With TTL flash units you can normally disable the TTL mode and revert back to the older-fashioned manual power mode. Note: ‘manual’ here refers to a mode on the flash unit and is completely unrelated to and not to be confused with the ‘manual’ shooting mode of the camera itself. Typically, you can set the power in manual flash mode to full power (1/1), half-power(1/2), quarter-power(1/4), one-eight power(1/8) etc. With higher end flash units, you can normally also choose third stops between these settings.

How do we know what power is needed to correctly expose our main subject in an image? Well, one way would be to use a light meter on our subject in much the same way as a light meter is used in a studio with strobe lights – i.e. set the shutter speed and ISO to target desired levels on both the camera and light meter and then adjust the power of the flash and/or the distance of the flash from the subject in order to achieve a target aperture value. This is an iterative process until the desired aperture is reported by the light meter based on adjustments made to the flash power output or adjustments to the distance between flash and subject.

Another way is to use the Flash Guide Number. I have two Canon Flash units and two Sigma Flash units. The Canon flash unit model names are the EX430 and EX580. These have respective guide numbers of 43 metres and 58 metres respectively. Can you see the relationship to the model name? Both my Sigma units  are ’530 DG Super’ models with a guide number of 53 metres.

So, what does this guide number mean?
Answer: The guide number is the product (or multiplication) of the distance to the subject by the aperture value – i.e.  Guide Nr. = distance x Aperture.  It is normally quoted at ISO 100 so that guide numbers can be reasonably compared.

Example: In the case of the Canon EX580 which has a guide number of 58 metres, the guide number tells us that we can photographically illuminate a subject 58 metres away if we use a lens with an aperture of 1.0 and we are shooting at ISO-100 with the flash set to full-power. One further constraint is that you will normally only achieve the maximum guide number distance when shooting at longer focal lengths (longer zoom) – e.g. in the case of the EX580, the 58metre value is only quoted for a lens focal length of 105mm. This is referring to the zoom of a lens inside the flash unit that in auto zoom mode adjusts to narrow the beam as the focal length of the lens increases. You can, however, achieve your 58metres on a wider angle shot if you switch the zoom mode on the flash to manual and adjust it to a value of 105mm manually on the flash unit.

A more realistic example: Most of us do not have an f/1.0 lens. The average low cost zoom lens starts at about f/3.5 or f/4.0   Let’s assume we are shooting at f/4. What then is the maximum distance I can place between the flash and the subject in the case of my EX580?
Answer:  Using the rule,   Guide Nr. = distance x Aperture.   i.e. 58m = distance x 4  …. for an aperture of f4 meaning that the distance is 14.5metres as 4 x 14.5 = 58. Again this assumes I am shooting with the flash lens zoomed to the equivalent of 105mm and that my ISO is set to 100 and that my manual power is 1/1. If I increase the ISO, I can actually increase the effective guide number or distance to the subject. However, if I decrease the zoom on the flash (either manually or linked to the lens zoom), the beam spreads wider and will not reach the maximum distance at the required strength.

Why bother with manual flash when we have TTL flash?
I generally don’t bother with it myself, but there are situations where it is useful. Firstly, if you have an old flash unit or a cheap modern flash unit, it may not support TTL mode. Secondly, TTL flash can be a bit hit and miss – e.g. if the camera picks up a ‘false’ subject closer to the lens than your intended subject. In manual mode, the flash should always consistently fire out the same amount of light from shot to shot if the settings have not changed. Thirdly, if you want to set up flash ratios with multiple off-camera flashes, this is probably easier and quicker to do with manual flash mode using a light meter – or at least it’s probably quicker if you are used to setting up studio lights with a meter.  Yes, I know … you can prescribe flash ratios with off-camera TTL flash units if you have the right types of compatible flash units but to my mind, this takes longer to do with all the settings that are required. But maybe that’s just me.

What happens your distance if you reduce the flash power?
For example, let’s say you are using a flash with a guide number of 60 metres at full-power and an aperture of f/4 allowing you a distance of 15metres between flash and subject. What happens if you reduce the power from 1/1 to say 1/2 ?  You might think the distance would reduce by a factor of 2, … but it doesn’t. It reduces by a factor of 1.414 (which is the square root of 2 for the mathematically inclined among you). In other words, the distance would fall from 60 metres to 42.43 metres. If you further reduced the power again to 1/4, the distance would fall by a further factor of 1.414 bringing it down to 30 metres ….. which interestingly is half the original distance of 60metres.

