Saturday, November 20, 2010

A Practical Guide to Working with Guide Numbers

Recently I've had a number of inquiries about the articles I wrote about Guide Numbers (in feet and in meters).
The embarrassing thing was that each time I had to re-read my own articles and work through the whole thing just to remind myself how it works.  More embarrassingly was that I couldn't figure it out straight away and had to take quite a bit of time to work it all out again.

So after listening to my readers (and getting frustrated with myself) I decided that I would write this article to make it easier how to use guide numbers - and the truth be told so that I don't have to work so hard next time I am asked how it works!

I think that looking at the calculations by themselves is what makes it confusing. It's better to put yourself into the situation and ask yourself what would you be doing in a real situation? So let me try to explain using this approach.

Situation 1
A person has asked you to do a portrait of them sitting on a chair. You have a camera (Canon 5D MKII) and a flash (Canon 580EX II) with a remote trigger and a light stand (but you forgot to bring your umbrella and soft box!).

The person doesn't have much time, who does nowadays? so you need to quickly set things up and fire away. You already know a few things.

1) You would like to have enough depth of focus to have the whole head in focus, so will use your 24-105mm lens at somewhere between 50-90mm depending on how much of their body they want to include. To get the right depth of focus you will use roughly F/7.1.

2) The other thing you know is that, as you do not have an umbrella or soft box, to get softer lighting you will use a fairly wide flash zoom, maybe 24mm or 28mm (you may also like to try a 35mm flash zoom).

3) Because it's indoors and relatively close you know that you'll probably use a 1/8 or 1/16th power. What you need to know now is how far your lights need to be away from the subject.

So now you know that:
a) You're using F/7.1 on your lens.
b) You will try first with a 24mm zoom on your flash head
c) You will use between 1/8th and 1/16th power

So now you do some calculations based on the calculation (D=GN/F : Distance (Flash to Subject in feet) equals the Guide Number divided by the F-Stop)

You look up the guide number (G/N) for 24mm flash coverage (zoom) and 1/8 power which you find is 32.5. To follow the formula you need to divide this G/N by your lens aperture 7.1 which gives you 4.5 feet. If you were to use 1/16th power the GN is 23 and for the same 7.1 lens aperture would give you the distance of 3.2 feet.

Situation 2
You have a small room where you want to photograph a bunch of items you want to sell on e-Bay. The room is small so you are limited to where you can place your lights. After placing the light in the room on the side of the table you measure the distance from the flash head to the place where you will position the items and find that the distance is 2.6 feet. Now you can calculate what settings you need for your flash and/or the F-stop setting for your camera.

For this you will use the calculations:
a) F*D=G/N : F-Stop by Distance (Flash to Subject in feet) equals the Guide Number.
b) F=GN/D : F-Stop equals the Guide Number divided by Distance (Flash to Subject in feet).

You're going to be using around an 80mm lens and you would like a fair depth of focus for the whole product. As your camera is quite close to the items being photographed you will choose an aperture of F/11 for good clarity.

So now you know that:
a) You're using F/11 on your lens
b) Your distance from flash to subject is 2.6 feet

So to get the guide number you multiply the F-Stop (11) with the Distance (2.6) which gives you a guide number of 28.6. Now you look up on the table in the white numbers for the closest number to 28.6. The closest you can find with be the flash coverage of 70mm with the flash output at 1/32 power (G/N=28.9).

Alternately you could think about moving the lights closer to 2 feet which would give you a G/N of 22 (2 * 11) which would give you some options of 35mm @ 1/32 or 24mm @ 1/16.

Say you weren't concerned about the F-Stop number so much but you knew that you wanted to have fairly hard shadows so wanted to have a narrow flash coverage say 105mm and you decided you would use 1/8th power. Now you would have to calculate what F-Stop you would need to set on your lens.

So now you know that:
a) Your distance from flash to subject is 2.6 feet
b) Your G/N number is 67.3 (105 mm with 1/8th power)

Your camera F-Stop would therefore be 67.3 divided by 2.6, which would give you an F/Stop of F/25 (or F/22 which is the closest one).

You may then decide that you don't want to use such a high f-stop, but you still want to use 105mm flash zoom. Your only option is to use a lower flash output, maybe 1/32. The G/N number for those settings is now 33.8. So now your F-stop would be 33.8 (G/N) divided by 2.6 (Distance) which would be 13 (or F/11).

Obviously these things are averages and you will need to make minor adjustments to get the exposure right. Remember that these settings are good for finding a good starting point, which you can then adjustment from.

The last table I created helps you to change the guide number based on if you use a light modifier or you change the ISO settings.

If you were to add a shoot through umbrella you will need to multiply the G/N by 0.5 before you use it in the calculations.

In the previous example above the G/N for 105mm flash coverage at 1/8 power with a shoot through umbrella becomes 67.3 multiplied by 0.5 which equals 33.65.

So now your F-stop would be 33.65 (G/N) divided by 2.6 (Distance) which would be 12.9 (or F/11).

Well that wraps up this post.  I hope that the examples above help to make more sense of how to use guide numbers.

Please feel free to leave comments or questions below or email them to me.

Tuesday, October 26, 2010

Tricycles, Food and Street Scenes

I have decided in the short time I have been here in Shanghai that I will start a few personal projects for myself. I've read that having personal projects can be good for the photographers soul as it keeps your eyes open and helps bring your senses alive (or in my case bring them back to life!).

