Very basic flash questions - long post

[Bunter1815]

Hi folks

My first post here, not sure what the M.O is but as it's New Years Eve my card's behind the virtual bar...

Had my 40D since late Jan and the wife bought me a 430EXII for Xmas . I'm an enthusiastic amateur but I've never used anything on any of my previous cameras except on board flash, so the dedicated flash unit is a new thing for me. For background info, I'm not sure if I don't use it correctly but the results I got with the 40D's on-board flash always look rubbish, so much so that I bought a fast prime (Canon 50mm F1.8 II) just to use at the NEC motorbike show earlier in the year. I was happy with the results but now I can do far more with a dedicated unit.

So a couple of questions spring up.

When I have the camera in Av mode and have the 40D set to flash synch at 1/250 sec. I'm able to a use wide range of apertures and get reasonable exposures. If I switch to Tv mode and leave everything as is, and set the shutter to 1/250, the widest aperture setting is still not "on scale" as far as the metering goes. Why is that ?

One of the benefits of a dedicated flash is the ability to bounce the flash, and I've already found this gives much nicer results than using it without any bounce. But what do you do where there is no ceiling to use for the bounce? Are you restricted to using it in the direct mode? I've seen people with camera mounted flashes units with small white pieces of card poking out the top of the flash. Is that to act as a bounce surface? Relatedly, I can understand how the camera knows what exposure settings to use when the flash is pointing at the subject but how does the camera/flash know how much light is going to be reflected when using bounce? I realise that the flash knows when it is being used in bounce mode.

I do quite a lot of macro photography and was reading a book on macro work by Robert Thompson and he quite often uses a flash as a fill in flash. But for macro work he recommends mounting the flash on a flash bracket above the lens and pointing at ~ 45 degrees to the subject, with the flash angle fully open. If I get a flash bracket and do this then the flash will think it's in bounce mode but it will in fact be pointing directly at the subject. So how does that work?

Sorry this is so basic, if there are any good links for basic flash information they would be greatly appreciated, as would any answers to these questions and any tips on settings for the 40D/430EXII combination.

All the best for the New Year

Cheers

Bill

 

[SealBeard]

When I have the camera in Av mode and have the 40D set to flash synch at 1/250 sec. I'm able to a use wide range of apertures and get reasonable exposures. If I switch to Tv mode and leave everything as is, and set the shutter to 1/250, the widest aperture setting is still not "on scale" as far as the metering goes. Why is that ?

I'm not 100% on what your getting at here but.. I wouldnt bother setting the sync speed, just set your flash to highspeed sync - this will allow it to be effective over max sync speed. the flash will take care of itself in AV mode when set to ttl.
I never really use TV mode with flash to be honest, so I'm a little stuck as to what to suggest, you don't have to use a speed of 1/250 though incase you didnt know

One of the benefits of a dedicated flash is the ability to bounce the flash, and I've already found this gives much nicer results than using it without any bounce. But what do you do where there is no ceiling to use for the bounce? Are you restricted to using it in the direct mode? I've seen people with camera mounted flashes units with small white pieces of card poking out the top of the flash. Is that to act as a bounce surface? Relatedly, I can understand how the camera knows what exposure settings to use when the flash is pointing at the subject but how does the camera/flash know how much light is going to be reflected when using bounce? I realise that the flash knows when it is being used in bounce mode.

If there is no ceiling to bounce off, you could try bouncing the flash off a wall, either to the side or behind you over your shoulder. The piece of card you talk of is a bounce card, and while the flash is fired at the roof, this card will direct some of the light forwards to create some fill and brighten shadows in the eye sockets etc.
When the flash is set to bounce, the flash still fires a pre-flash so the camera can meter the scene, you probably wont notice the preflash however because its very fast just before the main flash happens. In ttl mode the flash will always preflash to meter the scene.

I do quite a lot of macro photography and was reading a book on macro work by Robert Thompson and he quite often uses a flash as a fill in flash. But for macro work he recommends mounting the flash on a flash bracket above the lens and pointing at ~ 45 degrees to the subject, with the flash angle fully open. If I get a flash bracket and do this then the flash will think it's in bounce mode but it will in fact be pointing directly at the subject. So how does that work?

I wouldnt think this would really matter, all that is going on is the flash is off axis (to create less harsh shadow, and allow the flash to be aimed at a close target), the flash and camera will still meter the same.
Your losing your flash's ability to zoom when in bounce mode, and thats what ttl handles when in the normal direct flash position. since you will set the flash angle fully open, you will get a broader beam of light, that should (i think) appear softer - the flash and camera will still meter appropriately however.

 

[Halflap]

Welcome to Talk Photography

I have not used flash a lot so cannot directly answer your questions but I do know a site which may be able to.

http://photonotes.org/articles/eos-flash/

It's a bit heavy going in places but it does explain how the flash and camera interract in allthe different modes.

Hope this helps. I am sure some of the more learned members will be along to give you a better answer

 

[Bunter1815]

Thanks for both those replies, there's a lot to read on that link.

I'm not 100% on what your getting at here but.. I wouldnt bother setting the sync speed, just set your flash to highspeed sync - this will allow it to be effective over max sync speed. the flash will take care of itself in AV mode when set to ttl.
I never really use TV mode with flash to be honest, so I'm a little stuck as to what to suggest, you don't have to use a speed of 1/250 though incase you didnt know

If I set the flash to high speed synch and change the camera back to the normal setting for Av mode (rather than the "force it to 1/250 in Av mode" setting), the camera sets rather slow shutter speeds when using the flash. Confused!

Bill

 

[SealBeard]

Thanks for both those replies, there's a lot to read on that link.



