[Mike Cash]

Is that only a problem when the flashes are in auto mode? I thought the wireless trigger would make the flash fire no matter what.

It isn't a problem of the flash not getting a signal to fire. It is a problem of the flash sensor circuitry getting ready to fire, catching the light from the other flash, and saying, "Oh, nothing for me to do here." What the auto circuitry does is to cut off the flash output when it senses enough light reflected back from the subject to give a correct exposure. It has no way of knowing if it is its own light reflected back or light from some other source, nor does it matter.

Well if the manual mode is not complicated to set up for a shoot then maybe I'll look at getting one or two with wider manual control, as it looks like some of them come pretty cheap. It seems to be the PTTL compatible flashes that cost big bucks.

I think in many cases the manual stuff may actually be easier to set up, but I base that solely on seeing posts from people who are having trouble with the "easy" automated stuff. With the manual stuff you can't help but be aware of what the settings are on everything and hence having at least a starting point for knowing what to move around or adjust. You see what effect those changes had and learn from them.

For most uses, especially for the casual hobby photographer, there is no need to spend big bucks in order to play around with off-camera flash, get good photos from it, and have fun doing it. You can do it with older inexpensive gear quite well.

[jolepp]

...
Well if the manual mode is not complicated to set up for a shoot then maybe I'll look at getting one or two with wider manual control, as it looks like some of them come pretty cheap. It seems to be the PTTL compatible flashes that cost big bucks.
...

It is not too complicated really: the simple thing is to set shutter speed to 1/180s (=maximum sync) and, say, ISO=200, 8 for aperture, 1/4 output, take a test snap, check the result and adjust to suit:

underexposed : increase ISO <or> open aperture <or> increase flash output

overexposed: decrease ISO <or> close aperture <or> decrease flash output

As for a cheap, decent all manual flash with straightforward output control I'd vouch for the YN-560 (got one from ebay for ~$65, shipping included, saw a similar price with an Amazon seller the other day).

[Mike Cash]

I'll expand a little bit on what Jolepp had to say, if I may:

Getting your exposure in the ballpark when setting up manually is not hard at all. All it takes is a very little bit of in-your-head math and the ability to roughly estimate distances.

The output of flashes is usually expressed in terms of "GN" (Guide Number), which is really nothing more than a shorthand way of removing all the hard math from figuring out exposure. The important thing for figuring out exposure is flash-subject distance (camera-subject distance is irrelevant). The strength of the light varies tremendously depending how far the subject is away from the light source and with the same output level we need to use different apertures depending on the flash-subject distance. This is where our dear friend the GN comes in and rescues us from hard math....

GN divided by distance equals aperture. So easy to do that it is hard not to feel like a fraud when you use it.

What you need to know about GN is that it is a number that is sometimes expressed in feet and sometimes in meters....depends on what is common where you live. All that is important is that you know whether you're using feet or meters for the GN and to guesstimate your distances the same way so the math doesn't get all funky. GN is also usually expressed as being for ISO100 on your camera. Some off-brand flash manufacturers list their GN for ISO200 to make their flash look more powerful than it really is (the GN would appear to be twice as big), so check specifications carefully if you buy a new one.

Examples would make it easier to see what I'm talking about and how drop-dead easy the math is:

My Pentax AF200T has a maximum GN of 20 (meters).....GN20. If I have it set on full power (GN20) and aim it at a subject 5 meters away.....20 divided by 5 equals 4.....so my aperture is f4.

My National PE-3057 has a maximum of GN30 (meters). So on full power a subject 2 meters away would require an aperture of f15. I don't have an "f15" setting, so f16 is close enough. If the subject is 10 meters away....f3. Ain't got one of those either, so f2.8 is fine. Either that or f4. Extreme precision isn't necessary.

See what I mean about it not being hard at all to set up the flash and have a good ballpark estimate of what aperture you're going to be using? Once you're set up, put your shutter speed to 1/180 (1/160 if your camera is set for 1/3 EV steps...the difference isn't worth worrying about). Set your aperture to what you guesstimated it to be, and fire off a test shot. Review it on the rear screen and see which way you need to adjust, if at all.

One very important point to keep in mind is that shutter speed plays no role whatsoever as far as the flash portion of your lighting is concerned. For mechanical reasons having to do with the camera you have to stay at or below sync speed (1/180 for us), but that has nothing to do with whether the flash portion of the light is correct or not and no amount of monkeying with the shutter speed will help you adjust the flash exposure up or down. You do that solely with the aperture.

If you can't get an aperture you like in a given situation you can adjust your ISO. You could make a little chart or try to keep up with in your head all the different GN numbers you'll get if you change your ISO, but it is entirely unnecessary. Just remember that each bump in ISO will require a similar bump in aperture to compensate.