Why does shutter speed not feature in the guide number rule?
If the primary source of light in the photo is from the flash rather than from ambient lighting (i.e. we are not talking about ‘fill flash’), then shutter speed does not really feature in the equation. This is because the burst of light from the flash is so intense that it effectively dwarfs the effect of ambient light on the exposure. This is true up to a point but eventually if you progressively slow down the shutter speed, there comes a point where it does contribute noticeably to lighting the subject.
Consider a simple analogy that might help make this clearer. Imagine you are filling a bucket of water with a slowly dripping tap and the hose from a fire engine both at the same time. Let’s say it takes the fire hose one second to fill the bucket and it takes the dripping tap 5 minutes to fill the bucket when operating independently. When both sources are filling the bucket together, if the fire hose is switched on for approximately one second and then turned off, it doesn’t really matter if the dripping tap is left on for one second or several seconds. It has a negligible effect relative to the fire hose. Similarly, in low light situations, ambient light has a negligible effect on exposure relative to the intensity of the light coming from the flash unit.

Just to complicate things further, here’s another thing that might surprise you. Shutter speed, aperture and ISO affect your background exposure. However, in theory with TTL flash mode, none of these affect your subject’s exposure. This is because, within reason, the idea of TTL flash is that it will blast enough flash at your subject to light your subject properly irrespective of what combination of shutter speed, aperture and ISO you have chosen. Of course if your settings are such that the image would be over-exposed without flash, it stands to reason that the flash is not going to darken it down for you!
The photo below was taken at 6:14PM on 4th Feb 2012 in Ireland. In other words, even though I could see clearly, light was starting to fall. I deliberately put my camera in P-mode (programme-shift) and set my flash unit to TTL with no compensation applied. ISO was set to ISO-100.

P-mode with TTL-Flash (ISO-100, F/4.0, 1/60th sec)

Analysis:  When you put your camera into P-mode with the flash in TTL mode in falling light, the camera will attempt to get you a ‘hand-holdable’ shutter speed – in other words about 1/30th or 1/60th sec. To achieve this, it will open up the aperture as wide as it can (or as wide as it needs to ) and then if that is not going to adequately expose the subject, it will blast just enough flash at the subject to properly expose your subject. In this mode of operation, the camera does not care about your background. It is simply concerned with lighting your subject. This can be seen in the photo above. I could clearly see my subject and the background but yet the photo shows a heavily under-exposed background.

So, what do I do if the background is important to me? Say for example, I’m photographing a wedding couple beaming with pride in front of the castle they have paid a small fortune to hire for the occasion. They won’t be happy if the castle does not appear in the background.

Here are the steps with photos to show it works:
Step 1: Switch your camera to manual M-mode and although not necessary, you might like to start with the settings that failed miserably in P-mode just to have a reference starting comparison point. Keep your flash in TTL mode. If you take a photo now, you will get the exact same result as you did in P-mode because you are essentially forcefully replicating the settings the camera chose for you in P-mode.

Step 2: You now have four ways of increasing the background lighting while maintaining the proper subject exposure. These are:
(i)  increase your ISO
(ii)  slow down your shutter speed
(iii) open up the lens aperture
(iv) a combination of the above

Let’s look at these in turn and discuss some advantages and disadvantages of each.
(1) Increase your ISO:  In manual M-mode, if you leave your shutter speed and aperture setting unchanged but increase your ISO, the background will start to brighten up as you would expect when you increase ISO. Interestingly, your subject does not brighten up. This is because your camera knows the ISO has been increased and this information is communicated automatically to the flash unit. As a result, the flash unit knows that to maintain proper exposure on the foreground, it must slightly reduce its flash power output (in reality it reduces the duration of the flash but this is effectively the same as reducing power). So the subject lighting remains unchanged when the ISO is increased but the background gets brighter. This is because the flash has no effect on the background so the fact that it has reduced in power is irrelevant to the background. The background is brighter simply because the ISO has increased. While this same ISO increase in theory also brightens your foreground subject, this is compensated for by a reduction in flash power resulting in zero net change.

The series of photos below shows what happens as I progressively increase my ISO value without changing anything else. As can be seen, we go from having no visible background to a normal visible background with negligible change in subject lighting.

M-mode with TTL-Flash (ISO-200, F/4.0, 1/60th sec)

Now let’s try increasing the ISO from 200 to 400 without changing anything else.

M-mode with TTL-Flash (ISO-400, F/4.0, 1/60th sec)

We are now clearly starting to get a brighter background. Let’s increase the ISO again by one stop – i.e. from ISO 400 to ISO 800.

