implication of the above list is that the most compromisable variable is ISO, followed by aperture and leaving shutter speed as the least compromisable variable.

Still speaking in very general terms, another implication is that if you had to choose one variable to float, ISO would be the best choice, since it is the most compromisable variable (this is especially true of the most recent cameras, some of which have exceptional high ISO performance).

Feel free to agree or disagree with any of the above and feel free to share your own take on the subject.

ClarkJohnson Loc: Fort Myers, FL and Cohasset, MA

R.G., you have presented a thoughtful and thorough analysis of why Auto ISO is so popular. For the very reasons you mention, my bird photography uses a locked shutter speed (1/2000), a set aperture, and auto ISO. Takes most of the worry out of rhe settings and lets me concentrate on getting the shot.

Interested to hear other opinions.

R.G. Loc: Scotland

Thanks for your comments, MrBumps. In general terms I'd say that letting us concentrate on the important stuff is a general benefit, even when things aren't tight.

Grahame Loc: Fiji

In general terms I would agree with your priorities order 1, 2, and 3.

The only exceptions I can think of at present is that 2 and 3 may differ in specific situations with my macro work if using natural light and night skies.

As for floating ISO, it's the only one I ever float, which is very often and I know roughly where it will float to.

Delderby Loc: Derby UK

It seems that your concerns are to do with reducing blur and eliminating the causes, whether from camera shake, subject movement, focus and DOF, or noise/grain. In difficult situations there will almost certainly be a trade off. The problem with a 'floating' ISO is that high ISO can/will introduce it's own "blur", whether or not there is a capability for higher performance. The best ISO will always be base ISO.
I agree that your suggestion will usually be the best option, provided a suitable upper limit is in place, leaving the photographer to set the triangle according to his subject.
However, at the PP stage (with a difficult image) the choice might be apparent optical sharpness versus noise?
Keep safe.

R.G. Loc: Scotland

Thanks for your comments, Grahame. I don't do macro but I got the impression that there's a near-constant need to get sufficient DOF due to the focus point being so close. I got the impression that macro shots were often judged on how sufficient the DOF is. But I can understand that extreme ISO noise has significant potential to spoil a shot. And (I'm speculating again) if the movement isn't constant, isn't it often a case of waiting for the subject to stay still long enough, or using continuous shutter release hoping that at least one of the exposures will be optimum?

Grahame Loc: Fiji

Out of interest why do you equate 'floating ISO' with 'high ISO'?

R.G. Loc: Scotland

To clarify the purpose of the above list of priorities, I was placing effects in what I consider to be the order of their potential to spoil a shot. I'm not suggesting that blur is the only possible shot-spoiler, but I would say that even small amounts of motion blur can be very detrimental, and the same applies to an even moderately insufficient DOF. High ISOs do introduce softness in various forms but it has to be extreme before it could be ranked as a shot spoiler.

As far as PP is concerned, motion blur is typically the most difficult to treat, even in small amounts, followed by DOF problems. Soft focus is typically not a good thing, but moderate amounts are treatable, and if it's only some of the shot that's insufficiently sharp, the photographer may consider that to be acceptable.

Grahame Loc: Fiji

There are two schools of thought here, some consider the greater the DoF the greater (better) the result, and others consider the greater the IQ of what is in focus (within achieved DoF) the greater (better) the result. There is no right or wrong.



Yes, for those that consider IQ a priority.



The speed required is no different than in any form of photography, the 'minimum' must be capable of addressing any subject movement plus photographer/camera shake at shutter release.

R.G. Loc: Scotland

My assumption was that the closeness of the focus point forces the shooter to use high f-stops, and if light is low there will be an incentive to avoid using fast shutter speeds (in order to avoid using high ISOs). However, if in addition to those pressures the subject is also moving quickly, instead of trying to keep the shutter speed up, an alternative is to wait for the subject to either stop moving or at least slow down. Timing the shot is one possibility, using continuous shutter release is another.

Delderby Loc: Derby UK

I don't - I was mindful of when R.G. said -
"if you had to choose one variable to float, ISO would be the best choice, since it is the most compromisable variable (this is especially true of the most recent cameras, some of which have exceptional high ISO performance)."
ISO up to 800 or perhaps even 1600 would not really be subject to introducing the "blur" to which I next referred.

Tomfl101 Loc: Mount Airy, MD

I totally agree ISO is the compromisable variable. An increase in grain/noise is always desirable over a lack of sharpness due to focus or motion blur even at extremely high ISO settings. The ability to shoot variable/high
ISO is the single greatest feature on a digital camera as compared to shooting film.

R.G. Loc: Scotland

Indeed (but not the only advantage). Thanks for commenting, Tom.

Grahame Loc: Fiji

Ok, I must have interpreted your sentence incorrectly then.

Delderby Loc: Derby UK

Well - sometimes maybe - but noise can be extremely objectionable. Depends on the subject.