Example:

GN20 (at ISO100) for a subject 5 meters away gives me f4....but I don't want to shoot at f4. I want to shoot at f8. I can either move the subject or the flash to about 2 1/2 meters (2.5m x f8 = GN22...close enough) or I can bump up the ISO and leave the subject and flash where they are. From f4 -> f5.6 -> f8.....that's two stops of adjustment, so I can adjust my ISO from 100 -> 200 -> 400.

[BrianR]

Doing the math with guide numbers isn't really hard and is worth understanding and Mike has given a good rundown. However, if doing the math on the fly is intimidating (and you are already intimidated by your flash), many flash models have built in calculators on the back, including the AF280T. You enter the iso and aperture you are using, set the power of the flash and it will tell you the distance for 'correct' exposure.

Also, these things become second nature after you've done it enough and you'll start to get a good idea how far away from the subject the flash should be at given settings you use frequently.

There are also light meters available that will measure the light from a flash. Great for accurately and quickly setting the power levels and invaluable for getting your lights to a given power ratio from one another. It's never strictly necessary to use a meter given the instant results of digital, but it can make life easier.

[Mike Cash]

I should be ashamed of myself for overlooking what Brian has pointed out. I'm so used to eyeballing and just doing the math in my head while my hands are busy setting up the lights that I don't even bother referring to the very easy to understand scales on the back of my flashes. That is indeed a great thing about the old flashes, which pretty much all have those easy handy-dandy scales and simple slide switches. I've seen the back of some of the latest flashes and I don't understand how anyone can use some of them.

[hoanpham]

Hi Yukoner777,

Lots of replies already.

My experience about manual and off camera flash is not hard, especially in digital when you can have a preview. Strobist is a very good resource. It can be addicted ;-)

I always plan the shoot, ie. by looking for background, distances, ambient, gels and other light modifiers. Setup for portrait indoor will take from a minute to 10-15 min. Setups for parties and weddings require several flash units and planning. Private parties 10-15min. For weddings I need an hour to go through and setup all flashes to cover every spot, all use the same radio channel - a bit waste of battery, but since I shoot alone and this saves me the time to move light stands.

I use to do some practice with the new flash unit just to know how I can adjust them, not exact science, not hooking up with GN. GN (related to distance) is important, but I don't have time to worry about. Need more power, use multiple units. In most cases, I know the shooting location, this helps to reduce planning time.

My flashes are manual only, adjustable power, tilt&sw&zoom. It is important to have ability to wake-up a flash using center pin synch or disable power save function. The Sigmas cannot do this. Why buy p-ttl when I can buy 3-4 manual units for the same price?

[Yukoner777]

What the auto circuitry does is to cut off the flash output when it senses enough light reflected back from the subject to give a correct exposure.

So if I had a manually controlled flash it would be forced to flash no matter what, right.

With the manual stuff you can't help but be aware of what the settings are on everything and hence having at least a starting point for knowing what to move around or adjust. You see what effect those changes had and learn from them.

I think that's where I'd like to get, where I can do the quick calculation in my noggin. Otherwise I'd tend to become totally dependent on just checking the little slidebar calculator on the back of the flashes.

As for a cheap, decent all manual flash with straightforward output control I'd vouch for the YN-560 (got one from ebay for ~$65, shipping included, saw a similar price with an Amazon seller the other day).

Jolepp, how much (or what increments of) direct control do you have over the power output on this flash?

Getting your exposure in the ballpark when setting up manually is not hard at all. All it takes is a very little bit of in-your-head math and the ability to roughly estimate distances.

The output of flashes is usually expressed in terms of "GN" (Guide Number), which is really nothing more than a shorthand way of removing all the hard math from figuring out exposure. The important thing for figuring out exposure is flash-subject distance (camera-subject distance is irrelevant). The strength of the light varies tremendously depending how far the subject is away from the light source and with the same output level we need to use different apertures depending on the flash-subject distance. This is where our dear friend the GN comes in and rescues us from hard math....

GN divided by distance equals aperture. So easy to do that it is hard not to feel like a fraud when you use it.

What you need to know about GN is that it is a number that is sometimes expressed in feet and sometimes in meters....depends on what is common where you live. All that is important is that you know whether you're using feet or meters for the GN and to guesstimate your distances the same way so the math doesn't get all funky. GN is also usually expressed as being for ISO100 on your camera. Some off-brand flash manufacturers list their GN for ISO200 to make their flash look more powerful than it really is (the GN would appear to be twice as big), so check specifications carefully if you buy a new one.

