Manual Flash: Clubsnap 'Wikipedia'

[futsal123]

This is a minor contribution from me and it is not complete.
There are still several unanswered questions in my mind. While I input whatever I know, experts in Clubsnap may contribute as well. Lastly, if my input is wrong or misleading, kindly correct me. I want to learn as much as possible.

There is a lot more in flash techniques.
Due to my limited skills, I will touch on the very basic idea of manual flash.
It will be greatly appreciated if there are experts to touch on more advanced knowledge such as multiple manual flash lighting ratio, how light modifier/diffuser affect the aperture etc.

Ok, before I start, you must know the basics of photography.

My primary objective to this thread is to:
1. Share our knowledge together
2. Make manual flash knowledge easier to digest
3. Provide a cheaper alternative to those who want to try using a flash
4. Know what guide no flash that you may require
5. Know what type of flash you want

Pros of using manual flash:
- Majority is cheaper than TTL flashes etc
- Consistent results. Even if your image is over/under-exposed, it will be consistently over/under-exposed
- Good knowledge to have
- Better control over lightings, know what aperture to use

Cons:
- Can be troublesome to calculate
- Not so good for fast type of events

Months ago, the BBB virus hit me hard. I was thinking of what lens and flash to buy so that I can cover most focal length and lighting conditions. In reality, factors such as “want vs need”, budget constraints and best value for money, spin around in my mind. Basically, my heart is arguing with my mind.

I took the route of trying out flash 1st. After some searching here and there, I got a China flash for $55. The reason: If I don’t like it, it’s only $55 that I wasted.
After a few tries, sometimes my pic is always extremely over/under-exposed on the 1st image. I need to adjust a lot more times to get what I want to achieve. All I did was…anyhow adjust…ISO/aperture/flash power/shutter speed…all anyhow one.
I realized that I need to have the basic knowledge to shorten the time to adjust for the exposure I want. This is where our learning journey starts…

Nowadays, technology is very good and it can calculate everything for you. Manual flash is different from TTL (Nikon/Canon etc) calculation. Please do not be mixed up.

Basically, there are 4 components in manual flash calculation to get the correct exposure for your subject:
- Aperture (f/stop)
- Guide number (GN)
- Distance of flash to subject
- ISO multiplier

F/stop = GN (feet) / Distance of flash to subject (feet) * ISO multiplier

GN: This tells us the furthest distance that the light of the flash can reach at a certain ISO level. Normally, it is stated in feet at ISO 100.

Distance of flash to subject: Of course we use visual estimation here. Alternatively, if your lens has a distance marker, half-press the shutter button and look at the reading.

If you want to use meters instead of feet, just convert 1feet = ~0.3m.

ISO multiplier: Every 1 stop of ISO increased will affect the aperture output.
The multiplier is as follows:
ISO 100: 1.0
ISO 200: 1.4
ISO 400: 2
ISO 800: 2.8
ISO 1600: 4
ISO 3200: 5.6

Assuming that GN(feet) of my flash at ISO 100 is 40, distance of flash to subject is 4feet and I am using ISO 100:
F/stop = 40 / 4 * 1 = f/stop 10

Assuming GN(feet) at ISO 100 is 40, distance of flash to subject is 4 feet and I want to use ISO 400.
F/stop = 40 / 4 * 2. = f/stop 20
* you may use this to achieve larger DOF.

If you are considering getting a flash, you may use this equation also.
Assuming that you normally shoot at f/5.6, distance between you to subject is normally 20 feet.
5.6 = GN (feet) / 20 * 1
GN (feet) = 112
you may require a flash of minimum GN 112. This is base on ISO 100. You may also increase ISO to increase light sensitivity and high ISO is very well controlled in most DSLR nowadays.

Some may argue that TTL flash is faster to deploy in the sense that you don't waste time calculating. Some say that using lightmeter is more accurate.

Well, it's up to you whatever method that you want to use or whatever you like.
Basically, it's making the best/most of what we have.