M-mode with TTL-Flash (ISO-400, F/4.0, 1/60th sec)

The photo above is probably closest to the actual light as perceived by my eye.

Now let’s try one final increase from ISO 800 to ISO 1600.

M-mode with TTL-Flash (ISO-1600, F/4.0, 1/60th sec)

I’ve now reached the stage where I am arguably over-exposing the subject because my ISO, shutter speed and aperture combination are over exposed for the ambient light on the subject.

Let’s summarize on ISO:
By progressively increasing the ISO, the background became progressively brighter. The foreground subject lighting remained more or less unchanged because in each successive photo, the flash intensity or power was reduced to exactly cancel any brightening as a result of higher ISO.
The disadvantage of doing this is that the photo will become ‘grainier’ or exhibit more ‘ISO noise’. How much noise it exhibits depends on the camera model and whether it is a full-frame camera or an APS-C or other camera. It also depends how recent the model is as there are regular improvements in high ISO performance with each new sensor technology released.

Now, let’s look at changing the shutter speed.
(1) Slowing down your shutter speed:
Let’s start with our reference photo again to set the starting reference point.

M-mode with TTL-Flash (ISO-100, F/4.0, 1/60th sec)

 Now let’s slow down the shutter speed from 1/60th sec to 1/30th sec. This allows more time for light to hit the sensor and will result in a brightening of the background. In the case of the foreground, the flash simply fires with slightly less power resulting in no noticeable foreground exposure change.

M-mode with TTL-Flash (ISO-100, F/4.0, 1/30th sec)

Let’s slow down the shutter even more and watch the background brighten further below.

M-mode with TTL-Flash (ISO-100, F/4.0, 1/15th sec)

And now from 1/15th sec to 1/8th sec.

M-mode with TTL-Flash (ISO-100, F/4.0, 1/8th sec)

And finally from 1/8th sec to 1/4 sec.

M-mode with TTL-Flash (ISO-100, F/4.0, 1/4th sec)

Now let’s summarize on shutter speed:
By progressively using a slower shutter speed, the background became progressively brighter. The foreground subject lighting remained more or less unchanged because in each successive photo, the flash intensity or power was reduced to exactly cancel any brightening as a result of effective increases in ambient lighting.
The disadvantage of doing this is that unless you are using a tripod (as I was), you are going to get a progressively more blurred photo because I’ve yet to meet anyone who can hand hold a camera at 1/4 second and consistently get sharp images that can stand up to enlargement. Even with a tripod, you have a problem if your subject moves. That said, most adult subjects can hold a pose for about a second if requested to do so.

Overall Summary (so far)
As you can see from the photos, increasing ISO and slowing down your shutter speed both increase background lighting without (up to a point) affecting foreground exposure. Obviously you can temper the disadvantages of either method (ISO noise on the one-hand and potential blur on the other hand) by changing both a little bit instead of changing one on its own in a more extreme way.

You might also reasonably ask, what’s the point of flash if I’m simply going to adjust my exposure control settings to the point where I am exposed properly for ambient as is the case for the last one or two photos in both the ISO and shutter speed variation cases. Well, let’s reconsider one of the original scenarios I considered where a couple have hired a castle as their wedding venue. What I want to achieve here is at least a sense of the background. If the background is black or near black, no-one will see it. If I go too far with my ISO or shutter speed and either get a very ‘noisy’ photo or a  noticeably blurred photo, then this is not good either. If I go for a in-between trade-off where the couple are nicely exposed and the castle is somewhat underexposed but clearly identifiable as a castle, then everyone will probably be reasonably happy.

Photography is all about trade-offs and unless you know and understand your camera and flash settings, then you are not in control of the trade-offs.

Okay, there’s a lot more to flash and a lot more to come in this article.

Update: Actually there isn’t more to come in this article because I’ve decided to put the rest in separate articles. As of today (6th Feb 2012), I’ve put the first of these related posts covering the topic of manual flash and guide numbers in the following article.

Hi-key shot from previous course

We are running our popular weekend 3-person 2-day studio photography course on the following dates in January and February.

Course-1:  Sat/Sun 28th & 29th Jan 2012  (this course now full as of 7/1/2012)

Course-2: date changed to  …. Sat/Sun 10th & 11th March 2012  (two places remaining as of 5/1/2012)

Both courses are the same – i.e. the March course is a rerun of the Jan course. The maximum number of students on each course is three. This is a hands-on course where you will get a lot more practice than is the case on some shorter courses out there that take 8 to 10 students on each course.

For course details, click here to visit the course info page.

For a video overview of the course, click here.

