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I get very frustrated. When I take portraits, I want to use a flash because I think they turn out better. But if I use an f-stop that is high enough to blur the background, my shutter speed only goes up to 1/250s, which produces overexposure.
I have a Canon 60D, shoot in Manual, and don't understand how to fix this problem. Can you give me some advice?
Your camera is limiting your shutter speed to the 60D's maximum sync speed. If you were to use a faster shutter speed, you'd have black bars at the top and/or bottom of the frame, because the shutter curtains would be covering part of the sensor when the flash burst goes off. The only way to use a faster shutter speed than 1/250s with flash it to use high-speed sync or tail sync.
With high-speed sync, the body and the flash (if both can perform HSS) communicate so tha the flash can send out pulses as the gap in the shutter curtain sweeps across the sensor, so the full frame will be evenly illuminated by the flash. This does, however reduce the power output of the flash, by roughly two stops, so there's a game of diminishing returns going on.
With tail sync, (aka "supersync" or "hypersync"), the flash is fired (usually at full power) a little bit earlier than with regular sync, and then the exposure happens at the "tail" of the flash burst when the illumination is likely to be more even across the frame. The timing is critical, and again, you have diminishing returns on the amount of illumination you can get.
Your third alternative would be to place ND filters over the lens, so that you can can still have a large aperture, but use a shutter speed at or below your maximum sync speed.
See also Neil van Niekerk's tutorial on high speed sync on his Tangents blog.
Here are some options:
Find some shade
If there's too much light for your style you need a location with less light :-) in mid-day sunlight you may need something pretty big to block enough light but still it's an easy option
Shoot at a better time of day
At early morning and late evening there's less light and you'll be able to get the aperture/shutter speed you need, as a bonus the light will also be softer nicer and more directional.
Use something else instead of a flash
Flashes are not the only way to add controlled light, if there's a lot of ambient light you can easily control and shape light using reflectors - and as a bonus reflectors are cheap and easy to use.
High Speed Sync
If you have all TTL flashes (and triggers, if applicable) you can set them to HSS, this will let you use higher shutter speeds but also reduce the flash power considerably, as a rule of thumb an HSS flash needs to be really close to the subject to have noticeable effect
ND filter
And finally, you can use an ND filter to reduce the amount of light entering the camera.
I'll assume you have tried the following:
These will all reduce the amount of illumination arriving on your subject but may not be ideal for your situation. This is an atypical situation -- most photographers are looking for more or bigger lights. You're lucky you have more than enough. So, consider one of these two other alternatives:
Neither of these will affect your light shaping, but either/both will reduce the amount of light on your subject, allowing you to use wider apertures.
I've been exploring use of flash for the first time myself, using 50mm f1.8 lens. For me I get best results in camera manual mode (pick shutter speed and aperture), and then fine-tuning my flash's manual settings (i.e. for camera settings I leave them stable, and just tinker with the flash).
For example - I find flash power 1/16 and zoom 105mm gives really pleasing results, much more so than just basic ETTL and auto-zoom.
Pointing the flash at the ceiling to allow the light to bounce down is a basic technique which helps enormously, just in case you've not tried that.
(I learned this by taking about 100 shots of the kids' teddies with different settings: there's no substitute for trial and error: make small changes, try a photo: better? worse? and repeat!)
You don't mention what kind of flash you are using. If You are using a Canon Speedlite, You should make sure it is set to ETTL otherwise, If you are using a manual flash You need to turn the flash power down.
Not exactly sure of your setup, but they sell diffusers that attach to the flash. The quickest way, however, is to aim the flash at a light colored wall or ceiling instead of directly at the subject. Here is an example. Not only will it reduce the flash intensity, but it also softens and can often eliminate shadows. It is a good all around technique that works very well. Both methods are relying on the same principles.
Next, try reducing your ISO (you don't say what you were using) to 200 or 100 or less.
But if I use an f-stop that is high enough to blur the background, my shutter speed only goes up to 1/250s, which produces overexposure.
Flash photography is a little different in that you can't use the shutter speed to control the amount of light due to the flash. That's because the duration of the flash at full power is typically around 1/250 sec., and even less if you use the flash at lower power. (The intensity of light from a flash unit is always the same -- power is adjusted by changing the duration of the flash.) Since the flash duration is about the same or less than the fastest sync speed on most cameras, the flash ends before the shutter has a chance to close.
So, with flash photography, shutter speed is used to control ambient light, and other means are used to control the flash. Others have already mentioned aperture, neutral density filters, flash power, flash distance, gels and diffusers. There's one more that may help: sensitivity. If you haven't already done so, reduce the ISO setting to make the camera less sensitive the the light it's seeing.
Here's a quick breakdown on how the different options affect your lighting:
shutter speed: affects ambient light but not flash
aperture: affects both ambient and flash, as well as changing depth of field
ISO: affects both ambient and flash, doesn't change depth of field, may affect noise
flash power, diffuser, gels, distance, bounce, filters: affects flash but not ambient light