Experts, kindly correct me if my info is wrong.
Sorry that I did not post any image here cos my photography sucks.

Next part: Balancing ambient light with manual flash

 

[thedarknight]

wah lol a bit mathematical and technical. i like the old fashioned way of shooting with manual flash.. take first photo without flash, see how much light you wanna add, and where. agar-ration the flash power, shoot second time, see, correct, done.

but i get your point regarding TTL and how basic knowledge on manual flashes is good to have. cant agree more.

however, sometimes, when you are shooting outside and need things fast and automatic, TTL really helps a lot.

 

[derrickder]

Good initiative! Would love to have some images to add some visual appeal to the thread though.

 

[ST1100]

Can i know where you got the ISO multiplier numbers from?

ISO 100: 1.0
ISO 200: 1.44
ISO 400: 2.07
ISO 800: 2.99
ISO 1600: 4.30
ISO 3200: 6.19

Intuitively speaking, the numbers should go up sqrt(2) [1.414] per stop, so it should run 1.0, 1.4, 2.0, 2.8, 4.0, 5.6 instead of what you provided. Not saying your numbers are wrong, just wondering how/where you got them from.

 

[ST1100]

The manual calculation method has fallen into disuse largely bcoz the adjust-from-first-shot method is really a lot faster. Today with diffusers, domes, bounce flash, bounce cards and a gazillion other flash modifying gizmos/techniques, the formula is effective rendered useless. Honestly i cannot remember the last time i used direct-to-subject naked flash. Also, those who use manual flash a lot in repeatedly similar lighting condition can normally get the exposure right on the first shot.

 

[Edwin Francis]

Can i know where you got the ISO multiplier numbers from?

ISO 100: 1.0
ISO 200: 1.44
ISO 400: 2.07
ISO 800: 2.99
ISO 1600: 4.30
ISO 3200: 6.19

Intuitively speaking, the numbers should go up sqrt(2) [1.414] per stop, so it should run 1.0, 1.4, 2.0, 2.8, 4.0, 5.6 instead of what you provided. Not saying your numbers are wrong, just wondering how/where you got them from.

You're right. TS got the numbers wrong. Think he started with 1.44 instead of 1.414 and went wrong from there. His numbers fit this way.

Shd be:
ISO 100: 1.0
ISO 200: 1.414
ISO 400: 2
ISO 800: 2.8
ISO 1600: 4
ISO 3200: 5.6

 

[futsal123]

Hey ST 1100 & Edwin Francis, thanks for pointing out! Appreciate it.
Will edit the post.
Yup, I entered the 1.44 instead of 1.414 into excel spreadsheet.

 

[futsal123]

Good initiative! Would love to have some images to add some visual appeal to the thread though.

Thanks, will try to add some images.

but i get your point regarding TTL and how basic knowledge on manual flashes is good to have. cant agree more.

however, sometimes, when you are shooting outside and need things fast and automatic, TTL really helps a lot.

The manual calculation method has fallen into disuse largely bcoz the adjust-from-first-shot method is really a lot faster. Today with diffusers, domes, bounce flash, bounce cards and a gazillion other flash modifying gizmos/techniques, the formula is effective rendered useless. Honestly i cannot remember the last time i used direct-to-subject naked flash. Also, those who use manual flash a lot in repeatedly similar lighting condition can normally get the exposure right on the first shot.

Yup, newer technology really save us alot of time and did phase out some old methods.
As photography is my hobby, I can afford the luxury of time to adjust and I like to have a mathematical explanation to what I adjust.

After multiple tries, 'correct' exposure can be done in less than 20sec and sort of nail the 1st image correctly.

Having said that, 20sec means alot to wedding photographers, photojournalist etc.
The bottom line is to choose something that we are comfortable with, according to the situation.

 

[intrance]

thx futsal123, for starting this thread..

hopefully we can discuss purely on manual flash. and hope this thread will not become manual vs TTL flash.

