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08-21-2009, 01:56 PM   #1
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goodbye P-TTL, hello manual flash

I've been using P-TTL for a long time but would like to figure out manual control while I wait for my radio triggers to arrive. I've got a couple Pentax 540 FGZ's and a Metz 58AF-1. I will be shooting with a K20D. Could somebody throw me a clue or two about how to get started using flash in manual mode?

I can easily shoot in M exposure mode on the camera if that's required, but, using flash, I set to Av and set ISO to 400 - and after that, the flash seems in P-TTL seems to figure everything out pretty well most of the time. If I'm shooting normal candids at a wedding and staying, oh, about 10 ft from my subjects most of the time, I leave it set around f/5.6.

When I try to use manual mode on the flash now, I am just guessing wildly. I don't really understand what the ratios mean. I guess 1/1 = full power, the flash's absolute most powerful blast. Is that right? How do I know if that's what I need? I tried earlier and completely blew out my first shots. Eventually by trial and error figured out that a 1/8 setting was working okay, but I'd prefer to understand what I'm doing. Or, when setting flash manually, is it all about guessing until you get it right? I doubt that. Can't figure out how anybody could ever do that with film cameras....


Other than setting this ratio on the flash (whatever it means) is there anything else to worry about?

Thanks,

Will

08-21-2009, 02:15 PM   #2
Ash
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Hi Will.
Cool stuff - should be lots of fun experimenting.
The calculation to work out the flash intensity you need is quite simple: flash exposure at ISO 100 is GN = aperture × distance or distance = GN / aperture (working it out for full flash intensity), but it gets a little more complicated when you have 2 or more flashes working together. Though if just using one, then just remember for the aperture you've worked it out at, just reduce the flash intensity by one stop if you want to open the aperture by one stop, or alternatively, distance the flash source 'one stop' away from the subject (on a logarithmic scale) if you find that the flash intensity is one stop too strong for the exposure at full power, and so on...

In any case, if you have control over where you put the flashes and can afford to get them up close to the subject, then you'd rarely ever need full intensity (1/1). The fraction on the M setting is simply the fraction of full intensity the flash is using to fire. So 1/2 is half-power (or a stop less light), 1/4 is a quarter power (or 2 stops less light than full power) and so on. With 3 flashes you can get really creative with different intensities for each in different directions giving you harsh, muted, soft or gelled light sources as you desire. There really is nothing else to do with wireless manual flash.

All the best for that.
08-21-2009, 02:28 PM   #3
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Hi, Will,

I believe the ratio is for master/slave wireless sync flash... that is if you set it at 1/1 you will have both flashes blasting with equal strength. On the ON/OFF switch, there are three settings (dots). If you move the switch to the middle dot, you will see 1/1 default setting, but if you move the switch to the right position, you will not see that.

I use PTTL exclusively and find it to be pretty good... for outdoor shooting, I make sure HSS is on so I can set the camera in AV mode - good for fill flash. For indoor shooting, better use manual mode on the camera to control shutter (ambient light) and aperture (flash light). One time, I forgot that the flash was set to TTL mode, it didn't fire; changed back to PTTL mode it did fire. So, PTTL mode works for me.
08-21-2009, 02:41 PM   #4
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QuoteOriginally posted by aleonx3 Quote
Hi, Will,

I believe the ratio is for master/slave wireless sync flash... that is if you set it at 1/1 you will have both flashes blasting with equal strength. On the ON/OFF switch, there are three settings (dots). If you move the switch to the middle dot, you will see 1/1 default setting, but if you move the switch to the right position, you will not see that.

I use PTTL exclusively and find it to be pretty good... for outdoor shooting, I make sure HSS is on so I can set the camera in AV mode - good for fill flash. For indoor shooting, better use manual mode on the camera to control shutter (ambient light) and aperture (flash light). One time, I forgot that the flash was set to TTL mode, it didn't fire; changed back to PTTL mode it did fire. So, PTTL mode works for me.
Good tips, thanks

08-21-2009, 04:37 PM   #5
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QuoteOriginally posted by Ash Quote
Hi Will.
Cool stuff - should be lots of fun experimenting.
Yep, it has been already.