I’ve just created a blog for offering Junior and Leaving cert grinds in Ennis, County Clare. Click here to visit. I currently teach maths and physics to degree level on engineering programmes, so I’m offering grinds in these two disciplines at both Junior and Leaving Cert level. My wife is a fluent French speaker (12 year living and working in French speaking countries) who also has teaching experience and she is offering grinds to Junior cert level in Ennis.

Anyway, I have learned a lot since I joined – even on topics that I felt I already knew quite well. Let me give you some examples:

1. Composition:  I’m a bit of a camera technocrat. I teach the physics of light and lenses in a third level college and in an earlier career as an electronic engineer, I used to design component parts  for digital imaging products (industrial cameras, image compression systems etc.). However, I have always acknowledged a weakness on composition but I have learned a lot about this from talks in the club, field trips with the club and viewing other people’s photos on our club’s Flickr site.

2. Taking photos instead of talking about taking photos: I’ve found that being in the club encourages me to use my camera more often. This can be as a result of an interesting talk on a specific topic where I want to try some related ideas out or it can simply be from participating in our outdoor field trips.

3. Topics I already know very well: No matter how well you know or think you know a topic under discussion at your club, you will nearly always pick up some new angle by hearing it from someone else. Maybe it’s just a slightly different way of doing something you already do.

4. Chance incidental know-how: Here’s a very specific example but a good example. We were on a field trip recently when I complained to a fellow club colleague that my Manfrotto 322 ball head tripod was frustrating in that it severely limits the amount of upward tilt of the camera when the camera is mounted in landscape orientation. This is true …. if you have the grip facing back directly behind you. However, as my colleague showed me, if you mount the camera such that the grip is sticking out to the right, it does allow as much upward tilt as you need! There are two arrows on the baseplate to allow either type of positioning of the grip. I was aware of these arrows but I simply never thought of trying the other position. You might say this displayed great ignorance on my part. Well you’d be right.  But that’s exactly my point. I learned how to solve this problem in a chance way and I find you learn lots of little incidental things like this on a camera club outing. In my experience there are very few camera ‘experts’ out there, who really know everything about their equipment. Everyone can learn from everyone else.

5. Specific Club Talks: In a typical camera club, there are regular talks given by either guest speakers or the club’s own members on a given topic. You can learn a lot from these. One example that springs to mind for me was when a colleague in the club gave a talk on HDR (high dynamic range) photography and some of the software tools available to experiment with this. Now I knew of the concept and had practised it to a limited extent in a manual sort of way by blending layers in Photoshop with different exposures of the same scene. However, I was unaware of the capabilities of the latest batch of software tools that do this automatically for you. My colleague, by his own admission knew little about HDR before he volunteered to give the talk but he went off and researched it, took some photos and tried out some of the automatic software available to do the job. I learned a lot from listening to that talk and he learned a lot by doing the research for it. Click here to see a sample photo taken by my colleague for that talk. By his own admission it was a chance photo opportunity and he didn’t have time to whip out a tripod for stability … but I think it’s quite a striking photo.

So, in conclusion, if you’re in two minds about joining your local club, my suggestion is give it a go. By their nature, talks at any camera club are hit and miss. You can occasionally have speakers with great knowledge but who don’t know how to impart that knowledge very well or you might find that the topic under discussion is of no interest to you on a given night, but overall if you give it a bit of time, I think most people will both learn a lot and enjoy participating in camera clubs.

… my second video tutorial today … feeling very productive

Click here to view the video tutorial.

This video tutorial shows how to email photos using Picasa. You need either a Gmail address or else a proper email application program such as Outlook or Thunderbird. If you don’t have any of these, my advice is go and create a free Gmail a/c for yourself. You can still continue to use your regular email address as before but just use your new Gmail address for emailing photos. It’s so easy, it’s actually worth doing this!

Picasa Photo Collage

I’ve added a video tutorial (approx. 10 mins long) on how to create collages using Picasa. The emphasis is on the picture pile type which looks a bit like a traditional pin board collage. Click here to jump to the video tutorial page or select it from the dropdown menu on the training videos tab. It’s very simple to do and makes for a great unique gift.

If you manage to create some nice collages using this technique, why not have them block mounted by us (or board mounted as some call it). You email the image and we post you back the block mount – it’s that simple. Block mounts make great gifts for your friends or you can always treat yourself instead. To find out more about our block mount service (how it works, pricing etc.), visit our block mounting page on the main website. The pricing on the block mounting page is for ROI addresses only. However, we can quote for overseas deliveries.