av mode versus tv mode

in previous threads i have seen that most members shoot in manual mode or av mode
what about shooting in tv mode
van neil in his book says he shoots in m mode and in adequate light he sets the ss at the maximum sync speed to get the most out of his flash compared to the somewhat inefficient hss
manual mode may be difficult at events with constantly changing subject to flash distances so why not shoot in tv mode and set a ss that will guarantee against camera shake

Any mode is valid that gives you the results you want. But to answer your question, using a fast SS in Tv mode may NOT allow you to use the aperture you prefer.

patrick clarke wrote in post #8956445
.....so why not shoot in tv mode and set a ss that will guarantee against camera shake

In addition, there's a custom function on my XT (and I'm sure many other Canon cameras) that allows the shutter speed to default to 1/200th in Av when the flash is activated.

thanks for the reply sapearl
in situations where you dont really desire a shallow dof would it then make sense to use tv
i have found that in instances where i have a spoiled shot it is often because the camera selected a slow ss in av mode like the attached picture where the camera selected a ss of 1/8

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Patrick... Yes, when shooting in AV mode it is possible that the camera may give you a slower shutter speed than you may want... just bump your ISO up.

I personally find that my DOF control is much more important to me than shutter speed, so shooting in AV allows me to choose the DOF I want and the camera picks the shutter.

Patrick, I believe that part of the problem with the "ruined" shot is that you may not have understood some of the essentials of exposure as they related to it.

Now, I don't really know this but I suspect you were using a relatively low ISO for this picture and medium aperture for better DOF. The lens metered off the dark shirts, combined that with your aperture and decided that the image needed MORE exposure.... hence the slow 1/8 SS to give it that extra light. This in turn blew out the background and blurred the subjects due to camera shake from that 1/8 second exposure.

You have to evaluate each situation.

When I do weddings I tend to shoot in manual which gives me more consistency for the way I shoot. I have white dresses and black tuxedos. Those will throw the meter all over the place. So, if the lighting is uniform and generally unchanging, I tend to use Manual mode. But that's not say that I won't periodically switch to Tv or Av. It all depends upon the circumstances.

The first thing I do though upon entering a scene is to ask myself a few questions:
How much light do I have?
How will this affect my choice of ISO?
What is the quality of that light (do I need fill flash)?
From what direction is the light coming?
Do I want to freeze fast action, or is DOF more important?

Now in all fairness to the sample you provided, that was a fairly harsh shooting environment. You were trying to balance partially shaded subjects against a very bright background.

patrick clarke wrote in post #8956542
thanks for the reply sapearl
in situations where you dont really desire a shallow dof would it then make sense to use tv
i have found that in instances where i have a spoiled shot it is often because the camera selected a slow ss in av mode like the attached picture where the camera selected a ss of 1/8

thanks again sapearl
you are perfectly right
i was using spot metering with the focus on the guy in the brown shirt
in situations with such contrasting colours would evaluative have been a better choice?

Yes - evaluative would come closer to the mark.

Even better, select a midtone value in the scene, "pre-meter" off that area ( I use " * " on my 5D) hold that exposure setting, recompose the image and then shoot.

patrick clarke wrote in post #8958307
thanks again sapearl
you are perfectly right
i was using spot metering with the focus on the guy in the brown shirt
in situations with such contrasting colours would evaluative have been a better choice?

I found a new mode on my 7D today... B. Not so useful for weddings really.

Whatever mode you're in you have to keep a close eye on aperture, shutter speed, and ISO. Av/Tv just let you pay more attention to one than another. If it's that close you have to pay too much attention you might as well shoot M.

patrick clarke wrote in post #8956445
in previous threads i have seen that most members shoot in manual mode or av mode
what about shooting in tv mode
van neil in his book says he shoots in m mode and in adequate light he sets the ss at the maximum sync speed to get the most out of his flash compared to the somewhat inefficient hss
manual mode may be difficult at events with constantly changing subject to flash distances so why not shoot in tv mode and set a ss that will guarantee against camera shake

If I understand you post correctly I think you might be getting two different subjects overlapped and a bit confused.

The sync shutter speed is a limitation of your camera and varies from body to body. Some sync at 1/200, some 1/250 and some at 1/500. This is the fastest shutter speed you can use and get the entire frame exposed by the flash. If you exceed it, you will end up with a dark bar at the edge of the frame from where your shutter was still in the way and blocked part of the flash. HSS is a high tech way for your camera to use a flash at a shutter speed greater than your sync speed but has lots of technical details and complexity that make it difficult to predict what results you will get without lots of experience and even then, I still think it is a bit of a crap shoot.

Shutter speed does not not impact the exposure created by your flash. Shoot a subject at 1/10 or 1/250 with a flash and the subject will look exactly the same. Your background, or any other part of the frame that is exposed by ambient light will change but not the part exposed by the flash.

You may get what appears to be motion blur at 1/10 but this is because of the ambient light involved, not the flash, and is known as ghosting.

The flash duration is so quick, faster than 1/800 in almost all cases, that you get the full effect regardless of what shutter speed you use. If you want to test this, set up in a totally dark room with your flash on the camera and take a photo at your cameras sync speed then take one with an expsoure of 30 seconds. Assuming the room is totally dark, the photos will turn out exactly the same and you can even take the camera and spin it like a top for the 29+ seconds after the flash fires and it won't change anything.

You deal with changes in the flash/subject distance with either aperture changes (or ISO), which also affects the ambient settings, or flash power settings. Changing the shutter speed might make a slight difference on your subject but this is because of how much ambient light is being used, not the amount of flashed light.

ETTL is a whole other animal and factors in lots of things to determine the flash power.

To put it another way, when you are shooting with a flash, you are creating two exposures in one shot. One exposure is from the ambient light and one is from the flashed light.

Changing your shutter speed only effects the exposure created by ambient light. Changing your aperture (or ISO) effects both the ambient light exposure and the flashed light exposure.