QuoteQuote:
The calculation to work out the flash intensity you need is quite simple:....
I hate when somebody says that. ;-)


QuoteQuote:
...flash exposure at ISO 100 is GN = aperture × distance or distance = GN / aperture (working it out for full flash intensity), but it gets a little more complicated when you have 2 or more flashes working together. Though if just using one, then just remember for the aperture you've worked it out at, just reduce the flash intensity by one stop if you want to open the aperture by one stop, or alternatively, distance the flash source 'one stop' away from the subject (on a logarithmic scale) if you find that the flash intensity is one stop too strong for the exposure at full power, and so on...
I also hate it when someone uses the phrase "logarithmic scale..." :-)

But I think I've got the idea. The guide number for the Metz 58 AF-1 is 191 (ft) @ ISO 100. Let's round that GN up to 200 because it makes it possible for me to do the math without having to borrow my daughter's school calculator.

So if I'm 10 ft from my subject, shooting at ISO 100, and with the flash at 1/1 full power, here's how I would do the calculation:
GN/distance = aperture
200/10 = 20
And then remembering that my guide number isn't really 200 but only 190, I'd reckon then that I should set my aperture to f/18 or f/19. Right?

*

Now, if I wanted to increase the ISO to, say, 400, I could then DOUBLE the guide number (that's where the logarithmic scale comes in, I think), so shooting at ISO 400, my calculation would be:
400/10 = 40
But that's with the flash at full power (1/1). Since I don't have an f/40 on my camera/lens, I'll need to make some adjustments. And this is where it gets a little sketchy for me.

I don't have any trouble doing these calcs if I'm simply shooting without flash and trying to adjust my manual exposure settings. F/22 is two stops faster than f/44, so if my shutter speed at f/44 was 1/100th sec, I'd need to bump that up to 1/400th sec to shoot at f/22, or 1/1600th sec to shoot at f/11.

But working with the flash, I'm not sure it works that way. If the calculated right aperture with flash at full power is f/40, and I want the aperture somewhere around f/10 or f/11 (about four stops faster), what adjustment to I make to the flash? Would I set it at 1/4 or 1/16 or something else? If I'm opening the aperture four stops, I think I'd need to move the flash output to 1/16, right? Or have I got it all completely messed up?


*

I will note that the Metz 58 AF-1 seems to be trying to help me out here, if I can only learn to understand what it's saying better. With the flash mounted on the K20D's hot shoe and flash in M mode, the flash seems to be able to tell what the camera's ISO is, and it shows me a distance on the back display that seems to indicate how far Metz's engineers think I should be standing from the subject. (I know it's flash-to-subject distance that matters, not photographer-to-subject or camera-to-subject. But remember, at the moment, the photographer, flash, and camera are in the same place.) Right now I have the DA 40 on the camera and the closest zoom setting on the Metz is 35, so I've got it set there. As I change the ISO on the camera, the distance displayed on the Metz's led changes; likewise, if I change the power of the flash on the Metz without changing the ISO, the distance number changes. So perhaps I don't need to do math at all?

Will

Thanks,

Will
08-21-2009, 08:13 PM   #6
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Strobist: Lighting 101

pretty much everything you need to know about using your flash in manual mode.

There is a lot to read, take your time and try to understand it. They also have lighting 102, just look on the right side for more information.
08-21-2009, 08:54 PM   #7
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QuoteOriginally posted by SuperAkuma Quote
Strobist: Lighting 101

pretty much everything you need to know about using your flash in manual mode.

There is a lot to read, take your time and try to understand it. They also have lighting 102, just look on the right side for more information.
Thanks. Been familiar with Strobist for years but have never made my way through the whole 101 course. May do now, as I will be working with the radio triggers as soon as they make their way here from Korea. Place an order from G9Chon for 1 Flashwave transmitter and 2 receivers today!

08-21-2009, 09:30 PM   #8
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QuoteOriginally posted by WMBP Quote
Thanks. Been familiar with Strobist for years but have never made my way through the whole 101 course. May do now, as I will be working with the radio triggers as soon as they make their way here from Korea. Place an order from G9Chon for 1 Flashwave transmitter and 2 receivers today!
Great. Be sure to do your own personal review on this board when you get it. Looking forward to some of your pics that you create with it.
08-21-2009, 10:48 PM   #9
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QuoteOriginally posted by WMBP Quote
I've been using P-TTL for a long time but would like to figure out manual control while I wait for my radio triggers to arrive.
welcome to the world of thinking only time i'm on auto (camera and flash) is when doing documentary work at an event or some place where you can't play around and ask someone to wait while you do test shots hehe really getting used to manual everything, it's a little bit of work, but very satisfying
08-22-2009, 07:52 AM   #10
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You're ont he right track Will, but it doesn't need to be this complicated.
Just think of stops of light...

Direct full-power flash at 10ft away for f/22 (or so)?
Then it's 1/2 power at f/16 (one stop bigger), 1/4 power at f/11 (another stop bigger), 1/8 power at f/8 and so on... given that the distance remains the same.

