Debating Auto-ISO

What’s the similarity between marmite, beetroot and Auto-ISO? Yep – you got it, you either love them, or hate them! For some reason, Auto-ISO frequently evokes strong opinions, and most of the time, there’s no sitting on the fence. Why is that? To answer that question we firstly need to understand Auto-ISO. What is it? Should you use it? When should you use it? What Auto-ISO settings should you use? What about flash? And lastly, what about camera supports?

We’ll take a look at all these, but firstly, let’s cover some basics.

Firstly, what’s ISO?

ISO determines how reactive the image sensor is to light; with higher numbers being more sensitive. It’s similar to the ISO/ASA number associated with film. Moving from one ISO to another moves by one stop. At higher ISO’s the DSLR is more reactive to light, and therefore much better in low light, however this is offset by increased noise/grain in the picture. At ISO 100 you’ll get the best quality image, while at 6400 you’ll see some visible noise and a reduction in dynamic range.

NB: Nikon School has a good article called “Understanding ISO sensitivity” that gives more background.

Expert tip: If you set Custom Setting d3 ISO Display and Adjustment to Show ISO/Easy ISO the viewfinder and control panel will show ISO value instead of the number of remaining exposures possible.  This makes use of the unused wheel. In P and S modes, the front wheel (sub-command dial) now controls ISO, while in A the rear wheel (main command dial) controls ISO. This makes changing ISO very easy, and if you need to know frame count left, turn the D7100/D7000 off and it’s shown again in the top control panel.

What’s Auto-ISO, and how does it work?

Auto-ISO is a feature that enables the D7100/D7000 (and many other Nikon DSLRs) to automatically set ISO within tolerances you define. If Auto-ISO is enabled, the DSLR automatically adjusts ISO if optimum exposure cannot be achieved at the user selected ISO value i.e. it overrides your selected ISO value. If Auto-ISO is disabled, you are fully and manually controlling ISO.

It operates within the limits you set for Minimum shutter speed and Maximum sensitivity (ISO), which you set within the menu settings for Auto-ISO (SHOOTING MENU – ISO sensitivity settings – Auto ISO sensitivity control).

The benefits of Auto-ISO slightly differ according to the mode you’re in. We’ll explore those later, but first – should you enable Auto-ISO?

Should you use Auto-ISO?

I think the answer is; “It depends, on numerous factors”. These include your background, your profession, the lighting conditions, flash/tripod usage, and where you are on your “photographic journey”. How experienced a photographer are you? Have you just bought your first DSLR, or are you an experienced pro? When did you start photography, recently, or a long time ago? When did you start using Nikon cameras? Are you a photojournalist, private detective, wedding photographer, or sports photographer? And possibly, do you have a background of using a different DSLR manufacturer that doesn’t have Auto-ISO?

Whether you enable Auto-ISO or not, is partially dependent on how much experience you have, how much you have yet to learn; where are you on your “photographic journey”?

New to photography

If you’re just starting, maybe this is your first DSLR. If you’re relatively new, I would suggest you turn Auto-ISO on. That will allow you to concentrate on other things first.

Starting to take control

If you’re a bit further down your photography learning curve, you’re probably exploring the Aperture (A), Shutter (S) and Program (P) modes – wanting to take a bit more control. Perhaps you’re learning how shutter speeds, aperture and ISO (the “triangle” of settings that controls light to the sensor) affect the photo. If this is the case and your right at the early stages, then using Auto-ISO could be a good thing. Switching Auto-ISO on would enable you to concentrate on shutter speed and aperture and really those things well first.

I’d start this “experience” with Auto-ISO on, but then, several months down the line, when you want to take even more control, turn it off. In switching Auto-ISO off it forces you to make decisions about your ISO for each shot. This will be the best way of learning what ISO does and what settings to use – when, why and the impact of those decisions.

Experienced – with plenty of time for each shot

Many professional or experienced photographers would probably argue that if you have time to shoot, then you have time to set your ISO, and that the only way of truly knowing what the camera is doing is for you to be in control. However, even in these situations there is an argument that if you’ve set Auto-ISO appropriately then it’s still fine to use it – provided you fully understand it. It really depends on how much manual control you want to retain.