Excellent info, Mike! I didn't find any mention of GN in the manual for my AF280T flash, but I Googled it and found both GN28 and GN91 @ ISO100. So GN28 must be in metres and GN91 in feet. My K-X only goes down to ISO200, which would double the GN? So a subject 5 metres from the flash would require an aperture in the neighbourhood of (56/5) 11.

One very important point to keep in mind is that shutter speed plays no role whatsoever as far as the flash portion of your lighting is concerned. For mechanical reasons having to do with the camera you have to stay at or below sync speed (1/180 for us), but that has nothing to do with whether the flash portion of the light is correct or not and no amount of monkeying with the shutter speed will help you adjust the flash exposure up or down. You do that solely with the aperture.

So if I were to set the camera for a slower shutter speed it would make no difference at all to the exposure of the subject being illuminated by the flash, but would increase the exposure of the background?

Hi Yukoner777,
I always plan the shoot, ie. by looking for background, distances, ambient, gels and other light modifiers. Setup for portrait indoor will take from a minute to 10-15 min. Setups for parties and weddings require several flash units and planning. Private parties 10-15min. For weddings I need an hour to go through and setup all flashes to cover every spot, all use the same radio channel - a bit waste of battery, but since I shoot alone and this saves me the time to move light stands.
?

Hi hoanpham.
So assuming you have your locations picked out, and your gear is set up in the location(s), do you take a few test shots before the event to check the exposure? If so, are you taking shots of objects, volunteer test subjects, or what? Is it important/necessary to do test shots with people before the event or will any objects work?

Thank you all for taking the time to share what you've learned.

[Mike Cash]

One step up from GN28 is GN40. Two steps up is GN56.

One step down from GN28 is GN20. One down from that is GN14.

The GN moves like aperture numbers, with each successive full step being the previous number times 1.4 (square root of two). Every second jump is a doubling of the number. If you're ever stuck trying to figure out what one step down from any GN is, just cut it in half and then add back about 50%. For example, one step down from 30 you would make it 15 then add about half of 15, making it about 22ish. Not precise, but close enough. Same works for going one step up...just add on about half. So one up from GN30 is 30 plus roughly 15, let's call it 44 or 45. It's not hard to do these; all you need is a starting point.

You are correct in your understanding of what effect shutter speed has.

---

Last edited by Mike Cash; 01-10-2011 at 11:34 PM.

[Yukoner777]

Thanks for clearing that up, Mike.

[hoanpham]

So assuming you have your locations picked out, and your gear is set up in the location(s), do you take a few test shots before the event to check the exposure? If so, are you taking shots of objects, volunteer test subjects, or what? Is it important/necessary to do test shots with people before the event or will any objects work?

No need for people as test object. I turn on histogram, manual focus, place my left hand where the subject's face suppose to be and shoot a test pic. I don't need focus in the test pic, just enough to test the light setting/intensity and adjust f-stop/umbrella distance and speed for ambient. I do it every time I do set up, and so often that the whole procedure just takes 10 seconds. I do use a piece of tape to mark on the ground where the subject should put their feet on. Weddings, repeat the procedure for each room/shooting location.

Yes, it is important to have a test. First impression is important for me and the subject. I use to show them the few first pics, then talk and ask them to pose differently. Turning head few degree do make a big different since I don't have an assistant to move the light source.

[jolepp]

...
Jolepp, how much (or what increments of) direct control do you have over the power output on this flash?
...

There are 1 stop coarse steps: 1/2, 1/4,...,1/128 with fine tuning (-3,...,+3) between steps.

[Yukoner777]

There are 1 stop coarse steps: 1/2, 1/4,...,1/128 with fine tuning (-3,...,+3) between steps.

Sounds like a lot of flash for the money.

[jolepp]

Sounds like a lot of flash for the money.

I'm quite pleased with it :-)

[BrianR]

Excellent info, Mike! I didn't find any mention of GN in the manual for my AF280T flash, but I Googled it and found both GN28 and GN91 @ ISO100. So GN28 must be in metres and GN91 in feet. My K-X only goes down to ISO200, which would double the GN? So a subject 5 metres from the flash would require an aperture in the neighbourhood of (56/5) 11.

See page 21 of your manual.

So if I were to set the camera for a slower shutter speed it would make no difference at all to the exposure of the subject being illuminated by the flash, but would increase the exposure of the background?

This may be considered a picky point, but using a slower shutter speed increases the exposure of all ambient light, not just the light falling on the background. This is an important consideration as you can use the ambient to work with your flash when lighting your subject. You can think of the shutter speed as a lever that controls ambient light levels while leaving your flash exposure unchanged (within your sync speed restriction) when trying to adjust the relative power of these two sources.

[jolepp]

To further extoll the virtues of the YN-560: it has a special slave mode where it ignores the pttl preflash, which works with the k-x built-in flash, at least.