The personal projects I have decided to take up are:

These seem to be the main form of transportation for everything from live animals to rubbish to people and, from what I've seen so far, are not subject to any weight, height or width restrictions.

Now I know that many of you are thinking that this has all done before, but being unique is not always the point of personal projects. I chose this because having such old (and somewhat dangerous) modes of transport contrasts so sharply with such a modern and clean city as Shanghai. It provides an excellent juxtaposition, reminding me that Shanghai was built by the sweat and tears of such amazing people.

When your rated an XXL or above, as I am, food is always somewhere in the list of New Year's resolutions. Living in China makes including food into a personal project an obvious, almost a compulsory, choice. Food here is a way of life, and there are are very few places I have visited where almost everything, and any part, is used for cooking.

For the most part the dishes here in China are quite simply amazing, and depending on the recipient, the amazing could be either positive or negative. From Pig's ears to chicken heads to terrapin soup to starfish to duck's tongue to cow's intestines, everything is widely available and cooked in a variety of ways.

I have a strange feeling that this may be one of my most photographed personal projects :-)

Street Scenes
Since moving here three months ago I have walked around town more than in the whole 6 years I was in the Philippines. This is mostly due to the colder weather and the infrastructure which supports walking around on the street without risking your life (except for crossing the road here, which is worth a whole story by itself!).

There is so much going on in the streets and on nearly every road ventured you will bump into something or something that gets you reaching for your camera. The reason for this project are similar to the tricycle project, i.e. people and contrasts.

People also seem to like being photographed and are often willing to pose in a position while you press the button. Sometimes you are asked to send them the photograph and I've been happy to do so, whenever practical.

And of course Family - this is more a personal addiction rather than a project. I love taking photos of my family and so far they have not threatened to throw the cameras out of the window – although I think that's it may have been close on a few occasions!

and finally, if I can fit it in, I'd like to do some Strobist photography at the graffiti walls in Moganshan Road. There is something very addictive about Graffiti and Strobist Photography, putting them together seems to be a lethal combination for overkill or excellent images – only time will tell which path I take.

If you know of anywhere in Shanghai (or other places in China) that you think are great places to capture images please let me know, either in the comments below or my emailing me.

For now, stay well, keep shooting and keep dancing as if no one is watching.

Friday, October 22, 2010

Shanghai Day Out - Moganshan Road

We were looking to spend a relaxing day out together in Shanghai as a family and I had read and heard a lot about Moganshan Road (map) as somewhere to go and see art and especially graffiti . I hadn't expected much as we'd previously walked around the French Concession area in Shanghai looking for art galleries and only found one or two.

As this was a new part of town, we went there by car and got dropped off at one end of the road then slowly walked up the street. My initial impression was not so good, I had flash backs of traipsing around trying to find one or two galleries. The first one or two we saw were disappointing and we thought that lunch would come very early for us.

After the initial 2 galleries we suddenly came across a large open complex of what seemed to have previously been dock yards or old warehouses along the river which were full of different galleries. The address is 50 Moganshan Road, and I thoroughly recommend it as a place to go and visit. I don't know how many there were, but I estimated more than 50 different galleries of different sizes were located in that one complex.

The first gallery on the corner of the complex was called Yu Nancheng (Fish) Studio, and they have some amazing oil paintings of various scenes. The photos do not do the painting justice for their size (around 1.5 – 2 m) or their texture.

The texture of the main characters is layered oil paints to create an amazing 3D effect and they are truly beautiful to look at.

The simplicity of the red and black, with background figures done in black on black, create a very refined and strong image. 

Unfortunately they are not cheap, around USD 7,500 to USD 15,000, so I could only afford to look, but are definitely worth the money if you can afford.

We looked in many of the galleries, but were not allowed to take many photos. The galleries go from small art shops to medium size art galleries which sell paintings to exhibition halls which have a range of various styles from weird to interesting.

A lot of the galleries seem to have similar style of paintings. One style that is particularly hip at the moment is the modern pop-art of Chinese faces with very large mouths smiling.

(image from

Inside the complex there are a few cafes to sit and relax, all of which are arty and make you feel like sitting round and contemplate the meaning of life :-) We found a good cafe in the middle of the complex which had a wonderful rustic interior with great food and coffee, which made you feel like curling up by the fire place and reading a good book. I can't remember the name of the cafe, but look for the toilets towards the back of the complex in the middle and you'll find it.

After looking about for a while we headed out of the complex and saw the graffiti walls further down the road. I was not disappointed. There is about 200-300m of a wall completely covered in graffiti of all sorts.

We were lucky to be able to see someone, tag name “dezione”, actually creating a painting Many people stopped to watch him in action and at various times I thought a road accident was going to happen as cars also just stopped in the middle of the road to watch.

In the end I asked my family to pose at different places and vowed to myself to come back, with more equipment and try some really cool shots.

If you love art, you will love Moganshan Road.

Monday, August 9, 2010

Last Post Here For A While

I have recently moved to the wonderful city of Shanghai in China and am looking forward to spending a lot more time capturing another set of moments that will last forever.

Unfortunately I am unable to connect to blogger to update this blog - not that I did it regularly any way :-) So if you are interested in seeing more of my stuff come over to my website where you can catch my latest images and where, hopefully, I will also be able to post my stories.

Thanks for stopping by.

A little taste of my new life:

Most common form of cheap goods transportation in town

Cooking in the street

A typical old apartment block with washing hanging out the side

Jin Mao Tower and the Shanghai Financial Center

Wonderful lighting effects on the top of the Shanghai Financial Center