 

[futsal123]

thx futsal123, for starting this thread..

hopefully we can discuss purely on manual flash. and hope this thread will not become manual vs TTL flash.

Thanks Intrance and I agree with you deeply. This thread should not evolve into a manual vs TTL flash.
I enjoy the benefits of using manual as well as TTL technology.

How is your experience with manual flash? Feel free to drop some methods that you use.

I got 2 questions in my mind. Not sure if any expert can enlighten me.
1. Flash has power 1/1, 1/2, 1/4, 1/8, 1/16, 1/32, 1/64, 1/128. How will it affect the GN no?
2. How will a 2 stop diffuser affect the calculation? Do we calculate for aperture output den open up 2 stops to compensate?

 

[allenleonhart]

The manual calculation method has fallen into disuse largely bcoz the adjust-from-first-shot method is really a lot faster. Today with diffusers, domes, bounce flash, bounce cards and a gazillion other flash modifying gizmos/techniques, the formula is effective rendered useless. Honestly i cannot remember the last time i used direct-to-subject naked flash. Also, those who use manual flash a lot in repeatedly similar lighting condition can normally get the exposure right on the first shot.

and i agree with this.:thumbsup:

Ettl is way faster, more accurate. remember, flash u havent even calculate the effects of ambient light and u already got enough numbers...

my opinion is still shoot and adjust. its a nice to know regarding calculating flash, would be helpful in studio conditions i guess

 

[futsal123]

and i agree with this.:thumbsup:

Ettl is way faster, more accurate. remember, flash u havent even calculate the effects of ambient light and u already got enough numbers...

my opinion is still shoot and adjust. its a nice to know regarding calculating flash, would be helpful in studio conditions i guess

Sometimes I prefer manual, sometimes TTL. Whichever suits me at that moment, I will use it. :bsmilie:
With the introduction of newer technology, we tend to use it without knowing what is going on.
Similar to using calculator but dunno how to calculate it manually.

 

[ST1100]

1. Flash has power 1/1, 1/2, 1/4, 1/8, 1/16, 1/32, 1/64, 1/128. How will it affect the GN no?
2. How will a 2 stop diffuser affect the calculation? Do we calculate for aperture output den open up 2 stops to compensate?

1. Multiply the power reduction into the GN. Say flash has GN 100: if shooting at 1/2 power, use GN 50; if shooting at 1/4, use GN 25.

2. Same, multiply the reduction into the GN. If diffuser has 2 stops, use GN 25 (for a GN100 flash) in the formula. Diffusers are very tricky to calculate for. The formula only applies to light traveling directly from flash to subject. Ceiling/wall distance and colour affect the reduction factor, so there's really no way to gauge accurately. (You have to do it for every reflecting surface.) Plus, you move one step, and the walls change their relative positions (in some rooms, even the ceiling is uneven), and you have to re-factor the distances. The formula is only really practical for direct unmodified flash.

 

[ST1100]

After multiple tries, 'correct' exposure can be done in less than 20sec and sort of nail the 1st image correctly.

Having said that, 20sec means alot to wedding photographers, photojournalist etc.
The bottom line is to choose something that we are comfortable with, according to the situation.

Hi, i don't mean to be argumentative, but i think you missed the point. The manual flash can be nailed FIRST TIME, not after multiple tries, not after 20 secs. Not in wild or difficult lighting conditions, but in most situations that are repeatedly encountered for the working professional.

As an example, i do weddings. For dinner table shots, i use the same f stop, same ISO, and the subject distance is about the same almost every table, every wedding. i use manual flash (coz TTL is not very reliable with the huge white table and dress) on a bounce card and barring an exceptionally low ceiling, can usually get it right first try. The same goes for most HDB indoors. As long as i know my f-stop and ISO, i just vary subject distance with flash power when on manual, on the fly - absolutely essential for (backlit) candids, where there is no second try.

This is a variant of the basic formula that most ppl use. The original formula is impractical coz it's very hard to nail the modification factor on the GN when the light path is indirect or scattered.