Flash and ambiant light

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ulrich.von.lich

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Hi,

I'm going to try taking some photos with flash on a SLR with TTL capacity. I'll use low shutter speeds to preserve the ambiant light. But I wonder if there's a possibility to differ the shutter speed from the flash speed.

For example, I let the shutter stay open for about 1 second, and then flash at 1/250 second, then close the shutter. The background could be blurry but the subject will not. It sounds like first/second curtain feature, but if I don't care when the flash releases, only to be released at a different speed.

I don't have much experience with flashguns. And I don't know if it's a flashgun's feature or a camera's.

Thank you.

Best Regards
 
One technique some have tried to simulate the look and feel of the old-fashioned flashbulb is to do just this, shoot at a slow(er) shutter speed and let the ambient light provide just a wee bit of blur, as opposed to the stark stop-action you get with a modern strobe flash.
 
On a second thought, if I simply set shutter speed at 1 second, the flash speed would have differ. No flash can do a whole second regardless the flash power it chooses to use. All flashguns should have a minimum speed, right?
 
Well, the modern strobe flash duration is in the range of a few milliseconds, much faster than most shutter speeds. If it's an auto flash, the closer you are to the subject, the shorter the duration of the flash.

Flash bulbs, if and when you can find them, are longer burning.

Type FP flash bulbs, if you can still find them anywhere, are the longest burning ones there are.

LOL, unless you want to try flash powder. 🙂
 
Thanks DMR. And if I do so, will the TTL flashgun automatically lower its power and release at an appropriate speed? Can I control both speeds?

EDIT: I just check the flashgun on my Olympus DSLR, there's no chance to set the flash speed once TTL is chosen. There's TTL Auto, no TTL Manual.

DMR, I always saw your post after mine. I don't do a lot flash work so anything other than TTL would be too much a hassle 🙂
 
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I'd remove TTL from the picture and go with manual flash settings at first to get the hang of this.

Aperature is the primary control for flash. The duration of a flash is extremely short, but it is 'complete' for the subject (range of the flash). An example, in the dark 'bulb' the lens open for a few minutes and then trigger the flash to take the actual exposure.

Think of the power setting of the flash as your speed setting. If you use the TTL flash it's kind of like shutter-priority auto setting; you're out of control.

The shutter speed, as you say, controls only the quantity of ambient light. You need to consider that you are taking 2 exposures at once - one ambient and one flash (or, let the TTL flash mode decide for you).

Is your SLR digital? You can easily experiment to get the effects you want playing around with a digital camera cranking the power setting on a manual flash and trying different apertures and speeds.

- Charlie
 
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Ambient light around lamps in my home comes up around 1/15 sec F 5.6. So use that speed and let the flash do what it does, manual or auto. Bounce off the white ceiling and you get an incredable smooth fill over the room.

Modifiers let some light go forward, some bounce up for really nice effect. Use daylight film so flash balances and the lights will go warm which is a very nice effect.

Do this and you look like a pro.
 
What you are asking about is called "fill flash". Perhaps a bit of homework on this would help you iimmensely. It is do-able and is easy, even with TTL. Set the shutter speed manually at the sych speed or slower, not by "A".

When you say 'flashgun' I assume you are speaking about an electronic strobe, not flash bulbs, right?

Basically what you do is set the shutter speed for acceptable (desired) exposure of the background and the aperture for the flash exposure of your subject.
 
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Please consider that effectively, you are taking two shots in one exposure when using flash.

If you use a modern DSLR, your camera will always perform two measurements for the shot (when using a flash) - one for the available light exposure (w/o flash; preset aperture and let camera choose its ambient exp. time), and one for flash (camera uses preset aperture, triggers preflashes for measurement). The second exposure measurement is a time-gated measurement that will disregard the selected ambient exp. time (as that time will be much longer than the flash burn time).

I don't own an Olympus, so I suggest you consult your camera's user manual for details.