Experienced – with little time for each shot

You’ll fully understand ISO and all its implications, so there’s no real problem in enabling it and working within the parameters that you’re comfortable with i.e. you set the tolerance you’re prepared to allow for the two values. There are a few books that recommend you turn it off in pretty much all circumstances, but I don’t think that’s right at all. Many experienced photographers will set a minimum ISO according to how they read the light conditions, then enable Auto-ISO and allow it to control ISO within the tolerances they’ve decided that are acceptable for the current situation.

How does Auto-ISO work in the different exposure modes?

Auto-ISO is available in M, A, S, and P modes and works slightly differently dependant on the mode so let’s explore each.

NB: If you’re using Auto, No Flash, or SCENE exposure modes then Auto-ISO is not available. Also, U1 and U2 will be set to your saved exposure mode (M, A, S or P) so Auto-ISO operates in these modes too.

Program (P) or Aperture (A) modes

In Program and Aperture modes, the D7100/D7000 adjusts shutter speed to achieve optimum exposure given your selected aperture. Using your selected ISO, shutter speed is adjusted first, but if maximum or minimum shutter speed is reached and exposure not achieved, ISO is subsequently adjusted.

If you set an ISO higher than Maximum sensitivity, the latter is used in place of your setting as the start ISO. The minimum shutter speed the D7000 can select before increasing ISO is the one you’ve configured as Minimum shutter speed.

If underexposure occurs at the minimum, ISO is increased until exposure is correct. If Maximum sensitivity is reached before optimum exposure, shutter speed is further reduced.  Minimum shutter speed is now ignored and longer speeds are chosen to achieve correct exposure. This could result in shutter speeds that are too long for you.  So be careful, Minimum shutter speed is not an absolute minimum, it’s the lowest the D7100/D7000 will adjust shutter speed to before increasing ISO. If you set a very low Maximum sensitivity value, and/or a high initial ISO value, you will force slower shutter speeds than the minimum.

At the other end of the range, if the D7100/D7000 selects 1/8000s as the shutter speed and overexposure still occurs, ISO is reduced accordingly.

Benefits; it’s a safety net to help avoid motion blur. It minimises ISO.
Best practice; Set ISO to 100. Adjust Minimum shutter speed to a value acceptable for your conditions, subject movement and lens.

Shutter (S) mode

The D7100/D7000 adjusts aperture to achieve optimum exposure given your selected shutter speed. Using your selected ISO, aperture is adjusted first, but if maximum or minimum aperture is reached and exposure not achieved, then ISO is adjusted.

If you set ISO higher than Maximum sensitivity, the latter is used in place of your setting as the start ISO.

ISO is increased if your lens’ maximum aperture is reached and optimum exposure not achieved, avoiding under exposure. Equally, ISO is decreased if your lens’ minimum aperture is reached and over exposure would still occur, although this is highly unlikely.

Once Maximum sensitivity is reached, since the D7100/D7000 will have already selected maximum aperture, it cannot make any more adjustments. The under exposure indicators will appear i.e. “LO” and flashing meter bar.

Benefits; it’s a safety net again, but this time Auto-ISO ensures that you don’t underexpose if you’ve set too high a shutter speed for the available light conditions. It minimises ISO.
Best practice; set ISO to 100. Adjust Maximum sensitivity according to your noise v focus decision process.

Manual (M) mode

You may be surprised to know that if enabled Auto-ISO operates in manual mode too. So watch out for that, since if you change aperture or shutter speed, the D7000 will auto-change ISO to compensate to obtain optimum exposure. This catches people out expecting Manual mode to be totally manual.

In Manual mode, the Auto-ISO setting Minimum shutter speed is redundant. The D7100/D7000 will always use your manually defined shutter speed. Maximum sensitivity is used; the DSLR will only adjust ISO up to your defined Maximum sensitivity value.

The ISO setting you define manually is not used. The D7100/D7000 automatically adjusts ISO, which will mean reducing ISO below or above the setting you’ve chosen.

If Maximum sensitivity is reached and optimum exposure isn’t achieved the D7100/D7000 warns you the shot is underexposed via the flashing meter bar.

