Monday, May 26, 2008

Proof of the Pudding: Guide Numbers 101

This set of photos was done to test my previous article about using Guide Numbers to get a first shot pretty close to the correct exposure. The main aim below was to show you a series of shots I did using the guide number sheet posted in the above mentioned article.

I post the mistakes as well as the good shots below to show you what I went through and that I am human after all :-) The mistakes I made were all due to using the wrong chart to begin with. In light of this I am thinking of redesigning the print out to make it simpler to use.

Please remember that the aim of the guide numbers is to get as close as possible to getting the right exposure form the first shot. I had previously written about the vast amount of test shots I was taking to get a close shot. Once you get close, it's up to you to tweak them :-)

Anyway here are the shots:


Shot 1a
This shot was taken with a single strobe camera left, using a reflective umbrella @1/8 power and @50mm zoom. I read the wrong number for the wrong chart (2*580 GN number) which means it was shot at -1 stop.

Shot 1b
This is the same shot from Shot 1a, but I have increased the exposure by 1 stop in Adobe Lightroom. I feel that this would have been a good starting point for a shoot.

Shot 2a
This shot was taken with a single strobe camera left, using a reflective umbrella @1/8 power and @50mm zoom. This time I read the right chart and you can see that the exposure is similar tot he adjusted Shot 1b

Shot 3a
This shot was taken with a single strobe camera left, using a reflective umbrella @1/8 power and @50mm zoom. I read the wrong number for the wrong chart (2*580 GN number) which means it was shot at -1 stop.

Shot 3b
This is the same shot from Shot 3a, but I have increased the exposure by 1 stop in Adobe Lightroom. I feel that this would have been a good starting point for a shoot.

Shot 4a
This shot was taken with a single strobe camera left, using a reflective umbrella @1/8 power and @50mm zoom and ISO200.

I calculated the guide number to be -3 stops and it should have been -2 stops.

I used the wrong calculation and over exposed by 1 Stop

Shot 4b
This is the same shot from Shot 4a, but I have decreased the exposure by 1 stop in Adobe Lightroom. I feel that this would have been a good starting point for a shoot

Shot 5a
This shot was taken with a single strobe camera left, using a reflective umbrella @1/8 power and @50mm zoom.

I calculated the guide number to be -2.5 stops and I feel that this would have been a good starting point for a shoot

Shot 6a
This shot was taken with a single strobe camera right, using a reflective umbrella @1/8 power and @50mm zoom.

I calculated the guide number to be -2.5 stops and I feel that this would have been a good starting point for a shoot

For a really good starting point I would have changed the model (me) :-)

Shot 7a
This shot was taken with a two strobes:
1) camera right, using a reflective umbrella @1/8 power and @50mm zoom.
2) camera left, bare light @1/64 and @24mm zoom.

Although this wasn't too bad as a starting point I felt the the left strobe was too bright and I would have stopped in down 1 stop.

Shot 7b
This is the same shot as 7a but the left strobe was decreased by 1 stop and re-shot:
1) camera right, using a reflective umbrella @1/8 power and @50mm zoom.
2) camera left, bare light @1/128 and @24mm zoom.

I feel that this would be a good starting point for a shoot.

Shot 7c
This is the same shot as 7b but the I changed the settings on the left strobe but still aimed to get the same amount of light:
1) camera right, using a reflective umbrella @1/8 power and @50mm zoom.
2) camera left, bare light @1/32 and @14mm zoom.

You can see that the background is more lit than 7b, due to the wider angle of light, but I am lit pretty much the same as in 7b.

I feel that this would be a good starting point for a shoot.

Shot 7d
This is the same shot as 7c but the I added an 8" Honl Snoot without changing any settings to test the theory that a snoot won't change the amount of light just the coverage:
1) camera right, using a reflective umbrella @1/8 power and @50mm zoom.
2) camera left, bare light @1/32 and @14mm zoom with an 8" Honl Snoot.

You can see that the background is much darker than 7c, due to the snoot and the narrower angle of light, but I am lit pretty much the same as in 7c.

I feel that this would be a good starting point for a shoot.

Shot 7e
This is the same shot as 7d but changed the snoot to a Stofen diffuser and recalculated the settings:
1) camera right, using a reflective umbrella @1/8 power and @50mm zoom.
2) camera left, bare light @1/64 and @70mm zoom with a Stofen diffuser.

You can see that I am lit pretty much the same as in 7d.

I feel that this would be a good starting point for a shoot.

Shot 7f
This is the same shot as 7e but I added a pink filter to the Stofen diffuser and recalculated the settings:
1) camera right, using a reflective umbrella @1/8 power and @50mm zoom.
2) camera left, bare light @1/16 and @28mm zoom with a Stofen diffuser.

You can see that I am lit pretty much the same as in 7e.

I feel that this would be a good starting point for a shoot.

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

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Thursday, May 22, 2008

Guide Numbers 101: Canon 580EX II and 430EX (Meters)

UPDATE: I have republished this article using feet in the charts below

After reading the book Light Science & Magic and reading David Hobby's Lighting101 and Lighting102 courses at Strobist.com, I came to realize that I needed to put some effort into being able to get close to the right lighting setup from the start of a shoot, rather than my current method of randomly playing with the settings of the lights and the camera until I magically get a good picture - which of course I can never replicate.

The caveat here is that the Guide Numbers are just that - a guide. They are a place for you to get started not the law. Over time you will be able to get to know what settings you like for any given set of circumstances.

NOTE: The only calculations needed here are multiplication - nothing else I promise - as I can't do much else myself!

