The Easy Guide To Understanding Mirror Lock-up

Mirror lock-up sounds really iffy and risky, but it’s really quite simple.

Do you use an SLR?

When you look through the viewfinder, the image you see is courtesy of a mirror. When you press the shutter, the mirror has to firstly swivel up out of the way of the light path before the sensor captures the light coming through the lens – this action you see as a dark flash in the viewfinder immediately after pressing the shutter release.

When the mirror moves out of the way it slightly vibrates the camera. Not much, but more than the act of pressing the shutter release.

If you are taking a fast shot, this vibration, along with the vibration of pressing the shutter, doesn’t factor.

But for a long exposure it will reduce your clarity.

So, for the shutter release, we can use a remote release to avoid that vibration.

And for the mirror swivel vibration we can use mirror lock-up. How does it work?

When “enabled” – usually as a Custom Function, you take a photograph by pressing the remote shutter release twice.

First press and the camera goes “kerplunk!” as the mirror swivels out of the way. Second press and you hear a small “click” as the shutter opens, along with the red light appearing on the back of the camera indicating the shutter is open.

Not all digital SLRs have mirror lock-up as an option, and it is hard to do a search to create a list of the ones which do. However, as far as I can tell, the Canon EOS 20Da, released in 2005, was the first Canon digital SLR to offer it, and hence if you have a later model, eg 30D, 40D etc, they should all have it.

If you don’t have a remote shutter release, but rely on the self-timer, it seems the mirror lock-up will only work with a 2 second delay on some Canon digital SLRs, not 10 seconds. This is the case for certain at least with the Canon EOS 500D (aka Rebel T1i or Kiss Digital X3)



Originally published 16 October 2009 on
Republished 11 December 2010 on Peter Hill’s Weblog

Posted in mirror lock-up, photography, photography tutorial, tutorial | Tagged , , | 1 Comment

The Easy Guide To Understanding ISO


Recently I was asked to write a tutorial explaining ISO. This is it. I try not to get too technical, but this is one digital photographic concept that is immersed 100% in techo geekdom, so bear with me.

What does ISO stand for?

We have the ISO to thank for ISO. The ISO is the acronym of the International Organisation of Standards. (Yes, I know it should be IOS, but it isn’t, ok?) The ISO settled on “ISO” for the photography world as an abbreviated word as it stems from the Greek word isos, which means, in English, “equal” (eg isometric). Cute, huh?

Some say ISO is pronounced eye so and some, including me, say it as eye ess oh. Whatever. The term ISO replaced the term ASA, which stood for the American Standards Association, or maybe the Australian Scripture Assembly. Who really knows?

What is ISO?

ISO refers to the sensitivity of film to light according to speed of exposure. The higher the ISO rating, the more sensitive the film is.

The equivalent concept applies to digital cameras, where it is all about the sensitivity of the camera’s sensor to light.

Just stop now and think about this. It is a big difference between film and digital….

Choice of film is very important to a film photographer. The choice is 99% about ISO and 1% about colour or B&W. This is because using a film with an ISO 100 rating means putting into the camera a roll which will produce noiseless (non-grainy) photographs able to be shot in nice clear light conditions at high speed, whereas using a film with an ISO 1600 rating is preferable for low light conditions as the film is way more sensitive to light.

Once you’ve made that choice of ISO rating when shooting with a roll of film, you are stuck with it for the whole roll, with 2 exceptions. First, now you know why some cameras have interchangeable “film backs”, whereby an unfinished film roll at, say ISO 100, can be swapped for another unfinished film roll at a different ISO rating. Second, and this is something I do all the time when shooting with film, you can “trick” the camera into thinking it is shooting with, say, ISO 400 instead of ISO 100 by manually changing the ISO setting. (I did try upping ISO from 100 to 1600 on a rafting trip once, but the camera was on to me and produced crap. More recently I upped an ISO 25 roll to ISO 100 as I was shooting inside.)

Digital photography, however, affords us the luxury of calibrating the sensitivity of the sensor with each shot with equivalent ISO settings to film ISO ratings. Thus, sRGB image files created by a digital camera will have a similar lightness to what is achieved with a film camera using the same ISO rating, aperture, and speed. Setting the ISO on a digital camera is actually adjusting the sensitivity of the sensor. It is a pro-active process, as distinct from film, which is a re-active process.

What ISO setting should I use?

