Which flash unit should I buy for my SLR camera?

in Miscellaneous
By fmueller/Frank (1,202) Send mail to this user on September 4, 2002 2:24:52 AM CDT

Introduction
Types of flash units
What else is there to consider?
Some Links

Introduction

Many people have difficulties to choose the right flash unit for their SLR camera, and end up buying a flash of the same brand as their camera, just to be on the safe side. However, this is not always the best, and often not the cheapest option. Many of the older manual focus SLR cameras can't even make use of a 'dedicated flash'. Many very cheap flashes are available on the second hand market, eg on eBay - if only you knew what to look for. This article tries to explain which flash will fit your camera, and how some of the older flash units work.

 

Types of flash units

In principle there are three types of flash units, and they differ in the way a correct exposure is achieved:

  1. TTL Flash
  2. Auto Flash
  3. Manual Flash

What is TTL Flash?

For TTL (through the lens) flash metering, the flash uses the light meter of the camera. To make this possible, the camera and flash need to be able to ‘talk to each other’; ie. you need a dedicated flash. If your camera does support TTL flash metering, you could still use an auto or fully manual flash unit, but it would be better to get a flash that supports the TTL flash metering of your camera.

TTL flash metering is particularly useful if you shoot with filters, teleconverters or extension tubes, because there is no need to manually compensate for them, as you would have to do with auto flash or manual flash. TTL flash metering can also be useful when shooting with lenses of extreme focal lengths (eg 20mm wide angle or 400mm tele), when the area that the auto flash sensor meters is not representative of the whole picture.

A flash that is capable of TTL flash metering only, can only be used on a dedicated camera.

What will I need to do to use a TTL flash?

  1. You can set your camera to any shutter speed up to the flash sync speed. If in doubt, you camera manual will tell you what the flash sync speed of your camera is.
  2. Set the film speed (eg ISO 400) on the flash (some more advanced cameras will communicate the film speed to the flash).
  3. Set the flash to TTL mode.
  4. You can use any aperture you would like. You choice will depend on how much depth of field you want.
  5. Fire away! The flash and camera will determine the correct exposure automatically.
What is Auto Flash?

If your camera does not support TTL flash metering - and many of the older cameras don’t - auto flash is your next best option.

Auto flash means that the flash has its own built-in light meter, and uses this to determine the correct exposure. For this technology to work, the camera only needs to trigger the flash at the right time, usually via a standard hot shoe or a X sync cord with PC (Prontor-Compur) connection. There is no dedication in the true sense, but some flash units offer special features with some cameras. For example the Minolta x flashes will automatically set the X and XD series cameras to manual exposure mode and flash sync speed. However, if you can forego this convenience, eg for a better price, you can use these ‘dedicated’ auto flashes on any camera and any other auto flash on these cameras.

What will I need to do to use an auto flash?

  1. Set your camera to any shutter speed up to the flash sync speed. On older cameras it is often marked by an X on the shutter speed dial or highlighted; eg in red. If in doubt your camera manual will tell you what it is.
  2. Set the film speed (eg ISO 400) on the flash
  3. The flash will usually give you a choice of several apertures (eg f22, f11 and f5.6 at ISO 400). Choose one and set it on the lens. Your choice will depend on how much depth of field you need (at f22 you will have a wider range in focus than at f5.6), and how far your object is away (eg. at ISO 400 the effective flash range at 22 might be 1 to 3m, at 5.6 it could be 2 to 11m).
  4. Fire away! The flash will determine the correct exposure automatically. Note: because the automatic is in the flash, this even works with old manual SLRs (eg the Minolta SRT, Pentax K1000, Canon FTb, Nikon FM2 etc), that do not have an automatic exposure mode at all.
What is Manual Flash?

With manual flashes the flash strength can not be altered automatically. The correct exposure is achieved by setting the lens’ aperture to the correct value, depending on film speed and distance of the object to the camera. You need to calculate what this aperture is, and a table on the back of the flash unit usually helps you to do this.

Using manual flash is not that hard, but less convenient than using TTL flash or auto flash. If you have a flash unit that is capable of TTL flash or auto flash, there are very few reasons why you would ever want to use manual flash. One reason can be that you want to fine-tune your flash power; eg for fill flash. Many flash units allow you to vary the flash power from full to 1/2, 1/4, 1/8 and 1/16 in manual mode. There is often no straightforward way to achieve this in the automatic modes.

 

What else is there to consider?

Bounce flash

You will want to use direct flash only when it is unavoidable. Bouncing your flash off a wall or ceiling usually gives much more pleasing effects, and the pros do it all the time. To be able to do this, you will need a flash with a head that can be tilted and swivelled. Some units only offer tilt, and you can get away with it, but you need swivel if you want to bounce the flash off a wall for landscape format shots, and to bounce off the ceiling for portrait format shots.

Bouncing your flash is also useful if you want to use your flash with wide-angle lenses. Most flashes cover the angle of view of a 35mm wide-angle lens. You can increase the angle that is covered by the flash by using a wide-angle diffuser, a product like the Stofen Omnibounce, or by simply using bounce flash.

Thyristor flashes

Every time you fire a non-thyristor flash, all the power that would be required to fire the flash with full power is lost. If you fire a thyristor flash with less than full power, it will save the energy that was not required. This helps to improve flash recycle times, and helps to save batteries.

Trigger voltage

Some older flash units use very high trigger voltages. If they are triggered via the hot-shoe of modern electronic cameras, this can damage the electronics of the camera. There is quite a bit of information about this on the web; eg here and here.

Non-standard flash shoes

Some camera’s, notably Minolta’s autofocus cameras use non-standard hot shoes. This makes it necessary to use a dedicated flash, or to use a special adapter.

 

Some Links

All about electronic Flash
Electronic Flash Information
Kodak Flash Photography
Flash PhotographyTips.com
The Birth of Electronic Flash
Flash Trigger Voltage
Robert Monaghon’s Page
Sunpak Flashes
Vivitar Flashes
Metz Flashes

 

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