First time hotshoe flash user needs help...

[livinginthepast]

Hi everyone,

Forgive me if this is a really stupid question. I've never used a hotshoe flash before (I've only used the built in flash previously), so this may be self evident. But, at risk of punishing embarrassment, I throw this out to you experts.

My camera is a Canon 40D. I wanted to learn to shoot with hotshoe flash, so I bought an inexpensive Rokinon to play with.

In its most basic functionality, it seems to work. In other words, it flashes when I shoot a pic.

That said, there are a couple of issues.

1. When I switch to manual mode, I am unable to select a shutter speed faster than 1/250. I can slow the shutter, but I cannot increase the speed beyond 250.

2. Oddly, the camera indicates a shutter speed of 250, regardless of lighting, in full auto mode.

User error? By design and I just don't understand it? Or something amiss?

Thank you for your help!

Bill

[400duser]

1: 1/250th is the upper limit to most cameras settings (mine is 1/200th), so nothing is wrong there

2: Full auto mode will select that, because it is the camera selecting that

[Songman45]

Yep by design 1/250th is your maximum flash sync speed. The camera is recognizing a flash is present and is preventing your setting a shutter speed too fast for flash sync.

Steve

[400duser]

Though I have realised on my speedlite, and if your flash unit has it, that if you set it on High Sync flash, you will get a lot faster than 1/250th sec

[Songman45]

I did some checking and it doesn't look that these units offer high speed sync.

Steve

[400duser]

Originally Posted by Songman45

I did some checking and it doesn't look that these units offer high speed sync.

Steve

Erm, I never said that his unit did, Steve, just the 430 EX/II and the 580 EX/II are the only ones in the canon range

[peterst6906]

400duser, Steve was probably just clarifying your statement of "...and if your flash unit has it....".

livingthepast seems to be coming from a fairly basic understanding of flash at this stage and often, answers that seem helpful can sometimes confuse, so I think Steve's clarification was probably useful so that livinginthepast didn't start looking for high sync flash.

livinginthepast, there are probably a couple of additional explanations that might make it a bit clearer for you:

1. Flash Sync Speed

The 40D has a traditional focal plane shutter, which is a shutter made of two halves. During an exposure, one half of the shutter opens to expose the sensor and then the other half of the shutter closes behind it.

For a flash exposure, you are trying to add light into the scene so that the exposure is improved, and this requires the shutter to be fully open when the flash fires (ie. the sensor fully exposed).

To get faster shutter speeds (when not using flash), the first half of the shutter slides open and the second half begins to close even before the shutter is completely open. As a result, at fast speeds, only part of the sensor is exposed at any time and if you try to use flash, you'll only get the extra light in the part of the sensor that is exposed and the rest of the field will be dark.

In your case, the maximum shutter speed that will allow the whole sensor to see the flash is 1/250th and that's why your camera is not letting you go faster (it's taking that decision away from you because in general, people want an even exposure across the sensor and don't want to see dark parts of the frame covered by the shutter).

2. Shutter speed in auto

The duration of a flash from a speedlight is much shorter than the shutter speed. Depending on the power, the flash may have a duration of less than 1/10000th of a second.

As a result, the duration of the shutter doesn't really make much difference to the expose for the subject. The exposure is being determined by the amount of light coming from the flash. What is important for the exposure of the subject is the aperture.

The shutter speed primarily determines the exposure of the ambient area around your subject (ie. the background).

In your case, in auto mode, the camera is selecting a 1/250th because the flash will get the correct exposure for the subject and it is giving you no control over the exposure for the rest of the frame.

Best thing to do is move to manual mode because then if you want to lighten the background, you can select a slower shutter speed.

Hope that helps.

Regards,

Peter

[livinginthepast]

Thank you, everyone. This is very helpful info!

[Mike_PEAT]

This is the site I recommend (especially for Canon users although good for all), that covers the basics of flash (including hotshoe flash) is:
Tutorial Links

[KmH]

Originally Posted by peterst6906

The 40D has a traditional focal plane shutter, which is a shutter made of two halves. During an exposure, one half of the shutter opens to expose the sensor and then the other half of the shutter closes behind it.

Just a quick note on the underlined above. Canon calls them the first curtain and the second curtain.

Nikon calls them the front curtain and the rear curtain.

The flash can be sync'ed to either one and would be called first (front) curtain sync and second (rear) curtain sync.

[RocketRick]

Originally Posted by Mike_PEAT

This is the site I recommend (especially for Canon users although good for all), that covers the basics of flash (including hotshoe flash) is:
Tutorial Links

Also, you should take the time to read through all of the "Lighting 101" and "Lighting 102" posts (links in the right-hand bar) on David Hobby's Strobist.com site. You'll learn a lot (and you'll learn even more if you do the exercises).

- Rick