Some cameras even allow the user to apply a negative exposure correction factor so that the background can be speciffically underexposed by a certain EV value - all while you are using your camera in auto exposure mode both for ambient and flash illumination.
 
You cannot control flash _speed_ . Well, not directly - to some extent it is a function of the flash strength, but even so it will be in the region of 1/10.000 - 1/1.000 second which is in the realm of irrelevance in this discussion. Consider it instantaneous, for all practical purposes.

What you can control is flash strength, up to whatever maximum the flash is able to provide. Basically you use the aperture/ISO/shutter combination to determine the background exposure just as you would without a flash, and use the flash on top of this to fill in however much light you need or want... the laws of physics dictate that the flash will mainly affect the foreground and less so the background.

Aperture and flash output dictate the effect of the flash in the photo, shutter speed is irrelevant - as long as you are within the camera's sync speed of course.

Exactly how flash and ambient is combined by the automatic systems depends on the camera model and which mode the camera is in... for example, on my Canon DSLR, if I put the camera in aperture priority mode, the shutter time will be calculated for a correct ambient exposure and the flash will kick in as a fill-flash for the foreground automatically. Other modes on the same camera will use the flash as the main light and a very low ambient exposure. Some study of your camera and flash manuals may be necessary! Personally, I prefer to use M mode on the camera when I am using flash. I get fewer surprises that way.

Be aware that flash light is daylight blue-white in colour, while light bulbs are very orangey and fluorescents can be all over the place in terms of colour. It may (or may not) be desirable to use a coloured gel on the flash to match its light better to the ambient.
 
You could do it the old fashion way. Set your camera and flash on manual. Set the camera for just the ambient light that you want, then either use a flash meter to get the flash aperture and see if you can adjust the EV to that aperture (you should be able to as it is indoors). Or you can set for the ambient light and manually control the power level and chimp, I think that means look at the read out screen on the camera until it is right (you may have to use EV again to dial everything in). One of the few beauties of DSLR is the ease of shooting flash. It is like having a built in flash meter. I would really consider using manual on both the camera and the meter. In the end it is much more repeatable and consistent.
 
Flash is not easy thing to master so if you need to get real photos using flash I would advise to keep everything as simple as possible for now (= TTL and Program Mode) and do the needed homework later.

Just remember there are two kinds of TTL for flash. First is the "old" Through The Lens metering which means that the camera meters the amount of light at the film level. This method works very well but you cannot use it for fill flash. The camera always assumes flash is the only source of light so you cannot intentionally mix ambient light with flash light. The flash meters what amount of light is needed, you take a shot, shutter opens, flash bursts, light streams in and shutter closes immediately when there's enough light on the film. Very little room for ambient light here.

Second type of TTL is iTTL for Nikon and eTTL for Canon and something else for Olympus I guess. This is basically a mix of ambient light and flash light (fill flash). If you want to maximise the amount of ambient light, set your camera to "rear sync" or "slow sync" mode so that a good amount of ambient light will get in before the flash bursts and shutter closes.
 
Mablo said:
The camera always assumes flash is the only source of light so you cannot intentionally mix ambient light with flash light.
Click to expand...

The times I've tried it, I've had good luck on the Pentax (K1000) using fill flash just to punch through shadows, such as the north side of a building. This was using the Vivitar 2600, high power, auto mode. I metered for normal daylight exposure and let the flash do its thing in a very imprecise way.

Of course this does not have TTL or any fancy-schmancy stuff. Just auto flash and a "dumb" camera.

One gotcha! I learned the hard way that you need to always set the shutter speed at or lower than the max flash sync speed. I did a couple exposures at 1/125 and it was very obvious where the fill flash "ended" as the shutter curtain traveled across the scene.

This did not overexpose, at least not that I could tell.
 
Mablo said:
First is the "old" Through The Lens metering which means that the camera meters the amount of light at the film level. This method works very well but you cannot use it for fill flash. The camera always assumes flash is the only source of light so you cannot intentionally mix ambient light with flash light.
Click to expand...