Where the LOG scale comes in is only in distance...
Light intensity falls off rapidly with distance from its source, obeying the 'Inverse Square Law': intensity is proportional to the flash-to-subject distance SQUARED, e.g.:

2x the distance away is 1/4 as bright, and 1/2 the distance is 4x brighter (2 stops)
3x the distance away is 1/9 as bright, and 1/3 the distance is 9x brighter (3 stops)
4x the distance away is 1/16 as bright, and 1/4 the distance is 16x brighter (4 stops)
etc.

Doesn't work with reflected flash, though (too many variables involved).
Hope this helps just a little more...
08-22-2009, 08:34 AM   #11
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QuoteOriginally posted by zenimagery Quote
welcome to the world of thinking only time i'm on auto (camera and flash) is when doing documentary work at an event or some place where you can't play around and ask someone to wait while you do test shots ...
Well, for better or worse, I do most of my flash photography at wedding receptions, galas and similar events where, as you say, I don't have the luxury of doing a lot of test shots.



QuoteOriginally posted by Ash Quote
You're ont he right track Will, but it doesn't need to be this complicated.
Just think of stops of light...
...
Direct full-power flash at 10ft away for f/22 (or so)? Then it's 1/2 power at f/16 (one stop bigger), 1/4 power at f/11 (another stop bigger), 1/8 power at f/8 and so on... given that the distance remains the same.....

Doesn't work with reflected flash, though (too many variables involved). Hope this helps just a little more...
I wish you were right, Ash, but I'm afraid that there are more complexities to it than that. For starters, my 2 Pentax 540's are less powerful than the Metz 58, so the calculations won't be quite the same. And as it happens, at least when I'm shooting candids I tend to bounce quite a bit, so I have to adjust my distances. I'm quite familar with and comfortable with the inverse square law, so at least that's not a novel concept.

Last night, shooting with the flash head of the Metz 58 AF-1 pointed directly at the subject, I discovered that the Metz tries to make it really easy for me. It apparently can read both the ISO and the aperture setting on the camera, and of course it knows what its own flash power setting is currently (1/1 or 1/8 or whatever), so it calculates and displays what it thinks is the appropriate distance from the subject for those other three variables. So I don't need to do any math in my head, which is a blessing, in theory. All I need to do is either (a) make sure I'm approximately as far from the subject as the Metz says I should be, or (b) adjust one of the settings - flash power, ISO or aperture - until the distance from subject shown is equal to where I'm actually standing.

Unfortunately, as soon as I move the flash head away from its straight-on position, the Metz refuses to do any math at all. SO if I want to bounce, I'm on my own.

Will
08-22-2009, 09:16 AM   #12
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Is this in P-TTL mode Will?
The 540 should be able to do the same.
For me I tend to use P-TTL, but just set the FEC differently between the two flashes I use together to get the effect I want. Then even if I bounce, the exposure's still done reasonably well for me.
08-22-2009, 10:27 AM   #13
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QuoteOriginally posted by Ash Quote
Is this in P-TTL mode Will?
The 540 should be able to do the same.
For me I tend to use P-TTL, but just set the FEC differently between the two flashes I use together to get the effect I want. Then even if I bounce, the exposure's still done reasonably well for me.
Yes, I've used P-TTL in the past, exclusively, both when I've been shooting with 1 hot-shoe mounted flash and also when shooting with 2 or 3 units triggers by the Pentax optical/wireless triggering system.

But the point of this thread is that I want to learn to do things manually, in part because it's probably past time for me to know more about this, in part because I'm not overly thrilled with P-TTL, but mainly - most urgently - because I'm waiting for my radio triggers to arrive and P-TTL doesn't work with radio triggers.

Will
08-22-2009, 10:33 AM   #14
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Oh yes, Will. Sorry to get off track.
Sure thing - it'll just take more thought and a little guesstimation to make bounced multiple manual flashes work - but worth it...
08-28-2009, 10:39 PM   #15
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QuoteOriginally posted by WMBP Quote
Yes, I've used P-TTL in the past, exclusively, both when I've been shooting with 1 hot-shoe mounted flash and also when shooting with 2 or 3 units triggers by the Pentax optical/wireless triggering system.

But the point of this thread is that I want to learn to do things manually, in part because it's probably past time for me to know more about this, in part because I'm not overly thrilled with P-TTL, but mainly - most urgently - because I'm waiting for my radio triggers to arrive and P-TTL doesn't work with radio triggers.

Will
I am thinking about doing reviews on the Vivitar stars; the 285 and the 283. Would that help?
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