If I set the flash to high speed synch and change the camera back to the normal setting for Av mode (rather than the "force it to 1/250 in Av mode" setting), the camera sets rather slow shutter speeds when using the flash. Confused!

Bill

the camera will set low shutter speeds if the conditions are poorly lit. Basically, in AV mode, the camera will meter for the ambient light, and choose a shutter speed to suit. The flash will they light you subject, so camera will meter ambient light, then you flash will expose for your subject.

What I do, Is switch to manual, meter as best as you can generally for the scene, keeping your shutter speed above 1/60-80(depending on focal length). could be something similar to iso:400-800 shutter: 1/80th Aperture: f/4.0
I set my flash on ttl, bounce it off the roof and use a bounce card. the flash will take care of itself and should balance the exposure and provide some fill at the same time. This way you know you will keep a fast enough shutter speed, and can also control depth of field, and your ambient lighting.

 

[HoppyUK]

Welcome to TP Bunter Flash is puzzling, but so well worth a little effort to understand what's going on. It really opens up loads of new opportunities. Modern flash systems like Canon's E-TTL are very sophisticated with incredibly complex internal workings, but ignore that for now - they are actually very easy to use, just trust it!

You questions raise quite a lot of extensive issues, but I'll try to stick to the point. The link posted earlier is very good, but I also think you need a bit of basic understanding to get the most from it. Check out http://www.strobist.blogspot.com/ for tons of info and inspiration.

Hi folks

My first post here, not sure what the M.O is but as it's New Years Eve my card's behind the virtual bar...

Had my 40D since late Jan and the wife bought me a 430EXII for Xmas . I'm an enthusiastic amateur but I've never used anything on any of my previous cameras except on board flash, so the dedicated flash unit is a new thing for me. For background info, I'm not sure if I don't use it correctly but the results I got with the 40D's on-board flash always look rubbish, so much so that I bought a fast prime (Canon 50mm F1.8 II) just to use at the NEC motorbike show earlier in the year. I was happy with the results but now I can do far more with a dedicated unit.

So a couple of questions spring up.

When I have the camera in Av mode and have the 40D set to flash synch at 1/250 sec. I'm able to a use wide range of apertures and get reasonable exposures. If I switch to Tv mode and leave everything as is, and set the shutter to 1/250, the widest aperture setting is still not "on scale" as far as the metering goes. Why is that ?

With any auto mode like Av, Tv or P, the camera will meter for the ambient light, and then adjust the flash output to match the f/number. On Av or P, if it's dark you'll naturally get a long shutter speed but if you've locked it at 1/250sec in Tv, then it is forced to set the lowest f/number it can, quite likely off the end of the scale.

Tv isn't generally a very useful mode for flash. Most people use Av, set the f/number to taste and let the camera sort out the shutter speed to balance the flash and ambient light. The camera usually makes a a decent job of it, but you can easily moderate the ambient exposure by adjusting the +/- exposure on the camera, and adjust the flash exposure with +/- on the gun.

One of the benefits of a dedicated flash is the ability to bounce the flash, and I've already found this gives much nicer results than using it without any bounce. But what do you do where there is no ceiling to use for the bounce? Are you restricted to using it in the direct mode? I've seen people with camera mounted flashes units with small white pieces of card poking out the top of the flash. Is that to act as a bounce surface? Relatedly, I can understand how the camera knows what exposure settings to use when the flash is pointing at the subject but how does the camera/flash know how much light is going to be reflected when using bounce? I realise that the flash knows when it is being used in bounce mode.

Auto flash exposure is measured through the lens by the same sensor as ambient light. It works by firing a pre-flash just before the mirror rises, measuring the light reflected back and setting the output for the main flash, which goes off a fraction of a second later when the shutter opens. Many people don't realise that there are in fact two flashes because they go off so fast. (Actually, there can be a stream of dozens of flashes strobed at very high speed in the pre-flash, sending data to remote units.)

If there is no ceiling or wall, you can't use bounce flash - simple as. You have to create your own bounce surface and something like a Lumiquest bouncer http://www.lumiquest.com/strobist/ can work well at close range. To soften the light you need to make it bigger, much bigger really, with something like a softbox. I have a brolly mounted on a camera bracket that works superbly, but it's extremely cumbersome and you look like a complete idiot. Without an alternative bounce surface, there's nothing you can do about that

The bounce-card you mention works really well (very similar to a Stofen-type diffuser) but only if you have a ceiling to work with. You point the flash up to get plenty of soft bounce light, then the little card reflects just enough light directly forward to fill-in the shadows you can get under eyes and chins. Puts a sparkle in the eyes too. Very effective.

You can alter the ratio of bounce-to-fill with the size of the card, but it usually only has to be surprisingly small. Lots of info on this site www.abetterbouncecard.com

I do quite a lot of macro photography and was reading a book on macro work by Robert Thompson and he quite often uses a flash as a fill in flash. But for macro work he recommends mounting the flash on a flash bracket above the lens and pointing at ~ 45 degrees to the subject, with the flash angle fully open. If I get a flash bracket and do this then the flash will think it's in bounce mode but it will in fact be pointing directly at the subject. So how does that work?

For exposure metering, it doesn't matter where the flash is pointing, in bounce mode or not. The camera will see whatever light the subject is getting, measure it and moderate it through the lens.

Sorry this is so basic, if there are any good links for basic flash information they would be greatly appreciated, as would any answers to these questions and any tips on settings for the 40D/430EXII combination.

All the best for the New Year

Cheers

Bill

Happy New Year to you too

 

[Bunter1815]

Thanks again both, plenty to read there and my understanding just from your comments is better!

Cheers

Bill