Benefits; in manual mode, you’re controlling both aperture and shutter speed to achieve your desired “vision” (getting that bokeh, freezing the action, etc.). Auto-ISO dictates ISO as needed to ensure correct exposure – again minimising ISO.

Best practice; Adjust Maximum sensitivity according to your noise v focus decision process.

All modes (M, A, S or P)

When enabled:

  • Auto-ISO automatically adjusts your ISO to achieve optimum exposure.  The key is that it minimizes ISO without you getting involved; the lowest ISO available is always used to achieve the correct exposure;
  • If you manually set an ISO higher than Maximum sensitivity, then Maximum is used instead of your value;
  • ISO-AUTO will flash on the LCD if Auto-ISO will change the ISO;
  • The ISO number displayed in the meta-data turns red if Auto-ISO has stepped-in.

Remember, you still have the ability to fine control exposure by using exposure compensation.

What about supports (tripods/monopods)?

Using a tripod, or other totally rigid support

In Aperture mode (which you typically are when shooting landscapes for example), I’d generally turn Auto-ISO off, its purpose being negated by the fact that you can have long shutter times – enabled by the rigid support.

In Manual mode, Auto-ISO can be quite useful too though on a tripod. Say you were shooting with a specific aperture and shutter, but you faced constantly changing light conditions – say the clouds keep rolling in and out.  You could use Auto-ISO to hold exposure constant in conditions where light levels are constantly changing. And if you were using a remote release – it would certainly save you keep walking over to the camera for each shot.

Don’t forget, VR/OS off too.

Using a monopod, leaning against a wall or similar

Here you’ve stabilized a lot more than standing free, but you still have movement. Auto-ISO should still be enabled.

What about flash?

Another thing that surprises some people is that when Auto-ISO is enabled, it also operates with flash – both in-built flash and hot-shoe, when in M, A, S or P exposure modes. When using flash with SCENE and Auto exposure modes, Auto-ISO is not operational.

If you use the built-in flash in A, or P modes, both Auto-ISO settings (Minimum shutter speed and Maximum sensitivity) are used.  Minimum shutter speed is used as the minimum until it reaches the value defined in Custom Setting e1. No higher speeds will be set than e1. The default for e1 is 1/250s Auto-FP.

NB: On p104 of the D7000 manual it states “When a flash is used, the value selected for Minimum shutter speed is ignored in favour of the option selected for Custom Settings e1 (Flash Sync Speed).” When you half press the shutter the Minimum shutter speed is used. The absolute slowest shutter speed that will be selected is e1.

If you use the built-in flash in M or S modes, your chosen shutter speed is used. Minimum shutter speed is ignored, while the maximum shutter speed you can set will be e1.

The in-built flash has a default mode of TTL (Through The Lens). In this mode the D7100/D7000 cannot determine the amount of light the flash will fire until the camera’s shutter button is pressed and the pre-flash is returned to allow correct metering to include the light from the flash. If you put a hot-shoe flash into TTL mode it’ll work the same way.

What you’ll sometimes find is that the D7100/D7000 uses a poor combination of weak flash and high ISO, resulting in grainy photos. This happens even when the flash is perfectly capable of providing enough light to use a low ISO.

NB: On p103 of the D7000 manual it states “ISO sensitivity is adjusted appropriately when the flash is used”. A high ISO and weak flash will sometimes be inappropriate, unless you need to balance the background with the subject – which is really the purpose of the slow-sync mode.

NB: On p104 it states “Note that ISO sensitivity may be raised automatically when auto ISO sensitivity control is used in combination with slow sync flash modes“. However, this is true of all flash modes – not just slow sync.

And if you use a hot-shoe flash, things work differently again, but generally, lower ISO values are chosen than with the built-in flash.

NB: Francois Malan has an excellent article covering this if you’d like to read more. There are also discussions on Flickr and DPReview.

There seems to be two possible solutions:
  1. Disable Auto-ISO itself when using flash. I put “ISO sensitivity settings” at the top of My Menu to let me do this quickly at any time.
  2. Set the built-in flash (setting e3) to “Commander” mode, and in its sub-menu to “TTL mode” – thus preventing Auto-ISO from raising ISO. The downside here is that you have to wait for a longer pre-flash sequence.

What settings should you use?