Not true. The camera "assumes" nothing other than the total amount of light it detects at the film plane. Cameras don't think. Fill flash can be done as explained in earlier posts. A photographer who thinks and understands fill flash can use an "old style TTL metering camera" to do fill flash.

p.s. I heartily agree with your first paragraph in post #12!
 
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Mablo,

Check this out (the section named "Gripes with flash": http://www.camerapedia.org/wiki/Nikon_F3

This is how fill flash is done with TTL metering (averaging or matrix... doesn't really matter).

There are some "Nikon F3-unique" considerations here, like the fact that the Nikon flash automaticallys sets the camera to 1/80 sych speed) and this technique might not be directly applciable to any other make/model of camera.

The author uses the terms "gripes" and "workaround" inappropriately if anyone were to ask me. This is just how it is done with that kind of technology. The important tbing is to understand how your equipment works. Best idea is to read the manual; the manual likely discusses fill flash in addition to "normal" flash applications.
 
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Thanks everyone.

You cannot control flash _speed_ . Well, not directly - to some extent it is a function of the flash strength, but even so it will be in the region of 1/10.000 - 1/1.000 second which is in the realm of irrelevance in this discussion. Consider it instantaneous, for all practical purposes.
Click to expand...

So when flash is said to "be synchronized" with the camera, say, at the speed of 1/250, it only means that the flash will be released while the camera shutter is open, not that they will have the same speed, right? In this case I think I'll manually expose for ambiant light and see if the TTL flash could take care of the rest.

I will look for more information about fill flash.

It is an old style TTL that presents in my Olympus OM2/4.

I never really understand how TTL "Of The Film" flash works. Modern lenses communicate with the camera and flash but manual SLR lenses do not. So how can a proper exposure ever be made while the subject distance is not provided to the flash?
 
U.V.L. -

The "shutter speed" issue is a detail of clarity and accuracy of speech. A flash has no "shutter speed" per se.. Your camera has a "sych speed" - the fastest speed that it will sychronize with a strobe. When using a strobe you can use that X-synch speed or any speed slower. If you use a faster speed you'll get the cut-off that DMR mentioned. The strobe itself has a flash "speed" in the milliseconds.

It is my recommendation, trying to be as polite and constructive as possible, that you research flash photography and the capabilities of your particular camera... in addition to fill flash techniques. It sounds to me like you really need to know some of the basics.

Your idea of manually exposing for background and using the flash also mgiht actually work... as long as the shutter speed is at or below the X-synch speed.

TTL off-the-film metering is conceptually simple. For example, the Nikon F3 is TTL off-the-film: the light goes from the flash, reflects off of the subject, and is measured by a sensor inside the camera as that light reflects off of the film. On the other hand, a flash like a Vivitar 283/285 is automatic but NOT TTL. In that case, the light goes from the flash, reflects off of the subject, and is measured by a sensor in the flash unit. In both cases, when the sensor determines that the proper exposure has occured, the sensor (in both TTL or non-TTL) turns off the strobe light so it doesn't illumintate the subject anymore. Both are automatic flash modes with the basic difference of where the flash sensor is located.

Hope that helps!
 
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ulrich.von.lich said:
Thanks everyone.



So when flash is said to "be synchronized" with the camera, say, at the speed of 1/250, it only means that the flash will be released while the camera shutter is open, not that they will have the same speed, right? In this case I think I'll manually expose for ambiant light and see if the TTL flash could take care of the rest.

I will look for more information about fill flash.

It is an old style TTL that presents in my Olympus OM2/4.

I never really understand how TTL "Of The Film" flash works. Modern lenses communicate with the camera and flash but manual SLR lenses do not. So how can a proper exposure ever be made while the subject distance is not provided to the flash?
Click to expand...

As I understand it, the camera reads the amount of light that has come through the lens and quenches the flash. Incredible but apparently true. That's why they have all those contacts around the hot shoe and need a compatible flash. Many auto flashes work on the same principle, but with the sensor on the flashgun, not TTL.

Cheers,

R.
 
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