I thought manual meant manual?

Hello,

Recently purchased a 40D and am still a bit of a noob. I'm trying to take some water drops, using ISO100, f11, 1/250, but when I try and change the shutter speed to say 1/500 it keeps reverting back to 1/250.

I thought manual meant I had full control? How can I change the shutter speed? I tried upping the ISO but it still keeps going back to 1/250

Any help would be very much appreciated..

Thanks in advance.

I am guessing you are using the shutter and 1/250 is the fastest the camera will sync with the flash. I don't have a 40D but if you are using flash refer to that section of your manual and look for information about the shutter sync speed or do a search for that here. If you are not using flash then I have no idea.

ahh, the flash. I'll read up on that (just got a 430ex recently and have not fully read the manual).

Thanks very much

with the on-camera flash 1/250 is the fastests you could go but i dont think thats the case with off-camera. Im not sure though.

hmm, I was using the 430ex? Reading the manual may help

By the way, flash photography involves two exposures....one from the flash and one from the ambient light.

If you are shooting a scene where it will be 3 or more stops underexposed without the flash (based on ISO, aperture and shutter speed) then the flash exposure dominates. In that case, the shutter speed does not matter at all.

Flash expsoure duration is in the range of 1/3000 seconds, so fast that the entire scene is illuminated and exposed for just a small fraction of the time the shutter is open.

You can illustrate this in a dark room with a flash. Try taking a picture at f/4, ISO 400 and shutter speeds of 1/250 and 1 second with the flash on. If the room is truly dark the final images will be identical.

Incidentally this is how water drop photographs work....the really short duration of the flash is very effective at freezing water drops in motion.

With the 430EX you can set it for high-speed sync and then use all the available shutter speeds on the camera. See page 16 of the 430EX manual...

For you to understand "high speed sync", you first need to understand the concept of the focal plane shutter and the "max sync speed". At the end of this explanation I get back to the "high speed sync" thing.

Focal plane shutters (common on SLR cameras) consist of two "curtains", usually made of rubberized cloth (in old film cameras) or very thin metal blades (in most of today's SLR cameras). The first curtain (which I will call the "leading" curtain) normally covers the film or sensor, hiding it from the light coming through the lens. When you take a photo, the leading curtain moves across the film/sensor to expose it to the light. After the leading curtain has moved, another curtain (which I will call the "trailing" curtain) starts to move, again covering the film/sensor to hide the light from it.

At shutter speeds below the "Max Sync Speed", the leading curtain travels all the way across the film/sensor, fully opening the film/sensor to the light, before the trailing curtain starts to move. At higher shutter speeds, the trailing curtain starts to move before the leading curtain has completely travelled across the film/sensor. What happens to create the very fast "shutter speeds" is that an open slot between the two curtains travels across the film/sensor.

While old focal plane shutters (like in my Nikon F cameras from the 1960's) travelled horizontally, the shutters in most modern SLR's travel across the short distance of the film/sensor frame. The concept of "curtains" turns into one of "blades", but the travel concept is still the same. The leading blade moves first, uncovering the film/sensor, and the trailing blade follows, covering up the film/sensor.

The advantage of the blade style of focal plane shutter is that it can move across the whole film/sensor area faster than the old style curtains. Thus, the maximum sync speed is higher than in the old cameras (max 1/60 for my old Nikon F's, and 1/250 for the 20D).

The concept of a maximum sync speed, however, still applies. If you try to use a flash at higher shutter speeds (faster than the shutter speed at which the leading curtain/blade is fully open before the trailing curtain/blade starts to move), part of the film/sensor will be covered by one or the other of the curtains/blades when the flash (with a very short duration) goes off. Part of the film/sensor will not "see" the light from the flash, and that part of the image will be either black or very dark.

In the "high speed sync" mode, Speedlites emit a series of very short pulses of light for a long enough period to emulate a constant light source while the focal plane shutter moves across the film/sensor. The power output of the Speedlite is very low during the "high speed sync" operation because if it was putting out high power pulses it could not recycle fast enough.

The only use for "high speed sync" that makes any sense to me is for using the flash as a fill in an otherwise very brightly lit situation.

Thanks Skip that was a really helpful explanation.

Excellent description, Skip. I think it should be somewhere in a flash FAQ for future reference.

EDIT: I also have an old Nikon F.

-js

Skip,
Absolutely the best explanation I've seen for first/second curtain. I have to admit, it always confused me a bit until I read that. Thanks.

Skip, that should definitely be in the manual, great explanation!

Many thanks everyone, it's all much clearer now

Do you have the custom function for safety shift enabled? If you do, the camera will adjust to a bad exposure and over-ride your settings.