The default settings for “Auto ISO sensitivity control” are:

  • Maximum sensitivity                    - 6400
  • Minimum shutter speed               - 1/30

But are they OK to use, or should you change them? Well, for most people, you should change them, dependent on numerous factors as I’ll explain below. What you should change them to depends on several factors; light conditions, your subject’s movement, the lens you have fitted, supports (e.g. tripod), and your ability to shoot at slow shutter speeds.

Let’s look at the two settings separately.

NB: Please remember this is a guideline approach to how you should consider your settings. You may elect to include/exclude which ever factors you deem appropriate/inappropriate, or alter values to those you deem appropriate to your situation. This is not an exact science.

Selecting an appropriate Minimum shutter speed

Factors here to consider should include; the maximum focal length of the lens, availability of image stabilisation on the lens (i.e. Vibration Reduction on Nikkor lenses or Optical Stabilisation on Sigma lenses), camera supports and hand-holding abilities.

So, how do we calculate minimum shutter speed? This is my recommended process:

  1. Calculate the inverse of the maximum focal length (NB we need to multiple by 1.5 due to the crop factor)
  2. Allow for VR/OS;
    • VR helps you stabilize an image when you are using slow shutter speeds and don’t have rigid camera support. VR does not help you keep a moving subject from being blurry. The only way you can do that is with a faster shutter speed. What we are interested in here is how low we can set minimum shutter speed, so VR consideration is very important.
    • How many stops does image stabilisation give you? That’s debatable, subjective, and variable by lens and distance. For many lenses Nikon claims 4, but what about real-world experience/findings? You’ll probably need to test your lens or ask questions in forums. For the purposes of this exercise, let’s say 2 stops as a rule of thumb.
  3. Allow for supports;
    • If you’re always leaning on or against something (bean-bag/monopod etc.) you could perhaps reduce by another 1 or possibly even 2 stops. This is debatable and experience varies. If you chock the monopod against something, or use it as one leg of a tripod with your legs as the other two, my experience is that you can gain maybe 1 stop.
    • Ignore tripods here – they obviate Auto-ISO due to long shutter times being available.
  4. Allow for your hand-holding ability (if not using supports);
    • Some professional/experienced photographers are extremely good at taking shots hand-held at slow shutter speeds. They’ll have developed techniques and refined them over a long period of time. Those lucky enough to have these skills can consider reducing shutter speed by yet another one or two stops, but obviously there’s a limit to this, which many believe is near 1/30s.
    • If you’re relatively new to photography and believe you need to develop these skills then set a higher minimum shutter-speed than the default of 1/30s. If you believe you hold the camera steady, hold your breath, squeeze the trigger, have learnt how to hold it correctly etc. then choose 1/60, else I’d suggest 1/125.
  5. Round up to nearest shutter speed above the value calculated to avoid shake.
NB: Digital Photography School have a good article on how to hold a digital camera.
Let’s apply this to various lenses and use situations, and see what we get:

Nikon AF-S NIKKOR 50mm f/1.8G Lens, no support, used by a pro:

  • Crop factor; 1/50  x  1.5 = 1/75
  • Good hand-holding; 1 more stop down = 1/37.5
  • Round up; 1/40s

Sigma 24-70 f2.8 EX DG HSM (non OS lens), no support, average hand-holding:

  • Crop factor; 1/70  x  1.5 = 1/105
  • Round up; 1/125s

Nikon 18-200mm f/3.5-5.6G IF-ED AF-S VR DX Nikkor lens:

  • Crop factor; 1/200  x  1.5 = 1/300
  • For VR; 1 stop down = 1/150; 2 stops down = 1/75
  • Round up = 1/80s

Sigma 150-500 f5/6.3 DG OS HSM lens – used on a “steadied” monopod:

  • Crop factor; 1/500  x  1.5 = 1/750
  • For OS; 1 stop down = 1/375, 2 stops down = 1/187.5
  • For the monopod; 1 stop down = 1/93.75
  • Round up; 1/100s

Your lens:

  • Scroll to the end of this article!

Best practice; calculate what you believe is the minimum for your lens/scenario, take some sample shots at that minimum shutter speed, check focus and adjust as needed.