As a general proposition, the lower the ISO setting, the better. For example, and ignoring aperture for the moment, consider these two options for taking the same evenly exposed hand-held shot (approximately) of a non-moving object:

  • Speed of 1/1000th of a second, ISO of 1000
  • Speed of 1/100th of a second, ISO of 100

Which is preferable? ISO 100. There are several reasons. First, a speed of 1/100th of a second hand-held will rarely give you blurred images. It is fast enough to capture the object with a well-focused and sharp image. Second, the higher the ISO, the greater the noise from stuck pixels and grain.

Why is this? It’s because as you increase the ISO setting and make the sensor more sensitive to light signal, you are also making the sensor more sensitive to noise coming from everything in the frame, not just your light source or subject.

The higher the light signal to noise ratio (the S/N ratio), the better the image quality. Digital cameras are calibrated to achieve the greatest S/N ratio using the lowest available ISO setting. The smaller the sensor, the greater the problem with noise at high ISO. (Attention all geekheads – this is a general proposition, ok!)

Noise in the form of stuck pixels and grain can be dealt with by noise reduction applications, either in-camera or in post-production. However, it’s a bit like hitting a nail with a sledgehammer as the apps also remove detail from your image. And, in the case of noise-reduction in-camera, the application takes just as long as your shutter speed. Therefore, if you take a 120 second exposure with Noise Reduction “On”, the camera will then take another 120 seconds to do the noise reduction before you get to see the image on the camera’s rear LCD. As I said somewhere else, I’m a patient man but not that patient! (Technology is getting better, however, with in-camera noise reduction.)

So….. the idea is to use as low an ISO as possible. A suggestion would be to not let your camera choose an ISO for any shot (Auto ISO) but set it to ISO 100 (or your camera’s minimum ISO) as your default, and only increasing it when there is a need to compensate for poor light and you don’t want to stop down your aperture any more or shutter speed.

For example, my camera (EOS 5D Mark II) allows me to set the ISO to 50 as a Custom Function. This is my default setting. There are times however, when I want to take a shot without stopping down further than f8 (because I want a wide DOF) and without slowing down more than 1/30th second (particularly if I am shooting hand-held), but the light won’t let me get a good exposure. Changing the ISO is always my third and last option. Upping the ISO to 100 instantly means I can shoot faster, and thus avoid a blurred image, and I will routinely go up to 640 without hesitation. And to tell you the truth, there is bugger all difference that I can see between ISO 50 and 100. (Except for long exposures, where ISO 100 is probably preferable. But that’s another story.)

As a general proposition, the smaller the sensor, the bigger your problem with ISO noise and grain is going to be, sometimes even kicking in at ISO 400 (and rendering images unusable at 800 or 1000). This can be important when choosing a digital camera to buy.

Buying a camera and ISO

If you are in that position, check the ISO range of the potential purchase. The standard for a lot of digital cameras, even now, seems to be Auto, 100, 200, 400, 800, 1600, 3200, which, for example is the range applying to the Sony Alpha DSLR-A390. That’s not exactly a great range for a brand new model, to be honest. Apart from severely limiting your shooting options, I would want to make sure the camera can actually produce usable images at ISO 1600 and especially ISO 3200. The Sony Alpha DSLR-A390 has only one more ISO setting than the much older Olympus E-520 (3200) so you have to wonder where Sony’s ISO heads are at. I mean, look at the Olympus E-620, which was released a year ago. It’s ISO range is 100, 125, 160, 200, 250, 320, 400, 500, 640, 800, 1000, 1250, 1600, 2000, 2500, 3200. Now you’re talkin’!

So, if you are looking at which camera to buy, take the time to check out its ISO range as they can vary grealty. Also check out the camera yourself shooting at high ISO or take the time to research on-line for an in-depth review which covers ISO performance.

Still on the Nikon D700, it’s default ISO settings are in the range 200 to 6400, with a low boost to 100 and a high boost to 25600 – the same as the Nikon D3. The Nikon D300 has a default range of 200 – 3200, with a low boost to 100 and a high boost to 6400. Canon is much the same. The EOS 5D Mark II has a default range of 100 to 6400, expandable to 50 and 25600.

The reason why the “extreme” ISO settings are available separately, on any digital camera, is to do with calibration. The default range is the calibrated to international standard range, whereas the expandable settings are not.

I could go on and on about ISO, but I reckon I’ve said enough to get you started.



  1. Tutorial first published 30 June 2010 on
  2. Republished 11 December 2010 on Peter Hill’s Weblog.
Posted in iso, photography, photography tutorial, tutorial | Tagged , , , , | 18 Comments