For people like myself though who do not have enough time in the day to enjoy getting to be intimate with our cameras the Guide Numbers and the calculating factor table will help us get into or closer to the zone much faster.

I currently own two 580EX II and one 430EX and I wanted to be able to calculate the Guide Number of each of these units (which are in the manuals) and also a combination of the units when used together as one unit. Below are the results from my efforts.

The top 5 tables represent the Guide Number for the combination of the flashes listed. The final table shows you the multiplication factor to change the Guide Number based on if you are increasing or decreasing the available light. In the notes you can see what calculations you need to do if you increase the ISO and / or add on a light modifier (this is not an extensive list please leave a message as you learn what other modifier do and I will update the table).

The tables can be used to calculate both (1) F-Stop you need to set for a given subject to flash distance (2) the subject to flash distance needed for a given F-Stop. The calculations are:

F=GN/D : F-Stop equals the Guide Number divided by Distance (Flash to Subject). In meters

D=GN/F : Distance (Flash to Subject) equals the Guide Number divided by the F-Stop. In meters

The first table shows the Guide Number for a single 580EX II flash


The next table shows the Guide Number for a single 430EX flash


The next table shows the Guide Number for a two 580EX II flash units firing next to each as one unit


The next table shows the Guide Number for a 580EX II plus a 430EX flash unit firing next to each as one unit



The next table shows the Guide Number for two 580EX II plus one 430EX flash unit firing next to each as one unit


The final table shows the multiplication factor needed to calculate the new Guide Number based on any modifications you do to the camera to increase it's sensitivity to light, i.e. increase the ISO setting, or modifications you do to the flash, e.g. add a gel, a sto-fen filter, speed grid etc.

Some simple examples:
Using 1 580EX at F5.6 @50mm to shoot indoors for a portrait.
To get the distance we use the Guide Number for 50mm and divide it by the F-Stop number 5.6.
The best working values for us would then be 1/8 @ 2.6m or 1/16 @ 1.9 m.

If I wanted to warm up the image with a 1/2 CTO gel we need to reduce the Guide Number by 1/3 of a stop. We would then multiply the distance by 0.87. This would give us the new distance values 1/8 @ 2.3m or 1/16 @ 1.6 m.

If I were to now add a shoot through umbrella that reduced it a further 2 stops (multiply by 0.5) the values would change to 1/8 @ 1.14m or 1/16 @ 0.8 m.

I am a metric person, however if you would like I can also post this article for feet if you request it. Please send me an email if you would like the above tables in feet.

I have also created a spreadsheet (1.6MB) that contains worksheets with the Guide Numbers pre-calculated for each of the setups mentioned above. There is also a calculator for each of the setups mentioned above which allows you to enter in an F-Stop and it will give you the corresponding flash to subject distance and visa versa. The spreadsheet is 1.6MB and you can download the spreadsheet here.

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

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Tuesday, May 20, 2008

Off Topic: Making a Movie

I had a blast last weekend as an extra as a warrior in a futuristic movie called Road Raiders currently being made in the Philippines. The word was out that a movie was looking for western extras for a movie and I jumped at the chance. Not sure why but I've always wanted to do something like this - boyhood fantasy of playing army etc.

The best part of it was actually meeting a bunch of nice guys, from a wide range of backgrounds who all shared the same idea of this being a once in a life time experience not to be missed. Wasn't quite sure of the whole story line, but it didn't stop me from having loads of fun.

Road Raiders is a post-apocalypse action film in the style of Mad Max, and will star Michael Madsen (Reservoir Dogs, Kill Bill). The film is a US-Philippines co-production, shot entirely in English.

The movie will be directed by one of the Philippines' most internationally successful directors, Cirio H. Santiago (TNT Jackson, Stryker, Last Stand at Lang Mei) and is being made with legendary Hollywood producer Roger Corman.

This is Michael Madsen (in the glasses) with me (with the messy haircut). Michael is the leader of the Warriors who, of course, are the bad guys.

This is me on the right with another of the Warriors (who is in real life a Professor at one of the local Universities). This was the dress code for the bad guys with the addition of having a ski mask and goggles on - so in reality all you'll see is my chin and nose (but what a chin and nose it is!).
By the way I don't advise to wear ski masks in the Philippines for too long for two reasons: 1) It's already hot enough to cook an egg on the ground on a normal day; 2) you'd easily be mistaken for a terrorist/robber and shot after taking about 2 steps out of the door.

The lady below (Rizza Santos, from the Philippines) is one of the heroins, and was in everyone's word - stunning, and a very nice lady as well. Talk about turning heads!
I believe the plot should be written along the following lines:-
1. Bad guys do bad stuff
2. Heroin walks in
3. Bad guys repent and promise to do whatever Heroin asks
4. Bad guys go off and kill their former leader
5. The end

These were some of the futuristic vehicles we rode in. I stood on the top of the Hummer in the background as it drove fast across bumpy ground. I'm hoping that the "scared out of my wits look" will pass as a tough look. I nearly had to change my underwear after every take we were asked to do.

This was my gun - the big gun, the big heavy gun, the big heavy gun which on a hot day became incredibly heavy. I must be the biggest wimp of a Warrior in movie history!

This is the team of Warriors - post production. Not so tough looking in their ordinary clothes! That's why bad guys always dress in black - because it makes a statement.

I'm hopefully going to be doing this again on Saturday, and this time I'll take my eldest daugther Abigail, who will play one of the settlement children (good people). I'm hoping to play a good guy also as I don't want my daughter to see me get killed off.

Once the film is released I'll let you know and we can all have a good laugh together - however please don;t blink during the film as you may miss my appearance :-)