Selecting an appropriate Maximum sensitivity

The highest value Maximum sensitivity can be set to is; Hi2 (ISO 25,600 equivalent). Its default is 6400.

Factors to consider for setting the maximum should include:

  • How much is the subject moving?
  • Is sharp focus imperative, even at the cost of increased noise?
  • What’s the purpose of the photo and where is it going to be used?
  • Are you working in low light?
  • How fast is your lens? I.e. what’s its maximum aperture?
  • What’s the range of light in the shot?
How high you set the ISO depends on your tolerance to noise. Noise is the amount of grain in the photos. The D7000’s manual states noise is “…..randomly-spaced bright pixels, fog or lines”. Higher ISOs result in higher grain. At ISO 100 you have the best quality, but at ISO 6400 there is some grain. It also depends on how fast your subject is moving, and whether you need it sharp. It’s always better to have a grainy photo, than an out-of-focus one. So, if you’re shooting moving subjects, you’ll need higher shutter speeds that can be enabled if needed by higher ISOs. Set Maximum sensitivity to 3200 or even 6400. If you’re shooting relatively stationary subjects in good light you can lower this.
So is noise an issue? Well, pretty much everyone agrees, the D7000 has much lower noise than many previous DSLRs at 6400, so this might be fine for you. If you’d like slightly better picture quality, run with 3200 or even 1600. For an “all-round” general use setting I’d recommend 1600.

NB: ImageLabs have an excellent review that shows the D7000’s ISO and Noise performance. You can check out how much noise is visible at various ISOs here.

Why is subject movement a consideration? Well, you really need higher shutter speeds to freeze motion, and a high ISO might be the only way to achieve that. Dynamic range is also a consideration, since at both 3200 and 6400 dynamic range is reduced.

NB: Digital Photography School discuss limiting Auto-ISO here.

Best practice; take some shots with ISO set at 6400, 3200 and 1600 in low light conditions, check out the noise/dynamic range and make a decision yourself.

When would you suggest using it?

I’d recommend using it in numerous scenarios and perhaps even professions. For example, sports photographers, photojournalists and maybe private-detectives would probably consider using it all the time. They have little time for camera settings, but must always get the shot. They always need sharpness in favour of increased noise.

Personally, I recommend using it in any situation where you have little time to adjust camera settings, need sharp focus at the cost of noise, and you’re facing variable daylight conditions. Let’s take three situations I’ve been in, where it’s been useful:

Situation #1

During a Mediterranean cruise, we took numerous trips which had guided walking tours. The light was extremely variable, sometimes being outdoors in bright sunlight, then indoors (no flash allowed frequently), then in light shadow – on to deep shadow etc. Take walking around Pompeii for example, that included all those lighting scenarios and more; walking through the ruins and into several buildings. On each of the walks, the Guide talked through some history and moved on – due to timescales. There’s no time to make camera adjustments, you’re pretty much in a point and shoot situation. Read more!

Situation #2

I was photographing a wedding at a hotel, where they didn’t want flash during the ceremony. Following the bride and groom out of the ceremony area, they passed through numerous rooms, lobbies, corridors, atriums etc. Highly variable lighting conditions all on one walk. In the afternoon and early evening at the reception, I was walking around taking shots of guests, again in variable light conditions. And wanted normal skin tones – so didn’t use flash. I was talking to people, and taking casual shots, but didn’t want nor have time to adjust settings.

Situation #3

I was taking photos of wildlife in Canada. Shooting birds, bears, deer and lots more. Animals don’t sit still for very long, you need to concentrate on the shot, not ISO. So Auto-ISO frees up precious time for getting the shots. For example, I was following an osprey in woods, and Auto-ISO helped while tracking it across trees and sky.

So why does it have such a “love-hate” relationship?

I think many people that “find” Auto-ISO, that understand the photography triangle intimately, and want to minimise ISO without worrying about it, end up loving it. It’s extremely useful in variable daylight conditions for example. Some people are very keen to promote it; it’s almost a hidden gem that everyone should know about and use! However, without that “understanding”, it can lead to variable results, and maybe that’s a reason why some people end up disliking it; they see too much noise due to too high ISOs, especially if the default Maximum sensitivity is kept, since 6400 does produces visible noise on the D7000.
The D7100 seems to produce more noise than the D7100, due to the removal of the optical low pass filter. The images are considerably sharper however. The extra noise can be removed fine in software.
Another factor is tradition. Some photographers trained many years ago may have a strong preference for controlling everything manually, and dislike Auto-ISO because it removes control. For those in this camp, the fact that Auto-ISO works in Manual and flash can be a surprise!
And I also think “ISO history” is a factor. We all know that high ISO’s result in noise, but at what ISO is noise unacceptable? Of course that varies, according to DSLR capability and age. DSLRs even from two or three years ago still had noise at what I would call mid-range ISOs. However, the new Nikon D800 and CANON 5D Mark III produce exceptionally low noise. As Martin Bailey says about the new Mark III, “ISO 6400 is the new ISO 800”. So you could have used Auto-ISO some years back and been turned off due to the noise levels on the DSLR you were using then. Things have changed though – it’s time to re-evaluate when you replace your DSLR.

Quite simply the game keeps changing and in twenty years’ time, Auto-ISO will probably be a moot point anyway, since there may be no noise at high ISOs!

Conclusion

The key here is to fully understand ISO, the values, and the consequences of those values. You need to understand how ISO is associated with shutter speeds and aperture. With understanding of those values, you need to set appropriate Auto-ISO settings for your current shooting situation.

If you’re an absolute beginner, turning it on means you can concentrate on shutter speed and/or aperture. If you’re further down the learning curve and beginning to take control, turning it off gives you greater learning potential. If you’re experienced, understand implications, and think through your Auto-ISO values carefully, Auto-ISO can be fun and a great safety-net.

If you’re “old-school”, or perhaps switched from another manufacturer, then OK – feel free to turn it off if that’s your preference, but accept that others are validly doing something different with ISO and that you’re almost certainly missing out on an excellent and useful feature. If you’re strongly in favour of Auto-ISO, remember too that some photographer’s preference will be to control ISO manually – that’s their preference!

Be careful with flash! Read up before shooting Auto-ISO with flash.

And lastly, remember that if you do leave it enabled, each time you change a lens you need to think through your Auto-ISO Minimum shutter speed.

I don’t have Auto-ISO on all the time; I switch it on when I see a situation demands it. It’s truly a great failsafe for any situation where you face little time to adjust camera settings and variable daylight. My Menu lets me enable/disable it quickly.

Summary

So, should you use Auto-ISO?  It depends – on numerous factors including; experience, knowledge, profession, shooting circumstances, lighting conditions, flash/tripod use and lastly and possibly primarily – personal preference.

Hand-Holdable Minimum Shutter Calculator

Calculate the minimum for your lens:

  • Enter your lens maximum focal length, crop factor & hit calculate:


By camerablur.com

 

What’s your view of Auto-ISO?

Are you in the “love-it” camp? Or are you an “Auto-ISO hater?” Why do you feel that way?

How do you use Auto-ISO?

Go on – stop sitting on the fence!

4 comments to Debating Auto-ISO

  • thills

    Love it!

    I just can’t see the issue, you balance the triangle in your own way with auto iso “on” exactly the same way you would manually setting all three.
    If you don’t like the ISO (have your camera set to display it, not frames remaining), change shutter or aperture – your choice.
    This way your covered for an exposure change just as you shoot.

    I do always use M mode though, I know what I want from the shot & so the order of priority.

    For me, prints are just great up to 3200 ISO @ 16 x 20.
    You can pick any image apart on a screen if you zoom in enough.

    TH

  • Ronmio

    I’m in the “safety net” camp. Although I try to avoid noise, and the post-processing that it involves, I would rather make sure I get shots with my preferred depth of field and desired amount of motion blur. Auto ISO means I don’t have to fiddle with the third leg of the exposure triangle when the camera can figure it out for me.

  • boston

    i find the auto iso a very useful feature for macro work. i use the sigma 150mm, nikkor 60mm and 105mm. i keep an eye on the iso value in the viewfinder and only use flash as a last resort. i only started using this feature recently when i took my camera out without spare batteries for my macro flash. it has made a noticeable improvement to my work. wish i had used it years ago. (the d90 also has auto iso). it has shown me how well the d7000 can cope in lowish light situations.

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